RU2829404C1 - Secondary wrought aluminium alloy with calcium addition - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy of aluminium-based materials and can be used in production of articles operating under high loads at temperatures of up to 150-200 °C. Wrought aluminium-based alloy, melted on the basis of secondary raw materials, contains the following, wt.%: zinc 5.0-5.8, calcium 0.8-1.2, magnesium 1.2-1.6, iron 0.3-0.6, silicon 0.05-0.3, copper 0.05-0.3, manganese 0.05-0.3, aluminium – the rest, wherein it has a structure consisting of a solid solution of aluminium, containing secondary discharge, and eutectics with rounded particles (Al,Zn)₄Ca, Al₁₀CaFe₂, Al₂CaSi₂ and Al₂Mg₃Zn₃ size of not more than 5 mcm, wherein concentration of zinc in solid solution of aluminium containing secondary precipitates is not less than 3 wt. %, and concentration of magnesium is not less than 1 wt.%.

EFFECT: enabling creation of deformable sparingly alloyed aluminium alloy melted on the basis of secondary raw materials, as well as semi-finished products from this alloy, at the same time the alloy does not require ingot homogenisation and semi-finished product quenching.

5 cl, 2 dwg, 4 tbl, 3 ex

Description

The invention relates to the field of metallurgy of aluminum-based materials and can be used to produce articles operating under medium loads at temperatures up to 150-200°C: structural elements such as bridges, towers, frames for construction projects, conveyor frames for mechanical applications and truck bodies, as well as decorative items such as window frames, door frames and garden furniture. Currently, there is an urgent need to efficiently use secondary raw materials to produce semi-finished products from aluminum alloys with a level of properties no worse than those of the so-called "primary" alloys. From the point of view of environmental friendliness and cost-effectiveness, producing aluminum alloys using secondary raw materials as the main batch is much more attractive compared to using primary aluminum. This is due not only to the fact that primary aluminum is more expensive than aluminum scrap, but also to the fact that its production causes significant harm to the environment. Secondary aluminum raw materials contain all the main elements used to alloy grade alloys (Cu, Si, Mg, Zn, Mn), which allows for a reduction in the amount of primary additives and a reduction in the cost of alloy preparation (including by reducing melting time)

The use of secondary raw materials has already found quite a wide application for the production of 6000-group alloys based on the Al-Mg-Si system (GOST 4784-2019), in particular AD31 (6063) and AD35 (6082) grades. However, to achieve a high level of manufacturability and physical and mechanical characteristics for 6000-group alloys, it is necessary to use homogenization (for ingots) and quenching (for deformed semi-finished products) operations, which complicates and increases the cost of the technological cycle.

An aluminum-based alloy is known, disclosed in patent RU 2713526 05.02.2020 Bulletin No. 4. This alloy contains 6.0-6.5% Zn, 1.0-1.5% Ca, 1.5-2.0% Mg, 0.5-0.8% Fe. The technical result is the creation of a new high-strength casting alloy that does not require heat treatment. In special cases, the alloy can be made in the form of shaped castings that have the following tensile mechanical properties in the as-cast state (i.e. without heat treatment): tensile strength (σв) - at least 330 MPa, relative elongation (δ) - at least 4%.

The main disadvantage of this alloy is that in order to achieve the specified high complex of mechanical properties, it lacks the full range of impurities (silicon, copper, manganese) present in the main types of secondary raw materials. This means that the use of secondary raw materials for its production is limited. In addition, the alloy contains increased concentrations of zinc and magnesium (more than 7.5% in total), which worsens the processability of ingots during deformation processing. Therefore, this alloy is not considered for the production of deformed semi-finished products.

