Effect of Zn and Cu Content on Microstructure, Hardness and Tribological Properties of Cast Al-Zn-Cu Alloys

Abstract

Microstructure, micro-hardness and wear properties of Aluminium-Zinc-Copper (Al-Zn-Cu) alloys of various chemical compositions are investigated. Stir casting process is used to prepare the various alloy compositions with permanent metallic mould. Six different alloy compositions were developed by varying Zn and Cu content in aluminium matrix. The wear and frictional properties were studied using Pin-on-Disc wear tester in dry sliding condition under normal atmosphere. The developed Al-Zn-Cu alloy has inter-metallic stable θ (CuAl2) phase in the inter-dendrite region and is due to the addition of Cu from 1 to 5 wt. % in 60Al-(40-x) Zn alloy. When the Cu composition increases up to 2 wt %, the corresponding hardness increases significantly and is due to the formation of Cu-rich θ phase and also due to the solid solution hardening of Cu in Al-Zn alloy matrix. But after 2 wt % Cu addition it is observed that the hardness increase is marginal. Wear rate (WR) and specific wear rate (SWR) were increases with increase of load and sliding velocity and decreases with Cu addition. Coefficient of friction (COF) remains constant for entire load and velocity for each alloy. However, when the alloys were tested at elevated temperatures, it was found that initially WR, SWR and COF decreases with temperature and then increases rapidly.