Effects of silicon content on the mechanical and tribological properties of monotectoid-based zinc–aluminium–silicon alloys

In this work, one binary zinc–aluminium and eight ternary zinc–aluminium–silicon alloys were produced by permanent mould casting. Friction and wear properties of the alloys were investigated in both as-cast and heat-treated conditions using a block-on-ring machine and the results were related to their microstructure and mechanical properties. It was observed that the microstructure of the zinc–aluminium–silicon alloys consisted of aluminium-rich α, zinc-rich η phases and silicon particles. The size and distribution of silicon particles were found to be dependent on the silicon content of the alloys. The heat treatment involving quench-ageing removed the dendritic microstructure of the alloys and produced a fine-grained microstructure, but had no significant effect on the silicon particles. Silicon additions were found to be very effective on mechanical and wear properties of zinc-based alloys. The hardness and the tensile strength of the alloys increased with increasing silicon content up to 2 wt.% Si, above which it decreased as the silicon content increased further. It was also found that friction coefficient and wear rate of the alloys decreased with increasing silicon content up to 2 wt.% Si, but above this level they increased as the silicon content increased further. Among the alloys tested, the highest tensile strength and wear resistance was obtained with the Zn–40Al–2Si alloy. It was also observed that the wear behaviour of the Zn–Al–Si alloys correlates strongly with their hardness, tensile strength and friction coefficient.