Effects of silicon content on the microstructural features and mechanical and sliding wear properties of Zn–40Al–2Cu–(0–5)Si alloys

Abstract

In this study, one ternary zinc–aluminium–copper and eight quaternary zinc–aluminium–copper–silicon alloys were produced by permanent mould casting. The friction and wear properties of the alloys were investigated using a block-on-disc machine. The results obtained from these investigations were explained in terms of microstructure and mechanical properties of the alloys and compared with those obtained from SAE 660 bronze under the same test conditions. The microstructure of the ternary Zn–40Al–2Cu alloy consisted of aluminium-rich α, zinc-rich η and copper-rich ɛ phases while the quaternary Zn–40Al–2Cu–(0.5–5)Si alloys revealed silicon particles in addition to the phases observed in the ternary alloy. The silicon particles showed a homogeneous distribution in the alloys containing up to 2.5% Si. However, when the silicon content exceeded this level, silicon particles gave rise to microsegregation in the alloys by gathering in some areas as separate groups. The hardness and tensile strength of the Zn–40Al–2Cu–(0.5–5)Si alloys increased with increasing silicon content up to 2.5% Si, above which these values decreased as the silicon content increased. It was found that the coefficient of friction of the alloys decreased with increasing silicon content up to 1% Si. However, above this level, it increased as the silicon content increased. It was also found that the volume loss due to wear of the alloys decreased with increasing silicon content up to 2.5%, above which it increased as the silicon content increased. All the Zn–40Al–2Cu–(0–5)Si alloys were found to be much superior to the SAE 660 bronze as far as their tribological properties are concerned and among them, the best wear performance was obtained with the Zn–40Al–2Cu–2.5Si alloy.