Cast Aluminum Alloy

Abstract

Develop a new aluminum alloy for casting. [Solution] The alloy contains 2.0 to 5.2 mass% calcium, 0.05 to 0.8 mass% silicon, 0.05 to 1.0 mass% iron, 0.01 to 5.0 mass% zinc, 0.01 to 2.0 mass% magnesium, and at least one of 0.01 to 1.4 mass% copper, 0.01 to 1.5 mass% manganese, 0.01 to 0.2 mass% chromium, 0.01 to 0.2 mass% titanium, and 0.01 to 0.2 mass% zirconium, with the remainder being aluminum and unavoidable impurities.

Description

[Technical Field]

[0001] The present invention is in the field of metallurgy, particularly aluminium-based alloys, and can be used for the production of complex shaped castings by permanent mold casting, particularly pressure casting. [Background technology]

[0002] Complex shaped castings are typically made from alloys that can be hardened by heat treatment and those that cannot. In particular, Al-Si and Al-Mg alloy structures are commonly used. Castings made from Al-Si alloys with added magnesium or copper are often used for critical parts that require high strength, and their strength properties are usually improved by applying T7, T6, or T5 heat treatments.

[0003] Al-Si alloys that cannot be hardened by heat treatment (e.g., A413.2 and AlSi11 alloys) have excellent workability and corrosion resistance when cast. However, a drawback of this alloy group is their low strength properties, especially the yield strength in the as-cast state, which does not exceed 80 MPa. Strength can be improved by adding copper, for example, A383.1 and AlSi12Cu2 alloys. However, these alloys have drawbacks such as a significant decrease in corrosion resistance and low elongation (usually less than 1-2% by mass).

[0004] Furthermore, Al-Mg cast alloys that cannot be heat-treated hardened (e.g., AMg6L, AMg5K, AMg5Mc (GOST1583), Magsimal® 59 (Rheinfelden Alloys)) have good workability, corrosion resistance, strength, and elongation during casting. However, drawbacks of this alloy group include high linear shrinkage and poor airtightness of thin-walled castings.

[0005] To achieve a balance of high strength, elongation, and corrosion resistance, heat-hardenable alloys based on the Al-Si system with 0.2-0.5% magnesium (e.g., AK9 (GOST 1583), Silafont® 36 (Rheinfelden Alloys), Trimal® 37 (Trimet), etc.) are used. However, quenching significantly complicates the manufacturing process, as it can cause distortion (especially with water cooling), dimensional changes, and cracking of the casting.

[0006] Alcoa developed an Al-Ni-Mn casting alloy, disclosed in US Patent No. 6,783,730 (issued August 31, 2004), which is used in automotive and aerospace structural components and is known as a replacement for Bland silumin alloys. This alloy contains 2-6% nickel, 1-3% manganese, 1% iron, and less than 1% silicon by weight, and exhibits an excellent balance of castability and mechanical properties. However, a drawback of this alloy is that high-purity aluminum and a high nickel content are required to achieve good castability and mechanical properties, which significantly increases the cost of the casting. Furthermore, this material cannot be heat-treated hardened over the entire concentration range, limiting its range of use. Furthermore, the corrosion resistance of the casting is significantly reduced at high nickel concentrations.

[0007] Additionally, Al-Ni and Al-Ni-Mn casting alloys and methods for producing castings using them are described in Alcoa's US Patent 8,349,462 (published January 8, 2013) and Rheinfelden Alloys GmbH & Co. KG's patent application EP 2011055318. These inventions propose alloys intended for use in the cast state. A common feature of the proposed inventions is the high nickel content (1-6% by mass), which significantly reduces corrosion resistance, a major drawback. Cast alloys with relatively low nickel and manganese contents have poor strength properties.

[0008] The Al-Ni-Mn alloy developed by MISIS (Moscow Institute of Steel and Alloys), a national scientific and technical university, is described in patent RU 2478131 (published March 27, 2013). The composition of this material is 1.5-2.5% by mass of nickel, 0.3-0.7% by mass of iron, 1-2% by mass of manganese, 0.02-0.2% by mass of zirconium, 0.02-0.12% by mass of scandium, and 0.002-0.1% by mass of cerium. Castings obtained from alloys that have only been annealed (without quenching) have tensile strengths of 250 MPa or more and elongations of 4% or more by mass. The first drawback of this alloy is its high tendency to form concentrated porosity, making it difficult to produce high-quality castings of relatively large sizes. The second drawback is the high temperature required during casting, which can be difficult to achieve depending on the equipment conditions of foundries.

