Each chemical element can be considered from the point of view of three sciences: physics, chemistry and biology. And in this article we will try to characterize aluminum as accurately as possible. This is a chemical element that is in the third group and third period, according to the periodic table. Aluminum is a metal that has medium chemical activity. Also in its compounds, amphoteric properties can be observed. The atomic mass of aluminum is twenty-six grams per mole.

Physical characteristic of aluminum

Under normal conditions, it is a solid. The formula for aluminum is very simple. It consists of atoms (do not unite into molecules), which are built with the help of a crystal lattice into a continuous substance. Aluminum color - silver-white. In addition, it has a metallic luster, like all other substances of this group. The color of aluminum used in industry may vary due to the presence of impurities in the alloy. It is a fairly light metal.

Its density is 2.7 g / cm3, that is, it is approximately three times lighter than iron. In this, it can only yield to magnesium, which is even lighter than the metal in question. The hardness of aluminum is quite low. In it, it is inferior to most metals. The hardness of aluminum is only two. Therefore, to strengthen it, harder ones are added to alloys based on this metal.

The melting of aluminum occurs at a temperature of only 660 degrees Celsius. And it boils when heated to a temperature of two thousand four hundred and fifty-two degrees Celsius. It is a very ductile and fusible metal. On this physical characteristic aluminum is not finished. I would also like to note that this metal has the best electrical conductivity after copper and silver.

Prevalence in nature

Aluminum, the technical characteristics of which we have just reviewed, is quite common in the environment. It can be observed in the composition of many minerals. The element aluminum is the fourth most common element in nature. Its in earth's crust is almost nine percent. The main minerals in which its atoms are present are bauxite, corundum, cryolite. The first is a rock, which consists of oxides of iron, silicon and the metal in question, and water molecules are also present in the structure. It has a heterogeneous color: fragments of gray, reddish-brown and other colors, which depend on the presence of various impurities. From thirty to sixty percent of this breed is aluminum, the photo of which can be seen above. In addition, corundum is a very common mineral in nature.

This is aluminum oxide. Its chemical formula is Al2O3. It can be red, yellow, blue or brown. Its hardness on the Mohs scale is nine units. The varieties of corundum include well-known sapphires and rubies, leucosapphires, as well as padparadscha (yellow sapphire).

Cryolite is a mineral that has a more complex chemical formula. It consists of aluminum and sodium fluorides - AlF3.3NaF. It looks like a colorless or grayish stone with a low hardness - only three on the Mohs scale. In the modern world, it is synthesized artificially in the laboratory. It is used in metallurgy.

Also, aluminum can be found in nature in the composition of clays, the main components of which are oxides of silicon and the metal in question, associated with water molecules. In addition, this chemical element can be observed in the composition of nephelines, the chemical formula of which is as follows: KNa34.

Receipt

The characterization of aluminum involves consideration of methods for its synthesis. There are several methods. The production of aluminum by the first method occurs in three stages. The last of these is the electrolysis procedure on the cathode and carbon anode. To carry out such a process, aluminum oxide is required, as well as auxiliary substances such as cryolite (formula - Na3AlF6) and calcium fluoride (CaF2). In order for the process of decomposition of aluminum oxide dissolved in water to occur, it must be heated together with molten cryolite and calcium fluoride to a temperature of at least nine hundred and fifty degrees Celsius, and then a current of eighty thousand amperes and a voltage of five- eight volts. Thus, as a result of this process, aluminum will settle on the cathode, and oxygen molecules will collect on the anode, which, in turn, oxidize the anode and turn it into carbon dioxide. Before carrying out this procedure, bauxite, in the form of which aluminum oxide is mined, is preliminarily cleaned of impurities, and also goes through the process of its dehydration.

The production of aluminum in the manner described above is very common in metallurgy. There is also a method invented in 1827 by F. Wehler. It lies in the fact that aluminum can be mined using a chemical reaction between its chloride and potassium. It is possible to carry out such a process only by creating special conditions in the form of a very high temperature and vacuum. So, from one mole of chloride and the same volume of potassium, one mole of aluminum and three moles as a by-product can be obtained. This reaction can be written as the following equation: АІСІ3 + 3К = АІ + 3КІ. This method has not gained much popularity in metallurgy.

Characteristics of aluminum in terms of chemistry

As mentioned above, this is a simple substance that consists of atoms that are not combined into molecules. Similar structures form almost all metals. Aluminum has a fairly high chemical activity and strong reducing properties. The chemical characterization of aluminum will begin with a description of its reactions with other simple substances, and then interactions with complex inorganic compounds will be described.

Aluminum and simple substances

These include, first of all, oxygen - the most common compound on the planet. Twenty-one percent of the Earth's atmosphere consists of it. The reactions of a given substance with any other are called oxidation, or combustion. It usually occurs at high temperatures. But in the case of aluminum, oxidation is possible under normal conditions - this is how an oxide film is formed. If this metal is crushed, it will burn, while releasing a large amount of energy in the form of heat. To carry out the reaction between aluminum and oxygen, these components are needed in a molar ratio of 4:3, resulting in two parts of the oxide.

This chemical interaction is expressed as the following equation: 4АІ + 3О2 = 2АІО3. Reactions of aluminum with halogens are also possible, which include fluorine, iodine, bromine and chlorine. The names of these processes come from the names of the corresponding halogens: fluorination, iodination, bromination and chlorination. These are typical addition reactions.

For example, we give the interaction of aluminum with chlorine. This kind of process can only occur in the cold.

So, taking two moles of aluminum and three moles of chlorine, we get as a result two moles of chloride of the metal in question. The equation for this reaction is as follows: 2АІ + 3СІ = 2АІСІ3. In the same way, aluminum fluoride, its bromide and iodide can be obtained.

With sulfur, the substance in question reacts only when heated. To carry out the interaction between these two compounds, you need to take them in molar proportions of two to three, and one part of aluminum sulfide is formed. The reaction equation has the following form: 2Al + 3S = Al2S3.

In addition, at high temperatures, aluminum interacts with carbon, forming a carbide, and with nitrogen, forming a nitride. The following equations of chemical reactions can be cited as an example: 4AI + 3C = AI4C3; 2Al + N2 = 2AlN.

Interaction with complex substances

These include water, salts, acids, bases, oxides. With all these chemical compounds, aluminum reacts in different ways. Let's take a closer look at each case.

Reaction with water

Aluminum interacts with the most common complex substance on Earth when heated. This happens only in the case of preliminary removal of the oxide film. As a result of the interaction, amphoteric hydroxide and hydrogen is released into the air. Taking two parts of aluminum and six parts of water, we get hydroxide and hydrogen in molar proportions of two to three. The equation of this reaction is written as follows: 2АІ + 6Н2О = 2АІ (ОН) 3 + 3Н2.

Interaction with acids, bases and oxides

Like other active metals, aluminum is able to enter into a substitution reaction. In doing so, it can displace hydrogen from an acid or a cation of a more passive metal from its salt. As a result of such interactions, an aluminum salt is formed, and hydrogen is also released (in the case of an acid) or a pure metal precipitates (one that is less active than the one under consideration). In the second case, the restorative properties that were mentioned above are manifested. An example is the interaction of aluminum with which aluminum chloride is formed and hydrogen is released into the air. This kind of reaction is expressed as the following equation: 2AI + 6HCI = 2AICI3 + 3H2.

An example of the interaction of aluminum with salt is its reaction with. Taking these two components, we will eventually get pure copper, which will precipitate. With acids such as sulfuric and nitric, aluminum reacts in a peculiar way. For example, when aluminum is added to a dilute solution of nitrate acid in a molar ratio of eight parts to thirty, eight parts of the nitrate of the metal in question, three parts of nitric oxide and fifteen parts of water are formed. The equation for this reaction is written as follows: 8Al + 30HNO3 = 8Al(NO3)3 + 3N2O + 15H2O. This process occurs only in the presence of high temperature.

If we mix aluminum and a weak solution of sulfate acid in molar proportions of two to three, we get the sulfate of the metal in question and hydrogen in a ratio of one to three. That is, an ordinary substitution reaction will occur, as is the case with other acids. For clarity, we present the equation: 2Al + 3H2SO4 = Al2(SO4)3 + 3H2. However, with a concentrated solution of the same acid, everything is more complicated. Here, as in the case of nitrate, a by-product is formed, but not in the form of oxide, but in the form of sulfur, and water. If we take the two components we need in a molar ratio of two to four, then as a result we get one part of the salt of the metal in question and sulfur, as well as four of water. This chemical interaction can be expressed using the following equation: 2Al + 4H2SO4 = Al2(SO4)3 + S + 4H2O.

In addition, aluminum is able to react with alkali solutions. To carry out such a chemical interaction, you need to take two moles of the metal in question, the same amount or potassium, as well as six moles of water. As a result, substances such as sodium or potassium tetrahydroxoaluminate are formed, as well as hydrogen, which is released as a gas with a pungent odor in molar proportions of two to three. This chemical reaction can be represented as the following equation: 2AI + 2KOH + 6H2O = 2K[AI(OH)4] + 3H2.

And the last thing to consider is the patterns of aluminum interaction with some oxides. The most common and used case is the Beketov reaction. It, like many others discussed above, occurs only at high temperatures. So, for its implementation, it is necessary to take two moles of aluminum and one mole of ferrum oxide. As a result of the interaction of these two substances, we obtain aluminum oxide and free iron in the amount of one and two moles, respectively.

The use of the metal in question in industry

Note that the use of aluminum is a very common occurrence. First of all, the aviation industry needs it. Along with this, alloys based on the metal in question are also used. We can say that the average aircraft is 50% aluminum alloys, and its engine is 25%. Also, the use of aluminum is carried out in the process of manufacturing wires and cables due to its excellent electrical conductivity. In addition, this metal and its alloys are widely used in the automotive industry. The bodies of cars, buses, trolleybuses, some trams, as well as ordinary and electric train cars are made of these materials.

It is also used for smaller purposes, for example, for the production of packaging for food and other products, dishes. In order to make silver paint, a powder of the metal in question is needed. Such paint is needed in order to protect iron from corrosion. We can say that aluminum is the second most commonly used metal in industry after ferrum. Its compounds and itself are often used in the chemical industry. This is due to the special chemical properties of aluminum, including its reducing properties and the amphoteric nature of its compounds. The hydroxide of the considered chemical element is necessary for water purification. In addition, it is used in medicine during the production of vaccines. It can also be found in some plastics and other materials.

Role in nature

As already mentioned above, aluminum is found in large quantities in the earth's crust. It is especially important for living organisms. Aluminum is involved in the regulation of growth processes, forms connective tissues, such as bone, ligamentous and others. Thanks to this microelement, the processes of regeneration of body tissues are carried out faster. Its deficiency is characterized by the following symptoms: developmental and growth disorders in children, in adults - chronic fatigue, reduced performance, impaired coordination of movements, slowdown in tissue regeneration, muscle weakness, especially in the limbs. This phenomenon can occur if you eat too few foods containing this trace element.

However, a more common problem is an excess of aluminum in the body. In this case, the following symptoms are often observed: nervousness, depression, sleep disturbances, memory loss, stress resistance, softening of the musculoskeletal system, which can lead to frequent fractures and sprains. With a prolonged excess of aluminum in the body, problems often arise in the work of almost every organ system.

A number of reasons can lead to this phenomenon. First of all, it has long been proven by scientists that dishes made from the metal in question are unsuitable for cooking food in it, since at high temperatures part of the aluminum gets into food, and as a result, you consume much more of this microelement than the body needs.

