Flow Behavior and Microstructural Evolution of 7A85 High-Strength Aluminum Alloy During Hot Deformation

Hot deformation behavior of 7A85 high-strength aluminum alloy was investigated at 593 K to 713 K (320 °C to 440 °C) and 0.01-10 s−1. The manifestation of flow curves was related to the strain rate. Typical single-peak curves were shown below 10 s−1, while two stress peaks appeared in the case of 10 s−1 and the second peak strain was almost three times larger than the first one. A constitutive equation considering the effect of strain was developed. Flow stress values predicted by the constitutive model demonstrated a good agreement with the experimental results over the entire range of strain rates and temperatures. Microstructure characterization revealed that dynamic recovery (DRV) and continuous dynamic recrystallization (CDRX) which depended on the Zener–Hollomon parameter (Z) closely, co-occurred at large strain (e = 0.7). With decreasing Z-value, the dominant dynamic restoration mechanism gradually transformed from DRV to CDRX. The average subgrain size (d sub) showed a power-law relationship with Z. Recrystallization was sensitively dependent on the strain rate at above 683 K (410 °C). The fine equiaxed grains appeared at original grain boundaries and in deformed grains interior owing to CDRX. The high-curvature subgrain boundaries can also cause the nucleation of recrystallization within deformed grains.