CONTROLLING THE FORMABILITY AND STRENGTH OF Al-Mg-Si ALLOYS

摘要

In the processing of 6000 series Al-Mg-Si sheet alloys for automobile applications a processing sequence of solution treatment, quench, hold at ambient, cold forming and paint baking at ～175°C applies. It has been demonstrated that raising the silicon content of a l%Mg alloy in the as quenched condition improves the strength without a significant change in uniform elongation. Holding for 14 days at ambient increases the strength irrespective of silicon content and maintains the ductility but reduces the work hardening coefficient. On ageing at 175°C for 30 mins (typical of a paint bake) after the 14 day hold, a reduction in strength can occur in high silicon alloys. This reduction has been interpreted as being caused by the dissolution of clusters of solute atoms.