RU2708729C1 - Cast aluminum alloy - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy and can be used to produce shaped castings by gravity casting into mold, injection molding, pressure crystallization used in automotive industry, for housings of electronic devices, as well as critical parts capable of operating at high temperatures. Foundry alloy based on aluminum contains, wt%: iron 0.1–1.1, manganese 0.5–2.5, nickel 1.2–2.2, chrome 0.02–0.20, titanium 0.02–0.15, zirconium 0.02–0.35, aluminum – the rest, iron and nickel are represented mainly in the form of eutectic aluminides in amount of not less than 4 wt%.

EFFECT: invention is aimed at creation of a new high-tech aluminum alloy capable of hardening without using a hardening operation into water.

4 cl, 3 ex, 5 tbl, 1 dwg

Description

Technical field

The invention relates to the field of metallurgy, specifically to aluminum-based alloys, and can be used in the preparation of complex castings by casting into a metal mold by various types of casting, in particular injection molding, low pressure casting, gravity casting, etc.

State of the art

Complex castings, depending on the purpose, are made of thermally not hardened and hardened silumins. Castings intended for the most critical parts are usually used after complete heat treatment of type T6 (GOST 1583-93), including quenching in water and aging for maximum strength. In this case, the maximum level of strength characteristics in the T6 state for non-copper silumins (for example, AK7pch alloy (GOST 1583-93)) is usually up to 250-300 MPa for temporary tensile strength and 170-240 MPa for yield strength values. Hardening significantly complicates the technological cycle of producing castings, since when it is used, warping of castings, change in overall dimensions and the appearance of cracks are possible.

Thermally unstrengthened alloys are usually characterized by low values of mechanical properties, in particular for AK12pch alloy (GOST 1583-93), the temporary resistance when casting into a metal mold does not exceed 180-210 MPa, the yield strength is at the level of 70-80 MPa, and typical values are relative elongation reach a level of 6-15%. Low values of elongation correspond to the structure of an alloy with a rough morphology of silicon of eutectic origin, in order to increase elongation, silumins are modified in this case, however, often, this results in an increase in porosity, which in turn leads to a deterioration in the tightness of thin-walled castings.

Known cast alloy system Al-Ni-Mn, designed to obtain structural components for automotive and aerospace applications, which is an alternative to branded silumin, developed by Alcoa and disclosed in US patent 6783730 B2 (publ. 08/31/2004). It is possible to obtain castings from this alloy with a good combination of casting and mechanical properties with a content (mass%) of 2-6% Ni, 1-3% Mn, 1% Fe, less than 1% silicon, as well as other inevitable impurities. Among the disadvantages of the proposed invention, it should be noted that a high level of casting and mechanical properties is ensured by the use of high purity grades of aluminum and a high nickel content, which significantly increases the cost of the obtained castings. In addition, the proposed material is thermally unstrengthened in the entire concentration range, which limits its use. Moreover, in the region of high nickel concentrations, the corrosion resistance of castings is significantly reduced.

Known cast aluminum alloys based on Al-Ni and Al-Ni-Mn systems and a method for producing cast parts from them, which are described in the invention of Alcoa US 8349462 B2 (publ. 08.01.2013). The invention provides alloy compositions for use in the molten state and a method for producing them to achieve a given structure that provides the required level of mechanical properties and the formation of decorative anodized coatings. The chemical composition of the proposed invention contains the following range of alloying elements (wt.%): 6.6-8.0% Ni; 0.5-3.5% Mn, up to 0.25% of any element from the group of Fe and Si; up to 0.5% of any element of the group Cu, Zn, and Mg; up to 0.2% of any element from the group Ti, Zr, and Sc, optionally B and C can be included to the content of 0.1%. As in the invention US 6783730 B2 a high level of casting and mechanical properties is ensured by using high purity grades of aluminum and a high nickel content, which significantly increases the cost of the obtained castings. At the same time, high nickel concentrations significantly reduce corrosion resistance. Moreover, in the region of high nickel concentrations, the corrosion resistance of castings is significantly reduced. With a relatively low nickel and manganese content, cast alloys have a low level of strength characteristics.

