Aluminum Casting Alloy

Abstract

The present invention relates to the field of metallurgy, in particular to aluminum-based alloys, and can be used to manufacture thin-walled complex-shaped castings by casting in metal molds, in particular for automotive components, parts of electronic devices, etc. The aluminum-based casting alloy contains: 1.5-5.1% by weight of calcium; up to 0.7% by weight of iron; up to 1.0% by weight of silicon; 0.1-1.8% by weight of zinc; optionally, one or more of the following: 0.2-2.5% by weight of manganese; 0.005-0.1% by weight of titanium; 0.05-0.14% by weight of zirconium; 0.05-0.15% by weight of chromium, wherein calcium and zinc are mainly present in the structure of the alloy in the form of eutectic particles. The technical result is to provide the desired combination of process properties and corrosion resistance in casting.

Description

Technical Field

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

[0002] For industrial non-heat-treatable alloys of the A-Si system, such as A413.2 or AK12pch (GOST1583), they are characterized by high workability during casting and a relatively low level of strength properties; in particular, the yield strength does not usually exceed 60-80 MPa, depending on the thickness of the casting. A higher level of strength properties of the casting already in the cast state is provided by the addition of copper; in particular, alloys such as AA383.1 or AK12M2 are known. The improvement of the mechanical properties in this case is accompanied by a significant reduction in elongation and a deterioration in 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) and 59 (Rheinfelden Alloys), etc., are characterized by satisfactory workability during casting, good corrosion resistance, high levels of strength properties and elongation. The disadvantages of alloys of this system include high linear shrinkage and insufficient compactness of thin-walled castings.

[0004] A combination of high levels of strength properties, elongation and corrosion resistance is achieved in aluminum silicon alloys with 0.2-0.5 wt. % magnesium; in particular, AK9 (GOST 1583), 36 (Rheinfelden Alloys), 37 (Trimet) and other alloys are known. Hardening significantly complicates the casting production cycle as it can cause warping (especially when water quenching is used), dimensional changes and cracking of the casting.

[0005] The NITU MISIS invention disclosed in patent RU2660492 is known. The material used in the cast state contains 5.4-6.4% by weight of calcium, 0.3-0.6% by weight of silicon and 0.8-1.2% by weight of iron. The disadvantages of the proposed invention include a low relative elongation of no more than 2.6%, which limits the use of the material in core castings.

[0006] Al-Ni-Mn casting alloys known for structural components of automotive and aerospace applications are alternatives to the brand silicon aluminum alloys developed by Alcoa and disclosed in patent US6783730B2 (published on August 31, 2004). In the case of 2-6 wt. % Ni, 1-3 wt. % Mn, 1 wt. % Fe, less than 1 wt. % silicon, and in the case of other unavoidable impurities, the alloy can be used to produce castings with a good combination of casting and mechanical properties. The disadvantages of the proposed invention include the fact that a high level of casting and mechanical properties is ensured by using high purity aluminum grades and high nickel content, which significantly increases the cost of the produced castings. In addition, the proposed material is not heat treatable in 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 area.

[0007] Casting aluminum alloys based on the Al-Ni and Al-Ni-Mn systems and methods for producing cast parts therefrom are known and described in Alcoa invention US8349462B2 (published on January 8, 2013) and in the application EP2011055318 of Rheinfelden Alloys GmbH & Co. KG. The invention proposes alloy compositions for casting applications. High nickel contents of 1-6% are common in the proposed inventions, which determine the main disadvantage that the corrosion resistance is significantly reduced. Due to the relatively low nickel and manganese contents, the casting alloys have low levels of strength properties.

[0008] Known is a material based on the Al-Ni-Mn system disclosed in Russian patent 2478131C2 proposed by NITU MISIS and published on March 27, 2013. This material contains 1.5-2.5% by weight of Ni, 0.3-0.7% by weight of Fe, 1-2% by weight of Mn, 0.02-0.2% by weight of Zr, 0.02-0.12% by weight of Sc and 0.002-0.1% by weight of Ce. Castings made from the alloy after annealing (without quenching operation) are characterized by a limiting resistance of at least 250 MPa and an elongation of at least 4%. A first disadvantage of this alloy is its increased tendency to form concentrated pores, which makes it difficult to obtain relatively large castings of high quality. A second disadvantage is the need to use higher casting temperatures, which cannot always be achieved under the conditions of the foundry.

