Effect of As-Cast Cooling on the Microstructure and Mechanical Properties of Age-Hardened 7000 Series Aluminium Alloy

This study investigates the influence of as-cast cooling on the microstructure and mechanical properties of age-hardened Al-Zn-Mg-Cu alloy. The material was cast in the form of cylindrical rods in green sand mould where some samples were rapidly cooled and others gradually cooled to room temperature. From the samples that were gradually cooled, some were annealed while others were T6 tempered. Both the as-cast and heat treated samples were subjected to tensile and hardness tests and the morphology of the resulting microstructures were characterised by optical and scanning electron microscopy. The results revealed formation of microsegregations of MgZn 2 during gradual solidification which was not present during rapid cooling. It was also found that age hardening and annealing heat treatment operations eliminated microsegregations thus improving mechanical properties of Al-Zn-Mg-Cu alloy.