Softening Behavior during Annealing of Overaged and Cold-rolled Aluminum Alloy 7075

Abstract

This work proposes studying the softening kinetics of aluminum alloy 7075-T6. Firstly, AA 7075 strips were overaged (300°C and 5 hours). Then, the overaged strips were cold-rolled at room temperature (45% in thickness reduction) and, after that, annealed at different temperatures (200°C and 250°C) and time intervals (30 minutes - 4 hours). By using polarized light microscopy, EBSD and Vickers hardness measurements, the softening mechanisms were determined and proper mathematical models (Kuhlmann, Johnson-Mehl-Avrami-Kolmogorov and Austin-Rickett) were used to analyse the experimental data. The results show that although almost all observed softening can be attributed to recovery, the phenomena is well described by using mathematical models for phase transformations (JMAK and Austin Riccket). In order to promote recrystallization of overaged AA 7075, an additional thickness reduction (75%) were used. These samples were annealed isocronically during 1 hour (100 - 400°C) and it was found that recrystallization only took place at 400°C.