Journal of Materials Science, Vol.52, No.3, 1390-1404, 2017
Effect of Zn addition on the precipitation behaviors of Al-Mg-Si-Cu alloys for automotive applications
Effect of Zn addition on the precipitation kinetics and age-hardening response of Al-Mg-Si-Cu alloys was investigated by differential scanning calorimetry (DSC), hardness measurements, tensile tests and microstructural characterization. The results show that, compared with the Zn-free alloy, both the starting and peak temperatures in the DSC curve, and activation energy of beta aEuro(3) precipitation of Zn-added Al-Mg-Si-Cu alloy decrease significantly, corresponding to the greatly improved precipitation kinetics and age-hardening response, i.e., a hardness increment of 70HV after aging at 185 A degrees C for 20 min. Moreover, the peak hardness and tensile properties can also be greatly enhanced after adding 3.0 wt% Zn even exhibiting a ductile fracture feature in the peak-aged state. No precipitates of the Al-Zn-Mg alloy system appear in the Zn-added Al-Mg-Si-Cu alloys after aging at 185 A degrees C, and pre-beta aEuro(3), beta aEuro(3), and L precipitates are still the main precipitates in the two alloys after peak aging treatment. Finally, based on the microstructural evolution, a schematic diagram of precipitation in the Al-Mg-Si-Cu-Zn alloy is put forward, and the relationship between mechanical properties and microstructure is also established.