Effect of aging time on mi̇crostructure and mechanical properties of Zn-27Al-1Cu alloy

In this study, Zn-27Al-1Cu alloy was produced by permanent mould casting. As-cast alloy aged at different periods after subjected to solution treatment and water quenching. The structural, mechanical and fatigue behavior of heat treated alloy and as-cast alloy were investigated. As a result of the researches, it was determined that the microstructure of as-cast Zn-27Al-1 Cu alloy consisted of aluminum-rich α dendrites surrounded by zinc-rich η and eutectoid α + η phase and copper-rich ε phase. The quench-ageing treatment removed the dendritic microstructure of the alloy and produced aluminum-rich α grained microstructure together with zinc-rich and copper-rich precipitates. As the hardness and tensile strength increased, ductility and toughness values decreased with the heat treatment. The longest fatigue life was obtained from the Zn-27Al-1Cu alloy after 0.5 hour aging time. It has been concluded, all the mechanical properties have considerable effect on fatigue behavior. However fatigue performance mostly depends on the ductility and especially toughness. It was also found that Basquin's equation could be used to express the fatigue behaviour of Zn-27Al-1Cu alloy in both as-cast and in heat treated states. All the fatigue samples, especially the heat treated fatigue samples showed brittle fracture behavior.