Aluminum alloy for casting

Abstract

To provide an aluminum alloy for casting satisfying mechanical characteristics as automobile components, by improving the mechanical characteristics by suppressing generation of an acicular structure crystallizing in an eutectic portion.SOLUTION: The aluminum alloy for casting is obtained by dissolving an aluminum alloy containing 6.5 to 7.5 wt.% of Si, 0.5 wt.% or less of Fe, 0.20 to 0.4 wt.% of Mg, 0.6 wt.% or less of Mn, and the balance Al and inevitable impurities as a recycled lump aluminum, and adding 0.1 to 0.5 wt.% of V and 0.1 to 0.5 wt.% of Ni. An addition ratio of V and Ni added to the recycled lump aluminum can be V: Ni=1:1, the number of acicular structures in a micro-observation cross-section is 236 pieces / mm2 or less, and a value of elongation at break is 13.0% or more.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an aluminum alloy for casting. [Background technology]

[0002] AC4CH is a known aluminum-silicon-magnesium alloy for casting. AC4CH has excellent elongation and corrosion resistance due to its small Fe content, and is used for aluminum wheels and suspension parts of automobiles (for example, see Patent Document 1 below). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-8142 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, virgin aluminum is used for AC4CH, which is a high-purity alloy, as disclosed in the above-mentioned Patent Document 1. Since the production of virgin aluminum requires high energy costs and emits a large amount of CO2, there has been a strong demand for the use of recycled aluminum, which is a recycled material.

[0005] One possible method to meet these industrial demands would be to substitute AC4CH for a material called AC4C, which can be used to manufacture alloys using recycled aluminum. However, recycled aluminum AC4C has a large number of acicular structures made of Fe and Mn compounds that crystallize in the eutectic portion, which significantly reduces the breaking elongation and makes it impossible to meet the mechanical properties required for automotive parts as mentioned above.

[0006] The present invention has been made in consideration of the problems existing in the prior art described above, and has an object to obtain an aluminum alloy for casting that satisfies the mechanical properties required for automobile parts by adding new alloy components to recycled aluminum ingots to suppress the occurrence of acicular structures crystallizing in the eutectic portion and improve the mechanical properties. [Means for solving the problem]

[0007] The casting aluminum alloy according to the present invention is obtained by melting an aluminum alloy containing 6.5 to 7.5 wt. % Si, 0.5 wt. % or less Fe, 0.20 to 0.4 wt. % Mg, 0.6 wt. % or less Mn, with the remainder being Al and unavoidable impurities, as recycled aluminum ingot, and adding 0.1 to 0.5 wt. % V and 0.1 to 0.5 wt. % Ni.

[0008] In the aluminum alloy for casting according to the present invention, it is preferable that the ratio of V and Ni added to the regenerated aluminum ingot is V:Ni=1:1.

[0009] In addition, in the casting aluminum alloy according to the present invention, the number of acicular structures in a microscopic observation cross section is set to 236 / mm 2 It can be as follows:

[0010] Furthermore, in the aluminum alloy for casting according to the present invention, the breaking elongation can be set to 13.0% or more. Effect of the Invention

[0011] According to the present invention, by adding new alloy components to recycled aluminum ingot, the occurrence of acicular structures crystallizing in the eutectic portion can be suppressed, improving the mechanical properties, and it is possible to obtain an aluminum alloy for casting that satisfies the mechanical properties required for automobile parts. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a microscopic cross-sectional view showing an example of the occurrence of acicular structures crystallizing in a eutectic portion of an aluminum alloy. [Diagram 2] FIG. 2 is a diagram showing the results of counting the number of acicular structures crystallizing in a eutectic portion based on microscopic observation cross sections of the casting aluminum alloy according to the present embodiment, Comparative Example 1, and Comparative Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] In order to obtain a reclaimed aluminum alloy equivalent to AC4CH, which is an aluminum-silicon-magnesium-based cast aluminum alloy, the inventors have been investigating a means of adding various alloying elements to AC4C, which can be used to manufacture alloys using reclaimed aluminum, to obtain a new cast aluminum alloy that can replace AC4CH. According to preliminary experiments by the inventors, one of the reasons why the mechanical properties of AC4C, which is reclaimed aluminum, are inferior to those of AC4CH, which is new aluminum, is thought to be the occurrence of an acicular structure crystallized in the eutectic part of the aluminum alloy, as shown in FIG. 1. Thus, through extensive research, the inventors came up with the idea that a cast aluminum alloy that satisfies the mechanical properties required for automobile parts could be obtained by adding alloying elements such as V (vanadium) and Ni (nickel) to AC4C, which is reclaimed aluminum.

