HEAT-RESISTANT MAGNESIUM ALLOY FOR CASTING

Abstract

A magnesium alloy which has excellent tensile strength and elongation at a room temperature, as well as an excellent heat resistance represented by creep resistance is obtained. The magnesium alloy is produced which comprises 3.0% by mass or more and less than 6.0% by mass of Al, 0.10% by mass or more and 0.60% by mass or less of Mn, more than 0.50% by mass and less than 2.0% by mass of Ca, and more than 0.10% by mass and less than 0.40% by mass of Si, and has a balance composed of Mg and unavoidable impurities.

Claims

1. A magnesium alloy comprising 3.0% by mass or more and less than 6.0% by mass of Al, 0.10% by mass or more and 0.60% by mass or less of Mn, more than 0.50% by mass and less than 2.0% by mass of Ca, and more than 0.10% by mass and less than 0.40% by mass of Si, and having a balance composed of Mg and unavoidable impurities.

2. The magnesium alloy of claim 1, comprising 4.5% by mass or more and less than 6.0% by mass of Al.

3. The magnesium alloy of claim 2, comprising 0.90% by mass or more and less than 2.0% by mass of Ca.

4. The magnesium alloy of claim 1, which is for casting.

5. The magnesium alloy of claim 2, which is for casting.

6. The magnesium alloy of claim 3, which is for casting.

Description

EXAMPLE

[0025] An example of actually preparing the magnesium alloy according to the present invention is shown. The magnesium alloy was prepared so that components of elements other than Mg have % by mass of contents described in Table 1 below, respectively, to prepare an alloy material based on d “collection of test materials required for producing a tensile test piece” of JIS H 5203 “8. Inspection” (corresponding to ISO16220-5). That is, test materials were collected from the magnesium alloy adjusted to have % by mass of contents described in Table 1, respectively, by a gravity casting method. Besides, elements other than the elements described were below a detection limit.

[0026] Each alloy was tested based on the tensile test method specified in JIS Z 2241 (corresponding to ISO6892-1). A test sample was produced by machining the above-described alloy material to measure tensile strength and elongation using a universal tester (UH-500kNX manufactured by Shimadzu Corporation) as a tester.

[0027] Moreover, a test was conducted based on the creep test method specified in JIS Z 2271 (corresponding to ISO204: 2009). A test sample was produced by machining the above-described alloy material to measure a creep strain (%) after 100 hours under a test temperature at 175° C. and an applied stress of 50 MPa using SK-3 manufactured by Sinkou Kagaku Kikai Co., LTD. as a creep tester.

[0028] Furthermore, a test was conducted based on the salt spray test method specified in JIS Z 2371 (corresponding to ISO 9227: 2012). A test sample was prepared by being molded by gravity casting and then machined. A test was conducted for 96 hours by a neutral salt spray test as a test method using a tester manufactured by Suga Test Instruments Co., Ltd. After the test, the test sample was boiled in a mixed aqueous solution of chromium (VI) oxide and silver nitrate for 1 minute to remove corrosion products, and a corrosion weight loss was measured.

[0029] Table 1 below shows tensile strength, elongation, creep strain, and overall evaluation, as well as a component ratio of each test sample. As evaluations, from the worst, “B” shall be Bad, “G” be Good, and “VG” be Very Good. For tensile strength, less than 150 MPa was evaluated as “B”, 150 MPa or more and less than 170 MPa as “G”, and 170 MPa or more as “VG”. For elongation, less than 3.5% was evaluated as “B”, 3.5% or more and less than 4.0% as “G”, and 4.0% or more as “VG”. For creep strain, more than 0.25% was evaluated as “B”, more than 0.18% and 0.25% or less as “G”, and 0.18% or less as “VG”. For the above-mentioned three items, when there was one or more “B”, the overall evaluation was scored as “B”. When there was “G” or “VG” for all items, without including “B”, the overall evaluation was scored as “G”. Furthermore, when all the items were scored as “VG”, the overall evaluation was scored as “VG”.

