Effect of pre-aging temperature on multi-step aging behavior of Al-Mg-Si alloys

The effect of pre-aging temperature on the natural age hardening and bake hardening behavior of Al-Mg-Si alloys was investigated by means of Vickers hardness test, tensile test, differential scanning calorimetry analysis (DSC) and transmission electron microscopy (TEM). Both the hardness and yield strength change with the natural aging time indicating that the lower pre-aging temperature increases the natural age hardening and decreases the bake hardening response. The DSC analysis confirms that the cluster (l) is formed during natural aging after the pre-aging treatment and the amount increases with the natural aging time. And then, increased pre-aging temperature suppresses the formation of cluster (l), but even if the case of specimens pre-aged at 383 K, the formation of cluster (l) started after natural aging for a longer time than 10.4Ms. These results are explained by taking into consideration that the remained solute Si, Mg atoms and excess vacancies depend on the amount of cluster (2) formed during pre-aging. © 2013 The Japan Institute of Light Metals.