Microstructure characterization of Al-cladded Al-Zn-Mg-Cu sheet in different hot deformation conditions

Al-cladded Al-Zn-Mg-Cu sheets were compressed up to 70% reduction on a Gleeble-3500 thermo-mechanical simulator with temperatures ranging from 380 to 450 °C at strain rates between 0.1 and 30 s−1. The microstructures of the Al cladding and the Al-Zn-Mg-Cu matrix were characterized by electron back-scattered diffraction (EBSD) and X-ray diffraction (XRD). The microstructure is closely related to the level of recovery and recrystallization, which can be influenced by deformation temperature, deformation pass and deformation rate. The level of recovery and recrystallization are different in the Al cladding and the Al-Zn-Mg-Cu matrix. Higher deformation temperature results in higher degree of recrystallization and coarser grain size. Static recrystallization and recovery can happen during the interval of deformation passes. Higher strain rate leads to finer sub-grains at strain rate below 10 s−1; however, dynamic recovery and recrystallization are limited at strain rate of 30 s−1 due to shorter duration at elevated temperatures.