Combined Effect of Pre-Straining and Pre-Aging on Bake-Hardening Behavior of an Al-0.6 mass percentMg-1.0 mass percent Si Alloy

摘要

The effect of pre-straining in combination with pre-aging on bake-hardening behavior of an Al-0.6mass percentMg-1.0mass percentSi 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 percent pre-strain suppresses the formation of clusters; i.e. 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 beta"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 beta"phase from more supersaturated solute atoms in final aging.