HIGH STRENGTH 6000 SERIES ALUMINUM ALLOY EXCELLENT IN STRESS CORROSION CRACKING RESISTANCE, AND HEAT TREATMENT

摘要

PROBLEM TO BE SOLVED: To improve the stress corrosion cracking resistance of a 6000 series aluminum alloy while maintaining its high strength. SOLUTION: In an Al-Mg-Si alloy or an Al-Mg-Si-Cu alloy, grain boundary precipitates are allowed to exist at intervals of >=110 nm and also the size of the precipitates in the direction of grain boundaries is regulated to >=70 nm. Further, such a form of precipitation can be obtained by subjecting a 6000 series aluminum alloy ingot to primary aging treatment consisting of holding at 150 to 200 deg.C for 3 to 80 hr after solution heat treatment, then to restoration treatment consisting of heating at >=300 deg.C/min temperature rise rate, holding at 200 to 270 deg.C for 0.5 to 20 min, and cooling at a rate of >=500 deg.C/min, and further to reaging treatment consisting of holding at 150 to 190 deg.C for 8 to 80 hr.