Effect of heat treatment on plasticity of Al–Zn–Mg alloy: Microstructure evolution and mechanical properties

The effect of heat treatment on the plastic properties of an aluminum alloy (Al–Zn–Mg) has been investigated by indentation and tensile tests. The microstructural evolution was investigated using optical, scanning and transmission electron microscopies. After various states of ageing, the Al–Zn–Mg alloy shows significant changes in the microstructure and mechanical behaviour. After quenching, the microstructure was characterized by high ductility. After ageing at 135 ∘C, corresponding to the maximum value of hardness, the alloy reveals small η’ precipitates. After two-step ageing at 70 ∘C plus at 135 ∘C, the volume fraction of this precipitates becomes higher. Consequently, the yield strength of the material increases and it maintains its ductility.