Effect of Quench-Ageing on Microstructural Evolution and Damping Behaviour of Zn-27Al-1Cu Alloy

Abstract

A ternary Zn-27Al-1Cu alloy was prepared by permanent mould casting. The microstructural evolution and damping behaviour of the Zn-27Al-1Cu alloy were investigated in different periods of ageing after subjected to solution treatment followed by water quenching. As a result of this investigation, it was determined that the microstructure of as-cast alloy consisted of aluminium-rich ? dendrites surrounded by zinc-rich ? and eutectoid ß phase and copper-rich ? particles. The quench-ageing treatment removed the dendritic structure of the as-cast alloy and transformed into a uniform microstructure consisting of large grains (ß-matrix) combined with zinc and copper-rich precipitates. Microstructural changes after quench-ageing were accompanied with the variance of damping behaviour. It was found that the damping capacity by means of impact toughness increased in early stage of ageing and then it decreased sharply with increasing ageing time and finally it increased slightly and reached constant values in the prolonged stage of ageing. The highest toughness was obtained from the alloy aged for 0.5 h. The change in damping behaviour with ageing time can be explained in terms of the microstructural variations and precipitation hardening mechanism.