Effects of Combined Pre-straining and Pre-aging on Natural Aging and Bakehardening Response of an Al-Mg-Si Alloy

For a series of Al-0.34%Mg-1.05%Si-0.08%Cu alloys, the effects of pre-treatment on natural aging, bake hardening response and plasticity were investigated using Vickers hardness test and tensile test. Differential scanning calorimetry (DSC) analysis was conducted to reveal corresponding precipitation mechanisms. The results showed that pre-straining and pre-aging alone couldn't completely suppress natural aging and improve bake hardening response simultaneously. The sensitivity of the pre-straining and pre-aging on the mechanical properties was evaluated. It was found that pre-aging was the main factor which greatly improved bake hardening response and pre-treatment had a weak influence on plasticity in pre-treated samples. DSC analysis showed that the dissolution trough of clusters disappeared in pre-treated samples, both beta '' and beta' precipitation peak shifted to lower temperature and were reduced in pre-strained and pre-aged samples. It was concluded that the formation of Mg/Si clusters was replaced by the accelerated precipitation of beta '' and beta' phases, which caused the suppression of natural aging and the improvement of bake hardening response (BHR).