The second reason is the regular use of cosmetics containing the metal in question or its salts. Before using any product, you need to carefully read its composition. Cosmetics are no exception.

The third reason is taking drugs that contain a lot of aluminum for a long time. As well as the improper use of vitamins and nutritional supplements, which include this microelement.

Now let's figure out which products contain aluminum in order to regulate your diet and organize the menu correctly. First of all, these are carrots, processed cheeses, wheat, alum, potatoes. From fruits, avocados and peaches are recommended. In addition, white cabbage, rice, many healing herbs. Also, the cations of the metal in question can be contained in drinking water. To avoid an increased or decreased content of aluminum in the body (however, just like any other trace element), you need to carefully monitor your diet and try to make it as balanced as possible.

This light metal with a silvery-white tint is found almost everywhere in modern life. The physical and chemical properties of aluminum allow it to be widely used in industry. The most famous deposits are in Africa, South America, in the Caribbean region. In Russia, bauxite mining sites are located in the Urals. The world leaders in aluminum production are China, Russia, Canada, and the USA.

Al mining

In nature, this silvery metal, due to its high chemical activity, is found only in the form of compounds. The most well-known geological rocks containing aluminum are bauxite, alumina, corundum, and feldspars. Bauxite and alumina are of industrial importance, it is the deposits of these ores that make it possible to extract aluminum in its pure form.

Properties

Physical properties aluminum make it easy to draw blanks of this metal into wire and roll into thin sheets. This metal is not durable; to increase this indicator during smelting, it is alloyed with various additives: copper, silicon, magnesium, manganese, zinc. For industrial purposes, another physical property of aluminum is important - this is its ability to quickly oxidize in air. The surface of the aluminum product vivo usually covered with a thin oxide film, which effectively protects the metal and prevents its corrosion. When this film is destroyed, the silvery metal is rapidly oxidized, while its temperature rises noticeably.

The internal structure of aluminum

The physical and chemical properties of aluminum largely depend on its internal structure. The crystal lattice of this element is a kind of face-centered cube.

This type of lattice is inherent in many metals, such as copper, bromine, silver, gold, cobalt and others. High thermal conductivity and the ability to conduct electricity have made this metal one of the most sought after in the world. The remaining physical properties of aluminum, the table of which is presented below, fully reveal its properties and show the scope of their application.

Alloying of aluminum

The physical properties of copper and aluminum are such that when a certain amount of copper is added to an aluminum alloy, its crystal lattice is bent, and the strength of the alloy itself increases. Alloying of light alloys is based on this property of Al to increase their strength and resistance to aggressive environments.

The explanation of the hardening process lies in the behavior of copper atoms in the aluminum crystal lattice. Cu particles tend to fall out of the Al crystal lattice and are grouped in its special areas.

Where copper atoms form clusters, a CuAl 2 mixed-type crystal lattice is formed, in which silver metal particles are simultaneously part of both the general aluminum crystal lattice and the composition of the CuAl 2 mixed-type lattice. The forces of internal bonds in a distorted lattice are much greater than in normal. This means that the strength of the newly formed substance is much higher.

Chemical properties

The interaction of aluminum with dilute sulfuric and hydrochloric acid is known. When heated, this metal dissolves easily in them. Cold concentrated or highly dilute nitric acid does not dissolve this element. Aqueous solutions of alkalis actively affect the substance, during the reaction forming aluminates - salts, which contain aluminum ions. For example:

Al 2 O 3 + 3H2O + 2NaOH \u003d 2Na

The resulting compound is called sodium tetrahydroxoaluminate.

A thin film on the surface of aluminum products protects this metal not only from air, but also from water. If this thin barrier is removed, the element will violently interact with water, releasing hydrogen from it.

2AL + 6H 2 O \u003d 2 AL (OH) 3 + 3H 2

The resulting substance is called aluminum hydroxide.

AL (OH) 3 reacts with alkali, forming hydroxoaluminate crystals:

Al(OH) 2 +NaOH=2Na

If this chemical equation add to the previous one, we get the formula for dissolving an element in an alkaline solution.

Al (OH) 3 + 2NaOH + 6H 2 O \u003d 2Na + 3H 2

Burning aluminum

The physical properties of aluminum allow it to react with oxygen. If the powder of this metal or aluminum foil is heated, it flares up and burns with a blinding white flame. At the end of the reaction, aluminum oxide Al 2 O 3 is formed.

Alumina

The resulting aluminum oxide has the geological name alumina. Under natural conditions, it occurs in the form of corundum - solid transparent crystals. Corundum has a high hardness, its indicator is 9 on the solids scale. Corundum itself is colorless, but various impurities can color it red and blue, so it turns out gems, which in jewelry are called rubies and sapphires.

The physical properties of aluminum oxide make it possible to grow these gemstones under artificial conditions. Tech gems are not only used for jewelry, they are used in precision instrumentation, for the manufacture of watches and other things. Artificial ruby ​​crystals are also widely used in laser devices.

A fine-grained variety of corundum with big amount impurities deposited on a special surface is known to everyone as emery. The physical properties of aluminum oxide explain the high abrasive properties of corundum, as well as its hardness and resistance to friction.

aluminum hydroxide

Al 2 (OH) 3 is a typical amphoteric hydroxide. In combination with an acid, this substance forms a salt containing positively charged aluminum ions; in alkalis, it forms aluminates. Amphotericity of a substance is manifested in the fact that it can behave both as an acid and as an alkali. This compound can exist in both jelly and solid form.

It practically does not dissolve in water, but reacts with most active acids and alkalis. The physical properties of aluminum hydroxide are used in medicine, it is a popular and safe means of reducing acidity in the body, it is used for gastritis, duodenitis, ulcers. In industry, Al 2 (OH) 3 is used as an adsorbent, it perfectly purifies water and precipitates harmful elements dissolved in it.

Industrial use

Aluminum was discovered in 1825. At first, this metal was valued above gold and silver. This was due to the difficulty of extracting it from the ore. The physical properties of aluminum and its ability to quickly form a protective film on its surface made it difficult to study this element. It was not until the end of the 19th century that the convenient way smelting a pure element, suitable for industrial use.

Lightness and ability to resist corrosion are the unique physical properties of aluminum. Alloys of this silvery metal are used in rocket technology, in auto, ship, aircraft and instrument making, in the production of cutlery and utensils.

As a pure metal, Al is used in the manufacture of parts for chemical equipment, electrical wires and capacitors. The physical properties of aluminum are such that its electrical conductivity is not as high as that of copper, but this disadvantage is compensated by the lightness of the metal in question, which makes it possible to make aluminum wires thicker. So, with the same electrical conductivity, an aluminum wire weighs half as much as a copper wire.

Equally important is the use of Al in the aluminizing process. This is the name of the reaction of saturation of the surface of a cast iron or steel product with aluminum in order to protect the base metal from corrosion when heated.

At present, the explored reserves of aluminum ores are quite comparable to the needs of people in this silvery metal. The physical properties of aluminum can bring many more surprises to its researchers, and the scope of this metal is much wider than one might imagine.

Natural aluminum consists of one nuclide 27Al. The configuration of the outer electron layer is 3s2p1. In almost all compounds, the oxidation state of aluminum is +3 (valency III).

The radius of the neutral aluminum atom is 0.143 nm, the radius of the Al3+ ion is 0.057 nm. The sequential ionization energies of a neutral aluminum atom are 5.984, 18.828, 28.44, and 120 eV, respectively. On the Pauling scale, the electronegativity of aluminum is 1.5.

The simple substance aluminum is a soft, light, silvery-white metal.

Properties

Aluminum is a typical metal, the crystal lattice is face-centered cubic, parameter a = 0.40403 nm. The melting point of pure metal is 660°C, the boiling point is about 2450°C, the density is 2.6989 g/cm3. The temperature coefficient of linear expansion of aluminum is about 2.5·10-5 K-1 Standard electrode potential Al 3+/Al is 1.663V.

Chemically, aluminum is a fairly active metal. In air, its surface is instantly covered with a dense film of Al 2 O 3 oxide, which prevents further access of oxygen (O) to the metal and leads to the termination of the reaction, which leads to high anti-corrosion properties of aluminum. A protective surface film on aluminum is also formed if it is placed in concentrated nitric acid.

Aluminum actively reacts with other acids:

6HCl + 2Al \u003d 2AlCl 3 + 3H 2,

3H 2 SO 4 + 2Al \u003d Al 2 (SO 4) 3 + 3H 2.

Aluminum reacts with alkali solutions. First, the protective oxide film is dissolved:

Al 2 O 3 + 2NaOH + 3H 2 O \u003d 2Na.

Then the reactions take place:

2Al + 6H 2 O \u003d 2Al (OH) 3 + 3H 2,

NaOH + Al (OH) 3 \u003d Na,

or in total:

2Al + 6H 2 O + 2NaOH \u003d Na + 3H 2,

and as a result, aluminates are formed: Na - sodium aluminate (Na) (sodium tetrahydroxoaluminate), K - potassium aluminate (K) (potassium tetrahydroxoaluminate) or others. Since the aluminum atom in these compounds is characterized by a coordination number of 6, not 4 , then the actual formulas of these tetrahydroxo compounds are as follows:

Na and K.

When heated, aluminum reacts with halogens:

2Al + 3Cl 2 \u003d 2AlCl 3,

2Al + 3Br 2 = 2AlBr 3 .

Interestingly, the reaction between aluminum and iodine (I) powders begins at room temperature, if a few drops of water are added to the initial mixture, which in this case plays the role of a catalyst:

2Al + 3I 2 = 2AlI 3 .

The interaction of aluminum with sulfur (S) when heated leads to the formation of aluminum sulfide:

2Al + 3S \u003d Al 2 S 3,

which is easily decomposed by water:

Al 2 S 3 + 6H 2 O \u003d 2Al (OH) 3 + 3H 2 S.

Aluminum does not interact directly with hydrogen (H), however, indirectly, for example, using organoaluminum compounds, it is possible to synthesize a solid polymeric aluminum hydride (AlH 3) x - the strongest reducing agent.

In the form of a powder, aluminum can be burned in air, and a white refractory powder of aluminum oxide Al 2 O 3 is formed.

The high bond strength in Al 2 O 3 determines the high heat of its formation from simple substances and the ability of aluminum to reduce many metals from their oxides, for example:

3Fe 3 O 4 + 8Al = 4Al 2 O 3 + 9Fe and even

3CaO + 2Al \u003d Al 2 O 3 + 3Ca.

This method of obtaining metals is called aluminothermy.

Amphoteric oxide Al 2 O 3 corresponds to amphoteric hydroxide - an amorphous polymer compound that does not have a constant composition. The composition of aluminum hydroxide can be conveyed by the formula xAl 2 O 3 yH 2 O; when studying chemistry at school, the formula of aluminum hydroxide is most often indicated as Al (OH) 3.

In the laboratory, aluminum hydroxide can be obtained in the form of a gelatinous precipitate by exchange reactions:

Al 2 (SO 4) 3 + 6NaOH \u003d 2Al (OH) 3 + 3Na 2 SO 4,

or by adding soda to an aluminum salt solution:

2AlCl 3 + 3Na 2 CO 3 + 3H 2 O \u003d 2Al (OH) 3 + 6NaCl + 3CO 2,

and also by adding an ammonia solution to an aluminum salt solution:

AlCl 3 + 3NH 3 H2O = Al(OH) 3 + 3H 2 O + 3NH 4 Cl.

