Microstructure Evolution of New Al-Zn-Mg-Cu Alloy During Hot Deformation

Microstructure evolution during hot deformation of a new Al-Zn-Mg-Cu alloy was investigated by Gleeble-1500D thermal-mechanical simulator at 300-450℃ and strain rate of 0.001-10s-1.The microstructure features at different hot deformation conditions were analyzed with optical microscope (OM) and transmission electron microscope (TEM).The results show that the dislocation density decreases and the subgrain sizes increase with the increase of deformation temperature and the decrease of the strain rate;the main softening mechanism of the alloy is dynamic recovery and dynamic recrystallization.Only dynamic recovery occurs when the temperature is 300-400℃.Dynamic recrystallization occurs when the strain rate is 0.001-10s-1 at 450℃.The nucleation mechanism is grain boundary bowing,subgrain growing and subgrain incorporation during dynamic recrystallization.