[0014] Here, V is an element that acts on the formation and growth of Al-Si-Fe intermetallic compounds in the eutectic structure and significantly reduces the occurrence of needle-like compounds. The purpose of adding V to AC4C is to obtain the effect of improving the breaking elongation.

[0015] In addition, Ni is known as an element that improves high-temperature strength and heat resistance, and when added to AC4C together with V, a synergistic effect is created that significantly reduces the occurrence of needle-shaped Al-Si-Fe intermetallic compounds in the eutectic structure, resulting in equal or greater strength and elongation than when V is added alone.

[0016] The inventors then decided to investigate the mechanical properties of the aluminum alloy for casting manufactured based on the above-mentioned idea, as will be described in detail below.

[0017] First, the inventors performed a material composition analysis of AC4CH, which is new lump aluminum, and AC4C, which is recycled lump aluminum, as aluminum alloys that serve as a reference for the mechanical properties required for the casting aluminum alloy according to this embodiment. Table 1 shown below is a table showing the material composition analysis results of AC4CH, which is new lump aluminum, and Table 2 shown below is a table showing the material composition analysis results of AC4C, which is recycled lump aluminum. In Tables 1 and 2, the first line shows the contained elements, the second line shows the steel grade specifications for each contained element, the third and fourth lines show the measurement results of two samples of AC4CH and AC4C used in the verification experiments conducted by the inventors, and the fifth line shows the average value of the measurement results of the two samples.

[0018] [Table 1]

[0019] [Table 2]

[0020] The inventors used AC4CH shown in Table 1 as Comparative Example 1, AC4C shown in Table 2 as Comparative Example 2, and melted AC4C, which is recycled aluminum lump, and added 0.1 wt% V as Comparative Example 3. Melted AC4C, which is recycled aluminum lump, and added 0.1 wt% V and 0.1 wt% Ni as the casting aluminum alloy according to the present embodiment. Then, the mechanical properties of these four types of aluminum alloys were investigated. The data of the results are shown in Tables 3 to 6, and the data shown in Tables 3 to 6 are summarized and summarized in Table 7.

[0021] Table 3 shows the results of casting 10 steering knuckles, an automotive part, using AC4CH, the new ingot aluminum whose composition was analyzed in Table 1, and creating test specimens from the right (R) and left (L) positions of the 10 steering knuckles. The tensile strength (MPa), 0.2% yield strength (MPa), breaking elongation (%), and hardness value (HRF; Rockwell hardness) of each test specimen were then measured, along with the average, maximum (MAX), and minimum (MIN) values ​​of these result data.

[0022] Table 4 shows the results of casting 10 steering knuckles, an automobile part, using AC4C, the recycled ingot aluminum whose composition was analyzed in Table 2, creating test specimens from the right (R) and left (L) positions of the 10 steering knuckles, and measuring the tensile strength (MPa), 0.2% yield strength (MPa), breaking elongation (%), and hardness value (HRF; Rockwell hardness) of each test specimen, as well as a compilation of the average, maximum (MAX), and minimum (MIN) values ​​of these result data.

