Cast aluminum alloy

Abstract

The invention relates to the field of metallurgy, and more particularly to aluminum-based alloys, and can be used to produce thin-walled castings of complex shapes, preferably by die casting. The aluminum-based casting alloy contains the following components in percentage by weight: 2.0-5.2% of calcium; the silicon accounts for 0.05 to 0.8 percent by weight; iron is 0.05%-1.0% in percentage by weight; the zinc accounts for 0.01 to 5.0 percent by weight; the magnesium accounts for 0.01 to 2.0 percent by weight; optionally, at least one alloy element is selected from the following groups: 0.01-1.4% by weight of copper; the manganese accounts for 0.01 to 1.5 percent by weight; by weight, 0.01 to 0.2% of chromium; the titanium accounts for 0.01 to 0.2 percent by weight; the alloy comprises the following components in percentage by weight: 0.01-0.2% of zirconium, aluminum and inevitable impurities. The technical object of the present invention is to provide high strength performance while maintaining plasticity, workability during casting and high corrosion resistance.

Description

Technical Field

[0001] The present invention relates to the field of metallurgy, namely to aluminium-based alloys, and can be used to produce castings of complex shapes by casting into metal moulds, mainly by injection moulding. Background Art

[0002] Complex castings are usually made from non-heat-hardenable and hardenable alloys based mainly on the Al-Si and Al-Mg systems. Castings produced from Al-Si based alloys with magnesium and / or copper additions, intended for highly critical components, are usually used after heat treatment to T7, T6 and T5 tempers to enhance their strength properties.

[0003] Well-known non-heat-hardenable Al-Si based alloys, such as A413.2 or AlSi11 alloys, are known for their high castability and good corrosion resistance. Disadvantages of this group of alloys include low levels of strength properties, in particular, the yield strength in the as-cast state usually does not exceed 80 MPa. Higher strength properties of castings in the as-cast state are provided by the addition of copper, in particular AA383.1 or AlSi12Cu2 type alloys. Disadvantages of these alloys include significantly reduced corrosion resistance and poor elongation of no more than 1–2%.

[0004] Also known are non-heat-hardenable casting alloys based on the Al-Mg system, such as AMg6L, AMg5K, AMg5Mz (GOST 1583), 59 (Rheinfelden Alloys), etc., which are distinguished by satisfactory castability, good corrosion resistance and adequate strength properties and elongation. The high linear shrinkage of thin-walled castings and the insufficient tightness should be highlighted among the disadvantages of the alloys of this system.

[0005] A high level of combination of strength properties, elongation and corrosion resistance is achieved in Al-Si system alloys with addition of 0.2-0.5 wt.% magnesium. AK9 type (GOST 1583), 36 (Rheinfelden Alloys), Alloys such as Trimet® 37 are particularly known. Quenching significantly complicates the process cycle for obtaining the casting, since it can lead to warping of the casting (especially when quenching in water), changes in the overall dimensions and the appearance of cracks.

[0006] Casting alloys of the Al-Ni-Mn system are known for the production of structural components for automotive and aerospace applications, as well as a replacement for the brand of silicon aluminum alloys developed by Alcoa, and are disclosed in patent US 6,783,730 B2 (publication date: August 31, 2004). In the case of (weight %) 2-6% Ni, 1-3% Mn, 1% Fe, less than 1% 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 alloy include ensuring a high level of casting and mechanical properties by using high purity aluminum grades and having a high nickel content, thus significantly increasing the cost of the castings produced. In addition, the proposed material is not heat hardenable in the entire concentration range, thus limiting its use, while the corrosion resistance of the castings is significantly reduced in the area of ​​high nickel concentration.

[0007] Casting aluminum alloys based on the Al-Ni and Al-Ni-Mn systems and methods for producing castings therefrom are known and described in Alcoa invention US8349462 (published on January 8, 2013) and Rheinfelden Alloys GmbH & Co. KG application EP2011055318. The present invention proposes alloy compositions for casting applications. Common in the proposed inventions is a high nickel content of 1-6%, which determines the main disadvantage, namely a significant reduction in corrosion resistance. In the case of relatively low nickel and manganese contents, the casting alloys show low levels of strength properties.

[0008] There is a known material based on the Al-Ni-Mn system proposed by the National University of Science and Technology 'MISIS' (Moscow Institute of Steel and Alloys) and disclosed in patent RU 2478131 (publication date: March 27, 2013). This material contains (weight %): 1.5-2.5Ni, 0.3-0.7Fe, 1-2Mn, 0.02-0.2Zr, 0.02-0.12Sc, 0.002-0.1Ce. The castings obtained from the alloy after annealing (without quenching operation) are characterized by an ultimate tensile strength of at least 250MPa 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 foundry conditions.

