Effects of Mg, Si contents and natural aging conditions on the bake hardenability of Al-Mg-Si alloys

Abstract

Effect of natural aging conditions on split aging, especially bake hardenability at 170°C for 1.2ks and 86.4ks on Al-1%Mg2Si, Al-1.5%Mg2Si and Al-1%Mg2Si-0.6%Si alloys have been studied using hardness measurement, DSC analysis and electrical resistance measurement. The increasing hardness of an AI Mg -Si alloy with excess Si during baking at 170°C for 1.2ks without natural aging is higher than that of Al-Mg-Si alloys without excess Si. However, the hardness of the high Si content alloy after baking at 170°C for 1.2ks was decreasing with increasing natural aging time before baking clearly. It could be considered that the cluster which did not transfer to β″ phase formed using vacancy during natural aging on the high Si content alloy, The β″ phase of the high bake hardenability sample on DSC analysis appeared at lower temperature compared with the low bake hardenability sample. The β″ phase which was located at lower temperature on DSC analysis precipitates quickly during bake at 170°C, and the hardness was increased during baking at 170°C for 1.2ks.