The closest to the proposed one is an aluminum-based alloy disclosed in patent RU 2 790 117, published 14.02.2023 Bulletin No. 5. This aluminum-based alloy contains: mass%: calcium 2.0-3.0, manganese 1.2-2.0, iron 0.2-0.4, silicon 0.1-0.3, copper 0.05-0.3, zinc 0.1-1.0, aluminum - the rest, and the total content of calcium, manganese and iron should be in the range from 4.6 to 6.0 mass%. The technical result of the invention is the creation of a new economically alloyed corrosion-resistant aluminum alloy, smelted on the basis of secondary raw materials, which does not require heat treatment and is intended for the production of both shaped castings and deformed semi-finished products (in particular, sheets and rods) with stable mechanical properties:

Sheets: tensile strength (σ _in ) - not less than 240 MPa, yield strength (σ _0.2 ) - not less than 140 MPa, relative elongation (δ) - not less than 5%;

Rods: tensile strength (σ _in ) - not less than 260 MPa, yield strength (σ _0.2 ) - not less than 160 MPa, relative elongation (δ) - not less than 5%.

The main disadvantage of this alloy is that it does not have high enough strength properties, not exceeding the properties of currently used deformable alloys such as AD31.

The technical result of the invention is the creation of a deformable, economically alloyed aluminum alloy intended for smelting based on secondary raw materials and obtaining various deformed semi-finished products (in particular sheets and rods) and not requiring homogenization operations (for ingots) and hardening (for deformed semi-finished products).

The technical result is achieved due to the fact that the aluminum-based alloy, containing zinc, calcium, iron, silicon, copper and manganese, is characterized in that it additionally contains magnesium, with the following ratio of components, wt.%:

Zinc 5.0-5.8 Calcium 0.8-1.2 Magnesium 1.2-1.6 Iron 0.3-0.6 Silicon 0.05-0.3 Copper 0.05-0.3 Manganese 0.05-0.3 Aluminum Rest

The ranges of zinc and magnesium concentrations are justified by the need to ensure, under the conditions of casting medium-sized ingots (in particular, cylindrical ones with a diameter of 100-200 mm), a sufficient content of these elements in the aluminum solid solution (hereinafter (Al)): not less than 3 wt.% Zn and not less than 1 wt.% Mg.

A zinc concentration in the alloy of less than 5 wt.% will be insufficient to ensure high mechanical properties, a concentration above 5.8 wt.% will lead to an excessively high amount of eutectic [(Al)+(Al,Zn) _4Ca ], which will affect the formation of needle-shaped inclusions _of the _Al3Fe phase due to a smaller amount of eutectic [(Al)+(Al,Zn) _4Ca + _Al10CaFe2 ], as well as an increase in the amount of the T phase _{( Al2Mg3Zn3} ), which will lead to _a decrease in mechanical properties.

Magnesium concentration in the alloy below 1.2 wt. % will result in a decrease in mechanical properties due to a decrease in its amount in the aluminum solid solution during crystallization. Magnesium concentration above 1.6 wt. % will result in an increase in the amount of eutectic inclusions of the T phase (Al ₂ Mg ₃ Zn ₃ ), which will result in a decrease in ductility. The ranges of calcium, iron, silicon, copper and manganese concentrations are justified by the need to obtain a dispersed calcium-containing eutectic as a result of crystallization, which will improve the processability during casting of ingots and avoid the formation of needle-shaped inclusions of Fe- and Si-containing phases.

A calcium concentration below 0.8 wt. % will be insufficient for complete binding of iron into eutectic ternary compounds included in the dispersed eutectic [(Al)+(Al,Zn) _4Ca + _Al10CaFe2 ]. A calcium concentration above 1.2 wt. % will result in an excessively high amount of eutectic [(Al)+(Al,Zn) _4Ca ], which may result in a decrease in the amount of zinc in the aluminum solid solution and _a decrease in deformation plasticity.

Concentrations of iron, silicon, copper and manganese below the specified values will result in the formation of an insufficient amount of eutectic and, as a consequence, in a decrease in the technological properties during casting of ingots. In addition, achieving such concentrations is possible only with the use of expensive high-purity raw materials. Concentrations of these elements above the specified values will result in a coarsening of the structure, which will negatively affect the mechanical properties and deformation plasticity during pressure processing (in particular, during rolling and pressing).