[0009] There is a known material based on the Al-Ca system proposed by the Russian State University of Science and Technology 'MISIS' (Moscow Institute of Steel and Alloys) and disclosed in patent RU2660492. The material for use in the as-cast condition contains (in weight %): 5.4-6.4% calcium, 0.3-0.6% silicon and 0.8-1.2% iron. The disadvantages of the proposed alloy include a low elongation of no more than 2.6%, thus limiting the use of the material in critical castings.

[0010] The alloy most closely resembling the proposed alloy was invented by the Institute of Lightweight Materials and Technology and is disclosed in claim RU2745595. The material for use in the cast state contains (in weight %): 1.5-5.1% calcium, 0.1-1.8% zinc, up to 1.0% silicon and up to 0.7% iron. Disadvantages of the proposed alloy include poor yield strength in the cast state, which is due to the poor solubility of the alloying elements other than zinc in the solid solution, resulting in insufficient solid solution hardening. Summary of the invention

[0011] The purpose of the present invention is to provide a new aluminum casting alloy that is mainly used to produce castings by high pressure, but the effects include but are not limited to this. It can be used without heat treatment, has good casting processing performance, good mechanical properties, including a yield strength of not less than 100MPa, and high corrosion resistance.

[0012] Key applications are castings for automotive engineering, electronic housings, etc. Components for critical applications can be manufactured from this material.

[0013] The technical purpose of the present invention is to ensure high strength properties while maintaining plasticity, castability and high corrosion resistance.

[0014] The technical effect is achieved by using an aluminum-based casting alloy containing calcium, silicon, iron, zinc, magnesium and optionally at least one element selected from the group consisting of copper, manganese, chromium, titanium and zirconium, and having the alloying element concentrations by weight as described below.

[0015] Calcium 2.0–5.2

[0016] Silicon 0.05–0.8 (preferably 0.3–0.8)

[0017] Iron 0.05–1.0 (preferably 0.1–0.5)

[0018] Zinc 0.01–5.0 (preferably 1.0–2.0)

[0019] Magnesium 0.01–2.0 (preferably 0.05–0.5).

[0020] Optionally, the alloy comprises at least one alloying element from the following group:

[0021] Copper 0.01–1.4 (preferably 0.02–0.5)

[0022] Manganese 0.01–1.5 (preferably 0.5–1.0)

[0023] Chromium 0.01–0.2 (preferably 0.05–0.1)

[0024] Titanium 0.01–0.2 (preferably 0.05–0.1)

[0025] Zirconium 0.01–0.2 (preferably 0.05–0.1)

[0026] The balance is aluminum and inevitable impurities.

[0027] For a particular embodiment of the present invention, magnesium is disposed in an aluminum matrix and copper combines with calcium and forms a eutectic phase, thereby providing enhanced strength properties without compromising ductility.

[0028] The alloy is used to produce castings having the following tensile properties in the cast state: yield strength ≥ 100 MPa.

[0029] Various modifications and improvements are possible without departing from the scope of the disclosure of the invention as described and claimed. DETAILED DESCRIPTION

[0030] The concentrations (weight %) of calcium (2.0-5.2), silicon (0.05-0.8), iron (0.05-1.0), zinc (0.01-5.0) and copper (optionally 0.01-1.4) are restricted to specified limits to ensure the formation of a structure representing an aluminum solid solution and a corresponding eutectic phase containing calcium and the following elements: silicon, iron, zinc and optionally copper.

[0031] Calcium, silicon, iron, zinc and optionally copper affect the total amount of eutectic phase in the alloy. At the minimum contents of calcium, silicon, iron, zinc and optionally copper (as specified), the eutectic content is about 2.5 volume %.

[0032] The presence (weight %) of magnesium (0.01-2.0) and optionally at least one element chosen from manganese (0.01-1.5), chromium (0.01-0.2), titanium (0.01-0.2) and zirconium (0.01-0.2) allows, when combined with the above elements (calcium, silicon, iron, zinc and, if present, copper), the formation of a structure representing a solid solution of aluminum as the main crystalline phase and a eutectic containing at least one alloying element (including manganese, chromium, titanium and zirconium).

[0033] Magnesium, and optionally at least one element within specified ranges, including manganese, chromium, titanium and zirconium, can enhance hardening by dissolving in aluminum solid solution (solid solution hardening), while also increasing crystal spacing, adversely affecting casting properties.

[0034] Studies have surprisingly shown that a suitable combination of eutectic contents with respect to the considered concentration range of alloying elements provides acceptable casting properties and hardening, wherein all eutectic phases are associated with calcium and aluminum solid solution alloying and crystallization intervals up to 50° C. The presence of magnesium and silicon aids in the dispersion of the calcium-containing eutectic phase. Figure 1 A typical structure of an as-cast casting (HPDC casting) is provided in .