Alcoa in the invention US 8950465 B2 (publ. 02/10/2015) on aluminum alloys and the method for their production has expanded the concentration range of alloying elements reflected in the invention US 8349462 B2. In the proposed invention, castings in the cast state can be made of alloys of the Al-Ni and Al-Ni-Mn systems in the following concentration range of alloying elements (wt.%), In particular, 0.5-8.0% for the Al-Ni system Ni and for Al-Ni-Mn contain 0.5-8.0% Ni and 0.5-3.5% Mn. Among the disadvantages of the proposed invention, it should be noted that a high level of casting and mechanical properties is ensured by the use of high purity grades of aluminum and a high nickel content, which significantly increases the cost of the obtained castings.

The closest alloy to the proposed one is an aluminum-based alloy developed by NITU "MISiS" and disclosed in RF patent 2478131 C2 publ. 03/27/2013, This alloy contains (wt.%): L, 5-2.5% Ni, 0.3-0.7% Fe, 1-2% Mn, 0.02-0.2% Zr, 0.02% -0.12% Sc and 0.002-0.1% Ce. Castings obtained from the alloy after annealing (without using the hardening operation) are characterized by a temporary resistance of at least 250 MPa with a relative elongation of at least 4%. The first disadvantage of this alloy is its increased tendency to form concentrated porosity, which makes it difficult to obtain high-quality relatively large castings. The second drawback is associated with the need to use elevated casting temperatures, which cannot always be implemented in foundry conditions.

Disclosure of invention

The objective of the invention is the creation of a new aluminum alloy designed to produce shaped castings and satisfying specified requirements for a range of technological and mechanical characteristics, especially elongation.

The technical result is to provide the required combination of technological and mechanical properties of the alloy during casting.

The technical result is achieved by the fact that the casting alloy based on aluminum contains iron, nickel, manganese, at least one element selected from the group of titanium and zirconium at the following concentrations of alloying elements, mass. %:

Iron 0.1-1.1 Manganese 0.5-2.5 Nickel 1.2-2.2 Chromium 0.02-0.20 Titanium 0.02-0.15 Zirconium 0.02-0.35 Aluminum  rest

in this case, the following conditions must be fulfilled: the eutectic elements iron and nickel should be represented mainly in the form of aluminides of eutectic origin in an amount of at least 4 masses. %

In a private embodiment, this alloy allows castings to be obtained in which the following mechanical tensile properties are provided:

- at a ratio of 0.02≤Zr + Ti≤0.45: in the molded state, the temporary resistance is not less than 200 MPa and the elongation is not less than 15%;

The amount of eutectic should be calculated using the Thermo-Calc software (TTAL5 database).

Zirconium can be redistributed between the solid solution and secondary precipitates with a size of up to 20 nm and a lattice type L1 ₂ .

The alloy may contain aluminum obtained by an inert anode electrolysis technology.

The above particular embodiments of the invention are not the only ones possible. Various modifications and improvements are allowed without departing from the scope of the invention defined by the first claim.

SUMMARY OF THE INVENTION

The concentration of iron and nickel within the stated limits provides the necessary amount of aluminides of eutectic origin in an amount of at least 4 mass. %, which, in turn, provides the required combination of manufacturability during casting (primarily in terms of heat resistance). If the content of iron and nickel is less than the declared amount, the proportion of eutectic phases will be less than the required level, which will not provide the necessary level of casting properties, and if the content of the more claimed concentration range of iron and nickel is contained, and primary crystals of Fe, Ni-containing phases are formed in the crystallization structure, which will lead to a decrease in the overall level of mechanical properties.

Manganese within the stated limits is necessary to provide solid-solution hardening in the case of a cast state and for dispersion hardening for a heat-treated state. Lower concentrations of manganese will be insufficient to achieve the required level of strength properties, and with large quantities there will be a high probability of the formation of primary crystals of the Al ₆ (Fe, Mn) phase, which will lead to a decrease in the level of mechanical properties and a decrease in processability during casting.

Zirconium in the claimed amounts is necessary for solid solution hardening (when used in a molten state) or for the formation of secondary precipitates of the Al ₃ Zr phase with a L1 ₂ crystal lattice (in the case of using heat treatment). At lower concentrations, the number of the latter will be insufficient to achieve the specified strength characteristics, and at large quantities, it will be necessary to increase the casting temperature above a predetermined level.

