Iron-aluminum alloy: history of discovery, properties, advantages

Designation - Al (Aluminum);
Period - III;
Group - 13 (IIIa);
Atomic mass - 26.981538;
Atomic number - 13;
Atomic radius = 143 pm;
Covalent radius = 121 pm;
Electron distribution - 1s22s22p63s23p1;
melting temperature = 660°C;
boiling point = 2518°C;
Electronegativity (according to Pauling/according to Alpred and Rochow) = 1.61/1.47;
Oxidation state: +3.0;
Density (no.) = 2.7 g/cm3;
Molar volume = 10.0 cm3/mol.

Aluminum (alum) was first obtained in 1825 by the Dane G. K. Ørsted.
Initially, before the discovery of an industrial method of production, aluminum was more expensive than gold. Aluminum is the most abundant metal in the earth's crust (mass fraction is 7-8%), and the third most abundant of all elements after oxygen and silicon. Aluminum is not found in free form in proirod.

The most important natural aluminum compounds:

aluminosilicates - Na2O Al2O3 2SiO2; K2O Al2O3 2SiO2
bauxite – Al2O3 nH2O
corundum - Al2O3
cryolite – 3NaF AlF3

Aluminum in D.I. Mendeleev’s Periodic Table of Chemical Elements is numbered “13” and belongs to group 13(IIIa) (See Atoms of group 13(IIIa).

Rice. Structure of the aluminum atom.

Aluminum is a chemically active metal - at its outer electronic level there are three electrons that participate in the formation of covalent bonds when aluminum interacts with other chemical elements (see Covalent bond). Aluminum is a strong reducing agent and exhibits an oxidation state of +3 in all compounds.

At room temperature, aluminum reacts with oxygen contained in the atmospheric air to form a strong oxide film, which reliably prevents the process of further oxidation (corrosion) of the metal, as a result of which the chemical activity of aluminum decreases.

Thanks to the oxide film, aluminum does not react with nitric acid at room temperature, therefore, aluminum cookware is a reliable container for storing and transporting nitric acid.

Physical properties of aluminum:

silver-white metal;
solid;
lasting;
easy;
plastic (stretched into thin wire and foil);
has high electrical and thermal conductivity;
melting point 660°C
natural aluminum consists of one isotope 2713Al

Chemical properties of aluminum:

when removing the oxide film, aluminum reacts with water: 2Al + 6H2O = 2Al(OH)3 + 3H2;
at room temperature it reacts with bromine and chlorine to form salts: 2Al + 3Br2 = 2AlCl3;
at high temperatures, aluminum reacts with oxygen and sulfur (the reaction is accompanied by the release of a large amount of heat): 4Al + 3O2 = 2Al2O3 + Q; 2Al + 3S = Al2S3 + Q;
at t=800°C reacts with nitrogen: 2Al + N2 = 2AlN;
at t=2000°C reacts with carbon: 2Al + 3C = Al4C3;
reduces many metals from their oxides - by aluminothermy (at temperatures up to 3000°C) tungsten, vanadium, titanium, calcium, chromium, iron, manganese are produced industrially: 8Al + 3Fe3O4 = 4Al2O3 + 9Fe;
reacts with hydrochloric and dilute sulfuric acid to release hydrogen: 2Al + 6HCl = 2AlCl3 + 3H2; 2Al + 3H2SO4 = Al2(SO4)3 + 3H2;
reacts with concentrated sulfuric acid at high temperature: 2Al + 6H2SO4 = Al2(SO4)3 + 3SO2 + 6H2O;
reacts with alkalis with the release of hydrogen and the formation of complex salts - the reaction occurs in several stages: when aluminum is immersed in an alkali solution, the durable protective oxide film that is on the surface of the metal dissolves; after dissolving the film, aluminum, as an active metal, reacts with water to form aluminum hydroxide, which interacts with alkali as an amphoteric hydroxide: Al2O3+2NaOH = 2NaAlO2+H2O - dissolution of the oxide film;
2Al+6H2O = 2Al(OH)3+3H2↑ - interaction of aluminum with water to form aluminum hydroxide;
NaOH+Al(OH)3 = NaAlO2+2H2O - interaction of aluminum hydroxide with alkali
2Al+2NaOH+2H2O = 2NaAlO2+3H2↑ - the overall equation for the reaction of aluminum with alkali.

History of discovery

The first attempts to use aluminum and iron alloys were made by Faraday in 1820. There have been attempts to use aluminum alloy as an alloying element to produce high-strength steel, but these have proven ineffective.

Thorough research was resumed after 1918 in the USSR, Germany, and England. It has been shown that the addition of Al increases the heat-resistant properties of cast iron. The samples have increased strength and fragility, withstand contact with acidic environments, and are not prone to the formation of scale.

It was found that the appearance of scale depends on the thickness of the oxide film on the samples: the thicker and more uniform it is, the higher the surface protection. It is important that the oxides do not form a eutectic phase and do not undergo sublimation, and their ionic conductivity is minimal.