[0035] Figure 1 A typical alloy structure in the as-cast state is shown, characterized by a primary aluminum solid solution and a eutectic phase. The as-cast structure is represented by an aluminum solid solution containing zinc, magnesium and eutectic phase particles, which include compounds of aluminum, calcium with zinc, aluminum, calcium with iron and aluminum, calcium with silicon, depending on the presence of certain elements in the alloy. In the case of additional alloying with copper, manganese, chromium, titanium and zirconium, the as-cast structure is similar in nature and consists of an aluminum solid solution containing zinc, magnesium manganese, chromium, titanium and zirconium, and eutectic phase particles with compounds of aluminum, calcium with zinc, aluminum, calcium with iron, aluminum, calcium with silicon and aluminum, calcium with copper.

[0036] The effects of alloying elements are discussed in detail below.

[0037] Calcium contents below 2.0 wt. % lead to poor casting properties and do not ensure the bonding of elements such as silicon, iron, zinc and optionally copper to calcium. Calcium contents above 5.2 wt. % lead to the formation of coarse inclusions of the primary phase Al4Ca, which reduces the mechanical properties.

[0038] In the as-cast state, the silicon content is between 0.05-0.8 wt. %, and calcium provides good elongation because silicon helps to disperse the eutectic. At silicon contents above 0.8 wt. %, coarse intermetallic compounds containing silicon are formed, thus reducing mechanical properties. Silicon below 0.05 wt. % is insufficient to form eutectics with favorable morphology, resulting in insufficient elongation in the as-cast state.

[0039] In the case of calcium, iron contents of 0.05 to 1.0 wt. % enhance casting properties while maintaining acceptable elongation levels. Iron contents below 0.05 wt. % deteriorate the alloy casting processability, manifested by increased adhesion of the casting to the mold. Iron contents above 1.0 wt. % form coarse intermetallic compounds containing crystalline sources of iron and calcium, thereby reducing mechanical properties.

[0040] Zinc contents between 0.01 and 5.0 wt. % increase corrosion resistance and improve casting properties. Zinc contents below 0.01 wt. %: No beneficial effect of zinc on strength properties is observed. From 0.01 wt. %, there is a modification effect, which manifests itself as a change in the morphology of the calcium-containing eutectic. Zinc contents above 5.0 wt. % form a coarse crystalline source phase containing zinc and calcium, which adversely affects the mechanical properties of the alloy.

[0041] A copper content between 0.01 and 1.4 wt. % (optionally) improves the strength properties without compromising the casting properties and keeps the corrosion resistance at an acceptable level. The copper content maintains satisfactory corrosion resistance by combining copper with calcium in one phase. Copper content below 0.01 wt. %: No positive influence of copper on mechanical or other properties is observed. At low copper contents starting from 0.01 wt. %, there is a modifying effect of changing the morphology of the calcium-containing eutectic phase by forming phases with copper and calcium.

[0042] A magnesium content between 0.01 and 2.0 wt. % improves the strength properties of the cast state. When the magnesium content exceeds 2.0 %, the crystal spacing becomes significantly widened, which unacceptably deteriorates the casting properties, especially the hot cracking tendency. Magnesium content below 0.01 wt. %: No positive influence on the strength properties and other elements within the specific chemical composition is observed.

[0043] Manganese contents between 0.01 and 1.5 wt. % have a positive influence on the strength properties together with the other elements within the defined chemical composition through solid solution hardening. Manganese contents above 1.5 wt. % form coarse crystallization precursor phases which reduce the mechanical properties.

[0044] Chromium contents between 0.01 and 0.2 wt. % promote solid solution hardening in the cast state. At higher contents, primary crystals of the Al7Cr phase form significantly more easily, which reduces the mechanical properties.

[0045] Titanium contents between 0.01 and 0.2 wt. % contribute to the modification of primary precipitation of aluminum solid solution during crystallization. Higher titanium contents in the structure may lead to the appearance of primary crystals, thereby reducing the overall level of mechanical properties, while lower titanium contents will not achieve the positive effect of this element. When titanium is added as multinary Al-Ti-B or Al-Ti-C, boron or carbon may be present in the alloy in proportion to their content in the parent alloy. Boron and carbon, as independent elements, have no significant effect on mechanical and casting properties for the ranges described.

[0046] Zirconium contents between 0.01 and 0.2 weight percent favor solid solution hardening in the as-cast state. Larger amounts require the casting temperature to be raised above typical levels, thereby reducing mold durability and increasing hot cracking tendencies.

[0047] The structure may contain up to 0.3% by volume of primary crystals, including manganese, chromium, zirconium or titanium, in order to reduce the adhesion of the casting to the mold wall.

[0048] Embodiments of the present invention are supported by the following methods.

