RU2713526C1 - High-strength foundry aluminum alloy with calcium additive - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy of aluminum-based materials and can be used in production of articles operating under high loads at temperatures of up to 150–200 °C, in particular, parts of aircrafts, cars and other vehicles, sports equipment parts, etc. Aluminium-based alloy contains following, wt%: 6.0–6.5 Zn, 1.0–1.5 Ca, 1.5–2.0 Mg, 0.5–0.8 Fe, the rest is aluminum. In particular cases during casting in graphite and steel mold the following level of mechanical properties is achieved without application of heat treatment: temporary resistance (σ_t) is not less than 330 MPa, yield point (σ_0.2) is not less than 220 MPa, relative elongation (δ) is not less than 4 %.

EFFECT: invention is aimed at creation of foundry high-strength aluminum alloy intended for production of shaped castings.

1 cl, 2 ex, 2 tbl, 4 dwg

Description

The invention relates to the field of metallurgy of aluminum-based materials and can be used to obtain products operating under high loads at temperatures up to 150-200 ° C: details of aircraft (aircraft, helicopters, missiles, unmanned aerial vehicles), cars and other transport tools (bicycles, scooters, trolleys), parts of sports equipment (cases of golf clubs, tennis rackets), etc.

The most stable aluminum alloys of type B95 (σ _in = 500-600 MPa) are deformable and refer to the system Al-Zn-Mg-Cu (Industrial aluminum alloys / Ref. Ed. / Alieva SG, MB and Altman Dr. M., Metallurgy, 1984. 528 p.). They have low casting properties, so these alloys are practically not used to produce shaped castings.

Known alloy based on aluminum, disclosed in patent RU 2245388 (publ. 27.01.2005). This alloy contains zinc, magnesium and nickel, and is characterized by a structure that is a matrix formed by a solid solution of aluminum with dispersed secondary precipitates of the hardener phase uniformly distributed in it and particles of nickel aluminides of crystallization origin uniformly distributed in the matrix. The amount of nickel aluminides is 5.3-7.0 vol. %, the matrix as dispersed particles contains 6-10 vol. % of particles of the T 'phase, which are metastable modifications of the T phase (Al ₂ Mg ₃ Zn ₃ ), and the temperature of the equilibrium solidus of the material is at least 540 ° C.

From this alloy, castings with an improved combination of mechanical properties and manufacturability during shaped casting can be obtained. However, this alloy contains an expensive nickel additive in an amount of 3.2-5 mass. %, which complicates its widespread industrial use. In addition, nickel increases the density of the alloy, which reduces its specific strength.

Known aluminum-based alloy disclosed in patent US 4126448 (11/21/1978). This alloy contains 2-8% Ca, 1.5-15% Zn, up to 2% Mg, Si, Mn, and up to 2% of other elements. The structure of this alloy contains a dispersed Al-Ca-Zn eutectic, and the alloy itself has superplasticity and is designed to produce deformed semi-finished products. The disadvantage of this alloy is low strength: σ _in = 182 MPa; σ _0.2 = 162 MPa. The second disadvantage of this alloy is that it is not intended to produce shaped castings.

Closest to the proposed is an alloy based on aluminum, disclosed in patent RU 2478132, publ. 03/27/2013. This alloy contains 7-12% Zn, 2-5% Ca, 2.2-3.8% Mg, 0.02-0.25% Zr, while its hardness is at least 150 HV. The technical result is the creation of a new high-strength alloy capable of heat hardening after heat treatment, including hardening. In special cases, the alloy can be made in the form of shaped castings in which the following strength level is achieved: σ _in > 450 MPa. σ _0.2 > 400 MPa. The main disadvantage of this alloy is that in order to achieve a high complex of mechanical properties it is necessary to conduct heat treatment of castings, including hardening (T6 mode). The second disadvantage is the absence of iron in its composition (in the example given, alloys were prepared on the basis of high-purity aluminum of grade A99). These disadvantages cause a fairly high cost of castings.

The technical result of the invention is the creation of a new high-strength economically alloyed aluminum alloy designed to produce shaped castings containing at least 0.5% iron and not requiring heat treatment.

The technical result is achieved due to the fact that the aluminum-based alloy containing zinc, magnesium and calcium, additionally contains iron at the following concentrations of components, wt. %:

Zinc 6.0-6.5 Magnesium 1.5-2.0 Calcium 1.0-1.5 Iron 0.5-0.8 Aluminum Rest

The alloy is made in the form of castings having the following mechanical tensile properties after casting (i.e., without heat treatment): temporary resistance (σ _in ) - not less than 330 MPa, yield strength (σ _0.2 ) - not less than 220 MPa, elongation (δ) - at least 4%.

The invention is illustrated in the drawing, where in FIG. 1 shows a natural view of a casting of the type of bar stock according to GOST 1583-93 from the inventive alloy, FIG. 2 shows samples for uniaxial tensile testing according to GOST 1497-84 from the inventive alloy, FIG. 3 shows the microstructure of the inventive alloy in the cast; FIG. 4 shows a natural view of shaped different thickness castings of the inventive alloy.

