Physically based constitutive analysis and microstructural evolution of AA7050 aluminum alloy during hot compression

The hot compression tests of AA7050 aluminum alloy were conducted under conditions of 603-693 K and 0.001-10 s(-1) and the related microstructures were observed. Physically based constitutive analysis was conducted to describe the flow behaviors, which can relate the microstructural evolution with flow behaviors for high stacking fault energy (SFE) and/or precipitation-strengthened alloys. A revised model considering the coupling effects of lattice diffusion and grain boundary diffusion was proposed to characterize the transition of diffusion mechanisms under different deformation conditions. The main diffusion mechanism is determined as lattice diffusion at 633-693 K and grain boundary diffusion at 603 K. The microstructural evolution can be reflected by the deviation of creep exponent n from the theoretical value (n=5). The reasons for the creep exponent n>5 could be related to the change of internal stress and creep rate by dynamic precipitates at lower temperatures. At higher strain rates, it could be related to the impediment of dislocations motion by defects and the change of rate controlling mechanism. The operation of grain boundary sliding (GBS) may lead to n<5 at higher temperatures and lower strain rates. Moreover, the mechanisms of dynamic recrystallization under wide conditions and high strain -rate superplasticity were discussed. (C) 2016 Elsevier Ltd. All rights reserved.