Name and history of the discovery: Latin aluminum comes from the Latin alumen, meaning alum (aluminum and potassium sulfate (K) KAl (SO 4) 2 12H 2 O), which have long been used in leather dressing and as an astringent. Due to the high chemical activity, the discovery and isolation of pure aluminum dragged on for almost 100 years. The conclusion that "earth" (a refractory substance, in modern terms - aluminum oxide) can be obtained from alum was made back in 1754 by the German chemist A. Marggraf. Later it turned out that the same "earth" could be isolated from clay, and it was called alumina. It was only in 1825 that the Danish physicist H. K. Oersted could obtain metallic aluminum. He treated aluminum chloride AlCl 3 , which could be obtained from alumina, with potassium amalgam (an alloy of potassium (K) with mercury (Hg)) and, after distilling off mercury (Hg), isolated a gray powder of aluminum.

Only a quarter of a century later, this method was slightly modernized. The French chemist A. E. St. Clair Deville in 1854 suggested using metallic sodium (Na) to produce aluminum, and obtained the first ingots of the new metal. The cost of aluminum was then very high, and jewelry was made from it.

An industrial method for the production of aluminum by electrolysis of a melt of complex mixtures, including oxide, aluminum fluoride and other substances, was independently developed in 1886 by P. Eru (France) and C. Hall (USA). Aluminum production is associated with high flow electricity, so it was realized on a large scale only in the 20th century. In the Soviet Union, the first industrial aluminum was obtained on May 14, 1932 at the Volkhov aluminum plant, built next to the Volkhov hydroelectric power station.

Section 1. Name and history of the discovery of aluminum.

Section 2. General characteristics aluminum, physical and chemical properties.

Section 3. Obtaining castings from aluminum alloys.

Section 4 Application aluminum.

Aluminum- this is an element of the main subgroup of the third group, the third period of the periodic system of chemical elements of D. I. Mendeleev, with atomic number 13. It is designated by the symbol Al. Belongs to the group of light metals. The most common metal and the third most abundant chemical element in the earth's crust (after oxygen and silicon).

Simple substance aluminum (CAS number: 7429-90-5) - light, paramagnetic metal silver-white color, easy to form, cast, machined. Aluminum has high thermal and electrical conductivity, resistance to corrosion due to the rapid formation of strong oxide films that protect the surface from further interaction.

The achievements of industry in any developed society are invariably associated with the achievements of the technology of structural materials and alloys. The quality of processing and the productivity of manufacturing items of trade are the most important indicators of the level of development of the state.

Materials used in modern designs, in addition to high strength characteristics, must have a set of properties such as increased corrosion resistance, heat resistance, thermal and electrical conductivity, refractoriness, as well as the ability to maintain these properties under conditions long work under loads.

Scientific developments and production processes in the field of foundry production of non-ferrous metals in our country correspond to the advanced achievements of scientific and technological progress. Their result, in particular, was the creation of modern chill casting and pressure casting workshops at the Volga Automobile Plant and a number of other enterprises. Large injection molding machines with a mold locking force of 35 MN are successfully operating at the Zavolzhsky Motor Plant, which produce aluminum alloy cylinder blocks for the Volga car.

At the Altai Motor Plant, an automated line for the production of castings by injection molding has been mastered. In the Union of Soviet Socialist Republics (), for the first time in the world, developed and mastered process continuous casting of ingots from aluminum alloys in an electromagnetic mold. This method significantly improves the quality of ingots and reduces the amount of waste in the form of chips during their turning.

The name and history of the discovery of aluminum

The Latin aluminium comes from the Latin alumen, meaning alum (aluminum and potassium sulfate (K) KAl(SO4)2 12H2O), which has long been used in leather dressing and as an astringent. Al, a chemical element of group III of the periodic system, atomic number 13, atomic mass 26, 98154. Due to the high chemical activity, the discovery and isolation of pure aluminum dragged on for almost 100 years. The conclusion that "" (a refractory substance, in modern terms - aluminum oxide) can be obtained from alum was made back in 1754. German chemist A. Markgraf. Later it turned out that the same "earth" could be isolated from clay, and it was called alumina. It was only in 1825 that he was able to obtain metallic aluminum. Danish physicist H. K. Oersted. He treated with potassium amalgam (an alloy of potassium (K) with mercury (Hg)) aluminum chloride AlCl3, which could be obtained from alumina, and after distilling off mercury (Hg), isolated a gray powder of aluminum.

Only a quarter of a century later, this method was slightly modernized. The French chemist A. E. St. Clair Deville in 1854 suggested using metallic sodium (Na) to produce aluminum, and obtained the first ingots of the new metal. The cost of aluminum was then very high, and jewelry was made from it.

An industrial method for the production of aluminum by electrolysis of a melt of complex mixtures, including oxide, aluminum fluoride and other substances, was independently developed in 1886 by P. Eru () and C. Hall (USA). The production of aluminum is associated with a high cost of electricity, so it was realized on a large scale only in the 20th century. IN Union of Soviet Socialist Republics (CCCP) the first industrial aluminum was obtained on May 14, 1932 at the Volkhov aluminum plant, built next to the Volkhov hydroelectric power station.

Aluminum with a purity of over 99.99% was first obtained by electrolysis in 1920. In 1925 in work Edwards published some information about the physical and mechanical properties of such aluminum. In 1938 Taylor, Wheeler, Smith, and Edwards published an article that gives some of the properties of 99.996% purity aluminum, also obtained in France by electrolysis. The first edition of the monograph on the properties of aluminum was published in 1967.

In subsequent years, due to the relative ease of preparation and attractive properties, many works on the properties of aluminum. Pure aluminum has found wide application mainly in electronics - from electrolytic capacitors to the pinnacle of electronic engineering - microprocessors; in cryoelectronics, cryomagnetics.

Newer methods for obtaining pure aluminum are the zone purification method, crystallization from amalgams (alloys of aluminum with mercury) and isolation from alkaline solutions. The degree of purity of aluminum is controlled by the value of electrical resistance at low temperatures.

General characteristics of aluminum

Natural aluminum consists of one nuclide 27Al. The configuration of the outer electron layer is 3s2p1. In almost all compounds, the oxidation state of aluminum is +3 (valency III). The radius of the neutral aluminum atom is 0.143 nm, the radius of the Al3+ ion is 0.057 nm. The sequential ionization energies of a neutral aluminum atom are 5, 984, 18, 828, 28, 44, and 120 eV, respectively. On the Pauling scale, the electronegativity of aluminum is 1.5.

Aluminum is soft, light, silvery-white, the crystal lattice of which is face-centered cubic, parameter a = 0.40403 nm. Melting point of pure metal 660°C, boiling point about 2450°C, density 2, 6989 g/cm3. The temperature coefficient of linear expansion of aluminum is about 2.5·10-5 K-1.

Chemical aluminum is a fairly active metal. In air, its surface is instantly covered with a dense film of Al2O3 oxide, which prevents further access of oxygen (O) to the metal and leads to the termination of the reaction, which leads to high anti-corrosion properties of aluminum. A protective surface film on aluminum is also formed if it is placed in concentrated nitric acid.

Aluminum actively reacts with other acids:

6HCl + 2Al = 2AlCl3 + 3H2,

3Н2SO4 + 2Al = Al2(SO4)3 + 3H2.

Interestingly, the reaction between aluminum and iodine (I) powders begins at room temperature if a few drops of water are added to the initial mixture, which in this case plays the role of a catalyst:

2Al + 3I2 = 2AlI3.

The interaction of aluminum with sulfur (S) when heated leads to the formation of aluminum sulfide:

2Al + 3S = Al2S3,

which is easily decomposed by water:

Al2S3 + 6H2O = 2Al(OH)3 + 3H2S.

Aluminum does not interact directly with hydrogen (H), however, indirectly, for example, using organoaluminum compounds, it is possible to synthesize solid polymeric aluminum hydride (AlH3)x - the strongest reducing agent.

In the form of a powder, aluminum can be burned in air, and a white refractory powder of aluminum oxide Al2O3 is formed.

The high bond strength in Al2O3 determines the high heat of its formation from simple substances and the ability of aluminum to reduce many metals from their oxides, for example:

3Fe3O4 + 8Al = 4Al2O3 + 9Fe and even

3СаО + 2Al = Al2О3 + 3Са.

This method of obtaining metals is called aluminothermy.

Being in nature

In terms of prevalence in the earth's crust, aluminum ranks first among metals and third among all elements (after oxygen (O) and silicon (Si)), it accounts for about 8.8% of the mass of the earth's crust. Aluminum is included in a huge number of minerals, mainly aluminosilicates, and rocks. Aluminum compounds contain granites, basalts, clays, feldspars, etc. But here is the paradox: with a huge number minerals and rocks containing aluminum, deposits of bauxite, the main raw material for the industrial production of aluminum, are quite rare. IN Russian Federation there are bauxite deposits in Siberia and the Urals. Alunites and nephelines are also of industrial importance. As a trace element, aluminum is present in the tissues of plants and animals. There are organisms - concentrators that accumulate aluminum in their organs - some club mosses, mollusks.

Industrial production: at the index of industrial production, bauxites are first subjected to chemical processing, removing from them impurities of oxides of silicon (Si), iron (Fe) and other elements. As a result of such processing, pure aluminum oxide Al2O3 is obtained - the main one in the production of metal by electrolysis. However, due to the fact that the melting point of Al2O3 is very high (more than 2000°C), it is not possible to use its melt for electrolysis.

Scientists and engineers found a way out in the following. Cryolite Na3AlF6 is first melted in an electrolysis bath (melt temperature slightly below 1000°C). Cryolite can be obtained, for example, by processing nephelines from the Kola Peninsula. Further, a little Al2O3 (up to 10% by mass) and some other substances are added to this melt, improving the conditions for the subsequent process. During the electrolysis of this melt, aluminum oxide decomposes, the cryolite remains in the melt, and molten aluminum is formed on the cathode:

2Al2O3 = 4Al + 3O2.

Aluminum alloys

Most metal elements are alloyed with aluminum, but only a few of them play the role of the main alloying components in industrial aluminum alloys. However, a significant number of elements are used as additives to improve the properties of alloys. The most widely used:

Beryllium is added to reduce oxidation at elevated temperatures. Small additions of beryllium (0.01 - 0.05%) are used in aluminum casting alloys to improve fluidity in the production of internal combustion engine parts (pistons and cylinder heads).

Boron is introduced to increase electrical conductivity and as a refining additive. Boron is introduced into aluminum alloys used in nuclear power engineering (except for reactor parts), because it absorbs neutrons, preventing the spread of radiation. Boron is introduced on average in the amount of 0.095 - 0.1%.

Bismuth. Low melting point metals such as bismuth, cadmium are added to aluminum alloys to improve machinability. These elements form soft fusible phases that contribute to chip breakage and cutter lubrication.

Gallium is added in the amount of 0.01 - 0.1% to the alloys from which the consumable anodes are further made.

Iron. In small quantities (>0.04%) it is introduced during the production of wires to increase strength and improve creep characteristics. Same way iron reduces sticking to the walls of molds when casting into a mold.

Indium. The addition of 0.05 - 0.2% strengthens aluminum alloys during aging, especially at low cuprum content. Indium additives are used in aluminum-cadmium bearing alloys.

Approximately 0.3% cadmium is introduced to increase the strength and improve the corrosion properties of the alloys.

Calcium gives plasticity. With a calcium content of 5%, the alloy has the effect of superplasticity.

Silicon is the most used additive in foundry alloys. In the amount of 0.5 - 4% reduces the tendency to cracking. The combination of silicon and magnesium makes it possible to heat seal the alloy.

Magnesium. The addition of magnesium significantly increases strength without reducing ductility, improves weldability and increases the corrosion resistance of the alloy.