[0009] Disclosure of the Invention The object of the present invention is to develop a new aluminum alloy for casting, which is suitable primarily for, but not limited to, high-pressure casting, can be used without heat treatment, and has excellent castability, good mechanical properties including a yield strength of 100 MPa or more, and high corrosion resistance.

[0010] Its main application is in the casting of automotive parts, electronic equipment housings, etc. The material is also suitable for the manufacture of critical structural parts.

[0011] The technical result of the present invention is to solve the problem by improving strength properties while maintaining plasticity, castability, and high corrosion resistance.

[0012] This technical result is achieved by applying an aluminum-based casting alloy containing calcium, silicon, iron, zinc, and magnesium, and optionally containing at least one of the following elements: copper, manganese, chromium, titanium, and zirconium, with concentrations of the alloying elements in the following ranges: Calcium 2.0 to 5.2 mass% Silicon 0.05 to 0.8 mass% (preferably 0.3 to 0.8 mass%) Iron 0.05 to 1.0 mass% (preferably 0.1 to 0.5 mass%) Zinc 0.01 to 5.0 mass% (preferably 1.0 to 2.0 mass%) Magnesium 0.01 to 2.0 mass% (preferably 0.05 to 0.5 mass%) Optionally, the alloy contains at least one alloying element from the following group of elements: Copper 0.01 to 1.4 mass% (preferably 0.02 to 0.5 mass%) Manganese 0.01 to 1.5 mass% (preferably 0.5 to 1.0 mass%) Chromium 0.01 to 0.2 mass% (preferably 0.05 to 0.1 mass%) Titanium 0.01 to 0.2 mass% (preferably 0.05 to 0.1 mass%) Zirconium 0.01 to 0.2 mass% (preferably 0.05 to 0.1 mass%) The balance is aluminum and unavoidable impurities.

[0013] In some embodiments of the invention, magnesium is distributed within the aluminum matrix and copper combines with calcium to form a eutectic phase, which improves strength properties without sacrificing plasticity.

[0014] This alloy is suitable for producing castings having a tensile strength of at least 100 MPa in the as-cast state.

[0015] Various improvements and modifications are possible within the scope of the present disclosure (description and claims). DETAILED DESCRIPTION OF THE INVENTION

[0016] Summary of the Invention The contents of calcium (2.0-5.2 wt%), silicon (0.05-0.8 wt%), iron (0.05-1.0 wt%), zinc (0.01-5.0 wt%), and copper (optional) (0.01-1.4 wt%) are limited to ranges that allow the formation of a structure consisting of an aluminum solid solution and its corresponding eutectic phase (containing calcium, silicon, iron, zinc, and copper (optional)). Calcium, silicon, iron, zinc, and copper (optional) affect the total amount of eutectic phase in the alloy. When the calcium, silicon, iron, zinc, and copper (optional) contents are within the minimum ranges (claimed ranges), the volume fraction of the eutectic phase is approximately 2.5 wt%.

[0017] Additionally, magnesium (0.01-2.0% by mass) and at least one optional element selected from manganese (0.01-1.5), chromium (0.01-0.2), titanium (0.01-0.2), and zirconium (0.01-0.2) interact with calcium, silicon, iron, zinc, and copper (if present) to form a structure consisting of a primary aluminum solid solution and a eutectic phase containing at least one of manganese, chromium, titanium, and zirconium.

[0018] Magnesium and at least one of manganese, chromium, titanium, and zirconium (optional) dissolve in aluminum solid solution within the claimed ranges, thereby providing solid solution strengthening. However, magnesium and at least one of manganese, chromium, titanium, and zirconium (optional) may widen the crystallization temperature range within the claimed ranges, which may adversely affect castability.

[0019] The results of the research unexpectedly showed that within the range of alloying element concentrations considered, the amount of eutectic phase was appropriately combined so that all eutectic phases were combined with calcium and the aluminum solid solution was alloyed, and the crystallization temperature range was kept to a maximum of 50°C, ensuring acceptable levels of both casting properties and strengthening.

[0020] In addition, the presence of magnesium and silicon promotes the refinement of the calcium-containing eutectic phase. Figure 1 shows a typical cast structure in the as-cast state (high pressure casting (HPDC)).

[0021] Figure 1 shows a typical structure of the as-cast alloy, which shows the presence of a primary aluminum solid solution and a eutectic phase. The structure of the as-cast material is an aluminum solid solution with zinc and magnesium and eutectic phase particles. Depending on the elements present in the alloy, the eutectic phase particles contain aluminum-calcium-zinc compounds, aluminum-calcium-iron compounds, or aluminum-calcium-silicon compounds.

