Two-stage dynamic recrystallization and texture evolution in Al-7Mg alloy during hot torsion

Hot torsion tests were performed on the Al-7Mg alloy at the temperature ranging from 300 to 500°C and strain rates between 0.05 and 5 s⁻¹ to explore the progressive dynamic recrystallization (DRX) and texture behaviors. The DRX behavior of the alloy manifested two distinct stages: Stage 1 at strain of ≤2 and Stage 2 at strains of ≥2. In Stage 1, there was a slight increase in the DRXed grain fraction (X_DRX) with predominance of discontinuous DRX (DDRX), followed by a modest change in X_DRX until the transition to Stage 2. Stage 2 was marked by an accelerated rate of DRX, culminating in a substantial final X_DRX of ∼0.9. Electron backscattered diffraction (EBSD) analysis on a sample in Stage 2 revealed that continuous DRX (CDRX) predominantly occurred within the ( \((1\bar{2}1)\) $$(1\overline{2}1)$$ ) [001] grains, whereas the (111) [110] grains underwent a geometric DRX (GDRX) evolution without a noticeable sub-grain structure. Furthermore, a modified Avrami’s DRX kinetics model was utilized to predict the microstructural refinement in the Al-7Mg alloy during the DRX evolution. Although this kinetics model did not accurately capture the DDRX behavior in Stage 1, it effectively simulated the DRX rate in Stage 2. The texture index was employed to assess the evolution of the texture isotropy during hot-torsion test, demonstrating significant improvement (>75%) in texture randomness before the commencement of Stage 2. This initial texture evolution is attributed to the rotation of parent grains and the substructure evolution, rather than to an increase in X_DRX.