The alloy can be produced in the form of various deformed semi-finished products, in particular:

- in the form of hot-rolled sheets, which in the initial state (i.e. without heat treatment) have a structure consisting of an aluminum solid solution containing secondary precipitates (which can be defined as an “aluminum matrix”), and uniformly distributed in it eutectic phases (Al, Zn) ₄ Ca, Al ₁₀ CaFe ₂ , Al ₂ CaSi ₂ of a round shape, and possessing the following mechanical tensile properties: tensile strength (σ _in ) - not less than 370 MPa, relative elongation (δ) - not less than 6%;

- in the form of cold-rolled sheets which, after annealing (at 400°C for 1 hour), have a structure consisting of an aluminum solid solution containing secondary precipitates (i.e., an “aluminum matrix”) and uniformly distributed eutectic phases (Al, Zn) ₄ Ca, Al ₁₀ CaFe ₂ , Al ₂ CaSi ₂ of a rounded shape, and possess the following mechanical tensile properties: tensile strength (σ _in ) - not less than 360 MPa, relative elongation (δ) - not less than 5%.

- in the form of rods, which in the initial state (i.e. without heat treatment) have a structure consisting of an aluminum solid solution containing secondary precipitates (i.e. "aluminum matrix"), and uniformly distributed in it eutectic phases (Al, Zn) ₄ Ca, Al ₁₀ CaFe ₂ , Al ₂ CaSi ₂ of a round shape, and possess the following mechanical tensile properties: tensile strength (σ _in ) - not less than 300 MPa, relative elongation (δ) - not less than 5%.

The invention is illustrated by a drawing, where Fig. 1 shows hot-rolled sheets of the claimed alloy and its microstructure, and Fig. 2 shows rods of the claimed alloy and their microstructure.

The essence of the invention is as follows.

The proposed alloy is designed to obtain a structure in the cast state consisting of primary crystals of an aluminum solid solution containing at least 3 wt.% Zn, at least 1 wt.% Mg, and a dispersed eutectic containing intermetallics (Al,Zn) ₄ Ca, Al ₁₀ CaFe ₂ , Al ₂ CaSi ₂ and Al ₂ Mg ₃ Zn ₃ no larger than 5 μm. It should be noted that not only partial dissolution of eutectic inclusions of the Al ₂ Mg ₃ Zn ₃ phase can occur during hot deformation, but also formation of secondary precipitates of this phase of submicron size. These structural changes at certain parameters of deformation treatment do not have a significant effect on the mechanical properties of the semi-finished product.

The presence of alloying elements within the stated limits allows for a high level of deformation manufacturability and mechanical properties without using homogenization (for ingots) and hardening (for deformed semi-finished products) operations.

EXAMPLE 1.

Six alloys were prepared in the form of flat ingots measuring 140x200x20 mm, obtained by casting in a graphite mold. The cooling rate was 10°C/s, which corresponds to the rates for obtaining medium-sized ingots by continuous casting (in particular, cylindrical ingots with a diameter of 100-200 mm). The alloy compositions are given in Table 1. The alloys were prepared in an electric resistance furnace in graphite-chamotte crucibles based on scrap and waste aluminum alloys (their share was not less than 90%), with subsequent additional charging with metallic calcium.

The ingots were hot rolled at 450°C to a thickness of 1 mm without preliminary homogenization (Fig. 1). Alloys 1-4 and 6 demonstrated good deformation processability, and there were no visible or microstructural defects. Alloy 5 was destroyed during rolling.

It is evident from Table 2 that only the claimed alloy (compositions 2-4) provides the required values of mechanical properties (σ _in , and δ), which is due to the implementation of the required structural parameters. As an example, Fig. 1b and 2b show the structure of alloy 3. In alloy 1 and the prototype (alloy 6), the strength is much lower than the required level, which is due to the low concentrations of zinc and magnesium in the aluminum solid solution.