[0009] The closest material to the proposed material is the material disclosed in the publication available at https: / / doi.org / 10.1016 / j.msea.2019.138410, which contains (wt%): Al-3.5% Ca-0.9% Mn-0.5% Fe-0.1% Zr-0.1% Sc. The authors of the publication consider this material to be a wrought alloy, the process chain of which does not include water quenching. The publication shows the non-obviousness of using the alloy mentioned in the publication for castings and in the cast state. Disadvantages of the proposed invention include the presence of expensive scandium and the need to use heat treatment to achieve the hardening effect of the combined addition of zirconium and scandium. Summary of the invention

[0010] The aim of the present invention is to create a new cast aluminium alloy designed to produce thin-walled castings by various methods of casting into metal moulds, in particular gravity casting, high pressure casting, low pressure casting, liquid forging, but not limited to meeting a set of specified requirements for process and corrosion properties.

[0011] The technical result of the invention is to provide a given combination of process characteristics in casting and corrosion resistance.

[0012] This technical result is achieved by proposing an aluminum-based casting alloy having the following alloying element concentrations:

[0013] 1.5-5.1% by weight calcium

[0014] 0.1-1.8 wt% zinc

[0015] Up to 0.7 wt.% iron

[0016] Up to 1.0 wt% silicon

[0017] Optionally, at least one element selected from the group consisting of:

[0018] 0.2-2.5 wt% manganese

[0019] 0.005-0.1 wt% titanium

[0020] 0.05-0.14 wt% zirconium

[0021] 0.05-0.15 wt% chromium

[0022] The balance is aluminum and unavoidable impurities.

[0023] In specific form, calcium and zinc are present in the structure primarily as eutectic particles. The alloy is produced in the form of castings.

[0024] Various modifications and improvements are possible without departing from the scope of the invention as defined by the first claim. DETAILED DESCRIPTION

[0025] Due to the combination of selected alloying elements, the proposed alloy is characterized by narrow crystal spacing, which, in combination with a large amount of eutectic phase, provides a good level of casting properties and, due to the elements dissolved in the aluminum solid solution, a satisfactory level of strength properties in the cast state. At the same time, for various combinations of selected alloying elements, the corrosion resistance within the claimed range is maintained at a good level.

[0026] The basic criterion for acceptable selection of alloying elements is the formation of the desired structure, excluding the presence of coarse primary crystals and / or coarsening of the eutectic phase; the justification for the concentration range is explained below.

[0027] Concentrations of 1.5-5.1 wt. % calcium and 0.1-1.8 wt. % zinc provide good casting properties, since calcium and zinc primarily form a sufficient amount of eutectic phases. The main effect of the joint introduction of calcium and zinc is the formation of a joint eutectic phase Al4(Ca,Zn), in which zinc atoms replace calcium. As a result, the level of strength properties is further increased. If the calcium content is below the stated level, a reduction in casting properties will result. If zinc is reduced below the stated level, no significant increase in strength properties will be observed. Calcium and zinc contents exceeding the stated levels will result in the formation of a coarse structure and a significant reduction in mechanical properties.

[0028] The iron and silicon contents are primarily determined by the purity of the aluminum used to prepare the alloy. However, iron and silicon can also be used as alloying elements, since silicon in amounts of up to 1.0 wt.-% redistributes between the solid solution and the eutectic, which on the one hand provides an increase in strength properties due to additional solid solution hardening in the cast state and on the other hand positively influences the alloy casting properties by increasing the eutectic. Due to the higher silicon content, the morphology of the eutectic phase deteriorates, which generally reduces the strength properties. Iron in amounts of up to 0.5 wt.-% primarily forms phases of eutectic origin, which positively influence the casting properties of the alloy by increasing the amount of eutectic. An increase in the iron concentration above 0.5 wt.-% can lead to a coarsening of the eutectic phase, with the result that the mechanical properties are reduced.

[0029] In order to improve the strength properties by providing solid solution hardening, mainly in the cast state, manganese in an amount of up to 2.5% by weight is necessary. When the manganese content is above 2.5% by weight, primary crystals of the Al6(Fe,Mn) phase can form in the structure, which can lead to a reduction in mechanical properties. Manganese contents below 0.2% by weight do not lead to significant solid solution hardening, so the increase in strength properties is small.

[0030] Zirconium and chromium within the specified limits of 0.05-0.14 wt. % and 0.05-0.15 wt. %, respectively, are necessary to provide solid solution hardening. Lower concentrations of these elements do not lead to a significant increase in strength properties in the cast state. Larger amounts would require higher than usual casting temperatures, which would reduce the stability of the casting mold; otherwise, the probability of forming primary crystals of Al7Cr and Al3Zr phases is high, which would not increase the level of mechanical properties due to the introduction of these elements.