The condition for heat resistance of a sample is loss with scale in the range of 2-10-3–4-10-3 g/cm2/h.

Many studies of Fe and Al alloys have resulted in the determination of their chemical and physical properties. This is due to problems with gas saturation of samples, aluminum waste, the formation of internal oxide films, and destruction of samples under normal conditions.

The most promising were alloys containing from 16 to 20% Al and 3% carbon, called “chugal”. They began to be smelted in the USSR.

Later, a group of inventors led by Z. Eminger developed a technology for the production of high-quality castings of iron-aluminum samples. Thanks to this, new data was obtained.

Mendeleev

“Biography of Dmitry Mendeleev” - Meniscus height. Medal of H. Davy. Cover of the first publication. In 1880 he put forward the idea of underground gasification of coal. Research in the field of gases. Naturalist. Founders of the Russian Chemical Society. Periodic law. Heidelberg period. Definitions of physical constants. Takes part in the first International Chemical Congress.

“Chemistry of Mendeleev” - Ivan Pavlovich Mendeleev - father of D.I. Mendeleev. Gold medal of the USSR Academy of Sciences (now RAS) named after D. I. Mendeleev. Academy and Society Awards. Aeronautics. Suitcases of D. I. Mendeleev. Development of the Far North. A monument installed on the facade of the Faculty of Food and Chemical Technology in Bratislava.

“Mendeleev biography” - Sculptor Petin V.P. Marble, granite. Mendeleev D.I. The doctrine of industry by D. Mendeleev. Members of the commission for the inspection of the Ural mining plants. USSR 1 ruble 1984 (D.I. Mendeleev). Author of the famous textbook “Fundamentals of Chemistry”. Dmitry Ivanovich Mendeleev (left) and Clemens Wiikler. Monuments to the great scientist D.I. Mendeleev.

“Mendeleev Dmitry Ivanovich” - D.I. Mendeleev with his children – Vladimir and Olga. “He worked hard and became a genius!” said Dmitry Ivanovich. The structure of the atom (1911. E. Rutherford). Since 1861, Dmitry Ivanovich taught in St. Petersburg. Only what you acquire through your own labor is lasting and fruitful. Lyubov Mendeleeva (“Beautiful Lady”) and Alexander Blok.

“The Life of Mendeleev” - “If you don’t know names, then the knowledge of things will die” K. Liney. Life and work of D.I. Mendeleev. Discovery of the periodic law. On July 18, D.I. Mendeleev graduated from the Tobolsk gymnasium. Family. Maria Dmitrievna Mendeleeva (1793 - 1830), mother of the scientist. 1834, January 27 (February 6) - D.I. Mendeleev was born in the city of Tobolsk, in Siberia.

“Mendeleev and environmental protection” - Chemistry of the hydrosphere. Selection of combustible material. Using "substances all over the place" Requirements for production processes. Reduce losses in the production process. DI. Mendeleev. Works of a scientist in atmospheric chemistry. DI. Mendeleev on the problems of nature conservation. Offers. Atmospheric chemistry. The greatest Russian scientist.

Composition and structure

The structure of the aluminum-iron alloy is a supersaturated solution of Al in α-Fe with an ordering of the FeAl structure (type B2) and the presence of Fe3AlCx inclusions. Properties are determined by alpha phase ordering and supersaturation. To form a homogeneous composition, annealing is necessary at a temperature above the ordering of the composition, followed by controlled cooling.

When the amount of Al is 8–14%, a columnar matrix structure is formed. During the annealing process, the structure becomes slightly ordered: inclusions up to 150 µm long are located along the grain boundaries. The release of inclusions occurs during cooling from the solid phase.

The metastable state of the phase is determined by the number of inclusions. Annealing allows them to be reduced to 2%. The more aluminum in the composition, the more inhomogeneous regions are created, as a result of which the microhardness of the matrix decreases to 0.4 GPa and the wear resistance of the sample decreases.

With increasing annealing speed during water or air cooling, the number of carbide inclusions decreases.

A 14-20% aluminum-iron alloy also has a matrix structure, but the carbide phase is depleted in Al and the FeAl structure is not ordered. When annealing in air, the number of carbide inclusions increases, due to which the wear resistance and strength properties increase. If cooling is carried out in water, then this effect is not observed and the sample turns out to be fragile.

When the Al content in the alloy is increased from 20 to 30%, the carbide phase becomes smaller; when the samples are cooled, this phase is absent from the structure or no more than 3%. Due to the large amount of aluminum, the sample acquires high strength and ductility. Air cooling after annealing stimulates the formation of hard wear-resistant phases.

An increase in the aluminum content in the melt causes the formation of the Fe4Al13 intermetallic compound, which is not eliminated after annealing, and the sample becomes unsuitable for any practical use.

To improve the properties of the melt, the following alloying elements are introduced into the composition:

0.1–10% Cr;
0.1–0.2% Nb;
0.1–2.0% Si;
0.1–5% B;
from 50 to 200 mg/kg Zr.

