RU2621499C2 - Method for producing castings of high-strength aluminium-based alloys - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method for producing castings of high-strength aluminium-based alloy includes the preparation of an aluminium melt containing zinc, magnesium, copper, nickel and iron, production of a casting by casting the prepared melt and heat treatment of the casting to form a structure consisting of a dispersively strengthened aluminium matrix and Al₉FeNi phase particles. Preparation of the aluminium melt is carried out using aluminium obtained by electrolysis technology with an inert anode. The melt is prepared at the following concentration of alloying elements, by weight %: zinc 6.3-7.5, magnesium 2.1-2.8, copper 0.2-0.35, nickel 0.6-0.8, iron 0.50-0.70, aluminium is the rest, and after the heat treatment, a structure with a dendritic cell size of the aluminium matrix of not more than 30 mcm and a microhardness of at least 170 HV is obtained.

EFFECT: producing castings with a temporary resistance of at least 500 MPa, a yield strength of at least 450 MPa, a relative elongation of at least 5 percent.

3 cl, 3 ex, 4 tbl, 3 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 ° C: details of aircraft (aircraft, helicopters, missiles), automobiles and other vehicles (including: bicycles, scooters, trolleys), parts of sports equipment, etc.

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

A known alloy based on aluminum-nickel eutectic and a method for producing castings from it (patent RU 2158780 from 10.11.2000). This alloy contains a matrix formed by a solid solution of zinc, magnesium and copper in aluminum with particles of nickel aluminides of crystallization origin uniformly distributed in the matrix and particles evenly distributed in the matrix of at least one of the aluminides selected from the group consisting of chromium aluminides and zirconium aluminides, with a total content of from 0.1 to 0.5 vol. % of the material. From this alloy, castings with improved casting properties can be obtained by adding nickel, which forms aluminides of eutectic origin. The disadvantage of this alloy is that its preparation requires high-purity aluminum, which significantly increases its cost, and also increases the percentage of rejects (due to the possible ingress of iron into the melt during its preparation).

Closest to the proposed is a method for producing an alloy based on aluminum, disclosed in patent RU 2484168 (publ. 06/10/2013, bull. No. 16). This alloy is based on aluminum, containing zinc, magnesium, nickel, iron, zirconium and copper, characterized in that it contains components in the following amount, wt. %:

Zinc 5.5-6.5 Magnesium 1.7-2.3 Nickel 0.4-0.7 Iron 0.3-0.7 Zirconium 0.02-0.25 Copper 0.05-0.3 Aluminum Rest

The known alloy can be made in the form of castings in which the following tensile properties are achieved: temporary resistance (σ _in ) - not less than 450 MPa, yield strength (σ _0.2 ) - not less than 400 MPa, relative elongation (δ) - not less than 4%. A method for producing castings from this alloy includes its smelting in an electric resistance furnace in graphite chamotte crucibles from aluminum of the A5E grade (99.5%), zinc of the Ts0 grade (99.9%), Mg90 grade magnesium (99.9%), M1 grade copper (99.9%) and Al-Ni, Al-Fe and Al-Zr ligatures.

High mechanical properties of the alloy are achieved due to the implementation of the structure, which is a matrix formed by a solid solution of aluminum with uniformly distributed dispersed particles of secondary precipitates and relatively globular particles of a phase Al ₉ FeNi of eutectic origin uniformly distributed in the matrix. The technical result is the creation of a new low-alloy high-strength alloy, designed to produce shaped castings.

The disadvantage of this method is the need for the introduction of iron from the Al-Fe ligature, which increases the melt preparation time. The second disadvantage is that the melt is prepared on the basis of vintage primary aluminum (in particular, grade A5E), which leads to a relatively high cost of castings. In addition, the known method does not allow to provide the following mechanical tensile properties: temporary resistance (σ _in ) - not less than 500 MPa, yield strength (σ _0.2 ) - not less than 450 MPa, relative elongation (δ) - not less than 5% .

