PURPOSE: To manufacture the title Al alloy having improved brightness and stress corrosion cracking resistance by subjecting an Al alloy ingot constituted of specific compsn. to homogenizing treatment, subjecting it to reheating and hot extruding and immediately water-cooling it.
CONSTITUTION: An Al alloy ingot contg., by weight, 4.0 to 4.5% Zn, 0.4 to 1.6% Mg, 0.05 to 0.40% Cu, 0.05 to 0.20% Mn, 0.05 to 0.20% Zr and the balance Al with inevitable impurities is subjected to homogenizing treatment. The ingot is then subjected to reheating and hot extruding; immediately after the hot extruding, it is water-cooled. By this method, the Al alloy for an automobile bumper having beautiful surface and excellent brightness and having stress corrosion resistance by chemical polishing anodization treatment can be obtd.
KAWASHIMA SHOHEI
MIYAMURA KENICHI
ARACO CORP