[0022] Furthermore, when alloyed with copper, manganese, chromium, titanium, and zirconium, the as-cast structure is similar in character and consists of zinc, magnesium, manganese, chromium, titanium, zirconium, and aluminum solid solution with eutectic phase particles including aluminum-calcium-zinc compounds, aluminum-calcium-iron compounds, aluminum-calcium-silicon compounds, and aluminum-calcium-copper compounds.

[0023] The detailed effects of the alloying elements are explained below.

[0024] If the calcium content is less than 2.0% by mass, the casting properties are reduced and calcium bonding with elements such as silicon, iron, zinc and (optionally) copper is not ensured. If the calcium content is more than 5.2% by mass, coarse inclusions of the primary phase Al4Ca are formed, which leads to a reduction in mechanical properties.

[0025] When silicon is combined with calcium in the range of 0.05-0.8% by weight, a good level of elongation is achieved in the as-cast state, since silicon promotes the dispersion of the eutectic structure. If the silicon concentration exceeds 0.8% by weight, coarse intermetallic compounds containing silicon are formed in the structure, resulting in a decrease in mechanical properties. If the silicon content is less than 0.05% by weight, the formation of a good morphology of the eutectic structure is insufficient, resulting in a lack of elongation in the as-cast state.

[0026] When iron is combined with calcium in the range of 0.05-1.0 wt.%, the casting properties are improved and acceptable elongation levels are achieved. If the iron content is less than 0.05 wt.%, the alloy's castability deteriorates, resulting in excessive adhesion of the casting to the casting or pouring mold. If the iron content exceeds 1.0 wt.%, coarse intermetallic compounds containing iron and calcium are formed in the structure, which causes a decrease in mechanical properties.

[0027] When the zinc content is within the range of 0.01 to 5.0 mass%, improvement in corrosion resistance and casting properties is promoted. When the zinc content is less than 0.01 mass%, no positive effect of zinc on strength properties has been confirmed. From 0.01 mass%, a transformation effect is observed, manifested as a morphological change of the calcium-containing eutectic. When the zinc content exceeds 5.0 mass%, a coarse phase of crystalline origin containing zinc and calcium is formed, which has a negative effect on the mechanical properties of the alloy.

[0028] When the copper content is within the range of 0.01-1.4% by weight, it improves strength properties without compromising casting properties and maintains acceptable corrosion resistance. The copper content maintains satisfactory corrosion resistance by combining with calcium to form a phase. At copper contents below 0.01% by weight, no positive effect of copper on mechanical or other properties has been observed. At low copper concentrations (from 0.01% by weight), a transformation effect is observed as a morphological change of the calcium-containing eutectic phase due to the formation of a copper-calcium-containing phase.

[0029] When the magnesium content is within the range of 0.01-2.0% by mass, it promotes the improvement of strength properties in the as-cast state. When the magnesium content exceeds 2.0% by mass, the crystallization range significantly expands, and the as-cast properties, especially the hot cracking susceptibility, become unacceptably deteriorated. When the magnesium content is less than 0.01% by mass, the positive effect of magnesium on strength properties has not been confirmed in combination with other elements in the described chemical composition.

[0030] When the manganese content is within the range of 0.01-1.5% by mass, its positive effect on strength properties has been confirmed by solid solution strengthening in combination with other elements in the described chemical composition. When the manganese content exceeds 1.5% by mass, coarse phases of crystalline origin are formed, which reduce the mechanical properties.

[0031] A chromium content in the range of 0.01-0.2% by mass promotes solid solution strengthening in the as-cast state. At higher concentrations, the probability of the formation of primary crystals of the Al7Cr phase increases significantly, resulting in a decrease in the level of mechanical properties.

[0032] Titanium contents in the range of 0.01-0.2% by weight promote the alteration of the primary precipitation of aluminum solid solution during crystallization. At higher titanium contents, primary crystals may appear in the structure, potentially reducing the overall level of mechanical properties. At lower titanium contents, the beneficial effects of this element are not realized. When titanium is introduced as a multicomponent composition, such as Al-Ti-B or Al-Ti-C, boron or carbon may be present in the alloy in amounts proportional to their content in the master alloy. Boron and carbon, as independent elements, do not significantly affect the mechanical and casting properties within the ranges considered.

[0033] A zirconium content of 0.01-0.2 wt% promotes solid solution strengthening in the as-cast state, whereas a higher content requires higher than typical casting temperatures, reduces mold durability, and increases the tendency for hot cracking during casting.

[0034] Primary crystals containing manganese, chromium, zirconium, and titanium are permitted in the structure up to a maximum of 0.3% by volume, which helps prevent the casting from adhering to the mold.

[0035] To verify the practice of the present invention, the following method was used.

