Effect of In addition on the precipitation behavior and mechanical property for Al-Mg-Si alloys

Abstract The impact of In addition on the precipitation behavior and properties for Al-Mg-Si alloys under different aging treatments was systematically studied by hardness measurements, atom probe tomography (APT), high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and density functional theory (DFT) calculations. We found that the In addition effectively suppresses the harmful effect of natural aging (NA), and improves the age hardening for the Al-Mg-Si alloy. Mg-Si-In clusters are formed in the early stage of aging caused by the incorporation of In atoms, which can facilitate the nucleation of the β" phase. During peak aging, In atoms distort the well-ordered structure of the β" and occupy the positions in the interface of the β", facilitating the transition of β" to post-β" (i.e. U2 and β′). During the following aging, In atoms are presented in two different configurations: forming In-rich particles and aggregation at the interfaces of β′. Most of the In-rich particles are formed at the edge of the β′ particles. The segregation of In atoms at the precipitate/matrix interface and the formation of In-rich particles can probably be attributed to the reduced strain energy of the β′ phase it brings about.