Aluminum casting alloy

Abstract

The present invention relates to the field of metallurgy, particularly to aluminum-based alloys that can be used to produce thin-walled, complex castings by casting into metal molds, particularly for automotive components, electronic device parts, etc. The aluminum-based casting alloy of the present invention contains 1.5 to 5.1 wt.% calcium; up to 0.7 wt.% iron; up to 1.0 wt.% silicon; 0.1 to 1.8 wt.% zinc; and optionally, one or more of 0.2 to 2.5 wt.% manganese; 0.005 to 0.1 wt.% titanium; 0.05 to 0.14 wt.% zirconium; and 0.05 to 0.15 wt.% chromium, with the calcium and zinc present in the alloy structure primarily in the form of eutectic particles. The technical result is to provide a desired combination of technical properties during casting, as well as corrosion resistance.

Description

Technical Field

[0001] The present invention relates to the field of metallurgy, and in particular, to aluminum-based alloys characterized by high corrosion resistance. The alloys can be used for manufacturing thin-walled and complex-shaped castings by casting in a metal mold. Prior Art

[0002] A-Si series industrial non-heat-treatable alloys, such as A413.2 or AK12pch (GOST1583), are characterized by high workability and relatively low strength properties when cast; in particular, although depending on the thickness of the casting, the yield strength generally does not exceed 60-80 MPa. Higher levels of strength properties of the casting are already provided by the addition of copper in the as-cast state; in particular, alloys such as AA383.1 or AK12M2 are known. In this case, the increase in mechanical properties is accompanied by a significant reduction in elongation and deterioration of corrosion resistance.

[0003] Non-heat-treatable and corrosion-resistant alloys include solid-solution alloys based on the Al-Mg system, such as AMg6L, AMg5K, AMg5Mz (GOST1583), Magsimal® 59 (Rheinfelden Alloys), and other alloys characterized by satisfactory workability, good corrosion resistance, high levels of strength properties, and elongation when cast. Disadvantages of alloys in this system include high linear shrinkage of thin-walled castings and insufficient hardness.

[0004] A combination of high levels of strength properties, elongation, and corrosion resistance is achieved in Al-Si alloys having 0.2-0.5 wt% magnesium; in particular, AK9 (GOST1583), Silafont® 36 (Rheinfelden Alloys), trimal® 37 (Trimet), and other alloys are known. Quenching can significantly complicate the casting production cycle as it can cause warping (especially when using water quenching), dimensional changes, and cracking of the casting.

[0005] The invention of NITU MISIS disclosed in Patent RU2660492 is known. The material for use in the as-cast state contains the following (wt%): 5.4 - 6.4% calcium, 0.3 - 0.6% silicon, and 0.8 - 1.2% iron. As a drawback of the proposed invention, the low relative elongation rate was cited, which did not exceed 2.6%, thus limiting the use of this material in important casting parts.

[0006] Al-Ni-Mn casting alloys for structural parts in automotive and aerospace applications are known as alternatives to branded silmin, developed by Alcoa and disclosed in Patent US6783730B2 (published on August 31, 2004). This alloy can be used to produce castings using a good combination of casting and mechanical properties when it contains (wt%) 2 - 6% Ni, 1 - 3% Mn, 1% Fe, less than 1% silicon, and other inevitable impurities. As a drawback of the proposed invention, the fact that high levels of casting and mechanical properties are ensured by using high-purity aluminum grades and a high nickel content significantly increases the cost of the castings produced. In addition, the proposed material is non-heat-treatable over the entire concentration range, which limits its use. At the same time, the corrosion resistance of the castings is significantly reduced in the high nickel concentration region.

[0007] Casting aluminum alloys based on Al-Ni and Al-Ni-Mn systems and methods for producing casting parts from them are known, which are described in Alcoa's invention US8349462B2 (published on January 8, 2013) and the application EP2011055318 of Rheinfelden Alloys GmbH & Co.KG. This invention proposes alloy compositions for casting applications. What is common to the proposed inventions is a high nickel content of 1 - 6%, which determines a major drawback, namely a significant reduction in corrosion resistance. At relatively low nickel and manganese contents, the casting alloys have low strength characteristics.

[0008] The material based on the Al-Ni-Mn system proposed by NITU MISIS and disclosed in the Russian patent 2478131C2 published on March 27, 2013 is known. The material contains the following (in wt%): 1.5 - 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. After annealing (without using a quenching operation), the castings made of the alloy are characterized by a final strength of at least 250 MPa with an elongation rate of at least 4%. The first drawback of this alloy is a higher tendency to form concentrated small pores, which makes it difficult to achieve high-quality, relatively large castings. The second drawback is the need to use a higher casting temperature, which is not always achievable under the conditions of a foundry.

