| 摘要 |
PROBLEM TO BE SOLVED: To obtain an Al-Mg-Si aluminum alloy cold forged part in which the coarse growth of crystal grains causing polarized optical reflection is suppressed and having surface properties pleasing in appearance. SOLUTION: This cold forged part contains, by mass, 0.3 to 1.3% Si, 0.4 to 1.3% Mg, 0.1 to 0.5% Cu, 0.1 to 0.5% Fe and 0.04 to 0.4% Cr, and in which the maximum grain size of crystal grains exposed to the surface is <=1.5 mm. If required, it may contain one or >= two kinds among 0.05 to 0.8% Mn, 0.05 to 0.4% Zr, 0.03 to 0.4% V, 0.01 to 0.4% Sn, 0.001 to 0.03% Ti and 0.003 to 0.03% B. It is produced by holding an extruded material at 520 to 580 deg.C for 1 to 10 hr, thereafter executing quenching at a cooling rate of >=200 deg.C/min, subjecting it cold forging, subsequently holding it at 160 to 220 deg.C for 1 to 12 hr and executing aging treatment. Instead of the solution heat treatment, die edge quenching may be executed. In the meanwhile of the quenching and cold forging, holding treatment in which it is held at 80 to 150 deg.C for 5 to 600 sec can be executed as well.
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