Combined effect of pre-straining and pre-aging on bake-hardening behavior of an Al-0.6 mass % Mg-1.0 mass % Si alloy

The effect of pre-straining in combination with pre-aging on bake-hardening behavior of an Al-0.6mass%Mg-1.0 mass%Si alloy was investigated by means of Vickers hardness test, electrical conductivity measurement, differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). Hardness change and DSC analysis revealed that only 3% pre-strain suppresses the formation of clusters; Le. cluster (1), during single aging below 343 K. On the other hand, by combining with pre-aging at 343 K, pre-straining was found to improve bake-hardening response during final aging at 443 K. TEM observation confirmed that the improvement of bake-hardening response by pre-straining is mainly due to the enhanced precipitation of β″ phase in the matrix. These results are explained by the consideration that dislocations induced by pre-straining reduce the concentration of quenched-in excess vacancies, resulting in both the suppressed clustering of solute atoms during pre-aging and the accelerated precipitation of the β″ phase from more supersaturated solute atoms in final aging.