Copper strengthens alloys, maximum hardening is achieved when the content cuprum 4 - 6%. Alloys with cuprum are used in the production of pistons for internal combustion engines, high-quality cast parts for aircraft.

Tin improves cutting performance.

Titanium. The main task of titanium in alloys is grain refinement in castings and ingots, which greatly increases the strength and uniformity of properties throughout the volume.

Although aluminum is considered one of the least noble industrial metals, it is quite stable in many oxidizing environments. The reason for this behavior is the presence of a continuous oxide film on the surface of aluminum, which immediately re-forms on the cleaned areas when exposed to oxygen, water and other oxidizing agents.

In most cases, melting is carried out in air. If the interaction with air is limited to the formation of compounds insoluble in the melt on the surface and the resulting film of these compounds significantly slows down further interaction, then usually no measures are taken to suppress such interaction. Melting in this case is carried out with direct contact of the melt with the atmosphere. This is done in the preparation of most aluminum, zinc, tin-lead alloys.

The space in which melting of alloys takes place is limited by a refractory lining capable of withstanding temperatures of 1500 - 1800 ˚С. In all melting processes, the gas phase is involved, which is formed during the combustion of fuel, interacting with the environment and the lining of the melting unit, etc.

Most aluminum alloys have high corrosion resistance in the natural atmosphere, sea water, solutions of many salts and chemicals, and in most foods. Aluminum alloy structures are often used in sea water. Sea buoys, lifeboats, ships, barges have been built from aluminum alloys since 1930. At present, the length of aluminum alloy ship hulls reaches 61 m. There is experience in aluminum underground pipelines, aluminum alloys are highly resistant to soil corrosion. In 1951, a 2.9 km long pipeline was built in Alaska. After 30 years of operation, no leaks or serious damage due to corrosion have been found.

Aluminum is widely used in construction in the form of cladding panels, doors, window frames, electric cables. Aluminum alloys are not subject to severe corrosion for a long time in contact with concrete, mortar, plaster, especially if the structures are not frequently wet. When wet frequently, if the surface of the aluminum trade items has not been further processed, it may darken, up to blackening in industrial cities with a high content of oxidizing agents in the air. To avoid this, special alloys are produced to obtain shiny surfaces by brilliant anodizing - applying an oxide film to the metal surface. In this case, the surface can be given a variety of colors and shades. For example, alloys of aluminum with silicon allow you to get a range of shades, from gray to black. Aluminum alloys with chromium have a golden color.

Industrial aluminum is produced in the form of two types of alloys - casting, parts of which are made by casting, and deformation - alloys produced in the form of deformable semi-finished products - sheets, foil, plates, profiles, wire. Castings from aluminum alloys are obtained by all possible casting methods. It is most common under pressure, in chill molds and in sandy-clay molds. In the manufacture of small political parties, it is used casting in gypsum combined forms and casting for investment models. Cast alloys are used to make cast rotors of electric motors, cast parts of aircraft, etc. Wrought alloys are used in automotive production for interior decoration, bumpers, body panels and interior parts; in construction as a finishing material; in aircraft, etc.

IN industry aluminum powders are also used. Used in metallurgical industry: in aluminothermy, as alloying additives, for the manufacture of semi-finished products by pressing and sintering. This method produces very durable parts (gears, bushings, etc.). Powders are also used in chemistry to obtain aluminum compounds and as catalyst(for example, in the production of ethylene and acetone). Given the high reactivity of aluminum, especially in the form of a powder, it is used in explosives and solid propellants for rockets, using its ability to quickly ignite.

Given the high resistance of aluminum to oxidation, the powder is used as a pigment in coatings for painting equipment, roofs, paper in printing, shiny surfaces of car panels. Also, a layer of aluminum is covered with steel and cast iron trade item to prevent their corrosion.

In terms of application, aluminum and its alloys are second only to iron (Fe) and its alloys. The widespread use of aluminum in various fields of technology and everyday life is associated with a combination of its physical, mechanical and chemical properties: low density, corrosion resistance in atmospheric air, high thermal and electrical conductivity, ductility and relatively high strength. Aluminum is easily processed in various ways - forging, stamping, rolling, etc. Pure aluminum is used to make wire (the electrical conductivity of aluminum is 65.5% of the electrical conductivity of cuprum, but aluminum is more than three times lighter than cuprum, so aluminum is often replaced in electrical engineering) and foil used as packaging material. The main part of the smelted aluminum is spent on obtaining various alloys. Protective and decorative coatings are easily applied to the surface of aluminum alloys.

The variety of properties of aluminum alloys is due to the introduction of various additives into aluminum, which form solid solutions or intermetallic compounds with it. The bulk of aluminum is used to produce light alloys - duralumin (94% aluminum, 4% copper (Cu), 0.5% magnesium (Mg), manganese (Mn), (Fe) and silicon (Si)), silumin ( 85-90% - aluminum, 10-14% silicon (Si), 0.1% sodium (Na)) and others. In metallurgy, aluminum is used not only as a base for alloys, but also as one of the widely used alloying additives in alloys based on cuprum (Cu), magnesium (Mg), iron (Fe), >nickel (Ni), etc.

Aluminum alloys are widely used in everyday life, in construction and architecture, in the automotive industry, in shipbuilding, aviation and space technology. In particular, the first artificial satellite Earth. An alloy of aluminum and zirconium (Zr) is widely used in nuclear reactor building. Aluminum is used in the manufacture of explosives.

When handling aluminum in everyday life, you need to keep in mind that only neutral (by acidity) liquids (for example, boil water) can be heated and stored in aluminum dishes. If, for example, sour cabbage soup is boiled in aluminum dishes, then aluminum passes into food, and it acquires an unpleasant “metallic” taste. Since the oxide film is very easy to damage in everyday life, the use aluminum cookware still undesirable.

Silver-white metal, light

density — 2.7 g/cm

melting point for technical aluminum - 658 °C, for high purity aluminum - 660 °C

specific heat of fusion — 390 kJ/kg

boiling point - 2500 ° C

specific heat of evaporation - 10.53 MJ / kg

tensile strength of cast aluminum - 10-12 kg / mm², deformable - 18-25 kg / mm², alloys - 38-42 kg / mm²

Brinell hardness — 24…32 kgf/mm²

high plasticity: for technical - 35%, for clean - 50%, rolled into a thin sheet and even foil

Young's modulus - 70 GPa

Aluminum has a high electrical conductivity (0.0265 μOhm m) and thermal conductivity (203.5 W/(m K)), 65% of the electrical conductivity of cuprum, and has a high light reflectivity.

Weak paramagnet.

Temperature coefficient of linear expansion 24.58 10−6 K−1 (20…200 °C).

The temperature coefficient of electrical resistance is 2.7·10−8K−1.

Aluminum forms alloys with almost all metals. The best known are alloys with cuprum and magnesium (duralumin) and silicon (silumin).

Natural aluminum consists almost entirely of a single stable isotope 27Al with traces of 26Al, a radioactive isotope with period a half-life of 720 thousand years, formed in the atmosphere during the bombardment of argon nuclei by cosmic ray protons.

In terms of prevalence in the earth's crust, the Earth occupies the 1st place among metals and the 3rd place among elements, second only to oxygen and silicon. aluminum content in the earth's crust data various researchers is from 7.45 to 8.14% of the mass of the earth's crust.

In nature, aluminum, due to its high chemical activity, occurs almost exclusively in the form of compounds. Some of them:

Bauxites - Al2O3 H2O (with admixtures of SiO2, Fe2O3, CaCO3)

Alunites - (Na,K)2SO4 Al2(SO4)3 4Al(OH)3

Alumina (mixtures of kaolins with sand SiO2, limestone CaCO3, magnesite MgCO3)

Corundum (sapphire, ruby, emery) - Al2O3

Kaolinite - Al2O3 2SiO2 2H2O

Beryl (emerald, aquamarine) - 3BeO Al2O3 6SiO2

Chrysoberyl (alexandrite) - BeAl2O4.

However, under certain specific reducing conditions, the formation of native aluminum is possible.

In natural waters, aluminum is found in the form of low-toxic chemical compounds, such as aluminum fluoride. The type of cation or anion depends, first of all, on the acidity of the aqueous medium. Aluminum concentrations in surface water bodies Russian Federation range from 0.001 to 10 mg/l, in sea water 0.01 mg/l.

Aluminum (Aluminum) is

Obtaining castings from aluminum alloys

The main challenge facing the foundry in our country, consists in a significant overall improvement in the quality of castings, which should find expression in a decrease in wall thickness, a decrease in machining allowances and gating systems while maintaining the proper operational properties of trade items. The end result of this work should be to meet the increased needs of mechanical engineering with the necessary number of cast billets without a significant increase in the total monetary emission of castings by weight.

Sand casting

Of the above methods of casting into disposable molds, the most widely used in the manufacture of castings from aluminum alloys is casting into wet sand molds. This is due to the low density of the alloys, the small force effect of the metal on the mold, and low casting temperatures (680-800C).

For the manufacture of sand molds, molding and core mixtures are used, prepared from quartz and clay sands (GOST 2138-74), molding clays (GOST 3226-76), binders and auxiliary materials.

The type of gating system is chosen taking into account the dimensions of the casting, the complexity of its configuration and location in the mold. The pouring of molds for castings of complex configuration of small height is carried out, as a rule, with the help of lower gating systems. At high altitude castings and thin walls, it is preferable to use vertically slotted or combined gating systems. Molds for castings of small sizes can be poured through the top gating systems. In this case, the height of the metal scab falling into the mold cavity should not exceed 80 mm.

To reduce the speed of the melt at the entrance to the mold cavity and to better separate the oxide films and slag inclusions suspended in it, additional hydraulic resistances are introduced into the gating systems - meshes (metal or fiberglass) are installed or poured through granular filters.

Sprues (feeders), as a rule, are brought to thin sections (walls) of castings dispersed around the perimeter, taking into account the convenience of their subsequent separation during processing. The supply of metal to massive units is unacceptable, as it causes the formation of shrinkage cavities in them, increased roughness and shrinkage "failures" on the surface of the castings. In cross section, the sprue channels most often have a rectangular shape with a wide side of 15-20 mm, and a narrow side of 5-7 mm.

Alloys with a narrow crystallization interval (AL2, AL4, AL), AL34, AK9, AL25, ALZO) are prone to the formation of concentrated shrinkage cavities in the thermal units of castings. To bring these shells out of the castings, the installation of massive profits is widely used. For thin-walled (4-5 mm) and small castings, the mass of the profit is 2-3 times the mass of the castings, for thick-walled castings, up to 1.5 times. Height arrived chosen depending on the height of the casting. When the height is less than 150 mm, the height arrived H-adj. take equal to the height of the casting Notl. For higher castings, the ratio Nprib / Notl is taken equal to 0.3 0.5.

