Comprehensive study of hot deformation behavior and microstructure evolution of solutioned AA7050 alloy based on HFQ process

The hot deformation behavior and microstructure evolution of AA7050 alloy were investigated through the combination of solid solution treatment (480 ℃/1 h) in hot form and quench (HFQ) process with isothermal compression under the temperature range of 250–450 ℃ and strain rate of 0.01–10 s ⁻¹. In this study, the Arrhenius constitutive model and processing map of the solutioned alloy were established. Besides, the microstructure evolution and dynamic recrystallization mechanism (DRX) were determined by transmission electron microscopy (TEM) and electron back scattered diffraction (EBSD). The results show that the optimum processing parameter was in the range of 390–450 ℃ and 0.01–0.1 s ⁻¹, and cracks were easily found at high strain rate due to the adiabatic shear bands (i.e. 250 ℃/10 s ⁻¹, 300 ℃/10 s ⁻¹). The precipitation of η` and η were observed on Al matrix during hot deformation, and the size of η` and η becomes larger with the decreasing strain rate and increasing temperature due to the high diffusion speed and sufficient time. The shape of η phase gradually changes from spherical to lath shape at the conditions of 450 ℃/0.1 s ⁻¹ and 450 ℃/0.01 s ⁻¹. The parameter lnZ dramatically affects the DRX mechanism during hot deformation. At low lnZ (25.96–30.87), the DRX mechanism is dominated by GDRX with the features of brick-like grains, which relies on grain boundary migration and sub-grain rotation. At middle ln Z (32.84–37.77), a large number of substructures were observed inside the grain, CDRX plays an important role in recrystallized progress, relying on sub-grain rotation. Grain boundary bulging occurs at high lnZ situation (38.57–44.56), the main DRX mechanism shifts to DDRX through grain boundary migration.