DRY SLIDING WEAR PROPERTIES OF Al-7Si-4Zn-(0-5)Cu ALLOYS

Abstract

In this study, one ternary Al-7Si-4Zn and five quaternary Al-7Si-4Zn-(1-5) Cu alloys were synthesised by permanent mould casting. Dry sliding friction and wear properties of the alloys were investigated by using ball-on-disc type tester after determining their microstructure and mechanical properties. The microstructure of the Al-7Si-4Zn alloy consisted of aluminium-rich alpha-dendrites, eutectic and primary silicon particles. Addition of copper less than 2% had no considerable effect on the microstructure of ternary alloy, but when the copper content exceeded this level the theta (CuAl2) phase formed in the microstructure of the quaternary alloys. The tensile strength and hardness of the alloys and microhardness of alpha-phase increased with increasing amount of copper but their percentage of elongation decreased with it. Copper addition up to 3% reduced the friction coefficient and volume loss of the alloys, above which they showed an increase. The wear surfaces of the alloys were characterised by smearing and de-lamination, but smearing appeared to be the dominant mechanism for their wear. The highest wear resistance was obtained with the Al-7Si-4Zn-3Cu alloy while the Al-7Si-4Zn alloy had the lowest wear resistance among the alloys tested.