The greatest application in casting aluminum alloys are the upper open profits round or oval section; lateral profits in most cases are made closed. To improve work efficiency profits they are insulated, filled with hot metal, topped up. Warming is usually carried out by a sticker on the surface of the form of sheet asbestos, followed by drying with a gas flame. Alloys with a wide crystallization range (AL1, AL7, AL8, AL19, ALZZ) are prone to the formation of scattered shrinkage porosity. Impregnation of shrinkage pores with profits ineffective. Therefore, in the manufacture of castings from the listed alloys, it is not recommended to use the installation of massive profits. To obtain high-quality castings, directional solidification is carried out, widely using the installation of refrigerators made of cast iron and aluminum alloys for this purpose. Optimum conditions for directional crystallization are created by a vertical slot gate system. To prevent gas evolution during crystallization and to prevent the formation of gas-shrinkage porosity in thick-walled castings, crystallization under a pressure of 0.4–0.5 MPa is widely used. To do this, the casting molds are placed in autoclaves before pouring, they are filled with metal and the castings are crystallized under air pressure. For the manufacture of large-sized (up to 2-3 m high) thin-walled castings, a casting method with successively directed solidification is used. The essence of the method is the successive crystallization of the casting from the bottom up. To do this, the casting mold is placed on the table of a hydraulic lift and metal tubes 12–20 mm in diameter, heated to 500–700°C, are lowered inside it, performing the function of risers. The tubes are fixedly fixed in the gating cup and the holes in them are closed with stoppers. After the gating cup is filled with melt, the stoppers are lifted, and the alloy flows through the tubes into the gating wells connected to the mold cavity by slotted sprues (feeders). After the level of the melt in the wells rises by 20-30 mm above the lower end of the tubes, the mechanism for lowering the hydraulic table is turned on. The lowering speed is taken such that the filling of the mold is carried out under the flooded level and the hot metal continuously flows into the upper parts of the mold. This provides directional solidification and makes it possible to obtain complex castings without shrinkage defects.

Filling sand molds with metal is carried out from ladles lined with refractory material. Before filling with metal, freshly lined ladles are dried and calcined at 780–800°C to remove moisture. The temperature of the melt before pouring is maintained at the level of 720-780 °C. Molds for thin-walled castings are filled with melts heated to 730-750°C, and for thick-walled castings up to 700-720°C.

Casting in plaster molds

Casting in gypsum molds is used in cases where increased requirements are placed on castings in terms of accuracy, surface cleanliness and reproduction of the smallest details of the relief. Compared to sand molds, gypsum molds have higher strength, dimensional accuracy, better resistance to high temperatures, and make it possible to obtain castings of complex configuration with a wall thickness of 1.5 mm according to the 5-6th accuracy class. Forms are made according to wax or metal (brass,) chrome-plated models. Model plates are made of aluminum alloys. To facilitate the removal of models from molds, their surface is covered with thin layer kerosene-stearin lubricant.

Small and medium molds for complex thin-walled castings are made from a mixture consisting of 80% gypsum, 20% quartz sand or asbestos and 60-70% water (by weight of the dry mixture). The composition of the mixture for medium and large forms: 30% gypsum, 60% sand, 10% asbestos, 40-50% water. To slow down the setting, 1-2% slaked lime is added to the mixture. The necessary strength of the forms is achieved by hydration of anhydrous or semi-aqueous gypsum. To reduce strength and increase gas permeability, raw gypsum molds are subjected to hydrothermal treatment - they are kept in an autoclave for 6-10 hours under a water vapor pressure of 0.13-0.14 MPa, and then for a day in air. After that, the forms are subjected to stepwise drying at 350-500 °C.

A feature of gypsum molds is their low thermal conductivity. This circumstance makes it difficult to obtain dense castings from aluminum alloys with a wide range of crystallization. Therefore, the main task in the development of a sprue-profitable system for gypsum molds is to prevent the formation of shrinkage cavities, looseness, oxide films, hot cracks and underfilling of thin walls. This is achieved by the use of expanding gating systems that provide a low speed of movement of melts in the mold cavity, directed solidification of thermal units towards the risers with the help of refrigerators, and an increase in the compliance of molds by increasing the content of quartz sand in the mixture. Thin-walled castings are poured into molds heated to 100–200°C by the vacuum suction method, which makes it possible to fill cavities up to 0.2 mm thick. Thick-walled (more than 10 mm) castings are obtained by pouring molds in autoclaves. Crystallization of the metal in this case is carried out under a pressure of 0.4–0.5 MPa.

Shell casting

Casting into shell molds is expedient to use in serial and large-scale production of castings of limited dimensions with increased surface finish, greater dimensional accuracy and less machining than when casting into sand molds.

Shell molds are made using hot (250–300 °C) metal (steel,) tooling in a bunker way. Model equipment is performed according to the 4th-5th accuracy classes with molding slopes from 0.5 to 1.5%. The shells are made two-layer: the first layer is from a mixture with 6-10% thermosetting resin, the second from a mixture with 2% resin. For better shell removal, the model slab is covered with a thin layer of separating emulsion (5% silicone fluid No. 5; 3% laundry soap; 92% water).

For the manufacture of shell molds, fine-grained quartz sands containing at least 96% silica are used. The half-molds are connected by gluing on special pin presses. Glue composition: 40% MF17 resin; 60% marshalite and 1.5% aluminum chloride (hardening). Filling of the assembled forms is carried out in containers. When casting into shell molds, the same gating systems and temperature conditions are used as when casting into sand molds.

The low rate of metal crystallization in shell molds and the lower possibilities for creating directed crystallization result in the production of castings with lower properties than when casting in raw sand molds.

Investment casting

Investment casting is used to manufacture castings of increased accuracy (3rd-5th class) and surface finish (4-6th roughness class), for which this method is the only possible or optimal one.

Models in most cases are made from pasty paraffin stearin (1: 1) compositions by pressing into metal molds (cast and prefabricated) on stationary or carousel installations. In the manufacture of complex castings with dimensions of more than 200 mm, in order to avoid deformation of the models, substances are introduced into the composition of the model mass that increase the temperature of their softening (melting).

As a refractory coating in the manufacture of ceramic molds, a suspension of hydrolyzed ethyl silicate (30–40%) and powdered quartz (70–60%) is used. Sprinkling of model blocks is carried out with calcined sand 1KO16A or 1K025A. Each coating layer is dried in air for 10-12 hours or in an atmosphere containing ammonia vapor. The necessary strength of the ceramic mold is achieved with a shell thickness of 4–6 mm (4–6 layers of a refractory coating). To ensure smooth filling of the mold, expanding gating systems are used with metal supply to thick sections and massive nodes. Castings are usually fed from a massive riser through thickened sprues (feeders). For complex castings, it is allowed to use massive profits to power the upper massive units with the obligatory filling of them from the riser.

Aluminum (Aluminum) is

Models are melted from molds in hot (85–90°C) water acidified with hydrochloric acid (0.5–1 cm3 per liter of water) to prevent saponification of stearin. After melting the models, the ceramic molds are dried at 150–170°C for 1–2 hours, placed in containers, filled with dry filler, and calcined at 600–700°C for 5–8 hours. Filling is carried out in cold and heated molds. The heating temperature (50-300 °C) of the molds is determined by the thickness of the walls of the casting. The filling of molds with metal is carried out in the usual way, as well as using vacuum or centrifugal force. Most aluminum alloys are heated to 720-750°C before pouring.

Die casting

Chill casting is the main method of serial and mass production of castings from aluminum alloys, which makes it possible to obtain castings of the 4th-6th accuracy classes with a surface roughness Rz = 50-20 and a minimum wall thickness of 3-4 mm. When casting into a chill mold, along with defects caused by high speeds of the melt in the mold cavity and non-compliance with the requirements of directional solidification (gas porosity, oxide films, shrinkage looseness), the main types of rejects and castings are underfills and cracks. The appearance of cracks is caused by difficult shrinkage. Cracks occur especially often in castings made from alloys with a wide crystallization interval, which have a large linear shrinkage (1.25–1.35%). Prevention of the formation of these defects is achieved by various technological methods.

In the case of supplying metal to thick sections, provision should be made for feeding the supply point by installing a supply boss (profit). All elements of the gating systems are located along the chill mold connector. The following cross-sectional area ratios of the gate channels are recommended: for small castings EFst: EFsl: EFpit = 1: 2: 3; for large castings EFst: EFsl: EFpit = 1: 3: 6.

To reduce the rate of melt entry into the mold cavity, curved risers, fiberglass or metal meshes, and granular filters are used. The quality of castings from aluminum alloys depends on the rate of rise of the melt in the mold cavity. This speed should be sufficient to guarantee the filling of thin sections of castings under conditions of increased heat removal and at the same time not cause underfilling due to incomplete release of air and gases through the ventilation ducts and risers, swirling and flowing of the melt during the transition from narrow sections to wide ones. The rate of rise of the metal in the mold cavity when casting into a mold is taken somewhat higher than when casting into sand molds. The minimum allowable lifting speed is calculated according to the formulas of A. A. Lebedev and N. M. Galdin (see section 5.1, “Sand casting”).

To obtain dense castings, as in sand casting, directional solidification is created by proper positioning of the casting in the mold and control of heat dissipation. As a rule, massive (thick) casting units are located in the upper part of the mold. This makes it possible to compensate for the reduction in their volume during hardening directly from the profits installed above them. The regulation of the intensity of heat removal in order to create directional solidification is carried out by cooling or insulating various sections of the mold. To locally increase heat removal, inserts from heat-conducting cuprum are widely used, they provide for an increase in the cooling surface of the mold due to fins, local cooling of the molds with compressed air or water is carried out. To reduce the intensity of heat removal, a layer of paint 0.1–0.5 mm thick is applied to the working surface of the mold. For this purpose, a layer of paint 1-1.5 mm thick is applied to the surface of the sprue channels and profits. The slowdown in the cooling of the metal in the risers can also be achieved by local thickening of the mold walls, the use of various low-heat-conductive coatings and the insulation of the risers with an asbestos sticker. Painting the working surface of the mold improves the appearance of the castings, helps to eliminate gas pockets on their surface and increases the durability of the molds. Before painting, the molds are heated to 100-120 °C. An excessively high heating temperature is undesirable, since this reduces the rate of solidification of the castings and the duration term mold service. Heating reduces the temperature difference between the casting and the mold and the expansion of the mold due to its heating by the casting metal. As a result, tensile stresses in the casting are reduced, causing appearance cracks. However, heating the mold alone is not enough to eliminate the possibility of cracking. It is necessary to timely remove the casting from the mold. The casting should be removed from the mold before the moment when its temperature equals the temperature of the mold, and the shrinkage stresses reach the maximum value. Usually, the casting is removed at the moment when it is strong enough that it can be moved without destruction (450-500 ° C). By this time, the gating system has not yet acquired sufficient strength and is destroyed by light impacts. The holding time of the casting in the mold is determined by the rate of solidification and depends on the temperature of the metal, the temperature of the mold, and the rate of pouring.

To eliminate metal sticking, increase service life and facilitate extraction, metal rods are lubricated during operation. The most common lubricant is a water-graphite suspension (3-5% graphite).

Parts of the molds that perform the external outlines of the castings are made of gray cast iron. The wall thickness of the molds is assigned depending on the wall thickness of the castings in accordance with the recommendations of GOST 16237-70. Internal cavities in castings are made using metal (steel) and sand rods. Sand rods are used to decorate complex cavities that cannot be made with metal rods. To facilitate the extraction of castings from molds, the outer surfaces of the castings must have a casting slope from 30 "to 3 ° towards the parting. The internal surfaces of castings made with metal rods must have a slope of at least 6 °. Sharp transitions from thick to thin sections are not allowed in castings. The radius of curvature must be at least 3 mm. Holes with a diameter of more than 8 mm for small castings, 10 mm for medium and 12 mm for large castings are made with rods. The optimal ratio of the depth of the hole to its diameter is 0.7-1.

Air and gases are removed from the mold cavity with the help of ventilation ducts placed in the parting plane and plugs placed in the walls near deep cavities.

In modern foundries, molds are installed on single-station or multi-station semi-automatic casting machines, in which the closing and opening of the mold, insertion and removal of cores, ejection and removal of the casting from the mold are automated. Automatic control of the mold heating temperature is also provided. Filling molds on machines is carried out using dispensers.

To improve the filling of thin mold cavities and remove air and gases released during the destruction of binders, the molds are evacuated, poured under low pressure or using centrifugal force.

