Bake-hardening Properties of Al-0.6Mg-1.2Si Alloy Sheets Fabricated by Twin Roll Casting

The effect of pre-aging treatment on the microstructure and mechanical properties of Al-0.6Mg-1.2Si aluminum alloy sheets fabricated by twin roll casting (TRC) was investigated. It was observed that two kinds of nanoclusters, cluster(1) and cluster(2), play an important role in the bake-hardening properties of Al-Mg-Si aluminum alloy. The hardness of the TRC Al-0.6Mg-1.2Si alloy sheets was continuously increased up to 48 h by natural-aging, and the highest yield strength value was about 146 MPa. The yield strength was 280 MPa after bake-hardening at 180 ℃ for 30 min immediately after quenching, whereas the yield strength was 172 MPa when natural-aging proceeded for about 1 week before bake-hardening. This result is due to fact that cluster(1) is formed during natural-aging at room temperature and has detrimental effects on bake-hardening. On the other hand, when pre-aged at 150 ℃ for 10 min, cluster(2) predominantly formed and promoted the precipitation of β″ phase. The yield strength was 256 MPa after bake-hardening, which indicates that the pre-aging treatment is an effective method, and also depresses the negative effects of natural-aging and promotes β″ precipitation. The Al-Mg-Si aluminum alloy sheets fabricated by twin roll casting method exhibited mechanical properties equal to or higher than those of the direct-chill (DC) casting sheets despite the simplified manufacturing process.