Effect of Zn content on the static softening behavior and kinetics of Al-Zn-Mg-Cu alloys during double-stage hot deformation

Zn content has significant influence on the hot workability and final properties of Al-Zn-Mg-Cu alloys. In the present work, single and double stage hot compression tests have been performed on Al-Zn-Mg-Cu alloys with various Zn contents at temperatures of 300 degrees C and 400 degrees C, and strain rates of 0.01 s(-1) and 0.1 s(-1), respectively. The results showed that the static softening curve plateau was observed, both the duration of static softening plateau and softening fraction decreased with increasing Zn content at deformation temperature of 300 degrees C. When deformation temperature increased to 400 degrees C, the static softening curves appeared approximate typical sigmoidal shape with slight influence from Zn content. By combining additional in-situ electrical resistivity measurement, hardness testing and microstructural observations, the static softening mechanisms were found to be the functions of static recovery and precipitates coarsening at lower temperature, and static recovery and static recrystallization at higher temperature. The increased Zn addition mainly affected static softening mechanisms at 300 degrees C by forming precipitates. The simplified static softening kinetics were also investigated based on Johnson-Mehl-Avrami-Kolmogorov model which coupling static recovery and static recrystallization. (C) 2019 Elsevier B.V. All rights reserved.