Squeeze casting

Squeeze casting is a type of die casting. It is intended for the manufacture of large-sized panel-type castings (2500x1400 mm) with a wall thickness of 2-3 mm. For this purpose, metal half-moulds are used, which are mounted on specialized casting-squeezing machines with one-sided or two-sided convergence of the half-moulds. A distinctive feature of this casting method is the forced filling of the mold cavity with a wide melt flow when the mold halves approach each other. There are no elements of a conventional gating system in the casting mold. Data This method is used to make castings from AL2, AL4, AL9, AL34 alloys, which have a narrow crystallization range.

The melt cooling rate is controlled by applying a heat-insulating coating of various thicknesses (0.05–1 mm) to the working surface of the mold cavity. Overheating of alloys before pouring should not exceed 15-20°C above the liquidus temperature. The duration of the convergence of the half-forms is 5-3 s.

Low pressure casting

Low pressure casting is another form of die casting. It has been used in the manufacture of large-sized thin-walled castings from aluminum alloys with a narrow crystallization interval (AL2, AL4, AL9, AL34). As in the case of mold casting, the outer surfaces of the castings are made with a metal mold, and the inner cavities are made with metal or sand cores.

For the manufacture of rods, a mixture consisting of 55% quartz sand 1K016A is used; 13.5% bold sand P01; 27% powdered quartz; 0.8% pectin glue; 3.2% resin M and 0.5% kerosene. Such a mixture does not form a mechanical burn. Forms are filled with metal by pressure of dried compressed air (18–80 kPa) supplied to the surface of the melt in a crucible heated to 720–750°C. Under the action of this pressure, the melt is forced out of the crucible into the metal wire, and from it into the gating system and further into the mold cavity. The advantage of low-pressure casting is the ability to automatically control the rate of metal rise in the mold cavity, which makes it possible to obtain thin-walled castings of better quality than gravity casting.

Crystallization of alloys in the mold is carried out under a pressure of 10–30 kPa until a solid metal crust is formed and 50–80 kPa after the formation of a crust.

Denser aluminum alloy castings are produced by low-pressure casting with back pressure. The filling of the mold cavity during casting with back pressure is carried out due to the pressure difference in the crucible and in the mold (10–60 kPa). Crystallization of the metal in the form is carried out under a pressure of 0.4-0.5 MPa. This prevents the release of hydrogen dissolved in the metal and the formation of gas pores. High blood pressure contributes to better nutrition of massive casting units. In other respects, back-pressure casting technology is no different from low-pressure casting technology.

Back pressure casting successfully combines the advantages of low pressure casting and pressure crystallization.

Injection molding

Die-casting from aluminum alloys AL2, ALZ, AL1, ALO, AL11, AL13, AL22, AL28, AL32, AL34, castings of complex configuration of the 1st-3rd accuracy classes with a wall thickness of 1 mm and more, cast holes with a diameter of up to 1.2mm, cast outer and internal thread with a minimum pitch of 1 mm and a diameter of 6 mm. The surface cleanliness of such castings corresponds to 5-8 roughness classes. The production of such castings is carried out on machines with cold horizontal or vertical pressing chambers, with a specific pressing pressure of 30–70 MPa. Preference is given to machines with a horizontal bale chamber.

The dimensions and weight of the castings are limited by the capabilities of the Injection Molding Machines: the volume of the pressing chamber, the specific pressing pressure (p) and the locking force (0). The area of ​​projection (F) of the casting, the gate channels and the pressing chamber on the movable mold plate should not exceed the values ​​determined by the formula F = 0.85 0/r.

The optimum slope values ​​for outdoor surfaces are 45°; for internal 1°. The minimum radius of curvature is 0.5-1mm. Holes larger than 2.5 mm in diameter are made by casting. Castings from aluminum alloys, as a rule, are machined only along the seating surfaces. The processing allowance is assigned taking into account the dimensions of the casting and ranges from 0.3 to 1 mm.

Various materials are used to make molds. Parts of the molds in contact with the liquid metal are made of steel ZKh2V8, 4Kh8V2, 4KhV2S; steels 35, 45, 50, pins, bushings and guide columns - from U8A steel.

The supply of metal to the cavity of the molds is carried out using external and internal gating systems. The feeders are brought to the parts of the casting that are subjected to machining. Their thickness is assigned depending on the wall thickness of the casting at the point of supply and the specified nature of the filling of the mold. This dependence is determined by the ratio of the Feeder thickness to the wall thickness of the casting. Smooth, without turbulence and air entrapment, the filling of molds takes place if the ratio is close to one. For castings with wall thickness up to 2 mm. feeders have a thickness of 0.8 mm; with a wall thickness of 3mm. the thickness of the feeders is 1.2 mm; with a wall thickness of 4-6 mm-2 mm.

To receive the first portion of the melt enriched with air inclusions, special wash tanks are located near the mold cavity, the volume of which can reach 20–40% of the casting volume. Washers are connected to the cavity of the mold by channels, the thickness of which is equal to the thickness of the feeders. Removal of air and gas from the mold cavity is carried out through special ventilation channels and gaps between the rods (pushers) and the mold matrix. Ventilation channels are made in the split plane on the fixed part of the mold, as well as along the movable rods and ejectors. The depth of the ventilation ducts when casting aluminum alloys is assumed to be 0.05-0.15 mm, and the width is 10-30 mm in order to improve ventilation, the cavity of the washers with thin channels (0.2-0.5 mm) is connected to the atmosphere .

The main defects of injection molded castings are air (gas) subcrustal porosity caused by air entrapment at high speeds of metal inlet into the mold cavity, and shrinkage porosity (or shells) in thermal nodes. The formation of these defects is greatly influenced by the parameters of the casting technology, the pressing speed, the pressing pressure, and the thermal regime of the mold.

The pressing speed determines the mold filling mode. The higher the pressing speed, the faster the melt moves through the gating channels, the greater the melt inlet speed into the mold cavity. High pressing speeds contribute to better filling of thin and elongated cavities. At the same time, they are the cause of air capture by the metal and the formation of subcrustal porosity. When casting aluminum alloys, high pressing speeds are used only in the manufacture of complex thin-walled castings. The pressing pressure has a great influence on the quality of castings. As it increases, the density of castings increases.

The value of the pressing pressure is usually limited by the value of the locking force of the machine, which must exceed the pressure exerted by the metal on the movable matrix (pF). Therefore, local pre-pressing of thick-walled castings, known as the Ashigai process, is gaining great interest. The low rate of metal entry into the mold cavity through large-section feeders and the effective pre-pressing of the crystallizing melt with the help of a double plunger make it possible to obtain dense castings.

The quality of castings is also significantly affected by the temperatures of the alloy and mold. In the manufacture of thick-walled castings of a simple configuration, the melt is poured at a temperature of 20–30 °C below the liquidus temperature. Thin-walled castings require the use of a melt superheated above the liquidus temperature by 10–15°C. To reduce the magnitude of shrinkage stresses and prevent the formation of cracks in castings, the molds are heated before pouring. The following heating temperatures are recommended:

Casting wall thickness, mm 1—2 2—3 3—5 5—8

Heating temperature

molds, °С 250—280 200—250 160—200 120—160

The stability of the thermal regime is provided by heating (electric) or cooling (water) molds.

To protect the working surface of the molds from sticking and erosive effects of the melt, to reduce friction during the extraction of the cores and to facilitate the extraction of castings, the molds are lubricated. For this purpose, fatty (oil with graphite or aluminum powder) or aqueous (salt solutions, aqueous preparations based on colloidal graphite) lubricants are used.

The density of castings from aluminum alloys increases significantly when casting with vacuum molds. To do this, the mold is placed in a sealed casing, in which the necessary vacuum is created. Good results can be obtained using the "oxygen process". To do this, the air in the cavity of the mold is replaced with oxygen. At high speeds of metal inlet into the mold cavity, which cause the capture of oxygen by the melt, subcrustal porosity in the castings is not formed, since all the trapped oxygen is spent on the formation of fine aluminum oxides, which do not noticeably affect the mechanical properties of the castings. Such castings can be subjected to heat treatment.

Depending on the requirements of the technical specifications, aluminum alloy castings can be subjected to various types control: X-ray, gamma-ray or ultrasonic for the detection of internal defects; markings for determining dimensional deviations; luminescent to detect surface cracks; hydro- or pneumocontrol to assess tightness. The frequency of the listed types of control is specified specifications or determined by the department of the chief metallurgist of the plant. Identified defects, if allowed by the technical specifications, are eliminated by welding or impregnation. Argon-arc welding is used for welding of underfills, shells, looseness of cracks. Before welding, the defective place is cut in such a way that the walls of the recesses have a slope of 30 - 42 °. Castings are subjected to local or general heating up to 300-350C. Local heating is carried out by an oxy-acetylene flame, general heating is carried out in chamber furnaces. Welding is carried out with the same alloys from which the castings are made, using a non-consumable tungsten electrode with a diameter of 2-6 mm at expense argon 5-12 l/min. The strength of the welding current is usually 25-40 A per 1 mm of the electrode diameter.

Porosity in castings is eliminated by impregnation with bakelite varnish, asphalt varnish, drying oil or liquid glass. Impregnation is carried out in special boilers under a pressure of 490-590 kPa with preliminary holding of castings in a rarefied atmosphere (1.3-6.5 kPa). The temperature of the impregnating liquid is maintained at 100°C. After impregnation, the castings are subjected to drying at 65-200°C, during which the impregnating liquid hardens, and repeated control.

Aluminum (Aluminum) is

Application of aluminum

Widely used as a structural material. The main advantages of aluminum in this capacity are lightness, ductility for stamping, corrosion resistance (in air, aluminum is instantly covered with a strong Al2O3 film, which prevents its further oxidation), high thermal conductivity, and non-toxicity of its compounds. In particular, these properties have made aluminum extremely popular in the manufacture of cookware, aluminum foil in Food Industry and for packaging.

The main disadvantage of aluminum as a structural material is its low strength, therefore, to strengthen it, it is usually alloyed with a small amount of cuprum and magnesium (the alloy is called duralumin).

The electrical conductivity of aluminum is only 1.7 times less than that of cuprum, while aluminum is approximately 4 times cheaper per kilogram, but, due to 3.3 times lower density, to obtain equal resistance, it needs approximately 2 times less weight . Therefore, it is widely used in electrical engineering for the manufacture of wires, their shielding, and even in microelectronics for the manufacture of conductors in chips. The lower electrical conductivity of aluminum (37 1/ohm) compared to cuprum (63 1/ohm) is compensated by an increase in the cross section of aluminum conductors. The disadvantage of aluminum as an electrical material is the presence of a strong oxide film that makes soldering difficult.

Due to the complex of properties, it is widely used in thermal equipment.

Aluminum and its alloys retain strength at ultra-low temperatures. Because of this, it is widely used in cryogenic technology.

The high reflectivity combined with the low cost and ease of deposition makes aluminum an ideal material for making mirrors.

In production building materials as a gas generating agent.

Aluminizing gives corrosion and scale resistance to steel and other alloys, such as piston engine valves, turbine blades, oil rigs, heat exchange equipment, and also replaces galvanizing.

Aluminum sulfide is used to produce hydrogen sulfide.

Research is underway to develop foamed aluminum as a particularly strong and lightweight material.

As a component of thermite, mixtures for aluminothermy

Aluminum is used to recover rare metals from their oxides or halides.

Aluminum is an important component of many alloys. For example, in aluminum bronzes, the main components are copper and aluminum. In magnesium alloys, aluminum is most often used as an additive. For the manufacture of spirals in electric heaters, Fechral (Fe, Cr, Al) is used (along with other alloys).