[0023] Table 5 shows the results of measuring the tensile strength (MPa), 0.2% yield strength (MPa), elongation at break (%), and hardness value (HRF; Rockwell hardness) of each test piece, measured using AC4C, the recycled aluminum lump that was analyzed for its components in Table 2, which was melted and 0.1% by weight of V was added. The measured values ​​also include the average, maximum (MAX), and minimum (MIN) values ​​of the measured data.

[0024] Finally, Table 6 shows the results of measuring the tensile strength (MPa; shown as tensile strength in Table 7), 0.2% yield strength (MPa), fracture elongation (%), and hardness value (HRF; Rockwell hardness) of each test piece, as well as the average, maximum value (MAX), and minimum value (MIN), of these result data. The AC4C recycled aluminum lump that was analyzed for its components in Table 2 was melted and 0.1% by weight of V and 0.1% by weight of Ni was added to the mixture, and 10 steering knuckles, which are automobile parts, were cast using this mixture. Test pieces were then made from the right (R) and left (L) positions of the 10 steering knuckles, and the tensile strength (MPa; shown as tensile strength in Table 7), 0.2% yield strength (MPa), fracture elongation (%), and hardness value (HRF; Rockwell hardness) of each test piece were then measured.

[0025] Table 7 shows a summary of the data shown in Tables 3 to 6.

[0026] [Table 3]

[0027] [Table 4]

[0028] [Table 5]

[0029] [Table 6]

[0030] [Table 7]

[0031] As shown in Table 7, compared to the mechanical properties of AC4CH made from virgin aluminum shown in Comparative Example 1, AC4C made from recycled aluminum shown in Comparative Example 2 has lower tensile strength (MPa), 0.2% yield strength (MPa), and breaking elongation (%). In particular, for use in automobile suspension parts such as steering knuckles, the breaking elongation (%) value needs to be closer to that of Comparative Example 1.

[0032] In contrast, in Comparative Example 3, in which AC4C, a recycled aluminum lump, was melted and 0.1 wt. % of V was added, the breaking elongation (%) value improved to 13.0%, which is equivalent to Comparative Example 1. However, the tensile strength (MPa) and 0.2% yield strength (MPa) of the material of Comparative Example 3 are the same as or worse than those of Comparative Example 2, leaving room for improvement.

[0033] In the case of the present embodiment, in which AC4C, which is the recycled aluminum ingot, is melted and 0.1 wt % V and 0.1 wt % Ni are added, the breaking elongation (%) is 13.0%, which is equivalent to Comparative Example 1, and the tensile strength (MPa) and 0.2% yield strength (MPa) are improved compared to Comparative Examples 2 and 3 and approach those of Comparative Example 1. The mechanical properties of the casting aluminum alloy according to this embodiment are satisfactory when used for suspension parts such as steering knuckles, which are automobile parts.

[0034] As described above, the casting aluminum alloy according to this embodiment has mechanical properties such as tensile strength (MPa), 0.2% yield strength (MPa), and fracture elongation (%) which are comparable to those of virgin aluminum AC4CH, and it has been confirmed that the casting aluminum alloy according to this embodiment can be used for automobile parts.

[0035] Based on the above findings, the inventors further performed cross-sectional microscopic observations using the test samples of Comparative Example 1, Comparative Example 2, and the present embodiment, and compared the number of acicular structures in the microscopically observed cross sections. The observation results are shown in FIG.

[0036] In the cross-sectional micro-observation shown in Fig. 2, five micro-observation cross-sectional photographs were prepared for each of Comparative Example 1, Comparative Example 2, and this embodiment, and the number of acicular structures observable in each micro-observation cross-sectional photograph was counted. More specifically, the scale shown in each micro-observation cross-sectional photograph was 100 µm = 7.4 cm, and the size of one micro-observation cross-sectional photograph was 25.4 cm x 19.05 cm = 343 µm x 257 µm = 88,151 µm. 2 =0.088mm 2 The actual area was calculated based on the number of acicular structures included in the microscopic cross-sectional photograph and the actual area, and the unit area (mm 2 The number of acicular structures per 100 mm was calculated.

