The effect of Cu additions and prestraining on the age-hardening behavior of AA6016 sheets

Abstract

In this study, we investigated the effect of Cu additions (0.1 and 0.3 wt%) on the age-hardening behavior of AA6016 Al–Mg–Si alloys with and without 3 % prestraining by hardness testing and transmission electron microscopy analysis. Our results showed that higher Cu addition slightly increased the peak hardness, but significantly shortened the time to reach peak aging in both alloys with and without prestraining. Prestraining can improve the peak hardness by making the higher Cu addition more pronounced. In alloys without prestraining, the higher Cu addition slowed the hardness reduction in the overaged state, and the 0.3Cu alloy consistently exhibited finer precipitates with higher number density than the 0.1Cu alloy throughout the aging process. In contrast, higher Cu addition in alloys with 3 % prestraining accelerated the hardness decrease in the overaged state and led to a coarser microstructure after 24 h aging. This is primarily because Cu atoms can slow down the reduction in dislocation density during aging, whereas the higher dislocation density promoted the growth of precipitates, resulting in accelerated coarsening of precipitates as the aging time proceeded. Moreover, dislocations accelerated the formation of precursors of the Q′ phase, which was more pronounced in the 0.3Cu alloy.