[0009] The material closest to the proposed material is the material containing (in wt%) Al - 3.5% Ca - 0.9% Mn - 0.5% Fe - 0.1% Zr - 0.1% Sc disclosed in the publication available at https: / / doi.org / 10.1016 / j.msea.2019.138410. The authors of the publication considered the material as a wrought alloy, and this processing chain excludes water quenching. The publication shows the non-obviousness of using the alloy described in the publication for castings and its use in the as-cast state. The drawbacks of the proposed invention include the presence of expensive scandium and the need to use heat treatment to achieve the hardening effect of the co-addition of zirconium and scandium. Disclosure of the Invention The objective of the present invention is to create a new cast aluminum alloy designed to produce thin-walled castings by various methods of casting into a metal mold, in particular, but not limited to, gravity casting, high-pressure casting, low-pressure casting, and melt forging, which meet the specified requirements for a series of processes and corrosion characteristics.

[0010] The technical result of the present invention is to provide a given combination of method characteristics in casting and corrosion resistance.

[0011] The technical result is achieved by proposing an aluminum-based cast alloy having the following concentrations of alloying elements, in weight%: Calcium 1.5 - 5.1 Zinc 0.1 - 1.8 Iron up to 0.7 Silicon up to 1.0 Optionally, at least one element selected from the following group Manganese 0.2 - 2.5 Titanium 0.005 - 0.1 Zirconium 0.05 - 0.14 Chromium 0.05 - 0.15 Aluminum and unavoidable impurities, the balance.

[0012] In a particular version, calcium and zinc are mainly represented in the form of eutectic particles in the structure. The alloy is made in the form of castings.

[0013] Various variations and improvements within the scope not exceeding the scope of the invention as defined by the first claim are acceptable.

Summary of the Invention

[0014] Thanks to the selected combination of alloying elements, the proposed alloy is characterized by a narrow crystallization interval, which, combined with a large amount of eutectic phase, provides a good level of casting characteristics. Furthermore, thanks to the elements dissolved in the aluminum solid solution, it provides a satisfactory level of strength characteristics in the as-cast state. At the same time, using various combinations of the selected alloying elements, the corrosion resistance within the claimed area is maintained at a good level.

[0015] The basic criterion for the acceptable selection of alloying elements was the formation of the desired structure excluding the presence of coarse primary crystals and / or coarsening of the eutectic phase; the justification of the concentration ranges is given below.

[0016] The concentrations (by weight %) of calcium in the range of 1.5 to 5.1% and zinc in the range of 0.1 to 1.8% provide good casting properties because calcium and zinc mainly form a sufficient amount of eutectic phase. The main effect of the co-introduction of calcium and zinc is the formation of the common eutectic phase Al4(Ca,Zn), in which zinc atoms are replaced by calcium atoms in the eutectic phase. As a result, the level of strength properties is further increased. If the calcium content is below the stated level, it will lead to a reduction in casting characteristics. When zinc decreases below the stated level, no significant increase in strength properties is observed. Calcium and zinc contents above the stated levels will result in the formation of a coarse structure and a significant reduction in mechanical properties.

[0017] The iron and silicon contents are mainly determined by the purity of the aluminum used to make the alloy. However, iron and silicon can also be used as alloying elements. This is because an amount of silicon up to 1.0% redistributes between the solid solution and the eutectic. On the one hand, this brings about an increase in strength properties by additional solution quenching in the as-cast state, and on the other hand, it has a positive effect on the alloy casting characteristics by increasing the eutectic. A higher silicon content deteriorates the morphology of the eutectic phase and generally reduces the strength characteristics. An amount of iron up to 0.5% mainly forms phases of eutectic origin, which has a positive effect on the casting characteristics of the alloy by increasing the amount of eutectic. When the iron concentration increases above 0.5%, it leads to coarsening of the eutectic phase and, as a result, may lead to a reduction in mechanical properties.

[0018] An amount of manganese up to 2.5% is necessary to mainly increase the strength properties in the as-cast state by providing solution quenching. At a manganese content above 2.5%, primary crystals of the Al6(Fe,Mn) phase can be formed in the structure, which may lead to a reduction in mechanical characteristics. At a manganese content below 0.2%, it does not bring about significant solution quenching, and as a result, the increase in strength characteristics is weak.

[0019] The stated limits (weight %), 0.05 - 0.14% and 0.05 - 0.15% of zirconium and chromium respectively, are necessary to provide solid - solution hardening. These elements at lower concentrations do not result in a significant increase in strength characteristics in the as - cast state. The higher the amount, the higher the casting temperature required compared to typical temperatures, which reduces the stability of the mold; otherwise, the probability of forming primary crystals of the Al7Cr and Al3Zr phases is high, and thus the introduction of these elements does not increase the level of mechanical properties.

