Flow Behavior and Microstructure Characterization of 7085 Aluminum Alloy Under Various Deformation Conditions

Thermal forming can improve the formability of Al alloy, but researchers do not thoroughly understand the effect of deformation parameters on the flow stress and microstructure evolution of die-casting 7085 Al alloy. In this study, we simulated compression with a Gleeble-3800 thermal simulator between 523 K and 723 K, and strain rates from 0.001 to 1 s −1 . We established an Arrhenius flow stress constitutive equation of the alloy. We were particularly interested in understanding the relationship between the flow stress and microstructure evolution. We used electron backscattered diffraction to study the microstructure evolution and grain refinement mechanism during thermal compression. We divided the dynamic softening mechanism of 7085 Al alloy into three stages in accordance with increasing compression temperature, which is associated with dynamic recovery (DRV) and dynamic recrystallization (DRX). In stage I (≤ 623K), many chaotic LAGBs randomly dispersed in the deformed microstructure at a low temperature. In stage II (673K), well-defined subgrains and recrystallized grains formed by DRV and DRX (including continuous DRX and discontinuous DRX), respectively. When we increased the deformation temperature to 723K (stage III), the discontinuous dynamically recrystallized (DRXed) grains developed from the original boundaries to the interior, whereas the continuous DRXed grains extended in the opposite direction, which resulted in formation of clustered DRXed grains with annihilation of the subgrains. Furthermore, formation of DRXed grains considerably decreased the peak stress at a higher deformation temperature; such DRXed grains had strong {100} texture, which was unfavorable to continuous deformation and resulted in a gradually increasing flow curve.