Investigation of tribological properties of Zn-25Al- based alloys

In this study, three binary Zn-Al, five ternary Zn-25Al-(1-5)Cu and four quaternary Zn-25Al-3Cu-(1-4)Si alloys were prepared by permanent mould casting. Tribological properties of the alloys were investigated using a pin-on-disc machine after studying their microstructure and mechanical properties. The microstructure of the binary Zn-25Al alloy consisted of large ß dendrites surrounded by aluminum-rich ? and zinc-rich ? phases. Addition of copper more than 3% produced ? phase mainly in the interdendritic channels of the alloy. The microstructure of the quaternary Zn-25Al-3Cu-1Si alloy revealed silicon particles, in addition to the phases observed in the ternary alloy. T6 heat treatment removed the dendritic microstructure of Zn-25Al-3Cu-1Si alloy and produced a new microstructure which consists of ? grains. The hardness and tensile and compressive strengths of the alloys increased with increasing copper and silicon contents, but when the copper and silicon contents exceeded certain levels the trend reversed. As the pressure increased working temperature and wear volume values of the alloys increased, but their friction coefficient decreased. Microstructural changes were observed underneath the surface of the Zn-25Al based alloys subjected to dry sliding wear tests. Among the alloys studied the highest strength and wear resistance were obtained with Zn-25Al-3Cu-1Si alloy. In addition, the Zn-25Al based ternary and quaternary alloys were found to be much superior to the SAE 660 bronze as far as their mechanical and tribological properties are concerned.