TABLE-US-00001 Component (unit: % by mass) Tensile strength Elongation Creep strain Overall No. Mg Al Mn Ca Si MPa % % evaluation Example 1 Bal. 3.47 0.38 0.81 0.14 169 G 7.8 VG 0.13 VG G Example 2 Bal. 3.59 0.33 1.76 0.14 150 G 3.5 G 0.03 VG G Example 3 Bal. 3.89 0.31 1.80 0.36 160 G 4.2 VG 0.07 VG G Example 4 Bal. 4.03 0.31 1.09 0.20 166 G 6.9 VG 0.08 VG G Example 5 Bal. 4.15 0.28 1.32 0.20 153 G 3.8 G 0.07 VG G Example 6 Bal. 4.57 0.35 0.82 0.33 170 VG 6.1 VG 0.22 G G Example 7 Bal. 4.67 0.21 1.26 0.22 175 VG 4.9 VG 0.08 VG VG Example 8 Bal. 5.55 0.34 0.64 0.13 204 VG 9.0 VG 0.19 G G Example 9 Bal. 5.71 0.36 1.09 0.29 177 VG 5.1 VG 0.16 VG VG Example 10 Bal. 5.74 0.26 0.96 0.19 171 VG 4.5 VG 0.17 VG VG Example 11 Bal. 5.97 0.33 1.33 0.31 175 VG 4.2 VG 0.14 VG VG Comparative Bal. 2.00 0.18 1.15 0.18 131 B 3.1 B 0.08 VG B Example 1 Comparative Bal. 6.10 0.30 1.83 0.40 151 G 2.3 B 0.11 VG B Example 2 Comparative Bal. 4.27 0.29 2.97 0.22 133 B 0.8 B 0.07 VG B Example 3 Comparative Bal. 3.24 0.22 1.84 0.42 141 B 2.2 B 0.06 VG B Example 4 Comparative Bal. 5.97 0.32 2.40 0.56 149 B 2.0 B 0.07 VG B Example 5 Comparative Bal. 8.73 0.28 0.87 0.20 165 G 2.3 B 0.26 G B Example 6

[0030] In Comparative Example 1 in which the Al content was insufficient, both tensile strength and elongation were insufficient. On the other hand, in Comparative Examples 2 and 6 in which the Al content was excessive, elongation was deteriorated. In Comparative Examples 3 and 5 in which the Ca content was excessive, there were problems in both elongation and tensile strength. In Comparative Examples 4 and 5 in which the Si content was excessive, there were also problems in both elongation and tensile strength.

[0031] All of Examples 1 to 5 were evaluated as “G” or higher, but in Examples 6 to 11 in which the Al content was further increased as compared with Examples 1 to 5, it was confirmed that tensile strength was improved. However, among Examples 6 to 11 in which the Al content was increased, in Examples 6 and 8 in which the Ca content was slightly insufficient, evaluation of creep strain remained at “G”. Meanwhile, among Examples 6 to 11, in Examples 7, 9, 10, and 11 having a large Ca content, evaluation of creep strain was scored as “VG”.

[0032] Table 2 below shows a corrosion weight loss, as well as a component ratio in each test sample.

TABLE-US-00002 TABLE 2 Corrosion Component (% by mass) weight loss Mg Al Mn Ca Si (mcd) Example 12 Bal. 4.83 0.39 1.30 0.26 0.48 Example 13 Bal. 5.03 0.43 1.79 0.27 1.17 Example 14 Bal. 3.69 0.32 1.15 0.27 2.89 Example 15 Bal. 4.04 0.33 1.49 0.28 3.31 Comparative Bal. 4.13 0.30 2.08 0.31 5.11 Example 7

[0033] As shown in Table 2, Examples 12 to 15 show a good corrosion resistance of less than 5.00 mcd (mg/cm.sup.2/day). However, in Comparative Example 7, corrosion resistance was 5.11 mcd, which was not sufficient. It is considered that this is because the Ca content was excessive and therefore corrosion resistance was deteriorated.