[0031] 0.005-0.1 wt. % titanium is required to modify the aluminum solid solution. Higher titanium contents in the structure may lead to the appearance of primary crystals, which will reduce the overall level of mechanical properties, while lower titanium contents will not achieve the positive effect of this element. Titanium can be introduced as a multi-component linker, such as Al-Ti-b and / or Al-Ti-c, so that the alloy can contain boron and carbon in compounds with titanium, in amounts proportional to the content of the corresponding linker. For the range in question, boron and carbon as independent elements have no significant effect on the mechanical and casting properties. In addition, in the presence of titanium, a reduced tendency to form hot cracks during casting was noted in some cases.

[0032] Example

[0033] The alloys were prepared using the following charging materials (weight %): aluminum grades A99 and A8, zinc grade C0, calcium as metallic calcium and linker Al-6Ca, manganese as linker Al-10%Mn, linker Al-10%Zr, Al-10%Cr, Al-5%Ti.

[0034] Example 1

[0035] In order to evaluate the effects of alloying elements on structure and properties, 13 alloy compositions were prepared under laboratory conditions (Table 1).

[0036] Table 1 - Chemical composition of experimental alloys (wt%)

[0037]

[0038] The content of other elements generally does not exceed 0.05% by weight. The chemical composition of the alloy is selected from the conditions for obtaining a structure consisting of an aluminum solid solution and a eutectic component. The test specimens are gravity cast in a metal mold, "single cast samples". The mold temperature can vary in the range of 20-60°C. The castings are tensile specimens with a diameter of 10 mm and an estimated length of 50 mm, which are subjected to tensile testing (determination of yield strength, tensile strength and elongation) immediately after casting without mechanical processing. The structure of the specimen is evaluated from the specimen head.

[0039] Table 2 – Mechanical properties in the cast condition (gravity cast into metal moulds)

[0040]

[0041] *- Composition of Table 1

[0042] The structural analysis of the studied alloys shows that the structures of the compositions considered in Table 1 are mainly composed of aluminum solid solution and eutectic phases formed by the corresponding elements. At the same time, calcium and zinc in all experimental alloys are mainly present in the form of eutectic particles.

[0043] Compositions 2, 5 and 12 are preferred because they have a good yield strength to elongation ratio when used in the cast state. The most desirable alloy structure for the example using composition 5 (Table 1) is shown in Figure 1 middle.

[0044] Example 2

[0045] The corrosion resistance of the examples of compositions 2, 5, 8 and 11 of the claimed alloy (Table 1) was evaluated by the method of accelerated corrosion test by exposure to neutral salt spray under the following procedure: 1 cycle: immersion in a salt spray chamber at a temperature of 25±1°C with a 5% NaCl solution spray for 8 hours, then immersion at 35±3°C for 16 hours without spraying the solution, for a total of 7 cycles. The results were evaluated by the change in the surface appearance of the specimens and the depth of the corrosion damage (metallographic method). The ADC6 type alloy was used as a reference, which is characterized by having the highest corrosion resistance among cast aluminum alloys.

[0046] From the comparative analysis of the results, it can be seen that during the test, the surface color of the examined compositions and standards changed from silver to silver-yellow, and the individual surface damage was at most 10 microns, and there was no obvious corrosion damage.

[0047] Example 3

[0048] The casting characteristics were evaluated using the hot shortness (HB) parameter using "harp casting", where the best criterion is to obtain castings with the maximum "bar" length ( Figure 2 ). The tendency to hot cracking was evaluated using alloys 2, 4 and 12 as examples (Table 1). An ADC6 type alloy was used as a comparison. The absence of cracks in alloys 2, 4 and 12 was shown (Table 1), which is a good indicator at the level of most Al-Si alloys, in contrast to the failure of about 40% of the bars cast from the maximum length for the ADC6 alloy.

[0049] Example 4

[0050] To evaluate the mechanical properties of alloy 12 (Table 1), 2 mm thick plates were cast by injection molding (HPDC). Casting was performed by vacuuming the mold. The mold temperature was about 150° C. The temperature of the melt was 710° C. The tensile test results of the samples cut from the cast plates are shown in Table 3.

[0051] Table 3 - Tensile test results of 2 mm HPDC cast plates (as cast)

[0052] <![CDATA[σ t ,MPa]]> <![CDATA[σ 0.2 (MPa)]]> δ,% 212 112 9.5

Claims

1. Aluminum-based casting alloys having the following alloying element distribution: 2.8-5.1% by weight calcium 0.1-1.3 wt% zinc 0.08-0.5 wt% iron 0.08-1.0 wt% silicon 0.2-0.9 wt% manganese Optionally, at least one element selected from the group consisting of: 0.005-0.05 wt% titanium 0.05-0.14 wt% zirconium 0.05-0.15 wt% chromium The balance is aluminum and unavoidable impurities.

2. The alloy according to claim 1, characterized in that The calcium and zinc are mainly in the form of eutectic particles.

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

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