Rheological behavior and dynamic softening mechanism of AA7075 sheet under isothermal tensile deformation

Rheological behavior and dynamic softening mechanism of high-strength AA7075 sheet were investigated by performing isothermal uniaxial tensile tests at deformation temperatures of 573-723 K and strain rates of 0.01-10 s(-1). On the basis of the obtained flow stress, response surface models for the ultimate tensile stress (UTS) and fracture strain were developed as a function of temperature and strain rate, respectively. Error analysis certified the reliability of the models. Besides, a constitutive model coupling with dislocation evolution was built to predict the deformation behavior of the alloy, and the dislocation evolution law was revealed based on the established constitutive model. In addition, the dynamic softening mechanism of the alloy during hot deformation was exposed according to the Zener-Hollomon parameter map, microstructural observation and apparent activation energy. Owing to precipitates pinning effect on the motion of dislocation and migration of subgrain boundaries, the dominant softening mechanism is concluded to be dynamic recovery (DRV), relating to cross-slip of screw dislocation. (C) 2020 The Author(s). Published by Elsevier B.V.