Effect of Combined Pre-Straining and Pre-Aging on the Precipitation Behavior and Age Hardening Response for Al-Mg-Si Alloys
Pre-strain (PS) and pre-aging (PA) treatments are often applied during the preparation of Al-Mg-Si automotive aluminum alloy. In this study, the effect of combined PS and PA on the precipitation behavior and age hardening response for Al-Mg-Si alloys was investigated through scanning electron microscopy (SEM), transmission electron microscopy (TEM), tensile test, Vickers hardness test, and differential scanning calorimetry (DSC). It was found that the dislocations introduced by PS treatment and the cluster (2) formed during PA treatment effectively inhibited the cluster (1), which further strengthened the inhibition of natural aging hardening at room temperature (RT). The strength increment of the alloys was kept below 10.0 MPa during two weeks RT storage. The dislocations provided heterogeneous nucleation for the precipitates forming and the cluster (2) transformed into β″ strengthening phase during bake hardening treatment. With the acceleration response of the dislocations and the cluster (2), the age hardening response of Al-Mg-Si alloys obviously improved with the denser and larger β″ strengthening phase formed.