ALUMINUM CASTING ALLOY

Abstract

The disclosed subject-matter 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 a metal mold, in particular for automotive components, parts of electronic devices, etc. The aluminum-based casting alloy comprises by wt. %: calcium 1.5-5.1; iron up to 0.7; silicon up to 1.0; zinc 0.1-1.8 and, optionally, one or more of manganese 0.2-2.5; titanium 0.005-0.1; zirconium 0.05-0.14; chrome 0.05-0.15, with calcium and zinc present in the alloy structure primarily as eutectic particles. The technical result is to provide a combination of process properties in casting and corrosion resistance.

Claims

1. An Aluminum-based casting alloy with a distribution of alloying elements by wt. % comprising: TABLE-US-00006 Calcium 1.5-5.1 Zinc 0.1-1.8 Iron up to 0.7 Silicon up to 1.0, and at least one element selected from the group comprising: TABLE-US-00007 Manganese 0.2-2.5 Titanium 0.005-0.1 Zirconium 0.05-0.14 Chromium 0.05-0.15 Aluminum and impurities—the rest.

2. The Aluminum-based casting alloy according to claim 1, wherein the distribution of the alloying elements by wt. % comprises: TABLE-US-00008 Calcium 2.8-5.0 Manganese 0.2- 1.2 Iron up to 0.5 Silicon up to 1.0, and Zinc 0.1-1.6.

3. The Aluminum-based casting alloy according to claim 2, wherein the Aluminum-based casting alloy is made in the form of a casting.

4. The Aluminum-based casting alloy according to claim 2, wherein the calcium and zinc are in the form of eutectic particles.

5. The Aluminum-based casting alloy according to claim 4, wherein the Aluminum-based casting alloy is made in the form of a casting.

6. The Aluminum-based casting alloy according to claim 1, wherein the calcium and zinc are in the form of eutectic particles.

7. The Aluminum-based casting alloy according to claim 6, wherein the Aluminum-based casting alloy is made in the form of a casting.

8. The Aluminum-based casting alloy according to 1, wherein the Aluminum-based casting alloy is made in the form of a casting.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 shows an exemplary alloy composition, according to some embodiments of this disclosure.

[0017] FIG. 2 illustrates the use of an exemplary “rod” length indicator to obtain a casting, according to some embodiments of this disclosure.

DETAILED DESCRIPTION

[0018] Because of the chosen combination of alloying elements, the proposed alloy is characterized by a narrow crystallization interval, which in combination with a large amount of eutectic phase provides a good level of casting characteristics, and because of the elements dissolved in aluminum solid solution—a satisfactory level of strength properties in the as-cast condition. At the same time, with various combinations of selected alloying elements, the corrosion resistance within the claimed area is maintained at a good level.

[0019] The basic criterion for the acceptable choice 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 range is given below.

[0020] Concentrations (wt. %) of calcium in the range 1.5-5.1% and zinc in the range 0.1-1.8% provide good casting properties because calcium and zinc predominantly form a sufficient amount of the eutectic phase. The main effect of the joint introduction of calcium and zinc is the formation of a joint eutectic phase Al4(Ca,Zn), where the zinc atom replaces that of calcium. As a result, the level of strength properties is further increased. If the calcium content is less than the declared level, it will lead to a decrease in casting characteristics. If zinc is reduced below the declared level, no significant increase in strength properties will be observed. Calcium and zinc content above the declared level will lead to the formation of a coarse structure and a significant decrease in mechanical properties.

[0021] The iron and silicon content is primarily determined by the purity of the aluminum used to make the alloy. However, iron and silicon can also be used as alloying elements because silicon in amounts of up to 1.0 wt. % is redistributed between solid solution and eutectics, which, on the one hand, provides an increase in strength properties due to additional solid-solution hardening in the as-cast condition and, on the other hand, positively affects the alloy casting characteristics by increasing the eutectics. With a higher silicon content, the morphology of the eutectic phase deteriorates, which generally reduces the strength characteristics. Iron in amounts of up to 0.5 wt. % predominantly forms phases of eutectic origin, which positively affects the casting characteristics of the alloy by increasing the amount of eutectics. An increase in iron concentration above 0.5 wt. % may lead to coarsening of the eutectic phase and, as a consequence, a decrease in mechanical properties.

[0022] Manganese in amounts of up to 2.5 wt. % may be required to increase the strength properties, primarily in the as-cast condition, by providing solid-solution hardening. With manganese content above 2.5 wt. %, primary crystals of the Al.sub.6(Fe,Mn) phase can be formed in the structure, which can lead to a decrease in mechanical characteristics. A manganese content of less than 0.2 wt. % will not result in significant solid-solution hardening and, as a consequence, an increase (e.g., a weak increase) in strength characteristics.

[0023] Zirconium and chromium in the declared limits (wt. %) of 0.05-0.14% and 0.05-0.15%, respectively, may provide solid-solution hardening. Lower concentrations of these elements do not result in a significant increase in strength characteristics in the as-cast condition. Larger quantities may lead to higher casting temperatures than typical, which would reduce the stability of the casting molds; otherwise, there would be a high probability of forming primary crystals of the Al.sub.7Cr and Al.sub.3Zr phase, which would not increase the level of mechanical properties from the introduction of these elements.