Titanium in the claimed amount is necessary for the modification of aluminum solid solution, in addition, titanium is able to dissolve in the secondary phase Al ₃ Zr with a crystal lattice Ll ₂ , increasing the effect of dispersion hardening in the case of using heat treatment. With a higher titanium content in the structure, primary crystals may appear that will reduce the overall level of mechanical properties, and with a lower one, the positive effect of the influence of this element will not be realized.

Chrome within the stated limits is necessary to provide solid-solution hardening for the cast state and / or for dispersion hardening for the heat-treated state. A lower concentration of chromium will not provide the required level of strength properties, and at a higher concentration there will be a high probability of the formation of primary crystals of the Al7Cr phase, which will lead to a decrease in the level of mechanical properties.

The presence of silicon as an impurity up to 0.15 mass. % will provide an additional effect of solid solution hardening. With a higher silicon content, a significant increase in the crystallization interval occurs, which will lead to a decrease in casting characteristics.

Concrete example

EXAMPLE 1

The alloy compositions indicated in Table 1 were prepared in laboratory conditions. The alloys were prepared in an induction furnace in graphite crucibles using aluminum grade A85, nickel grade H0 and alloys Al-10Cr, Al-10Mn, and Al-5Ti. The casting temperature for alloys was 750 ° C. The resulting alloys were poured into a metal rod “rod” to assess the mechanical properties and analysis of the microstructure. The casting properties of the alloys were evaluated by the index of heat capacity (GH) using a "ring test", where the best indicator is a ring with a minimum cross-section of the wall that crystallized without cracking. Using the calculation method, the phase composition and amount of the eutectic phase of the considered alloys are analyzed. The results are presented in table 2. For alloy 5 of table 1, the calculation was not performed due to incorrect calculation of the eutectic phase due to the presence of primary crystals.

An analysis of the results of tables 1 and 2 shows that alloys 2-5 in the claimed concentration range provide a good level of casting characteristics. Alloy composition 1 is characterized by an unsatisfactory level of casting properties (in terms of heat resistance), primarily due to the low content of eutectic. In the structure of alloy 5, primary crystals of the glandular phase were revealed, which negatively affected the mechanical properties and, above all, the relative elongation (table 3). The mechanical properties were determined from castings obtained by gravity casting with an average cooling rate in the crystallization range of about 10 K / s. Tensile tests were carried out on separately cast samples with a diameter of 10 mm and a design length of 50 mm. The test speed was 10 mm / min.

The formation in the structure of aluminides of eutectic origin with favorable morphology is a prerequisite for achieving a high level of elongation. A typical structure providing a good level of elongation is shown in Figure 1.

For use in the cast state, the composition corresponding to alloys 2 and 3 is most preferable (Table 1).

EXAMPLE 2

To assess the effect of the amount of eutectic, alloys were prepared with its variable content at a fixed content of iron and nickel, respectively. The chemical composition is presented in table 4. For alloy 5 of table 1, the calculation was not performed due to incorrect calculation of the eutectic phase due to the presence of primary crystals.

From table 4 it is seen that only the claimed alloys, provided the number of eutectics above 4 provide the required values in terms of heat resistance.

EXAMPLE 3

From the alloy composition 2 and 3 of Table 1, injection molding (HPDC) castings were obtained. The results are shown in table 5.

Claims (8)

1. Cast aluminum alloy based on iron, nickel and manganese characterized in that it additionally contains chromium and at least one element from the group comprising titanium and zirconium, at the following concentrations of alloying elements, wt. % Iron 0.1-1.1 Manganese 0.5-2.5 Nickel 1.2-2.2 Chromium 0.02-0.20 Titanium 0.02-0.15 Zirconium 0.02-0.35 Aluminum rest while iron, nickel are presented mainly in the form of aluminides of eutectic origin in an amount of at least 4 wt. % 2. The alloy according to claim 1, characterized in that it contains aluminum obtained by electrolysis with an inert anode. 3. The alloy according to claim 1 or 2, characterized in that it is made in the form of castings at a ratio of 0.02 <Zr + Ti≤0.35, having the following tensile properties: temporary resistance of at least 160 MPa and elongation of at least fifteen%. 4. The alloy according to claim 1 or 2, characterized in that it is made in the form of castings at a ratio of Ni / Fe≥1.1, having the following tensile properties in a molten state: temporary resistance of at least 160 MPa and elongation of at least 15 %

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