The concentration ranges of zinc and magnesium are justified by the need to ensure the amount of these elements as a result of crystallization in a solid aluminum solution of at least 6% Zn and at least 1.5% Mg, and the amount of the formed phase T (Al ₂ Mg ₃ Zn ₃ ) should not adversely affect mechanical and casting properties of the alloy.

The concentration of zinc is less than 6 wt. % will not be enough to ensure high mechanical properties, a concentration above 6.5 wt. % will lead to an excessively high amount of Al-Ca-Zn eutectic, which will affect the formation of needle-shaped inclusions of the Al ₃ Fe phase due to the smaller amount of Al-Ca-Fe eutectic, as well as an increase in the amount of the T phase (Al ₂ Mg ₃ Zn ₃ ), which will lead to a decrease in mechanical and casting properties.

The concentration of magnesium is below 1.5 wt. % will lead to a decrease in mechanical properties due to a decrease in its amount in solid aluminum solution as a result of crystallization. The concentration of magnesium above 2.0 wt. % will affect the increase in the amount of phase T (Al ₂ Mg ₃ Zn ₃ ), which will lead to a decrease in casting properties.

The ranges of calcium and iron concentrations are justified by the need to obtain Al-Ca-Fe dispersed eutectic as a result of crystallization, which will improve the casting properties and avoid the formation of needle-like inclusions of the Al ₃ Fe phase.

The concentration of calcium is below 1.0 wt. % will be insufficient for complete binding of iron to eutectic ternary compounds included in the dispersed Al-Ca-Fe eutectic, and, moreover, will lead to a decrease in casting properties. The concentration of calcium is above 1.5 wt. % will lead to an unnecessarily high amount of Al-Ca-Zn eutectic, which may affect less zinc in the aluminum solid solution and lower mechanical properties, respectively.

The concentration of iron is less than 0.5 wt. % will lead to the formation of an eutectic Al-Ca-Zn, which will lead to less zinc in the aluminum solid solution and lower mechanical properties, respectively. In addition, the achievement of such a concentration is possible only when using expensive raw materials of high purity. The concentration of iron is above 0.8 wt. % will lead to the formation of needle-like inclusions of the Al ₃ Fe phase, which will negatively affect the mechanical properties.

In a private embodiment, the alloy can be made in the form of castings having, after casting (i.e., without heat treatment) the following tensile properties: temporary resistance (σ _in ) - at least 330 MPa, yield strength (σ _0.2 ) - at least 220 MPa, elongation (δ) of at least 4%.

The invention consists in the following.

The proposed alloy is designed in such a way as to obtain in the molten state a structure consisting of primary crystals of aluminum solid solution, which contains at least 3% Zn and at least 1% Mg and particles of phases of eutectic origin, which contain calcium and iron.

The presence of alloying elements within the stated limits allows to ensure a high level of technological and mechanical properties, in particular during tensile tests: temporary resistance (σ _in ), yield strength (σ _0.2 ), relative elongation (δ).

EXAMPLE 1

6 alloys were prepared in the form of a bar stock with a massive profitable part (according to GOST 1583-93) obtained by casting in a graphite mold (Fig. 1). The compositions of the alloys are shown in table. 1. Alloys were prepared in an electric resistance furnace in graphite chamotte crucibles from aluminum grade A7 (99.7%), zinc grade Ts0 (99.9%), magnesium grade Mg90 (99.9%), calcium metal (99.9%) and ligature Al - 10% Fe.

The castings were not heat treated. The mechanical tensile properties were determined on turned samples according to GOST 1497-84 (Fig. 2). The experimental values are given in table. 2. The microstructure of alloy No. 3 shows the presence of dispersed intermetallic particles of calcium and iron phases (Fig. 3).

From the table. 2 shows that only the inventive alloy (compositions 2-4) provides the required values of the mechanical properties (σ _in , σ _0.2 and δ). In alloy 1, the strength is much lower than the required level. Alloy 5 is distinguished by brittleness and low values of σ _in and σ _0.2 . Alloy 6 (prototype) has significantly lower values of ductility and strength properties than the claimed alloy.

EXAMPLE 2

Alloy 3 and 5 were obtained in the form of shaped castings of different thicknesses (Fig. 4). Smelting was carried out similarly to the procedure described in example 1. The filling was carried out in a steel demountable mold, the half-forms of which were fastened with clamps. Alloy 5 castings showed cracks, and the microstructure contained needle-like inclusions of the Al ₃ Fe phase. Alloy 4 showed good fillability, there were no visible and microstructural defects. The microstructure consisted of compact intermetallic phases based on aluminum with iron and calcium.

Claims (3)

1. An aluminum-based alloy containing zinc, magnesium and calcium, characterized in that it additionally contains iron at the following component concentrations, wt.%: Zinc 6.0-6.5 Calcium 1.0-1.5 Magnesium 1.5-2.0 Iron 0.5-0.8 Aluminum Rest 2. The alloy according to claim 1, characterized in that it is made in the form of a casting having, after casting, the following mechanical tensile properties: temporary resistance (σ _in ) - not less than 330 MPa, yield strength (σ _0.2 ) - not less than 220 MPa, elongation (δ) - not less than 4%.

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