EA025066B1 - Method for casting aluminium alloys, aluminium alloy and method for producing intermediate articles therefrom - Google Patents

Abstract

The invention allows to produce the material with properties complying with the requirements of mechanical engineers. The alloy can be used for manufacturing various stamped products, e.g. after casting using deep drawing of parts of the vehicle body, aircrafts with operation characteristics exceeding the characteristics of parts made of currently used alloys. The method of aluminium alloys casting comprises its preparation in DC arc melting furnace, continuous feed of aluminium alloy melt to the forming device, heat removal from area of crystallising cast billet, treatment of the melt and crystallising metal under external effect. The aluminium based alloy produced mainly by such method contains, wt.%: silicium 4.0-20.0, magnesium 2.0-13.5, zirconium 0.05-0.2, beryllium 0.03-0.15, titanium 0.02-0.1, aluminium - the rest. The method for producing of intermediate products made of aluminium based alloy includes the billet rolling, with intermediate annealing, heat treatment of produced semi-product. The rolling is performed at temperatures not exceeding the temperature of magnesium stability in aluminium solid solution, the semi-product is heat treated by quenching.

Description

The invention relates to metallurgy of alloys, in particular to methods for casting aluminum alloys, aluminum alloys and methods for producing intermediate products from them, can be used in the production of cast and wrought semi-finished products (rolled, extruded) from alloys based on aluminum, as well as other alloys, for example copper, magnesium, zinc and others.

The most effective invention can be used in aircraft and automotive industry for the manufacture of airframe parts of aircraft, car body, molded fittings for various purposes, and the alloy from which they are made must have both high strength and high plastic and casting properties, good deformability, stampability, weldability, high corrosion resistance and have a small specific weight. Aluminum-magnesium alloys most fully meet these conditions.

The closest in technical essence is the method of casting aluminum alloys (patent KI 2111826, IPC Β22Ό11 / 04, C22C21 / 06, C22P1 / 04, publ. 27.05.1998), which includes a continuous supply of molten aluminum alloy to the mold, heat removal from the liquid metal region, the processing of the liquid metal in the mold is carried out by a spatially non-uniform magnetic field, crystallization and the formation of a casting.

The disadvantage of this method is the lack of structural and chemical homogeneity of the alloy and does not provide equal structure of the structure over the cross section of the ingot. In this case, when using this method, the width of the liquid-solid phase of the alloy with a wide interval remains sufficiently large and cannot sufficiently reduce the micro- and macrolinkage. Dendritic cells of the solid solution of aluminum and interdendritic inclusions are not crushed sufficiently, which reduces the plastic properties and manufacturability of the alloy during deformation and is transmitted to the properties of the finished product.

Currently known high-alloyed aluminum-magnesium alloys (Ryazanova N.I., Konkevich V.Yu., Lebedeva T.I., Filatov Y. Aluminum body - the future of the automotive industry. Collection. Technology of light alloys. M.VILS. No. 1955 2, pp. 55-66), used for the manufacture of automotive body parts, have insufficiently high mechanical properties (tensile strength from 210 to 310 MPa, yield strength from 100 to 160 MPa). In addition, these aluminum-magnesium during cold deformation exhibit a pronounced physical yield strength, manifested in the form of traces of Lüders lines, which impair the appearance of the product.

Known high-alloyed aluminum-magnesium casting alloys (Alieva S.G., Altman M.V., Ambartsumyan S.M. and others. Reference book. Industrial aluminum alloys. M., Metallurgy. 1984, p. 394-415), possessing high strength properties are not high enough plastic properties (low deformability at the stage of manufacturing sheet semi-finished products and limited stampability in the manufacture of products, as a result of which they cannot be used for the production of parts by stamping, especially when using deep-drawing.

It is required to develop an alloy with high strength and plastic properties, as well as methods of its preparation, technology for producing cast billets with a given microstructure and intermediate products for the production of parts.

Closest to the proposed alloy is an aluminum alloy (§I 439535 A, M. CL. C22C 21/00, publ. 15.08.74, containing, in wt.%:

magnesium 4.0-7.5; zirconium 0.5-3.5; manganese 0.2-1.0; cobalt 0.05-0.5; boron 0.05-0.3; titanium 0.01-0.3; zinc 0.01-0.7; chromium 0.01-0.3; beryllium 0.0001-0.005; aluminum - the rest.

The alloy possesses rather high strength properties and good weldability.