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When aluminum was very expensive, a variety of jewelry trade items were made from it. So, Napoleon III ordered aluminum buttons, and in 1889 Dmitry Ivanovich Mendeleev was presented with scales with bowls made of gold and aluminum. The fashion for them immediately passed when new technologies (developments) for its production appeared, which reduced the cost many times over. Now aluminum is sometimes used in the manufacture of jewelry.

In Japan, aluminum is used in the manufacture of traditional jewelry, replacing .

Aluminum and its compounds are used as high-performance rocket fuel in two-component rocket fuels and as a fuel component in solid rocket propellants. The following aluminum compounds are of the greatest practical interest as rocket fuel:

Powdered aluminum as a fuel in solid rocket propellants. It is also used in the form of powder and suspensions in hydrocarbons.

aluminum hydride.

aluminum borane.

Trimethylaluminum.

Triethylaluminum.

Tripropylaluminum.

Triethylaluminum (usually, together with triethylboron) is also used for chemical ignition (i.e., as a starting fuel) in rocket engines, as it ignites spontaneously in oxygen gas.

It has a slight toxic effect, but many water-soluble inorganic aluminum compounds remain in a dissolved state for a long time and can have a harmful effect on humans and warm-blooded animals through drinking water. The most toxic are chlorides, nitrates, acetates, sulfates, etc. For humans, the following doses of aluminum compounds (mg/kg of body weight) have a toxic effect when ingested:

aluminum acetate - 0.2-0.4;

aluminum hydroxide - 3.7-7.3;

aluminum alum - 2.9.

Primarily acts on nervous system(accumulates in the nervous tissue, leading to severe disorders of the central nervous system function). However, the neurotoxic property of aluminum began to be studied since the mid-1960s, since the accumulation of the metal in the human body is hindered by the mechanism of its excretion. Under normal conditions, up to 15 mg of an element per day can be excreted in the urine. Accordingly, the greatest negative effect is observed in people with impaired renal excretory function.

According to some biological studies, the intake of aluminum in the human body was considered a factor in the development of Alzheimer's disease, but these studies were later criticized and the conclusion about the connection of one with the other was refuted.

The chemical features of aluminum are determined by its high affinity for oxygen (in minerals aluminum enters into oxygen octahedra and tetrahedra), constant valency (3), poor solubility of most natural compounds. In endogenous processes during the solidification of magma and the formation of igneous rocks, aluminum enters into crystal lattice feldspars, micas and other minerals - aluminosilicates. In the biosphere, aluminum is a weak migrant; it is scarce in organisms and the hydrosphere. In a humid climate, where the decaying remains of abundant vegetation form a lot of organic acids, aluminum migrates in soils and waters in the form of organomineral colloidal compounds; aluminum is adsorbed by colloids and precipitated in the lower part of soils. The connection of aluminum with silicon is partially broken and in some places in the tropics minerals are formed - aluminum hydroxides - boehmite, diaspore, hydrargillite. Most of the aluminum is part of the aluminosilicates - kaolinite, beidellite and other clay minerals. Weak mobility determines the residual accumulation of aluminum in the weathering crust of the humid tropics. As a result, eluvial bauxites are formed. In past geological epochs, bauxites also accumulated in lakes and the coastal zone of the seas of tropical regions (for example, sedimentary bauxites of Kazakhstan). In the steppes and deserts, where there is little living matter, and the waters are neutral and alkaline, aluminum almost does not migrate. The migration of aluminum is most vigorous in volcanic areas, where highly acidic river and underground waters rich in aluminum are observed. In places of displacement of acidic waters with alkaline - marine (at the mouths of rivers and others), aluminum is deposited with the formation of bauxite deposits.

Aluminum is part of the tissues of animals and plants; in the organs of mammals, from 10-3 to 10-5% of aluminum (per crude substance) was found. Aluminum accumulates in the liver, pancreas and thyroid glands. IN herbal products aluminum content ranges from 4 mg per 1 kg of dry matter (potato) to 46 mg (yellow turnip), in animal products - from 4 mg (honey) to 72 mg per 1 kg of dry matter (). In the daily human diet, the content of aluminum reaches 35-40 mg. Known organisms are aluminum concentrators, for example, club mosses (Lycopodiaceae), containing up to 5.3% aluminum in the ash, mollusks (Helix and Lithorina), in the ashes of which 0.2-0.8% aluminum. Forming insoluble compounds with phosphates, aluminum disrupts the nutrition of plants (phosphate absorption by roots) and animals (phosphate absorption in the intestines).

The main purchaser is aviation. The most heavily loaded elements of the aircraft (skin, power reinforcing set) are made of duralumin. And they took this alloy into space. He even landed on the Moon and returned to Earth. And the stations "Luna", "Venus", "Mars", created by the designers of the bureau, which long years headed by Georgy Nikolaevich Babakin (1914-1971), they could not do without aluminum alloys.

Alloys of the aluminum-manganese and aluminum-magnesium system (AMts and AMg) are the main material for the hulls of high-speed "rockets" and "meteors" - hydrofoils.

But aluminum alloys are used not only in space, aviation, sea and river transport. Aluminum occupies a strong position in land transport. The following data speaks of the widespread use of aluminum in the automotive industry. In 1948, 3.2 kg of aluminum was used per one, in 1958 - 23.6, in 1968 - 71.4, and today this figure exceeds 100 kg. Aluminum also appeared in railway transport. And the Russkaya Troika superexpress is more than 50% made of aluminum alloys.

Aluminum is being used more and more in construction. In new buildings, strong and light beams, ceilings, columns, railings, fences, elements of ventilation systems made of aluminum-based alloys are often used. In recent years, aluminum alloys have entered the construction of many public buildings, sports complexes. There are attempts to use aluminum as roofing material. Such a roof is not afraid of impurities of carbon dioxide, sulfur compounds, nitrogen compounds and others. harmful impurities, extremely enhancing atmospheric corrosion of roofing iron.

As casting alloys, silumins are used - alloys of the aluminum-silicon system. Such alloys have good fluidity, give low shrinkage and segregation (heterogeneity) in castings, which makes it possible to obtain parts of the most complex configuration by casting, for example, engine cases, pump impellers, instrument cases, internal combustion engine blocks, pistons, cylinder heads and jackets piston engines.

Fight for decline cost aluminum alloys also met with success. For example, silumin is 2 times cheaper than aluminum. Usually, on the contrary, alloys are more expensive (to obtain an alloy, it is necessary to obtain a pure base, and then by alloying - an alloy). Soviet metallurgists at the Dnepropetrovsk Aluminum Plant in 1976 mastered the smelting of silumins directly from aluminosilicates.

Aluminum has long been known in electrical engineering. However, until recently, the scope of aluminum has been limited to power lines and, in rare cases, power cables. The cable industry was dominated by copper and lead. The conductive elements of the cable structure were made of cuprum, and the metal sheath was made of lead or lead-based alloys. For many decades (for the first time, lead sheaths for protecting cable cores were proposed in 1851) was the only metal material for cable sheaths. He is excellent in this role, but not without flaws - high density, low strength and scarcity; these are just the main ones that made a person look for other metals that can adequately replace lead.

They turned out to be aluminum. The beginning of his service in this role can be considered 1939, and work began in 1928. However, a serious shift in the use of aluminum in cable technology occurred in 1948, when the technology for manufacturing aluminum sheaths was developed and mastered.

Copper, too, for many decades was the only metal for the manufacture of current-carrying conductors. Studies of materials that could replace copper have shown that aluminum should and can be such a metal. So, instead of two metals, essentially different purposes, aluminum entered the cable technology.

This substitution has a number of advantages. Firstly, the possibility of using an aluminum shell as a neutral conductor is a significant savings in metal and weight reduction. Secondly, higher strength. Thirdly, facilitating installation, reducing transportation costs, reducing the cost of the cable, etc.

Aluminum wires are also used for overhead power lines. But it took a lot of effort and time to make an equivalent replacement. Many options have been developed, and they are used based on the specific situation. [Aluminum wires of increased strength and increased creep resistance are produced, which is achieved by alloying with magnesium up to 0.5%, silicon up to 0.5%, iron up to 0.45%, hardening and aging. Steel-aluminum wires are used, especially for the implementation of large spans required at the intersection of various obstacles with power lines. There are spans of more than 1500 m, for example, when crossing rivers.

Aluminum in transfer technology electricity over long distances, they are used not only as a conductor material. A decade and a half ago, aluminum-based alloys began to be used for the manufacture of power transmission towers. They were first built in our country in the Caucasus. They are about 2.5 times lighter than steel and do not require corrosion protection. Thus, the same metal replaced iron, copper and lead in electrical engineering and electricity transmission technology.

And so or almost so it was in other areas of technology. Tanks, pipelines and other assembly units made of aluminum alloys have proven themselves well in the oil, gas and chemical industries. They have supplanted many corrosion-resistant metals and materials, such as iron-carbon alloy containers enameled inside to store aggressive liquids (a crack in the enamel layer of this expensive design could lead to losses or even an accident).

Over 1 million tons of aluminum is spent annually in the world for the production of foil. The thickness of the foil, depending on its purpose, is in the range of 0.004-0.15 mm. Its application is extremely varied. It is used for packaging various food and industrial products - chocolate, sweets, medicines, cosmetics, photographic products, etc.

Foil is also used as a structural material. There is a group of gas-filled plastics - honeycomb plastics - cellular materials with a system of regularly repeating regular cells. geometric shape, the walls of which are made of aluminum foil.

Encyclopedia of Brockhaus and Efron

ALUMINUM- (clay) chem. zn. AL; at. in. = 27.12; beats in. = 2.6; m.p. about 700°. Silvery white, soft, sonorous metal; is in combination with silicic acid the main component of clays, feldspar, micas; found in all soils. Goes to…… Dictionary of foreign words of the Russian language

ALUMINUM- (symbol Al), a silver-white metal, an element of the third group of the periodic table. It was first obtained in its pure form in 1827. The most common metal in the bark the globe; its main source is bauxite ore. Process… … Scientific and technical encyclopedic dictionary

ALUMINUM- ALUMINUM, Aluminum (chemical sign A1, at. weight 27.1), the most common metal on the surface of the earth and, after O and silicon, the most important component of the earth's crust. A. occurs in nature, mainly in the form of silicic acid salts (silicates); ... ... Big Medical Encyclopedia

Aluminum- is a bluish-white metal, characterized by particular lightness. It is very ductile and can be easily rolled, drawn, forged, stamped, and cast, etc. Like other soft metals, aluminum also lends itself very well to ... ... Official terminology

Aluminum- (Aluminium), Al, a chemical element of group III of the periodic system, atomic number 13, atomic mass 26.98154; light metal, mp660 °С. The content in the earth's crust is 8.8% by weight. Aluminum and its alloys are used as structural materials in ... ... Illustrated Encyclopedic Dictionary

ALUMINUM- ALUMINUM, aluminum male., chem. alkali metal clays, alumina base, clays; as well as the basis of rust, iron; and yari copper. Aluminite male. an alum-like fossil, hydrous alumina sulphate. Alunit husband. fossil, very close to ... ... Dahl's Explanatory Dictionary

aluminum- (silver, light, winged) metal Dictionary of Russian synonyms. aluminum n., number of synonyms: 8 clays (2) … Synonym dictionary

ALUMINUM- (lat. Aluminum from alumen alum), Al, a chemical element of group III of the periodic system, atomic number 13, atomic mass 26.98154. Silvery white metal, light (2.7 g/cm³), ductile, with high electrical conductivity, mp 660 .C.… … Big Encyclopedic Dictionary

Aluminum- Al (from lat. alumen the name of alum, used in ancient times as a mordant in dyeing and tanning * a. aluminum; n. Aluminium; f. aluminium; and. aluminio), chem. group III element periodic. Mendeleev systems, at. n. 13, at. m. 26.9815 ... Geological Encyclopedia

ALUMINUM- ALUMINUM, aluminum, pl. no, husband. (from lat. alumen alum). Silvery white malleable light metal. Explanatory Dictionary of Ushakov. D.N. Ushakov. 1935 1940 ... Explanatory Dictionary of Ushakov

PROPERTIES OF ALUMINUM

Content:

Aluminum grades

Physical properties

Corrosion properties

Mechanical properties

Technological properties

Application

aluminum grades.

