Mechanical Properties, Thermal Properties and Microstructure of Heat-Treated Al-Zn-Mg-x%Cu (0.02 wt% Cu and 0.89 wt% Cu) Alloy

The effect of copper addition, solution heat treatment and aging on Al-Zn-Mg alloy's microstructure, mechanical and thermal properties is studied using an optical microscope (O.M.), scanning electron microscope (SEM), X-ray diffractometer (XRD), Micro-Vickers hardness, universal tensile machine (UTM) and differential scanning calorimetry (DSC). Al-Zn-Mg-xCu (0.02 wt% and 0.89 wt%) alloys are made using 5754 alloys, pure zinc and Al-Cu alloy. After casting, Al-Zn-Mg-xCu (0.02 wt% and 0.89 wt%) alloys are heat-treated in a solution (480 °C for 1 h). After solution heat treatment, aging (180 °C for 10 to 60 minutes) is applied. As-cast Al-Zn-Mg-xCu (0.02 wt% and 0.89 wt%) alloys contain η (MgZn₂) phase and T (Al₂Mg₃Zn₃) phase. After solution heat treatment, the η and T phase dissolves into a supersaturated solid solution. Adding copper into Al-Zn-Mg alloys increases hardness from 115.94 to 135.22 HV1. Solution heat treatment improves the hardness and strength due to the dissolution of precipitate phases and the formation of solid solution atoms. Aging improves hardness due to the formation of coherent G.P. zones. Adding copper decreases the precipitate phase's dissolution temperature from 472.2 to 468.6 °C.