Effects of strain rate on flow stress behavior and dynamic recrystallization mechanism of Al-Zn-Mg-Cu aluminum alloy during hot deformation

The flow behavior, microstructure evolution and softening mechanism of an AA7085 aluminum alloy are investigated by isothermal hot compression tests at 450 °C with the strain rates of 0.001 s−1 and 0.1 s−1. Optical microscopy (OM), electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM) are used to characterize microstructure evolution during deformation. The results reveal that the flow stress curves exhibit a single peak and then two types of flow stress curves are found in the present study. Microstructure characterization reveals that dynamic recovery (DRV) and recrystallization (DRX) occur in the both conditions. The microstructure discrepancy becomes significant with increasing strain rate after a certain strain level (ε≥0.3). In the case of 0.001 s−1, the dynamic recovery is thought to precede continuous dynamic recrystallization. As the strain rate increased, the absence of dynamic recovery provides enough stored energy for discontinuous dynamic recrystallization (DDRX), resulting in a retardation in the occurrence of continuous dynamic recrystallization (CDRX).