The technical result is the creation of a new method for producing castings of high-strength alloy based on aluminum containing zinc, magnesium, nickel, iron, copper and zirconium, which does not require the introduction of Al-Fe alloys into the melt and provides the following tensile mechanical properties in castings: temporary resistance (σ _in ) - not less than 500 MPa, yield strength (σ _0.2 ) - not less than 450 MPa, elongation (δ) - not less than 5%.

The technical result is achieved as follows.

A method for producing castings from a high-strength aluminum-based alloy involves the preparation of a melt containing zinc, magnesium, copper, nickel and iron, heat treatment of castings, leading to the formation of a structure consisting of dispersion-hardened aluminum matrix and compact particles of the Al ₉ FeNi phase. The melt is prepared on the basis of aluminum containing iron, produced by an inert anode electrolysis technology, while the concentration of alloying elements, casting and heat treatment modes are chosen so as to obtain a structure with a dendritic cell size of the aluminum matrix of not more than 30 μm and its microhardness not less than 170 HV.

Castings are obtained by casting in a chill mold, then they are homogenized, subjected to hot isostatic pressing (HIP) and hardening heat treatment, including hardening and aging, with the following tensile properties: temporary resistance (σ _in ) - at least 500 MPa, yield strength (σ _{0, 2} ) - not less than 450 MPa, elongation (δ) - not less than 5%.

Castings are obtained by injection molding.

The concentration of alloying elements of an aluminum-based alloy produced by an inert anode electrolysis technology belongs to the following ranges, wt. %:

Zinc - 6.3-7.5,

Magnesium - 2.1-2.8,

Copper - 0.2-0.35,

Nickel - 0.6-0.7,

Iron - 0.45-0.55.

Castings can also be obtained by injection molding with crystallization (liquid stamping).

The invention is illustrated in the drawing, where in FIG. 1 shows an aluminum alloy casting obtained by chill casting (Example 1), FIG. 2 shows the microstructure of the casting obtained by chill casting and heat treatment according to mode 2 (example 1), FIG. 3 shows aluminum alloy castings obtained by injection molding with crystallization (Example 3).

The invention consists in the following.

The preparation of a melt based on aluminum, produced by inert anode electrolysis (EIA) technology, eliminates the operation of introducing Al-Fe alloys into the melt, since the required amount of iron is already contained in EIA aluminum. In addition, the use of EIA aluminum instead of branded primary aluminum reduces the cost of castings. The introduction of the optimal amount of nickel allows one to obtain compact particles of the Al ₉ FeNi phase in the structure of castings, which favorably affects plasticity.

During the casting process, a structure is formed consisting of primary crystals of aluminum solid solution with an average dendritic cell size (d) of not more than 30 μm and eutectic particles of phases Al ₉ FeNi and T (Al ₂ Mg ₃ Zn ₃ ). These particles are located along the boundaries of dendritic cells; therefore, their size depends on the value of d. During the heat treatment, the T phase eutectic particles are dissolved in the aluminum solid solution, globular particles of Al ₉ FeNi phases are formed and, at the last stage (aging), metastable phases of nanosized particles are precipitated from the aluminum solid solution, which make the main contribution to hardening. Thus, in place of the aluminum solid solution, an aluminum matrix with nanosized particles is formed. The value of d remains virtually unchanged.

The limitation on the maximum average size of the dendritic cell of the aluminum matrix (not more than 30 μm) allows the formation of sufficiently dispersed particles of the Al ₉ FeNi phase, which positively affects the mechanical properties, primarily plasticity. The limitation on the minimum microhardness of the aluminum matrix (not less than 170 HV) allows to provide the required strength (not less than 500 MPa) in the casting.

The use of the ISU operation for chill castings and the production of castings by injection molding with crystallization under pressure makes it possible to sharply reduce casting porosity, which favorably affects the whole complex of mechanical properties.

EXAMPLE 1

Alloy castings were prepared, the calculated composition of which is given below, mass. %: 6.3% Zn, 2.8% Mg, 0.6% Ni, 0.55% Fe, 0.2% Cu, Al base (Alloy 1).

