Abstract
Hot compression tests over the temperature range from 300°C to 450°C and strain rates range from 0.01s−1 to 10s−1 of homogenized Al–7.68Zn–2.12Mg–1.98Cu–0.12Zr alloy were carried out on a Gleeble-3500 thermal simulation machine to characterize its hot deformation behavior. The results showed that the flow stress can be predicted by a two-stage constitutive model based on the dislocation density theory and kinetics of dynamic recrystallization (DRX) with the hot deformation activation energy of 125.4kJ/mol. The associated microstructure was studied using transmission electron microscopy (TEM) and electron back scattered diffraction (EBSD) technique. With the decrease of lnZ (Z represents the Zener–Hollomon parameter) value from 22.4 to 18.6, the microstructure analysis revealed a decrease of low angle boundaries (misorientation below 15°) from 96.1% to 78.2%, and an increase of the higher angle boundaries with the misorientation angles between 15° and 60° from 3.9% to 21.8%. Combining the results from processing map, it can be concluded that such an evolution is mainly due to the decrease of subgrains with the increase of Z values, and partly due to the partial DRX at low Z values. The softening mechanisms of homogenized Al–7.68Zn–2.12Mg–1.98Cu–0.12Zr alloy is dynamic recovery (DRV), together with a partial DRX at high temperature and low strain rate conditions (low Z value).
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