RU2691476C1 - 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. Foundry alloy based on aluminum contains, wt%: 5–6 Zn, 0.6–1.4 Ca, 1.2–1.8 Mg, 0.4–0.7 Fe, aluminum – the rest, wherein after casting alloy has: temporary resistance (σ) is not less than 320 MPa, yield point (σ) is not less than 210 MPa, relative elongation (δ) is not less than 5 %.EFFECT: creation of a new foundry high-strength aluminum alloy intended for production of shaped castings.1 cl, 4 dwg, 2 tbl, 2 ex

Description

The invention relates to the field of metallurgy of materials based on aluminum and can be used to obtain products operating under high loads at temperatures up to 150-200 ° C: details of aircraft (airplanes, helicopters, rockets, unmanned aerial vehicles), automobiles and other transport facilities (bicycles, scooters, carts), sports equipment parts (golf club bodies, tennis rackets), etc.

The most durable aluminum alloys of the type B95 (σ _в = 500-600 MPa) are deformable and belong to the Al-Zn-Mg-Cu system (Industrial aluminum alloys / Ref. Ed. / Alieva SG, Altman MB and et al., Metallurgy, 1984. 528 p.). They have low casting properties, so these alloys are practically not used for the production of shaped castings.

Known alloy based on aluminum, disclosed in the 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 evenly dispersed secondary precipitates of the hardening phase, and particles of crystallization nickel aluminides uniformly distributed in the matrix. The number of nickel aluminides is 5.3-7.0 vol. %, the matrix as dispersed particles contains 6-10 vol. % of particles of phase T, which are metastable modifications of phase T (Al ₂ Mg ₃ Zn ₃ ), and the equilibrium solidus temperature of the material is at least 540 ° C.

Castings with an improved combination of mechanical properties and manufacturability can be obtained from this alloy (with shaped casting and pressure treatment). However, this alloy contains an expensive nickel additive in the amount of 3.2–5 wt. %, which complicates its widespread industrial use. In addition, nickel increases the density of the alloy, which reduces its specific strength.

Known alloy based on aluminum, disclosed in the 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 dispersed eutectic Al-Ca-Zn, 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 designed to produce shaped castings.

The 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 thermal hardening after heat treatment, including quenching. In particular cases, the alloy can be made in the form of shaped castings, in which the following level of strength is achieved: σ _in > 450 MPa. σ _0,2 > 400 MPa. The main disadvantage of this alloy is that to achieve a high complex of mechanical properties it is necessary to conduct heat treatment of castings, including quenching (mode T6). 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 shortcomings cause a relatively 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 0.4% iron and not requiring heat treatment.

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

Zinc 5-6

Magnesium 1.2-1.8

Calcium 0,6-1,4

Iron 0.4-0.7

Aluminum Rest

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

The concentration ranges of zinc and magnesium are justified by the need to ensure that the amount of these elements as a result of crystallization in a solid aluminum solution is not less than 3% Zn and not less than 1% Mg, and the amount of T formed (Al ₂ Mg ₃ Zn ₃ ) was insignificant and should not adversely affect on the mechanical and casting properties of the alloy.

Zinc concentrations of less than 5 wt. % will not be enough to ensure high mechanical properties, the concentration is above 6 wt. % will lead to an excessively high amount of Al-Ca-Zn eutectic, which will affect the formation of needle-like inclusions of the Al ₃ Fe phase due to a smaller amount of Al-Ca-Fe eutectics, as well as an increase in the amount of T phase (Al ₂ Mg ₃ Zn ₃ ) , which will reduce the mechanical and casting properties.

Magnesium concentration below 1.2 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. Magnesium concentration above 1.8 wt. % will affect the increase in the number of phase T (Al ₂ Mg ₃ Zn ₃ ), which will lead to a decrease in mechanical and casting properties.

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

Calcium concentration below 0.6 wt. % will be insufficient for complete binding of iron into eutectic ternary compounds included in the dispersed eutectic Al-Ca-Fe, and, moreover, will lead to a decrease in casting properties. Calcium concentration above 1.4 wt. % will lead to an excessively high amount of eutectic Al-Ca-Zn, which may affect a smaller amount of zinc in the aluminum solid solution and reduce the mechanical properties, respectively.

Iron concentration less than 0.4 wt. % will lead to the formation of the eutectic Al-Ca-Zn, which will lead to a smaller amount of zinc in the aluminum solid solution and a decrease in 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 above 0.7 wt. % will lead to the formation of needle-like inclusions of the Al ₃ Fe phase, which will adversely affect the mechanical properties.

In the private version, the alloy can be made in the form of castings, possessing in the state after casting (ie, without performing heat treatment) the following tensile properties: temporary resistance (σ _in ) - not less than 320 MPa, yield strength (σ _0.2 ) - not less than 210 MPa, relative elongation (δ) not less than 5%.

The invention consists in the following.

The proposed alloy is designed to obtain a cast structure consisting of primary crystals of an aluminum solid solution containing 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 in the claimed limits allows to provide 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.

Were prepared 6 alloys in the form of bar blanks with a massive profitable part (according to GOST 1583-93), obtained by casting into 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-chambered crucibles made from aluminum of grade A7 (99.7%), zinc mark C0 (99.9%), magnesium grade Mg90 (99.9%), metallic calcium (99.9%) and Al - 10% Fe.

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

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

prototype

¹ see tab. 1, prototype

EXAMPLE 2.

Alloy 3 and 5 were obtained in the form of shaped casting of different thicknesses (Fig. 4). Melting was carried out similarly to the method described in example 1. The casting was carried out in a detachable steel mold, the molds 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 formability, there were no visible and microstructural defects. The microstructure consisted of compact intermetallic phases based on aluminum with iron and calcium.

Claims (3)

Foundry alloy based on aluminum, containing zinc, magnesium and calcium, characterized in that it additionally contains iron at the following concentrations of components, wt. %: Zinc 5-6 Calcium 0.6-1.4 Magnesium 1.2-1.8 Iron 0.4-0.7 Aluminum rest, while in the state after casting, it has the following mechanical tensile properties: temporary resistance (σ _in ) - not less than 320 MPa, yield strength (σ _0.2 ) - not less than 210 MPa, relative elongation (δ) - not less than 5% .

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