The disadvantage of the alloy is a high content of refractory alloying components such as zirconium, manganese, titanium, chromium, both individually and in their combination (total content) leads to the formation of a large number of refractory intermetallic compounds in the process of alloy crystallization, the presence of which leads to coarsening of its structure, reduction of plastic properties and cracking of products in the process of deformation, which makes it unsuitable for use in products obtained by stamping with Lubok hood.

A method of producing products from an aluminum-magnesium alloy (ΙΡ, application 502844) is known. It consists in that the casting of an aluminum-magnesium alloy is homogenized and then subjected to pre-deformation, obtained after this deformation, the billet is rolled with intermediate annealing, after which the semi-finished product is thermoprocessed and produce the finished product. At the same time, in order to achieve optimal properties, the alloy is subjected to forging as a preliminary deformation, and the alloy is held for 3-50 hours at 350-500 ° C (homogenized 10 025066) before the forging to completely dissolve the magnesium atoms. Hot rolling at 350–500 ° C and then cold rolling with 30–50% compression is used as a deformation. The semi-finished product thus obtained is subjected to final stabilization at 130 ° C for 4 hours to obtain the finished product. This method is effective for an aluminum alloy with a magnesium content of less than 8 wt.%, Since hot rolling of aluminum alloys containing more than 8 wt.% magnesium leads to an intensive decomposition of the solid solution of α-aluminum supersaturated with magnesium.

The disadvantage of the method is high-temperature heating with pre-deformation before rolling leads to intensive release of β-phase in the alloy structure of MD ₂ A1 ₃ and coagulation of its particles mainly along the grain boundaries with a continuous chain, which leads to a decrease in plastic properties (due to the brittleness of this phase) and a decrease in corrosion resistance of deformable semi-finished products and finished products. In addition, the resulting hot rolling recrystallized structure of the sheets during their subsequent cold deformation with deep drawing leads to the appearance of Lüders lines.

The basis of the present invention is to increase the density and purity of the metal, improve the plastic properties and deformability of aluminum alloy products with high magnesium content while maintaining their high strength properties, by reducing intradendritic and interdendritic segregation, grinding the dendritic cell of α-aluminum solid solution grains, grinding and reducing the number of intermetallic inclusions.

The problem is solved due to the fact that the method of casting aluminum alloys, including its preparation in a DC arc melting plant, continuous supply of molten aluminum alloy to a forming device, heat removal from the region of crystallized casting, the processing of molten and crystallizing metal under external influence, according to the invention , the processing of the melted and crystallizing metal is carried out by acoustic action.

In addition, the melting of the metal is carried out with acoustic exposure to the radio frequency range from 10 to 2000 kHz.

The formation of the cast billet is carried out with acoustic exposure to the radio frequency range from 10 to 2000 kHz.

Acoustic effects are carried out on the formed cast billet to the shop temperature (= 20 ° C).

Processing the metal during the melt preparation process with an acoustic effect allows to dissolve increased amounts, for example magnesium and silicon, practically at temperatures close to solidus, during crystallization to obtain a more dispersed microstructure of the alloy (dendritic cells of aluminum solid solution grains are crushed, primary and secondary intermetallic compounds, such as Ζη ₂ Α1 ₃ , 1 ₃ , Md ₂ A1 ₃ and others), providing an increase in technological plasticity during its subsequent deformation and improvement mechanical properties of semi-finished products. The acoustic effect of the gradient range in the crystallization process causes an increase in the melt viscosity and a change in the heat and mass transfer coefficient due to a change in the physical properties of the melt.

In addition, this effect reduces the content of oxide and non-metallic inclusions in the alloy. This occurs as a result of ejection of oxide and non-metallic inclusions in the process of crystallization of the product to the surface of the melt. At the same time, the rate of heat removal increases, new crystallization centers are generated and the effect of grinding the structure is observed.

All of the above leads to an increase in both the strength and plastic properties of the alloy of the cast billet. Obtaining equiaxial fine-grained structure allows to significantly reduce or eliminate subsequent homogenizing annealing. The elimination of homogenization makes it possible to preserve the α-aluminum solid solution, supersaturated with magnesium and silicon, obtained during casting, to reduce the secondary porosity in the alloy and to reduce energy costs during annealing.

The task is also solved by the creation of an alloy based on aluminum, obtained mainly by the method described above and additionally containing silicon, magnesium, zirconium, beryllium, titanium in the following ratio of components, wt.%:

silicon 4.0-20.0; magnesium 2.0-13.5; zirconium 0.05-0.2; beryllium 0.03 -0.15; titanium 0.02-0.1; aluminum - the rest

The presence of silicon within the specified limits in combination with other elements will provide the alloys: low coefficient of thermal expansion; high hardness and wear resistance; high thermal stability and heat resistance.

