RU2405852C2 - Castable aluminium alloy - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to metallurgy, and namely to alloys on the basis of aluminium and can be used when manufacturing parts of automobile motors operating under effect of high loads at temperatures of up to 150-200°C. Castable alloy on the basis of aluminium contains the following components, wt %: silicone 7.6-8.6, copper 0.3-0.5, magnesium 0.26-0.38, manganese 0.1-0.3, iron 0.1-0.3, when the following conditions are met: temperature of equilibrium solidus of the alloy is not less than 550°C, volume ratio of secondary separations of Al₅Cu₂Mg₈Si₆ phase is not less than 0.8 vol %.

EFFECT: sparingly alloyed silumin is obtained, which is intended for obtaining shaped castings of complex shape and which has high mechanical properties σ_H of not less than 320 MPa, δ not less than 4%.

3 cl, 1 dwg, 2 tbl, 3 ex

Description

The invention relates to the field of metallurgy, specifically to aluminum-based alloys, and can be used to obtain parts for automobile engines operating under high loads at temperatures up to 150-200 ° C: cylinder heads, water pump housings, intake pipes, etc.

The details of automobile engines differ in complex shape, so they are usually made of silumins (alloys based on the Al-Si system) by various shaped casting methods: in the earth, chill mold, under pressure, etc.

Castings intended for the most critical parts are usually used after complete heat treatment of type T6 (hardening and aging for maximum strength). To achieve the required quality of the latter, the alloy requires a combination of high technology (in particular, upon receipt of thin-walled castings of complex shape) and a sufficiently good level of various mechanical properties (strength, ductility, fracture toughness, etc.). To implement this combination, as a rule, special silumins are used, which differ from the usual ones in the following features:

1) a narrow concentration range of alloying elements (for example, for magnesium it is less than 0.1%);

2) a strict restriction on impurities (primarily iron), which greatly limits the possibility of using secondary raw materials for their preparation;

3) mandatory heat treatment, including hardening (usually type T6);

4) significantly more stringent (compared with conventional silumin) requirements for the preparation of the melt and its processing (refining, modification, degassing, filtration).

Silumins with the indicated features can be called high strength, since after complete heat treatment of type T6, the guaranteed level of σ _{in is} usually 300-400 MPa (i.e. higher than that of conventional silumins). Hardening after heat treatment is achieved due to secondary precipitates of the Mg ₂ Si, Al ₂ Cu and Al ₅ Cu ₂ Mg ₈ Si ₆ phases (usually metastable modifications). Therefore, thermally hardened silumins necessarily contain copper and magnesium additives necessary for the formation of these secretions. Many of them contain small additives, which, having a positive effect on some properties, often do even more harm. An example is beryllium, which, on the one hand, has a positive effect on the morphology of the Fe phase, and on the other hand, has a detrimental effect on human health.

The most durable industrial silumins (in particular, those included in GOST 1583-93) contain an addition of beryllium, which leads to their significant rise in price, and also requires special precautions in their production.

The most durable among them is AK8M3ch alloy, which contains, wt.%:

Silicon 7-8.5 Copper 2.5-3.5 Magnesium 0.2-0.45 Zinc 0.5-1.0 Beryllium 0.05-0.25 Titanium 0.1-0.25 Boron 0.015-0.1 Aluminum and impurities rest

In this silumine, hardening is achieved due to the phases Al ₂ Cu and Al ₅ Cu ₂ Mg ₈ Si ₆ . The disadvantage of AK8M3ch alloy, in addition to the presence of beryllium in its composition, is its low solidus (at the upper limit for magnesium and copper it is below 520 ° C), which does not allow to achieve sufficient spheroidization of the silicon phase during heating under quenching.

The closest alloy to the proposed one is the beryllium-free silumin disclosed in US Pat. No. 6,773,666 (2004, Lin; Jen C. etc., Alcoa Inc).

This alloy contains silicon, magnesium and manganese at the following concentrations of components, wt.%:

Silicon 6-9 Magnesium 0.2-0.8 Manganese 0.1-1.2 Aluminum rest

Castings with a good combination of casting and mechanical properties can be obtained from this silumin due to the addition of manganese, which allows iron to be bound into skeletal inclusions and reduce its harmful effect. The patent claims particularly emphasize the absence of beryllium and copper. The first disadvantage of this alloy is the limitation on the maximum working temperature. This is due to the fact that the secondary precipitates of the Mg ₂ Si phase during prolonged heating above 180 ° C are prone to coarsening, which leads to softening. The second disadvantage of this alloy is the strict restriction on the maximum permissible concentration of copper, which makes high demands on the purity of charge materials and complicates the use of recycled materials.

The objective of the invention is the creation of a new beryllium-free high-strength silumin, designed to produce shaped castings of complex shape and allowing at least 0.2% Cu. In this case, the alloy should not contain additives of zirconium, chromium, titanium, boron and strontium, and also have a solidus of at least 550 ° C.

The problem is solved in that an aluminum-based casting alloy containing silicon, magnesium, copper, manganese and iron, characterized by a structure that is a matrix formed by a solid solution of aluminum with dispersed particles of secondary precipitates uniformly distributed in it, and particles uniformly distributed in the matrix silicon of eutectic origin, contains alloying components in the following amount, wt.%:

Silicon 7.6-8.6 Copper 0.3-0.5 Magnesium 0.26-0.38 Manganese 0.1-0.3 Iron 0.1-0.3

the following conditions must be met:

a) the temperature of the equilibrium solidus of the alloy should not be lower than 550 ° C;

b) the volume of the secondary phase precipitates Al ₅ Cu ₂ Mg ₈ Si ₆ should not be less than 0.8 vol.%

The invention consists in the following.

