Softening mechanism and microstructure evolution of as-extruded 7075 aluminum alloy during hot deformation

Hot deformation behavior and microstructure evolution rule of as-extruded 7075 aluminum alloy have been investigated based on the thermal compression experiment and quantitative metallographic test. It was found that the dynamic recovery was the main softening mechanism, along with the dynamic recrystallization in the local area within the deformation temperature range of 300-450 °C and strain rate range of 0.01-10 s− 1. Deforming below 350 °C, only dynamic recovery occurred with a typical subgrain structure, above 350 °C, dynamic recrystallization happened in local area. The dynamic recrystallized grain size increased with the increase of temperature, and decreased as strain rate increasing, showing typical characteristics of continuous dynamic recrystallization. At a higher deformation temperature and a lower strain rate, geometric dynamic recrystallization occurred. A larger strain resulted in more dynamic recrystallization. The second phase particles in the alloy would hinder the slip of grain boundaries, while would promote continuous dynamic recrystallization.