Effect of Aging Treatment Technology on Properties of Al-Mg-Si-Cu-Zr-Er Alloy for Auto Sheets

Abstract

The effect of natural aging, pre-aging and paint-bake aging technology on properties of Al-Mg-Si-Cu-Zr-Er alloy for auto sheets was investigated by performance testing, microstructure observation, and differential thermal analysis. The results showed that the natural aging alloy before and after paint-bake aging presented the double peaks feature of both the mechanical properties and hardness, the maximum value of strength and hardness appeared on the second aging peak, and the paint-bake aging softening occurred. The result of differential thermal analysis showed that, compared with the artificial aging, the precipitation of β′′ phase was delayed after the natural aging; the precipitates were mainly β′′ nuclei at the paint-bake aging, and it is difficult to achieve paint-bake aging hardening. After pre-aging and nature aging treatment, the precipitates were mainly composed of β′′ phase at the paint-bake aging, and the paint-bake aging hardening was realized. The addition of Er and Zr elements accelerated the precipitation of β′′ phase, the precipitation temperature of β′′ phase reduced and the time of the first natural aging peak and pre-aging was shortened. The parameters of pre-aging treatment of alloy sheets was solution and water quenching, and then age at 170 °C for 5 min.