Copper and magnesium are within the stated limits in the aluminum matrix in the form of secondary precipitates of the Al ₅ Cu ₂ Mg ₈ Si ₆ phase, which makes the main contribution to the strength of the alloy. At the selected concentrations of copper and magnesium, a combination of high solidus temperature, high casting properties of the alloy, and thermal stability is achieved.

Manganese and iron within the declared limits are completely included in the eutectic inclusions of the Al ₁₅ (FeMn) ₃ Si ₂ phase, which crystallize mainly in the triple eutectic (Al) + (Si) + Al ₁₅ (FeMn) ₃ Si ₂ . This crystallization pattern has a favorable effect on the cast structure (namely, on the morphology of the silicon and glandular phases), which contributes to the formation of globular inclusions of the silicon phase during heating under quenching.

EXAMPLE 1

1. 6 alloys were prepared, the compositions of which are listed in Table 1. Alloys were prepared in an electric resistance furnace in graphite chamotte crucibles from aluminum of the A7 grade, AK12och alloy, Mg90 grade magnesium (99.9%), M1 copper (99.9%) and alloys: Al-10% Mn and Al-10% Fe. The castings were heat treated according to the T6 mode (heating under quenching at 545 ± 5 ° С, quenching in cold water and aging). Equilibrium solidus was determined by differential thermal analysis and refined by calculation using the Thermo-Calc program (TTAL5 database). The volume fraction of secondary precipitates of the Al ₅ Cu ₂ Mg ₈ Si ₆ phase was calculated using the Thermo-Calc program according to the procedure described in [Belov N.A., Savchenko S.V., Khvan A.V. Phase composition and structure of silumins. - M.: MISiS, 2007, 284 p.]. The mechanical tensile properties were determined according to GOST 1497-84 on cylindrical samples separately cast in a chill mold (obtained according to GOST 1583-93).

Table 1 The compositions of the experimental alloys and their properties after heat treatment T6 and exposure at 190 ° C for 8 hours No. Concentration,% by weight σ _in ¹ , MPa δ ² ,% HB ³ T _s ⁴ , ° C Q ⁴ , about % Si Mg Cu Mn Fe Al one 7 0.2 0.1 0.05 0.05 rest 260 10 80 570 2 7.6 0.26 0.26 0.3 0.3 rest 330 8 105 566 3 8 0.32 0.35 0.2 0.2 rest 345 6 110 563 four 8.4 0.38 0.45 0.1 0.1 rest 350 4,5 116 560 5 9 0.5 one 0.5 0.5 rest 320 1,6 120 548 6 7.5 0.5 <0.01 0.7 0.1 rest 270 3,5 85 561 0 ¹ temporary tensile strength; ² elongation; ³ Brinell hardness; ⁴ equilibrium solidus temperature (calculation), ⁵ volume fraction of secondary precipitates of the phase Al ₅ Cu ₂ Mg ₈ Si ₆

From table 1 it is seen that only the claimed alloy (compositions 2-4) provides the best combination of temporary resistance, elongation and equilibrium solidus. In alloy 1, the strength is less than the required level, which is associated with an insufficient amount of precipitation of the Al ₅ Cu ₂ Mg ₈ Si ₆ phase. Alloy 5 has a low value of δ, which is associated with partial burnout due to the fact that T _s <550 ° C. The prototype alloy (composition 6) is inferior to alloys 2-4 in terms of σ _in and HB, since there is no Al ₅ Cu ₂ Mg ₈ Si ₆ phase in it. Moreover, the inclusions of the silicon phase in all compositions of the claimed alloy had a globular morphology (see drawing).

EXAMPLE 2

The mechanical properties of alloys 3 and 6 were determined (see Table 1) at elevated temperatures. The mechanical tensile properties were determined according to GOST 9651-84 on cylindrical specimens machined from chill castings (according to GOST 1583-93). The results shown in table 2 show that the inventive alloy (No. 3) surpasses the known (No. 6) in strength, both at 150 ° C and at 200 ° C.

table 2 Strength properties of experimental alloys at elevated temperatures No. T, ° C σ _in , MPa σ _0.2 , MPa 3 150 190 170 200 95 70 6 150 150 135 200 70 fifty

EXAMPLE 3

Of the inventive alloy composition No. 3 (see table 1) in the factory, LLC “RosALit” were flooded 100 pcs. serial castings det. 514.1003015 "Cylinder head" (see drawing 1). All castings were of satisfactory quality.

Claims (3)

1. Cast aluminum alloy containing silicon, magnesium, copper, manganese and iron, characterized by a structure consisting of a matrix formed by a solid solution of aluminum with dispersed particles of secondary precipitates Al ₅ Cu ₂ Mg ₈ Si ₆ uniformly distributed in it and uniformly distributed in the matrix, globular particles of the silicon phase, characterized in that it contains alloying components in the following amount, wt.%:
Silicon 7.6-8.6 Copper 0.3-0.5 Magnesium 0.26-0.38 Manganese 0.1-0.3 Iron 0.1-0.3
under the following conditions: the temperature of the equilibrium solidus of the alloy is not lower than 550 ° C, the volume fraction of the secondary precipitates of the Al ₅ Cu ₂ Mg ₈ Si ₆ phase is not lower than 0.8 vol.%. 2. The alloy according to claim 1, characterized in that it is made in the form of a casting having the following tensile properties: temporary resistance σ of _at least 320 MPa, elongation δ of at least 4%. 3. The alloy according to claim 1, characterized in that it is made in the form of casting cylinder heads.

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