[0036] Quantitative assessment of the phase composition, especially the amount of eutectic phase and primary crystals, was performed by at least one of the following two methods: 1) calculation using the Thermo-calc program; 2) metallographic techniques.

[0037] The crystallization range was evaluated in at least one of two ways: 1) calculation using the Thermo-calc program; 2) experimentally by constructing a cooling curve in temperature-time coordinates and determining the crystallization range as the difference between the liquidus and solidus temperatures.

[0038] The verification of the technical results was carried out under laboratory conditions, and the alloy compositions described in the examples were prepared and studied. The alloys were prepared in graphite crucibles using induction or resistance furnaces, based on raw aluminum with purities of ≥99.8% and ≥99.99% by weight, zinc with a purity of ≥99.90% by weight, copper with a purity of ≥99.9% by weight, magnesium with a purity of ≥99.9% by weight (indicating the purity of the molten metal), and binary master alloys: AlCa10, AlFe10, AlMn20, AlSi10, AlTi5, AlCr10, and AlZr10. The total amount of other elements and unavoidable impurities in the alloys did not exceed 0.05% by weight, which is contained in the raw aluminum and master alloys and was not adjusted during the preparation of the melt.

[0039] For mechanical and structural analysis, the alloys were crystallized in metal molds. Single-cast cylindrical specimens had a working diameter of 10 mm and mold temperatures below 150°C. The alloys' casting properties were evaluated using a hot cracking susceptibility index, a "ring test." The best index was the ring with the smallest wall thickness that crystallized without cracking, across a series of ring thicknesses of 3, 7, and 10 mm, with a constant outer diameter of 40 mm. Mechanical properties were evaluated in the as-cast state by uniaxial tensile testing of single-cast specimens at a test speed of 10 mm / min and a working length of 50 mm, in accordance with GOST 1583-93. The criterion for "adhesion" was the material's ability to separate from the surface of the metal mold without mechanical action. [Example]

[0040] Example 1 EXAMPLE 1 To study and verify the chemical composition of the present invention, alloys were prepared under laboratory conditions according to the chemical compositions in Table 1. The results of the determination of the crystallization range and the analysis of the hot cracking tendency are shown in Table 2. The results of the analysis of the mechanical properties are shown in Table 3.

[0041] [Table 1]

[0042] [Table 2]

[0043] [Table 3]

[0044] Analysis of the results, as shown in Tables 2 and 3, showed that compositions 2-5 and 8-26, according to the concentration ranges stated, exhibit acceptable resistance to the formation of hot cracks. Compositions 1, 6 and 7 are not applicable. Composition 1 is characterized by a high tendency to adhere to the mold walls. Composition 6 has a high tendency to form hot cracks, while composition 7 has an unsatisfactory structure containing unacceptable primary crystals containing calcium, iron, silicon and zinc, which significantly reduces the elongation.

[0045] Example 2 To verify the suitability of the alloy for high-pressure casting, a 3 mm thick plate measuring 70 x 150 mm was cast, from which specimens for tensile testing were cut. The chemical composition of the alloy is shown in Table 4. The mechanical properties are shown in Table 4. The typical structure of alloy 31 is shown in Figure 1.

[0046] [Table 4]

[0047] [Table 5]

[0048] Analysis of the results in Tables 4 and 5 reveals that this alloy has an excellent balance of strength and ductility in high-pressure casting.

Claims

1. Contains calcium, silicon, iron, zinc, and magnesium in the following weight percent concentrations: Calcium 2.0-5.2, Silicon 0.05 to 0.8, Iron 0.05 to 1.0, Zinc 0.01-5.0, Magnesium 0.01 to 2.0, the balance being aluminum and unavoidable impurities; Aluminum-based alloy for casting.

2. The composition contains at least one of calcium, silicon, iron, zinc, and magnesium, and copper, manganese, chromium, titanium, and zirconium in the following concentrations by weight: Calcium 2.0-5.2, Silicon 0.05 to 0.8, Iron 0.05 to 1.0, Zinc 0.01-5.0, Magnesium 0.01 to 2.0, Copper 0.01-1.4, Manganese 0.01 to 1.4, Chromium 0.01 to 0.2, Titanium 0.01 to 0.2, Zirconium 0.01 to 0.2, the balance being aluminum and unavoidable impurities; Aluminum-based alloy for casting.

3. 3. A cast aluminum-based alloy according to claim 1, wherein the magnesium is disposed within an aluminum matrix.

4. 3. A cast aluminum-based alloy according to claim 2, wherein the copper combines with the calcium to form a eutectic phase.

5. 3. The aluminum-based alloy for casting according to claim 1, which has a yield strength of 100 MPa or more in a cast state.

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