The introduction of magnesium within the specified limits provides an increase in the tensile strength and the limit of the alloy creep, and also reduces its specific weight with an increase in the specific strength and improved corrosion resistance. Magnesium in the specified limits in the technology of casting semi-finished products provides good casting properties, which allows to obtain shaped castings, as well as from the cast billets, semi-finished products by deformation methods. Magnesium with silicon forms an intermetallic compound Μ§ ₂ δί with high microhardness, which affects the increase in wear resistance.

Zirconium within the specified limits in the proposed alloy stabilizes and hardens the solid solution of α-aluminum. The introduction of zirconium below 0.05 wt.% Is not enough to stabilize and harden the solid solution of a-aluminum. Zirconium content above 0.2 wt.% Leads to coarse precipitates of the needle intermetallic phase фазыτΖ1 ₃ , which reduces the ductility and efficiency of this component in the alloy.

Beryllium is introduced into the alloy to protect magnesium from oxidation during the preparation of the alloy. Within the specified limits, beryllium performs the function of protecting magnesium. With a decrease in its quantity, proper protection against oxidation will not be provided, and an increase in its content above the specified limit will impede the process of continuous casting.

Titanium within the specified limits is introduced as a modifier to improve the processability of the alloy during deformation. At the same time, it is a barrier for the formation of the brittle intermetallic phase of MD ₂ A1 ₃ . The introduction of titanium below 0.02 wt.% Is not enough to modify the alloy, and the introduction of it above 0.1 wt.% Leads to the release of aluminides, which reduces the efficiency of its use.

An increase in the degree of dispersion of released particles is observed with the introduction of 0.005-0.04 wt.% Be into the alloy, 0.005-0.020 wt.% Τι, 0.005-0.020 wt.% Ζτ. These additives increase the concentration of vacancies during quenching and intensify the processes of diffusion of magnesium and silicon during aging, facilitating the formation of nuclei of the metastable phase β.

It is advisable that the aluminum alloy additionally contains 0.01-0.05 wt.% Cobalt. Cobalt, which is an element with a smaller atomic radius compared to magnesium and zirconium, reduces the parameter of the crystal lattice of aluminum, improves the stability of the solid solution of α-aluminum and the processability of the alloy during rolling. Together with zirconium, cobalt favorably influences the strength and plastic properties of the proposed alloy. The introduction of cobalt below 0.01 wt.% Is not enough to achieve the specified positive effect, and the introduction of it above 0.05 wt.% Leads to the release of cobalt aluminides and reduce its positive effect. Since the solubility of cobalt at room temperature corresponds to 0.02 wt.%, And its greatest effect will be when it is in a solid solution of α-aluminum in the form of atoms uniformly embedded in the crystal lattice of aluminum.

Boron has a beneficial effect on the aluminum alloy at a content of 0.004-0.02 wt.%. Boron within the specified limits introduced into the alloy to enhance the modifying effect of titanium on α-aluminum grains. It is preferable to introduce boron in a ratio to titanium as 1: 5. In this case, their joint influence is most effective. Therefore, the lower limit is limited to 0.004 wt.%, And the upper - 0.02 wt.%. Its further increase may cause a large amount of boron aluminides to precipitate during alloy crystallization and a deterioration of technological properties, especially during deformation.

It is desirable that the aluminum alloy additionally contains 0.01-0.3 wt.% Chromium. Chromium is incorporated into the alloy as an anti-recrystallizer element, which, together with zirconium, increases the stability of the α-aluminum solid solution and improves the strength properties of the alloy. The decrease in the chromium content of less than 0.01 wt.% Does not increase the temperature of the recrystallization of the alloy, which reduces its strength properties. The increase in the chromium content above 0.3 wt.% Leads to the formation in the alloy structure of refractory intermetallic compounds Cr ₂ A1 ₃ , which impair its workability.

Thus, the proposed alloy in combination with the selected casting method allows to obtain a special fine-grained dense structure of the cast billet with enhanced strength and plastic properties that provide the required technological properties both during casting and deformation of the cast billet.

The task is also solved by creating a method for producing intermediate products from aluminum-based alloys, including casting thin-walled long profiles, flat blanks for deformation by rolling with acoustic impact, heat treatment of the obtained semi-finished product and manufacturing intermediate products from molded profiled billet or after deformations of the flat billet.

The manufacture of intermediate products from the proposed alloy with high concentrations of magnesium and silicon using the developed technology makes it possible to exclude from the technological scheme highly unfavorable high-temperature heating before deformation.

