Influence of Pre-straining and Pre-ageing on the Age-hardening Response of Al-Mg-Si Alloys

The effect of pre-straining (PS) and pre-ageing (PA) on the age hardening response of Al-0.6 wt.% Mg-0.8 wt.% Si alloy is studied by Vickers hardness measurement and differential scanning calorimetry (DSC). It is found that PA can suppress the formation of undesired clusters and keeps the structure stable for a certain period. A PA treatment can effectively reduce or avoid the negative effect of natural ageing on artificial ageing and even produce a positive effect. Cluster formation can also be reduced by PS, but the kinetics of clustering is still similar to that of the as-quenched condition. In contrast, after PS, the peak positions of beta '' and beta' move to lower temperatures and peak hardness is achieved in a shorter time, indicating that the formation of beta" and beta' is accelerated by PS. However, the negative effect of natural ageing still persists after PS. PS before PA can take advantage of both techniques and produce a positive strength response. PS after PA tends to destabilize the structure created by PA and can reactivate the clustering process, which has a negative effect on subsequent artificial ageing.