Recrystallization behavior of an Al-Zn-Mg-Cu alloy during hot deformation and subsequent heat treatment

Abstract

The presence of excessive residual recrystallization structure in the aero-structural part of the Al-Zn-Mg-Cu alloy negatively affects its strength and stress corrosion resistance. To achieve higher service performance, it is significant to reveal the recrystallization behavior of the Al-Zn-Mg-Cu alloy during hot working and subsequent heat treatment. In this work, the isothermal compression tests of an Al-Zn-Mg-Cu alloy were performed at the temperature range 300–450 °C and strain rate range 0.01–10 s−1. The subsequent heat treatment of the deformed specimens was conducted. The microstructure was characterized by EBSD and XRD techniques. The natural logarithm of Zener-Hollomon parameter (lnZ) was introduced, which increases with the increasing strain rate and decreasing temperature. During hot deformation, CDRX was identified to be the predominant DRX mechanism at high lnZ values, the corresponding recrystallization volume fraction was approximately 15 %. However, at low lnZ values, DDRX becomes the dominant mechanism, the corresponding recrystallization volume fraction was only around 5 %. Moreover, a kinetics analysis was conducted using a low proportion DRX model coupled with lnZ. By comparing the results obtained from finite element simulations with experimental findings, this model was proved to accurately predict the volume fraction of DRX during hot deformation. During the heat treatment process, due to the substantial storage of deformation energy, a significant portion (up to 84.5 %) of SRX was observed under high lnZ conditions. As the lnZ value decreases, the SRX weakens. This weakening is significant enough that under high temperature and low strain rate, the occurrence of SRX becomes extremely unlikely, which can be attributed to the low storage of deformation energy.