The alloy (in the amount of 4 kg per method) was prepared from aluminum grade A85 (GOST 11069-2001) and aluminum produced by the electrolysis technology with an inert anode in an electric resistance furnace in graphite chamotte crucibles. Alloying elements were introduced in pure form (zinc, magnesium, copper) and in the form of ligatures (Al-Ni, Al-Fe). The preparation time (i.e., the achievement of the calculated chemical composition) was determined by sampling from the melt, which was done every 5 min, and subsequent analysis of the chemical composition on an ARL4460 spectrometer.

Castings were cast in the steel mold given in GOST 1583-93 (Fig. 4. p. 33). Castings (Fig. 1) were heat treated in two modes:

1 - T6 (annealing, quenching in water and aging for maximum hardening);

2 - Special mode (homogenizing annealing, ISU, annealing, quenching in water, aging).

Were performed 5 methods for producing castings, which are given in table. one.

Mechanical properties were determined on cylindrical samples cut from castings according to GOST 1497-84.

As can be seen from the table. 1, when using single grade aluminum (method 1), the melt preparation time is maximum. When using equal amounts of aluminum A85 and IEA (methods 2 and 4) this time is reduced, and when using only one aluminum IEA (methods 3 and 5) it is minimal. From the table. 2 shows that when using heat treatment mode 1 (methods 1-3), the elongation is less than 5%. When using heat treatment mode 2 (methods 4 and 5), the required level of mechanical properties is achieved. This level is ensured by the structure, which consists of dispersion-hardened (nanoparticles) aluminum matrix and compactly distributed compact particles of the Al ₉ FeNi phase of eutectic origin (Fig. 2).

EXAMPLE 2

Of alloy composition, mass. %: 7.5% Zn, 2.1% Mg, 0.8% Ni, 0.7% Fe, 0.35% Cu, Al base (Alloy 2), castings were obtained by casting into a steel mold heated to different temperatures . The remaining melting parameters corresponded to method 5 in example 1 (see table. 1). The castings were heat-treated according to mode 2. Heating the steel mold to different temperatures allowed us to obtain a structure with different sizes d. As can be seen from the table. 3, methods 2 and 3, leading to coarsening of the structure (d value above 30 μm), do not allow to obtain the required mechanical properties in the casting.

EXAMPLE 3

From alloys of the same composition as in examples 1 and 2, castings were prepared by injection molding with crystallization under pressure (Fig. 3). The remaining melting parameters corresponded to method 3 in example 1 (see table. 1). The castings were heat-treated according to mode 1, then samples for tensile testing were cut from them. As can be seen from the table. 4, in castings obtained by this method, the required set of mechanical properties is achieved.

Claims (5)

1. A method of producing castings from a high-strength aluminum-based alloy, including the preparation of an aluminum melt containing zinc, magnesium, copper, nickel and iron, the production of castings by casting the prepared melt and heat treatment of the casting to form a structure consisting of dispersion-hardened aluminum matrix and phase particles Al ₉ FeNi, characterized in that the cooking is carried out with molten aluminum using aluminum produced by electrolysis technologies with an inert anode, wherein the melt is prepared at trace guide concentration of alloying elements, wt.%: zinc 6.3-7.5 magnesium 2.1-2.8 copper 0.2-0.35 nickel 0.6-0.8 iron 0.50-0.70 aluminum rest, and after heat treatment, a structure is obtained with a dendritic cell size of the aluminum matrix of not more than 30 μm and a microhardness of at least 170 HV. 2. The method according to p. 1, characterized in that the casting of the melt is carried out in a chill mold, and heat treatment is carried out according to a regime that includes homogenization, hot isostatic pressing (HIP), hardening and aging, with obtaining a temporary resistance (σ _in ) of at least 500 MPa, yield strength (σ _0.2 ) - not less than 450 MPa, elongation (δ) - not less than 5%. 3. The method according to p. 1, characterized in that the casting is carried out by casting with crystallization under pressure.

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