[0024] Titanium in an amount of 0.005-0.1 wt. % may be used to modify the aluminum solid solution. A higher titanium content in the structure may result in the appearance of primary crystals, which will reduce the overall level of mechanical properties, while a lower titanium content will not achieve the positive effect of this element. Titanium can be introduced as a multicomponent ligature, such as Al—Ti—B and/or Al—Ti—C, so that the alloy may contain boron and carbon in compounds with titanium in quantities proportional to the content of the corresponding ligature. Boron and carbon, as independent elements, had no significant effect on the mechanical and casting properties for the range in question. Besides, in the presence of titanium, a decrease in the propensity to form hot cracks during casting may be noted in some cases.

EMBODIMENT

[0025] The following exemplary charge materials were used to prepare the alloys (wt. %): Aluminum grade A99 and A8, zinc grade CO, calcium as metallic calcium and ligature Al-6Ca, manganese as ligature Al-10% Mn, ligature Al-10% Zr, Al-10% Cr, Al-5% Ti.

Example 1

[0026] To assess the effect of alloying elements on the structure and properties, 13 alloy compositions were prepared under laboratory conditions (Table 1).

TABLE-US-00003 TABLE 1 Chemical composition of experimental alloys (wt. %) No. Si Fe Ca Zn Mn Ti Cr Zr 1 1.0 0.08 1.5 0.1 <0.001 <0.001 <0.001 <0.001 2 0.05 0.2 3.5 0.8 <0.001 <0.001 <0.001 <0.001 3 0.08 0.7 5.1 1.8 <0.001 <0.001 <0.001 <0.001 4 0.08 0.5 2.8 0.1 1.2 <0.001 <0.001 <0.001 5 0.22 0.08 3.8 1.3 0.9 <0.001 <0.001 <0.001 6 1.0 0.2 5.0 1.6 0.2 <0.001 <0.001 <0.001 7 0.08 0.1 5.1 1.5 0.9 0.01 <0.001 <0.001 8 0.01 0.01 1.5 0.1 2.5 0.005 <0.001 <0.001 9 0.5 0.5 2.0 0.4 1.5 0.05 <0.001 <0.001 10 0.08 0.1 4.8 1.8 0.8 <0.001 0.05 0.12 11 0.61 0.5 5.0 1.4 0.9 0.002 0.15 0.14 12 0.16 0.19 2.3 0.32 1.2 0.1 0.10 0.09 13 0.05 0.08 1.5 0.45 1.5 0.01 0.05 0.05

[0027] The content of other elements typically did not exceed 0.05 wt. %. The chemical composition of the alloy was chosen from the condition of obtaining a structure comprising an aluminum solid solution and eutectic component. Specimens were cast gravitationally in a metal mold “Separately Cast Sample”. The mold temperature could vary in the range of 20-60° C. The casting was a tensile specimen 10 mm in diameter with an estimated length of 50 mm, which was tensile tested (with a determination of yield strength, tensile strength, and elongation) immediately after casting without machining. The structure of the specimens was evaluated from the specimen heads.

TABLE-US-00004 TABLE 2 Mechanical properties in the as-cast condition (gravity casting into a metal mold) No.* σ.sub.t, MPa σ.sub.0.2 (MPa) δ, % 1 165 74 4.5 2 181 101 3.9 3 176 123 2.0 4 191 118 2.4 5 202 143 3.1 6 212 166 2.1 7 179 155 1.0 8 152 109 3.1 9 150 90 2.0 10 235 179 2.0 11 229 204 1.2 12 201 130 3.1 13 191 124 3.6 *compositions of Table 1

[0028] Analysis of the structure of the alloys studied showed that the structure of the considered compositions of Table 1 comprises aluminum solid solution and eutectic phases formed by the corresponding elements. At the same time, calcium and zinc in all experimental alloys are predominantly represented in the form of eutectic particles.

[0029] Compositions 2, 5, and 12 are preferred because of their good yield strength to elongation ratio for use in the as-cast condition. The most desirable alloy structure, using the example of composition 5 (Table 1), is shown in FIG. 1.

Example 2

[0030] The corrosion resistance by the example of compositions 2, 5, 8, and 11 of the claimed alloy (Table 1) was evaluated by the method of accelerated corrosion tests conducted by exposure to neutral salt fog under the following program: 1 cycle soaking in a salt fog chamber at spraying of 5% NaCl solution for 8 hours at a temperature of 25±1° C., then soaking at 35±3° C. without spraying the solution for 16 hours, a total of 7 cycles. The result was evaluated by changing the surface appearance of the specimens and the depth of corrosion damage (metallographic method). The ADC6 type alloy was used as a reference, which is characterized by the highest corrosion resistance among cast aluminum alloys.

[0031] From the comparative analysis of the results, it follows that during the test, the surface color of the examined compositions and the standard changed from silver to silver-yellow, as well as single surface damage up to 10 microns without significant corrosion damage.

Example 3

[0032] Casting characteristics were evaluated using the hot brittleness (HB) parameter using the “harp casting”, where the best indicator is to obtain a casting with the maximum “rod” length (FIG. 2). The propensity for hot cracks was assessed using alloys 2, 4, and 12 as examples (Table 1). 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 ADC6 alloy, the casting from which about 40% of the rods failed starting from the maximum length.

Example 4

[0033] To evaluate the mechanical properties of alloy 12 (Table 1), 2-mm-thick plates were cast by injection molding (HPDC). Casting was done with vacuumization of the mold. The mold temperature was about 150° C. The temperature of the melt was 710° C. The results of the tensile test of specimens cut from the cast plate are shown in Table 3.

TABLE-US-00005 TABLE 3 Tensile test results of a 2 mm HPDC-cast plate (as-cast condition) σ.sub.t, MPa σ.sub.0.2 (MPa) δ, % 212 112 9.5