Investigation of microstructural change and damping behaviour of Zn–27Al–1Cu alloy in different aging periods

Abstract

The ternary Zn-27Al-1Cu alloy is produced from raw materials by the gravity casting method. The produced alloy was subjected to aging after solutionizing and quenching. The effect of ageing at different periods on the microstructure and damping behaviour of the alloy was investigated. The microstructural investigations revealed that the microstructure of the alloy in the as-cast state consisted of aluminium(Al)-rich α dendrites surrounded by eutectoid β phase, and zinc(Zn)-rich η phase and copper(Cu)-rich ε phase. The heat treatment eliminated the dendritic microstructure of the casting alloy and transformed it into a coarse-grained (β-matrix) stable form containing Zn-rich and Cu-rich precipitates. The microstructural changes after aging process were directly affected the mechanical properties of the alloy. The hardness and tensile strength increased with increasing ageing time up to 2.5 hours, but the percent elongation decreased. When the aging time reached 5 hours, hardness and tensile strength decreased while percent elongation increased significantly. The impact energy, namely toughness, increased in the early stage of aging, reduced sharply with increasing aging time and remained stable with a small increase in the prolonged stage of aging. The highest impact energy was attained from the aged alloy for 0.5 hours. The variation in damping energy was dependent on the changes in microstructural and mechanical properties caused by different aging periods. The prolonged aging process transformed the fracture characteristic of the as-cast alloy from relatively brittle to ductile fracture.