Flow softening behavior and microstructure evolution of Al–5Zn–2Mg aluminum alloy during dynamic recovery

The flow stress behavior and microstructure development of Al–5Zn–2Mg (7005) aluminum alloy were studied by hot compression tests at deformation temperatures between 300–500 °C and strain rates between 0.05–50 s−1. The deformed structures of the samples were observed by optical microscopy (OM), transmission electron microscopy (TEM) and electron backscattering diffraction (EBSD) analysis. The calculated activation energy is 147 kJ/mol, which is very close to the activation energy for lattice self-diffusion in aluminum (142 kJ/mol). Dynamic recovery is the dominant restoration mechanism during the deformation. At high strain rate of 50 s−1, temperature rise due to deformation heating leads to a significant flow softening. Microstructure observations indicated that the remaining softening after deformation heating correction at high strain rate and the softening observed at high temperature are associated with grain coarsening induced by grain boundary migration during dynamic recovery process.