Table 1

Compositions of experimental alloys

No. Concentrations, wt.% Zn Mg Sa Fe Si Cu Mn Al 1 4.0 0.5 0.3 0.2 0.05 0.05 0.05 rest. 2 5.6 1.6 1,2 0.6 0.05 0.05 0.05 rest. 3 5.0 1.3 1.0 0.5 0.2 0.2 0.2 rest. 4 5.8 1,2 0.8 0.3 0.3 0.3 0.3 rest. 5 7.0 2.5 2.0 1.0 0.5 0.5 0.5 rest. 6 ¹ 0.4 - 2.5 0.4 0.2 0.2 1.6 rest.

¹ prototype

Table 2

Characteristics of experimental alloys in hot rolled sheets

No. ¹ σ _in , _, MPa δ, % Concentration in (Al) ² , wt.% d, µm ³ Zn Mg 1 246 10.6 2.6 0.5 3.5 2 376 6.4 3.3 1.3 4.2 3 386 9.1 3.6 1,2 3.6 4 373 8.5 3.9 1,1 4.8 6 250 5.5 0.15 - 2.7

¹ see table 1, ² including secondary emissions ³ average particle size

Of all the alloys, alloys 2-4 fully satisfy the stated requirements.

EXAMPLE 2.

Sheets of alloys 2-4 were cold rolled from 1 mm to 0.5 mm. Cold rolled sheets were annealed at 400°C for one hour. Table 3 shows their properties, which correspond to the declared level.

Table 3

Characteristics of experimental alloys in the form of cold-rolled sheets with a thickness of 0.5 mm.

^Alloy σ_V, MPa δ, % 2 376 5.8 3 375 7.5 4 368 5.6

EXAMPLE 3.

Alloy 3 was obtained as a cylindrical ingot with a diameter of 40 mm and a length of 200 mm, from which rods with a diameter of 14 mm were obtained by the RSR (radial shear rolling) method (Fig. 2). Alloy 3 demonstrated good deformation processability, there were no visible and microstructural defects. The microstructure is dispersed, the particles of intermetallic compounds are small, rounded, uniformly distributed in the aluminum solid solution. As can be seen from Table 4, the rod made of alloy 3 has the required combination of strength and ductility.

Table 4

Characteristics of experimental alloy 3 in the form of deformed semi-finished products

Type of semi-finished product σ _in , MPa δ, % RSP rod, diameter 14 mm 320 5.5

Claims (7)

1. A deformable aluminum-based alloy, smelted from secondary raw materials, containing zinc, calcium, iron, silicon, copper and manganese, characterized in that it additionally contains magnesium in the following ratio of components, wt.%: Zinc 5.0-5.8 Calcium 0.8-1.2 Magnesium 1.2-1.6 Iron 0.3-0.6 Silicon 0.05-0.3 Copper 0.05-0.3 Manganese 0.05-0.3 Aluminum rest and has a structure consisting of a solid solution of aluminum containing secondary precipitates and a eutectic with rounded particles of (Al, Zn) ₄ Ca, Al ₁₀ CaFe ₂ , Al ₂ CaSi ₂ and Al ₂ Mg ₃ Zn ₃ no more than 5 μm in size, while the concentration of zinc in the solid solution of aluminum containing secondary precipitates is at least 3 wt.%, and magnesium is at least 1 wt.%. 2. A deformed semi-finished product made from an aluminum-based alloy smelted from secondary raw materials, characterized in that it is made from an alloy according to paragraph 1. 3. A semi-finished product according to item 2, characterized in that it is made in the form of a hot-rolled sheet and has the following mechanical tensile properties in its initial state: tensile strength (σ ₎ - not less than 370 MPa, relative elongation (δ) - not less than 6%. 4. A semi-finished product according to item 2, characterized in that it is made in the form of a cold-rolled sheet and has the following mechanical tensile properties in its initial state: tensile strength (σ _in ) - not less than 360 MPa, relative elongation (δ) - not less than 5%. 5. A semi-finished product according to item 2, characterized in that it is made in the form of a rod and has the following mechanical tensile properties in its initial state: tensile strength (σ _in ) - not less than 300 MPa, relative elongation (δ) - not less than 5%.