Using the proposed method of preparing the alloy, the casting method, the composition of the alloy, the proposed method of making intermediate products from it allows to significantly reduce intradendritic and interdendritic segregation, crush the dendritic cells of the grains of the α-aluminum solid solution, increase the number of eutectic colonies, grind and reduce the number of intermetallic 3 025066 inclusions, to increase the density and purity of the metal, which allows to improve the casting and plastic properties and deformability of aluminum products High magnesium and silicon alloys. Therefore, intermediate products with a tensile strength above 370 MPa with simultaneous cold deformability by Erickson of more than 8.5 mm and having a dense homogeneous crystal structure with particles uniformly distributed in the matrix with dispersity from 5,000 to 20,000 A. are obtained.

The best embodiment of the invention.

Take aluminum alloy containing the following components, wt.%:

magnesium 2.0-3.5;

silicon - 4.0–20.0;

zirconium - 0.05-0.2;

beryllium - 0.03-0.15;

titanium - 0.02-0.1;

aluminum - the rest.

When this alloy may contain: cobalt - 0.01-0.05; chromium - 0.01-0.3; boron - 0,004-0,02, taken separately or in combination.

The alloy is preheated to a temperature of, for example, 720 ° C with an acoustic impact of 500 kHz. The molten aluminum alloy is degassed, filtered and poured into the transfer furnace of the continuous casting plant and the billet is pulled out of the forming unit, where they carry out continuous heat removal. In the process of crystallization, the alloy is subjected to continuous acoustic effects, for example, 1000 kHz. The specified acoustic treatment is carried out using a single-channel F-1K shaper, which generates acoustic waves in the radio frequency range.

The use of this acoustic effect contributes to better absorption of poorly soluble alloying components, such as silicon, in liquid aluminum, during crystallization crushes the dendritic cells of the solid solution of α-aluminum and primary crystals, such as silicon, increases their homogeneity. To achieve the best effect, it is advisable to produce an acoustic effect from the region of the vertex of the liquidus isotherm until the end of crystallization. It was experimentally determined that the best effect from acoustic impact is provided from 200 to 1000 kHz.

The use of acoustic effects allows you to create synchronous oscillatory-rotational movements of the supramolecular structures of the alloy in the transition zone (liquid-solid phase), creating long chains - endless percolation clusters and changing the heat transfer mechanism, which leads to a streamlined structure and a change in hardness. When this occurs, an apparent change in the state diagram (pseudo-diagram) and the solubility of silicon and magnesium in aluminum increases. Silicon and magnesium will be uniformly dissolved in aluminum, and alloying additives and the formed dispersed intermetallic compounds will make the silicon and magnesium atoms less mobile and will fix them in the matrix of a-aluminum solid solution.

Further, if it is required to deform cast billets, they are homogenized, for example, at 420 ° C in a homogenization furnace, for example, for 4 hours. The homogenized cast billet is further heated and rolled at 350 ° C and lower to the required thickness with intermediate annealing at a temperature 227-360 ° C (if necessary). The resulting cast billets and sheets are quenched at 380-435 ° C and then cooled, for example in water at 20-100 ° C or in oil at 20 ° C or in air. Thus, the use of the proposed method of casting, the proposed aluminum alloy and the proposed method of obtaining products from it allows to produce products (intermediate), such as strips, profiles, pipes and others that have high technological properties both during casting and subsequent deformation. High rigidity , low specific weight, high corrosion resistance.

For a better understanding of the invention are specific examples of its implementation.

Example 1

Take aluminum alloy containing the following components, wt.%:

silicon - 4.0;

magnesium - 13.5;

zirconium - 0.08;

titanium - 0.04;

chromium - 0.02;

beryllium - 0.05;

boron - 0,004;

cobalt - 0.02;

- 4 025066 aluminum - the rest.

The alloy is melted in a DC arc furnace DCPT 0.06, heated to 750 ° C, degassed, then poured with filtration into a transfer furnace of a continuous casting plant. A shaper from a material inert to the molten metal is placed on a horizontal metal surface in a distributing furnace. Through the cavity of the shaper, which forms the profile of the workpiece, a seed of brass foil is lowered into the liquid metal along the profile of the workpiece. On the seed, the molten metal is frozen. Then the seed moves upwards and a crystallizing metal stretches behind it due to capillary forces. If it enters a region of lower temperature above the surface of the melt, the metal will crystallize with the design of the product profile. When selecting the cooling mode and speed, the product (sheet, pipe, profile) will be continuously pulled upwards. In the future, the product can be used as an intermediate blank for the manufacture of parts or be subjected to deformation, such as rolling a sheet of the desired thickness.