[0049] The phase composition, in particular the amount of eutectic phase, is quantitatively assessed as the amount of primary crystals in at least one of the following two ways: 1) by thermal calculation; 2) by metallography.

[0050] The crystallization interval is estimated by at least one of two methods: 1) by thermal calculations; 2) by coordinate experiments and the construction of a cooling curve in temperature-time coordinates and the crystallization interval value as the difference between the liquidus temperature and the solidus temperature.

[0051] The technical results were confirmed under laboratory conditions, in which the specified alloy compositions were prepared and checked. The alloys were prepared in an induction furnace or resistance furnace in a graphite crucible using primary aluminum with a minimum content of 99.8% by weight and 99.99% by weight, not less than 99.90% by weight of zinc, not less than 99.9% by weight of copper and not less than 99.9% by weight of magnesium (the purity of the base metals is specified for use in the melt) and master alloys: AlCa10, AlFe10, AlMn20, AlSi10, AlTi5, AlCr10, AlZr10. Other elements and unavoidable impurities in the alloy do not fully exceed the 0.05% by weight found in the primary aluminum and master alloys and are not adjusted for melt preparation.

[0052] For the determination of mechanical properties and structural analysis, the alloy was crystallized in a metal mold "separately cast cylindrical samples" with a working part diameter of 10 mm and a mold temperature of up to 150 ° C. The casting properties of the alloy were determined by the hot cracking tendency using "ring samples", where the best indicator was a ring with a minimum wall thickness at a constant outer diameter of 40 mm, crystallized in rows of 3, 7 and 10 mm without cracking. The mechanical properties were evaluated in uniaxial tension of the separately cast samples in the cast state. The test speed was 10 mm / min and the working part length was 50 mm, according to GOST 1583-93. Adhesion was tested based on the ability of the material to separate from the metal mold surface without mechanical impact.

[0053] Example

[0054] Example 1

[0055] In order to verify and confirm the required chemical composition under laboratory conditions, alloys were prepared according to the chemical composition listed in Table 1. The results of the crystallization spacing and hot cracking tendency analysis are provided in Table 2. The results of the mechanical tests are provided in Table 3.

[0056] Table 1: Chemical composition, weight %

[0057]

[0058]

[0059]

[0060] Table 2: Analysis of crystallization interval and hot cracking tendency

[0061]

[0062]

[0063] Table 3: Mechanical properties

[0064]

[0065]

[0066] The results given in Tables 2 and 3 show that compositions 2-5 and 8-26 according to the claimed concentration ranges provide acceptable levels of resistance to hot cracking. Compositions 1, 6, 7 are not suitable because composition 1 is more likely to adhere to the mold wall. Composition 6 is characterized by a high tendency to hot cracking and composition 7 is characterized by the fact that an unsatisfactory structure is obtained, in which unacceptable primary crystals contain calcium, iron, silicon and zinc, which significantly reduce the elongation.

[0067] Example 2

[0068] The suitability of the alloy for high pressure die casting was confirmed by casting 3 mm thick plates with dimensions of 70×150 mm and cutting tensile specimens from these plates. The chemical composition of the alloy is shown in Table 4. The mechanical properties of the alloy are shown in Table 5. A typical structure of the alloy 31 composition is shown in Figure 1 middle.

[0069] Table 4: Chemical composition, weight %

[0070] Serial number Ca Si Fe Zn Mn Mg Cr Zr Al 30 4.5 0.7 0.2 1.4 0.8 0.1 0.08 0.12 Base Metal 31 3.3 0.75 0.2 1.4 0.8 0.02 0.05 0.05 Base Metal 32 4.0 0.5 0.3 1.4 0.8 0.02 0.04 0.08 Base Metal

[0071] Table 5: Mechanical properties

[0072] Serial number Ultimate tensile strength, MPa Yield strength, MPa Elongation, % 30 270 205 6.1 31 235 110 11.5 32 250 125 8.5

[0073] The results in Tables 4 and 5 show that the alloy provides a good balance of strength and ductility in high pressure die casting.

Claims

1. An aluminum-based alloy for casting, containing calcium, silicon, iron, zinc, and magnesium, and having the following concentrations in weight percentage: The balance is aluminum and inevitable impurities.

2. An aluminum-based alloy for casting, containing calcium, silicon, iron, zinc, magnesium and at least one of the following alloying elements: copper, manganese, chromium, titanium, zirconium, and having the following concentrations in weight percentage: At least one of the following alloying elements: The balance is aluminum and inevitable impurities.

3. The alloy according to claim 1 or 2, characterized in that The magnesium is arranged in an aluminum matrix.

4. The alloy according to claim 2, characterized in that Copper combines with calcium to form a eutectic phase.

5. The alloy according to any one of claims 1 to 4, characterized in that It has a yield strength of at least 100 MPa in the as-cast state.

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