Aluminum is characterized by high electrical and thermal conductivity, corrosion resistance, ductility, and frost resistance. The most important property of aluminum is its low density (about 2.70 g / cc). The melting point of aluminum is about 660 C.

The physicochemical, mechanical and technological properties of aluminum are very dependent on the type and amount of impurities, which worsen most of the properties of pure metal. The main natural impurities in aluminum are iron and silicon. Iron, for example, present as an independent Fe-Al phase, reduces electrical conductivity and corrosion resistance, worsens ductility, but slightly increases the strength of aluminum.

Depending on the degree of purification, primary aluminum is divided into aluminum of high and technical purity (GOST 11069-2001). Technical aluminum also includes grades marked AD, AD1, AD0, AD00 (GOST 4784-97). Technical aluminum of all grades is obtained by electrolysis of cryolite-alumina melts. High purity aluminum is obtained by additional purification of technical aluminum. Features of the properties of aluminum of high and high purity are discussed in books

1) Metal science of aluminum and its alloys. Ed. I.N. Fridlyander. M. 1971.2) Mechanical and technological properties of metals. A.V. Bobylev. M. 1980.

The table below provides a summary of most aluminum grades. The content of its main natural impurities - silicon and iron - is also indicated.

brand	Al, %	Si, %	Fe, %	Applications
High purity aluminum
A995	99.995	0.0015	0.0015	Chemical equipment Foil for capacitor plates Special Purposes
A98	99.98	0.006	0.006
A95	99.95	0.02	0.025
Technical grade aluminum
A8 AD000	99.8	0.10 0.15	0.12 0.15	Wire rod for production cable and wire products (from A7E and A5E). Raw materials for the production of aluminum alloys Foil Rolled products (rods, strips, sheets, wire, pipes)
A7 AD00	99.7	0.15	0.16 0.25
A6	99.6	0.18	0.25
A5E	99.5	0.10	0.20
A5 AD0	99.5	0.25 0.25	0.30 0.40
AD1	99.3	0.30	0.30
A0 HELL	99.0	0.95 Up to 1.0% in total

The main practical difference between commercial and highly purified aluminum is related to differences in corrosion resistance to certain media. Naturally, the higher the degree of purification of aluminum, the more expensive it is.

High purity aluminum is used for special purposes. For the production of aluminum alloys, cable and wire products and rolled products, technical aluminum is used. Next, we will talk about technical aluminum.

Electrical conductivity.

The most important property of aluminum is its high electrical conductivity, in which it is second only to silver, copper and gold. The combination of high electrical conductivity with low density allows aluminum to compete with copper in the field of cable and wire products.

The electrical conductivity of aluminum, in addition to iron and silicon, is strongly affected by chromium, manganese, and titanium. Therefore, in aluminum intended for the manufacture of current conductors, the content of several more impurities is regulated. So, in A5E grade aluminum with an allowable iron content of 0.35% and silicon of 0.12%, the sum of impurities Cr + V + Ti + Mn should not exceed only 0.01%.

The electrical conductivity depends on the state of the material. Long-term annealing at 350 C improves the conductivity, while cold hardening worsens the conductivity.

The value of electrical resistivity at a temperature of 20 C isOhm*mm 2 /m or µOhm*m :

0.0277 - annealed aluminum wire A7E

0.0280 - annealed aluminum wire A5E

0.0290 - after pressing, without heat treatment from AD0 aluminum

Thus, the specific electrical resistance of aluminum conductors is approximately 1.5 times higher than the electrical resistance of copper conductors. Accordingly, the electrical conductivity (the reciprocal of the resistivity) of aluminum is 60-65% of the electrical conductivity of copper. The electrical conductivity of aluminum increases with a decrease in the amount of impurities.

The temperature coefficient of electrical resistance of aluminum (0.004) is approximately the same as that of copper.

Thermal conductivity

The thermal conductivity of aluminum at 20 C is approximately 0.50 cal/cm*s*C and increases with increasing purity of the metal. In terms of thermal conductivity, aluminum is second only to silver and copper (about 0.90), three times higher than the thermal conductivity of mild steel. This property determines the use of aluminum in cooling radiators and heat exchangers.

Other physical properties.

Aluminum has a very high specific heat (approximately 0.22 cal / g * C). This is much higher than for most metals (0.09 for copper). Specific heat of fusion is also very high (about 93 cal/g). For comparison, for copper and iron, this value is approximately 41-49 cal / g.

Reflectivity aluminum is highly dependent on its purity. For aluminum foil with a purity of 99.2%, the white light reflectance is 75%, and for foil with an aluminum content of 99.5%, the reflectance is already 84%.

Corrosion properties of aluminum.

Aluminum itself is very chemically active metal. This is connected with its use in aluminothermy and in the production of explosives. However, in air, aluminum is covered with a thin (about a micron) film of aluminum oxide. With high strength and chemical inertness, it protects aluminum from further oxidation and determines its high anti-corrosion properties in many environments.

In high-purity aluminum, the oxide film is continuous and non-porous, and has a very strong adhesion to aluminum. Therefore, aluminum of high and special purity is very resistant to the action of inorganic acids, alkalis, sea water and air. The adhesion of the oxide film to aluminum in the places where impurities are located significantly deteriorates and these places become vulnerable to corrosion. Therefore, aluminum of technical purity has a lower resistance. For example, in relation to weak hydrochloric acid, the resistance of refined and technical aluminum differs by 10 times.

Aluminum (and its alloys) usually exhibits pitting corrosion. Therefore, the stability of aluminum and its alloys in many media is determined not by a change in the weight of the samples and not by the rate of penetration of corrosion, but by a change in mechanical properties.

The iron content has the main influence on the corrosion properties of commercial aluminum. Thus, the corrosion rate in a 5% HCl solution for different grades is (in):

brand	ContentAl	Fe content	Corrosion rate
A7	99.7 %	< 0.16 %	0.25 – 1.1
A6	99.6%	< 0.25%	1.2 – 1.6
A0	99.0%	< 0.8%	27 - 31

The presence of iron also reduces the resistance of aluminum to alkalis, but does not affect the resistance to sulfuric and nitric acids. In general, the corrosion resistance of technical aluminum, depending on the purity, deteriorates in this order: A8 and AD000, A7 and AD00, A6, A5 and AD0, AD1, A0 and AD.

At temperatures above 100C, aluminum interacts with chlorine. Aluminum does not interact with hydrogen, but dissolves it well, so it is the main component of the gases present in aluminum. Water vapor, which dissociates at 500 C, has a harmful effect on aluminum; at lower temperatures, the effect of steam is insignificant.

Aluminum is stable in the following environments:

industrial atmosphere

Natural fresh water up to temperatures of 180 C. The corrosion rate increases with aeration,

impurities of caustic soda, hydrochloric acid and soda.

Sea water

Concentrated nitric acid

Acid salts of sodium, magnesium, ammonium, hyposulfite.

Weak (up to 10%) solutions of sulfuric acid,

100% sulfuric acid

Weak solutions of phosphoric (up to 1%), chromic (up to 10%)

Boric acid in any concentration

Vinegar, lemon, wine. malic acid, acidic fruit juices, wine

Ammonia solution

Aluminum is unstable in such environments:

Dilute nitric acid

Hydrochloric acid

Dilute sulfuric acid

Hydrofluoric and hydrobromic acid

Oxalic, formic acid

Solutions of caustic alkalis

Water containing salts of mercury, copper, chloride ions that destroy the oxide film.

contact corrosion

In contact with most technical metals and alloys, aluminum serves as an anode and its corrosion will increase.

Mechanical properties

Elastic modulus E \u003d 7000-7100 kgf / mm 2 for technical aluminum at 20 C. With an increase in the purity of aluminum, its value decreases (6700 for A99).

Shear modulus G \u003d 2700 kgf / mm 2.

The main parameters of the mechanical properties of technical aluminum are given below:

Parameter	Unit rev.	deformed	Annealed
Yield strength? 0.2	kgf/mm 2	8 - 12	4 - 8
Tensile strength? in	kgf/mm 2	13 - 16
Elongation at break?		5 – 10	30 – 40
Relative contraction at break		50 - 60	70 - 90
Shear strength	kgf/mm 2
Hardness	HB	30 - 35

The figures given are very indicative:

1) For annealed and cast aluminium, these values ​​depend on the technical aluminum grade. The more impurities, the greater the strength and hardness and the lower the ductility. For example, the hardness of cast aluminum is: for A0 - 25HB, for A5 - 20HB, and for high purity aluminum A995 - 15HB. The tensile strength for these cases is: 8.5; 7.5 and 5 kgf / mm 2, and elongation 20; 30 and 45% respectively.

2) For deformed aluminum, the mechanical properties depend on the degree of deformation, the type of rolled product and its dimensions. For example, the tensile strength is at least 15-16 kgf / mm 2 for wire and 8 - 11 kgf / mm 2 for pipes.

However, in any case, technical aluminum is a soft and fragile metal. Low yield strength (even for hard-worked steel it does not exceed 12 kgf/mm 2) limits the use of aluminum in terms of allowable loads.

Aluminum has a low creep strength: at 20 C it is 5 kgf/mm 2 , and at 200 C it is 0.7 kgf/mm 2 . For comparison: for copper, these figures are 7 and 5 kgf / mm 2, respectively.

The low melting temperature and the temperature of the beginning of recrystallization (for technical aluminum is about 150 C), the low creep limit limits the temperature range of aluminum operation from the side of high temperatures.

The ductility of aluminum does not deteriorate at low temperatures, up to helium. When the temperature drops from +20 C to -269 C, the tensile strength increases 4 times for technical aluminum and 7 times for high-purity aluminum. The elastic limit in this case increases by a factor of 1.5.

The frost resistance of aluminum makes it possible to use it in cryogenic devices and structures.

Technological properties.

The high ductility of aluminum makes it possible to produce foil (up to 0.004 mm thick), deep-drawn products, and use it for rivets.

Technical purity aluminum exhibits brittleness at high temperatures.

Machinability is very low.

The temperature of recrystallization annealing is 350-400 C, tempering temperature is 150 C.

Weldability.

Difficulties in aluminum welding are due to 1) the presence of a strong inert oxide film, 2) high thermal conductivity.

Nevertheless, aluminum is considered a highly weldable metal. The weld has the strength of the base metal (annealed) and the same corrosion properties. For details on aluminum welding, see, for example,www. weldingsite.com.ua.

Application.

Due to its low strength, aluminum is used only for unloaded structural elements, when high electrical or thermal conductivity, corrosion resistance, ductility or weldability are important. The parts are connected by welding or rivets. Technical aluminum is used both for casting and for the production of rolled products.

In the warehouse of the enterprise there are always sheets, wire and tires made of technical aluminum.

(see the relevant pages of the website). Under the order pigs A5-A7 are delivered.