In the process of preparation and crystallization, the melt is exposed to acoustic effects, for example at 500 kHz. The obtained sheets or the corresponding profile is subjected to quenching, for example at 380 ° C, after which they are ready for the production of products.

The following 5 examples (examples 2-6) are made as described in example 1 and are summarized in the table.

Example No The content of components, wt.% Flints th 8ί Magn II m ₈ Zircon AI Ζγ Tita n ΤΪ Chromium Cr Berylli th Be Cobal t With Boron AT Aluminum Αί one 2 3 four five 6 7 eight 9 ten 2 6 five 0.08 0.02 0.01 0.03 0.01 0.06 Rest 3 ten 7 0.08 0.04 0.3 0.08 0.03 0.09 Rest four 13 9 0.05 0.06 0.15 0.09 0.02 0.015 Rest five 15 eleven 0.12 0.08 0.8 0.12 0.04 0,018 Rest 6 20 13 0.2 0.1 0.2 0.15 0.05 0.02 Rest 7 0.2 eight 0.12 0.15 0.2 0.1 Mn = 0, 17 0.12 Rest eight - 7.4 0.5 0.1 Ζη = 0, 3 0.05 Mn = 0, five 0.41 Rest Example No. Specific mole energy connections UE e. with. Volume energy connections shah Optimal energy connections at Density alloy Volume Praying alloy Kgm / mol MPa MPa G / cm ³ V mol one 672.79 510.7 427.6 2.52 13.0 2 678.64 581.7 480.6 2.60 11.7 3 664.24 522.1 431.7 2.57 12.7 four 650.01 470.43 392.2 2.54 13.7 five 632.71 436.6 361.1 2.51 14.6 6 612.35 372.0 307.6 2.47 16.5 7 692.0 607.1 502.0 / 318 ' 2.60 11.4 eight 694.5 614.0 507.8 / 385 * 2.62 11.3

* The denominator indicates the properties of samples manufactured by serial technology.

For comparison, in example 7, the properties of an aluminum-magnesium-silicon system alloy used for shaped casting in mechanical engineering are given. Example 8 shows the mechanical properties of similar sheets of alloy prototype.

- 5 025066

As follows from the above table, the proposed alloy, the method of its casting and the method of producing intermediate products allow to obtain a material with properties that meet the requirements of machine builders. In this case, the alloy can be used for the manufacture of a variety of stamped products, for example, after casting with the use of deep drawing of car body parts, aircraft with operating characteristics superior to those of the alloys currently used.

Claims (12)

CLAIM 1. A method of casting aluminum alloys, including its preparation in a direct current arc smelter, continuously feeding the aluminum alloy melt into a forming device, removing heat from the area of the crystallized cast billet, processing the molten and crystallizing metal under external influence, characterized in that the processing of the molten and crystallizing metal is carried out by acoustic exposure. 2. The method according to claim 1, characterized in that the molten metal is carried out under acoustic exposure to the radio frequency range from 10 to 2000 kHz. 3. The method according to claim 1, characterized in that the formation of the cast billet is carried out under acoustic exposure to the radio frequency range from 10 to 2000 kHz. 4. The method according to claim 3, characterized in that the acoustic effect is carried out on the formed cast billet to the workshop temperature (= 20 ° C). 5. An alloy based on aluminum, characterized in that it is made by a casting method according to any one of claims 1 to 4. 6. The alloy according to claim 5, characterized in that it further comprises silicon, magnesium, zirconium, beryllium, titanium in the following ratio of components, wt.%: Silicon 4-20; magnesium 2-13; zirconium 0.05-0.2; beryllium 0.03-0.15; titanium 0.02-0.1; aluminum is the rest. 7. The alloy according to claim 6, characterized in that it further comprises 0.01-0.05 wt.% Cobalt. 8. The alloy according to any one of paragraphs.6, 7, characterized in that it further comprises 0.01-0.3 wt.% Chromium. 9. The alloy according to claims 6, 7, characterized in that it further comprises 0.004-0.020 wt.% Boron. 10. A method of manufacturing intermediate products from an aluminum-based alloy according to any one of claims 6 to 9, comprising rolling the thus obtained preform with intermediate annealing, heat treatment of the resulting semi-finished product, characterized in that the rolling is carried out at temperatures not exceeding the temperature of magnesium stability in solid aluminum solution, and the heat treatment of the semi-finished product is carried out by hardening. 11. The method according to claim 10, characterized in that the rolling is carried out at a temperature not exceeding 350 ° C with acoustic exposure. 12. The method according to claim 10, characterized in that the hardening of the semi-finished product is carried out at 380-435 ° C.