Microstructural, mechanical and tribological properties of Al-7Si-(0-5)Zn alloys

A series of Al-7Si-(0-5)Zn alloys were produced by permanent mould casting and their microstructure, mechanical and tribological properties were investigated in as-cast state. The microstructure of Al-7Si alloy consisted of α-Al dendrites surrounded by eutectic Al-Si mixture and a small amount of primary silicon particles. Addition of zinc into Al-7Si alloy resulted in the formation of α-solid solution and an increase in size and volume fraction of primary silicon particles. Moreover, these particles gathered inside interdendritic regions of the ternary Al-7Si-Zn alloys. The density, strength and hardness of Al-7Si-Zn alloys increased continuously with increasing zinc content, but their elongation to fracture and impact energy showed a reverse trend. It was also observed that zinc had no significant effect on the friction coefficient of the alloys, but their wear volume decreased with increasing zinc content up to 4%, above which the trend reversed. The wear surfaces of the alloys were characterized mainly by smearing layer with some degree of oxidation. In addition, delamination and fine scratches were observed on the worn surface. It was concluded that the addition of zinc up to 4% improves both mechanical and wear behaviour of Al-7Si alloy.