Carbon content - from 100 to 500 mg/kg.

Melting temperature

Welding aluminum to steel using the argon arc method

Before starting the welding process, it is recommended to clean the metal edges and apply a protective coating to them. The most affordable of them is zinc.

The filler material in this case is AD1 grade aluminum wire with a silicon additive (it has a good effect on the formation of a diffusion layer of stable quality) or AK-5 alloy wire.

Important! AMg-6 is not recommended for use, since this additive gives low weld strength.

To prepare a steel piece for welding, the butt joint should be beveled at a 70° angle for maximum joint strength.

The edges must be thoroughly sandblasted or mechanically treated, then a surface coat must be applied.

Argon arc welding of aluminum and steel is distinguished by the location of the arc : at the beginning of the welding of the first pass, it is held on the filler rod, and during the welding of subsequent passes - on the filler rod and the resulting bead. This will protect the coating from premature fading.

During the welding process, it is important to apply weld beads sequentially (depending on the type of connection).

Current selection:

MIG welding - occurs with a constant welding current of reverse polarity;
TIG welding - can be used with both alternating welding current and direct current of straight polarity.

The magnitude of the welding current should depend on the thickness of the metal being welded:

up to 3 mm : 110-130 A;
6-8 mm : 130-160 A;
9-10 mm : 180-250 A.

Characteristics and properties

Alloys of iron and aluminum have the following characteristics:

number of thermal heating cycles up to 240, depending on the chemical composition;
tensile strength 100 MPa;
excellent casting properties of the alloy;
Alloying elements can be used: Cr, Ni, Ti, Mo, Cu, B, Si, Nb, Zr.

Alloy properties:

good weldability subject to heat treatment above +7000C;
high chemical resistance;
the need to form a stable melt phase at temperatures up to 9000C;
corrosion resistance.

Other methods of welding aluminum to steel

The laser method is used not only to create miniature joints, but also to obtain long seams, for example, in the automotive industry. This method allows you to finely control the thermal power of pulsed laser radiation.

To make a lap joint, laser heating must be carried out from the steel side. It will heat up to a temperature where the aluminum will already melt, but will remain solid.

The strength of seams can be increased using an aluminum-based additive.

Diffusion

In this welding process, the parts being joined are not melted. But due to their prolonged contact at high temperatures, intermetallic phases are formed.

Electron beam

Buffer coatings of titanium, nickel and zirconium are applied to the steel: then the welding process will be successful.

Point contact

A good point connection between steel and aluminum is not always obtained, even if welded on capacitor machines with severe discharge conditions.

This can be avoided by using an intermediate bimetallic tape. The strength of the resulting point connections can be compared with riveted ones.

Manufacturing

The alloy is created from waste duralumin, aluminum and iron by aluminizing. In a heat-resistant container (electric arc furnace), pieces of steel, free of scale and dirt, are poured (purification degree 99%), a 49% mixture of Al or aluminum alloy containing 2% ammonium chloride, and then sintered in an argon atmosphere. The heat treatment temperature can range from +9000C to +15000C.

The container is heated by supplying current to the heating elements or through the structure itself, provided that it has a high ohmic resistance.

After heating, the optimal annealing method is selected, depending on the composition of the components, followed by natural cooling.

Features of welding aluminum to steel

The combination of these metals allows products made from them to combine their advantages. If you need to get a high-quality weld, it is mandatory to prepare the metals before the welding process and follow the welding technology.

Welding aluminum and its alloys with steel has its own nuances:

these two metals have a big difference in temperatures : while the steel is just warming up, aluminum is already becoming liquid;
the coefficient of linear expansion of both metals also differs greatly , since significant thermal stresses arise along the transition line from steel to aluminum;
different thermal conductivity and heat capacity of metals lead to thermal stresses;
A refractory oxide film may form in the weld . To eliminate it, it is recommended to use a special flux.

A high-quality welded joint must have ductility no lower than that of steel and strength no lower than that of aluminum.

To join aluminum and steel, argon arc welding with a non-consumable electrode or welding through bimetallic inserts are most often used. The industry also uses explosion welding, diffusion welding, laser welding, electron beam welding and spot welding.

Advantages and disadvantages

The advantage of an iron-aluminum alloy is its mechanical properties, which are comparable to some titanium and nickel superalloys. Tensile strength is up to 100 MPa.

Another advantage is resistance to oxidation and corrosion at temperatures up to +7000C. At higher temperatures, the use of such structures is permissible, but without significant mechanical loads.

The disadvantages include:

fragility, manifested under certain operating conditions and depending on temperature and loads;
when the aluminum concentration is less than 12%, the alloy is susceptible to oxidation, corrosion, and decreased ductility;
difficulty in obtaining a stable phase with specified characteristics;
low tensile strength.

The alloy melts easily, which reduces production costs. It is acceptable to use recyclable materials that have undergone the appropriate stages of purification from impurities.