Effect of Si addition on microstructure and mechanical properties of Al-Mg-Si-Zn alloy

The effect of Si addition on the microstructure and mechanical properties of Al-Mg-Si-Zn aluminum alloys were investigated. Results show that the microstructure of Al-Mg-Si-Zn alloy with low Si contents is mainly composed of Mg2Si and Mg5Si6 phases. With the increasing of Si content, Si and Al3.21Si0.47 phases precipitate in the form of eutectic phases in the alloys, at the same time, the mean shape factor of the second phase firstly increases and then decreases. Regression analysis results show that the Si content has the main influence and the mean shape factor has the least influence on tensile strength. Tensile strength increases significantly with the addition of Si, however, there is a remarkable drop in the elongation of the alloys. Decreased elongation is related to the formation of monotonous Al (200) structure and the enlargement of interplanar spacing of (111) and (200) crystalline planes.