[0020] An amount of titanium in the range of 0.005 - 0.1 wt% is necessary to modify the aluminum solid solution. A higher titanium content in the structure may result in the appearance of primary crystals, which reduces the overall level of mechanical properties. On the other hand, at lower titanium contents, the positive effect of this element is not exerted. Titanium can be introduced as a multicomponent ligature, e.g., Al - Ti - B and / or Al - Ti - C, and thus the alloy may contain boron and carbon in the compound along with an amount of titanium proportional to the content of the corresponding ligature. Boron and carbon, as independent elements, did not have a significant effect on the mechanical and casting properties for the target range. Also, in some cases, it was observed that the tendency to form hot cracks during casting was reduced in the presence of titanium. Aspects

[0021] The following input materials were used to prepare the alloy (weight %): aluminum grades A99 and A8, zinc grade C0, metallic calcium and calcium as ligature Al - 6Ca, manganese as ligature Al - 10%Mn, ligatures Al - 10%Zr, Al - 10%Cr, Al - 5%Ti.

[0022] Example 1 To evaluate the effect of alloying elements on the structure and properties, 13 alloy compositions were prepared under laboratory conditions (Table 1).

[0023]

Table 1

[0024] The content of other elements typically did not exceed 0.05% by weight. The chemical composition of the alloy was selected from the conditions for obtaining a structure consisting of an aluminum solid solution and eutectic components. The samples were cast by gravity using a metal mold "samples cast separately". The mold temperature could be varied in the range of 20 - 60°C. The casting was a tensile sample with a predicted length of 50 mm and a diameter of 10 mm. Immediately after casting without machining, a tensile test was performed on this sample (along with the determination of yield strength, tensile strength, and elongation). The structure of the sample was evaluated from the sample tip.

[0025]

Table 2

[0026] Analysis of the structure of the alloys tested showed that the structure of the considered compositions in Table 1 mainly consisted of an aluminum solid solution and eutectic phases formed by the corresponding elements. At the same time, calcium and zinc in all experimental alloys were mainly represented in the form of eutectic particles.

[0027] Compositions 2, 5, and 12 are preferred because of the good ratio of their yield strength to elongation for use in the as-cast state. The most desirable alloy structure using the example of Composition 5 (Table 1) is shown in Figure 1.

[0028] Example 2: The corrosion resistance of the examples of Compositions 2, 5, 8, and 11 of the claimed alloy (Table 1) was evaluated by an accelerated corrosion test method performed by exposure to neutral salt spray according to the following program: 1 cycle - Immerse in a salt spray chamber that sprays a 5% NaCl solution at a temperature of 25 ± 1°C for 8 hours, and then immerse at 35 ± 3°C for 16 hours without spraying the solution, for a total of 7 cycles. The results were evaluated by changing the surface appearance of the sample and the depth of corrosion damage (metallographic method). The ADC6 type alloy was used as a reference. This alloy is characterized by the highest corrosion resistance among cast aluminum alloys.

[0029] From the comparative analysis of the results, it can be seen that during the test, the surface color of the tested compositions and the reference substance changed from silver to silver-yellow, and a single surface damage up to 10 microns occurred without significant corrosion damage.

[0030] Example 3 The casting characteristics were evaluated using the hot brittleness (HB) parameter using "harp casting". Here, the best indicator is to obtain a casting with the maximum "rod" length (Figure 2). As examples, alloys 2, 4, and 12 (Table 1) were used to evaluate the tendency to hot cracking. The ADC6 type alloy was used as a comparison. It was shown that alloys 2, 4, and 12 had no cracks (Table 1). This is a good indicator at the level of most Al-Si alloys and is in contrast to the ADC6 alloy. The castings obtained from the ADC6 alloy started from the maximum length and about 40% of the rods had defects.

[0031] Example 4 To evaluate the mechanical properties of alloy 12 (Table 1), plates with a thickness of 2 mm were cast by injection molding (HPDC). The casting was carried out by evacuating the mold. The mold temperature was about 150 °C. The melting temperature was 710 °C. The results of the tensile tests of samples cut from the cast plates are shown in Table 3.

[0032]

Table 3

Claims

1. An aluminum-based cast alloy having the following alloying elements in weight %: Calcium 1.5 to 5.1 Zinc 0.1 to 1.8 Iron 0.08 to 0.5 Silicon 0.5 to 1.0 Manganese up to 0.9 Optionally, at least one element selected from the following group Titanium up to 0.05 Zirconium up to 0.14 Chromium up to 0.15 The balance being aluminum and unavoidable impurities.

2. The alloy according to claim 1, characterized in that it is produced in the form of a casting.

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