The effects of deformation parameters on the second phases and softening behavior of Al–Zn–Mg–Cu alloys

This study investigates the effects of deformation parameters on the second phase and softening behavior of Al–Zn–Mg–Cu alloy. The results are as follows: Firstly, the area fraction of the intermetallic phase fluctuates between 0.704 ± 0.092% and 1.886 ± 0.231% with varying deformation parameters. Secondly, in the temperature range of 270 °C to 430 °C, the area fraction of the η[Mg(Zn, Al, Cu)2] phase first increases and then decreases with rising deformation temperature, and gradually increases with decreasing strain rate. The highest area fraction is 12.613 ± 0.340% at 350 °C/0.001 s−1, and the lowest is 0.366 ± 0.068% at 470 °C/0.001 s−1. Additionally, the coarsening and dissolution of the η[Mg(Zn, Al, Cu)2] phase accelerate the dynamic recovery softening of the alloy. The sample at 350 °C/0.001 s−1 shows a low-angle grain boundary (LAGBs) percentage of 97.83% and a minimum average dislocation density of 8.493 × 102 μm2. Furthermore, at 470 °C/0.001 s−1, the Al7Cu2Fe phase has a weaker effect on stimulating nucleation and recrystallization, while the most significant promotion occurs at 430 °C/0.001 s−1. In the range of 270 °C to 350 °C and 0.1 s−1 to 0.5 s−1, the Al7Cu2Fe phase mainly stimulates the formation of sub-grains. These findings offer valuable insights for refining the grain size of alloys by regulating the content of the second phase during hot deformation.