Influence of treatment pathways on the precipitation behaviors of Al-Mg-Si-Cu-(Zn)-Mn alloys

Abstract

We report on a systematic study of the influence of three different treatment pathways on the precipitation behavior of Al-Mg-Si-Cu-(Zn)-Mn alloys involving microstructure characterization, property measurements and modelling. The results reveal that the formation of coarse Mg2Si and Si particles in a Al-Mg-Si-Cu-Mn alloy during annealing at 400 °C can be avoided by adding Zn; the latter can improve the nucleation of precipitates, and increase the number density of β″ precipitates in the Al-Mg-Si-Cu alloy in both the non-isothermal and isothermal peak aging states, corresponding to a decrease in the activation energies of precipitation calculated on the basis of a modified AJM kinetics model, and finally resulting in an enhanced age hardening response in Al-Mg-Si-Cu-Zn-Mn. Moreover, although β″, Q′ and β′ precipitates with structures similar to those of Al-Mg-Si-Cu-Mn alloys, and an absence of Mg-Zn precipitates were observed in the Zn-containing Al-Mg-Si-Cu-Mn alloy after different treatment pathways, the incorporation of Zn atoms in the precipitates formed in the Zn-containing alloy was confirmed using APT characterization and the changes in the lattice parameter.