[0037] As a result, the numbers of acicular structures in the five microscopic cross-sectional photographs shown in FIG. 2 for Comparative Example 1 were 12, 16, 22, 10, and 18 from the top, and the average number of these was 15.6 per sheet, resulting in an average of 177 per mm 2 The value obtained was:

[0038] The numbers of acicular structures in the five microscopic cross-sectional photographs shown in FIG. 2 for Comparative Example 2 are 308, 213, 148, 136, and 174 from the top, and the average number of these is 196 per photograph, so the average number is 2,227 per mm. 2 The value obtained was:

[0039] Finally, the numbers of acicular structures in the five microscopic cross-sectional photographs shown in FIG. 2 for this embodiment are 20, 22, 21, 21, and 20 from the top, and the average number of these is 20.8 per photograph, so the average number is 236 per mm. 2 The value obtained was:

[0040] The above results demonstrate that the inventors' prediction that suppressing the generation of acicular structures crystallizing in the eutectic portion contributes to improving mechanical properties is correct. The number of acicular structures in the microscopic cross-sectional photographs was an average of 177 / mm for AC4CH, a new ingot aluminum. 2 In the case of the casting aluminum alloy according to this embodiment, the average number of pieces is 236 / mm2 While the number of particles is equivalent to that of AC4C, which is recycled aluminum, is 2,227 particles / mm 2 It is clear that the casting aluminum alloy of this embodiment, obtained by adding 0.1% by weight each of the alloy components V and Ni to recycled aluminum ingot, has mechanical properties applicable to automotive parts, which is also proven by the number of acicular structures in the microscopic observation cross section.

[0041] As described above, the casting aluminum alloy of this embodiment contains 6.5 to 7.5 wt. % Si, 0.5 wt. % or less Fe, 0.20 to 0.4 wt. % Mg, 0.6 wt. % or less Mn, with the remainder being Al and unavoidable impurities, and is obtained by melting the aluminum alloy into recycled lump aluminum, and adding 0.1 to 0.5 wt. % V and 0.1 to 0.5 wt. % Ni. The ratio of V and Ni added to the recycled lump aluminum is preferably V:Ni=1:1, and the number of acicular structures in a microscopically observed cross section is 236 pieces / mm 2 The casting aluminum alloy according to the present embodiment is characterized in that the breaking elongation is 13.0% or more and the breaking elongation is 13.0% or more. According to the casting aluminum alloy according to the present embodiment, the occurrence of acicular structures crystallized in the eutectic portion can be suppressed to improve the mechanical properties, so that the casting aluminum alloy can be obtained as a regenerated ingot that satisfies the mechanical properties required for automobile parts. By using such a casting aluminum alloy as a regenerated ingot for automobile parts, it becomes possible to significantly reduce the energy cost and CO2 emissions during manufacturing.

Claims

1. An aluminum alloy for casting obtained by melting an aluminum alloy containing 6.5 to 7.5 wt. % Si, 0.5 wt. % or less Fe, 0.20 to 0.4 wt. % Mg, 0.6 wt. % or less Mn, with the balance being Al and unavoidable impurities, as recycled aluminum lump, and adding 0.1 to 0.5 wt. % V and 0.1 to 0.5 wt. % Ni.

2. 2. The casting aluminum alloy according to claim 1, A casting aluminum alloy, characterized in that the ratio of V and Ni added to the regenerated aluminum block is V:Ni=1:

1.

3. 3. The casting aluminum alloy according to claim 1, The number of acicular structures in the microscopic observation cross section was 236 / mm ２ 1. A casting aluminum alloy, characterized in that:

4. 3. The casting aluminum alloy according to claim 1, A casting aluminum alloy having a breaking elongation of 13.0% or more.

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