Pre-aging on early-age behavior and bake hardening response of an Al-0.90Mg-0.80Si-0.64Zn-0.23Cu alloy

Pre-aging on early-age behavior and bake hardening response of an Al-0.90Mg-0.80Si-0.64Zn alloy was investigated by differential scanning calorimetry (DSC), high resolution transmission electron microscopy (HRTEM), 3-dimensional atom probe (3DAP), Erichsen test and tensile test. The results indicated that pre-aged alloy exhibited excellent formability and bake-hardening response, while bake hardening response was poor in samples with natural aging. Clustering behavior during natural aging was inhibited by pre-aging. Numerous GP zones formed in pre-aged samples. GP zones were the nuclei of β′′ precipitates or directly transformed β′′ phases during paint baking process. A large number of β′′ phases were observed in pre-aged samples after paint bake treatment. There was no sign to indicate that β′′ phase precipitated in natural aged samples after bake hardening treatment.