Effect of strain rate on the recrystallization mechanism during isothermal compression in 7050 aluminum alloy

Isothermal compression tests were carried out on 7050 aluminum alloy at the temperature range of 300 °C to 450 °C and the strain rate range of 10−3 s−1 to 5 × 10−6 s−1. The microstructure of samples was observed using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) techniques. Results showed that the recrystallization mechanism changes from continuous dynamic recrystallization (CDRX) to discontinuous dynamic recrystallization mechanism (DDRX) as the Z (Zener-Hollomon parameter) value gradually decreases. For Z values larger than 2.76 × 1010 s−1, the dominant mechanism is CDRX and the ratio of high angle grain boundaries (HAGB) is larger than 28%. The mechanisms of DDRX and CDRX are occurred at the same time while the Z value change from 2.76 × 108 s−1 to 4.10 × 109 s−1, and HAGB% is between 28% and 41%. For Z values less than 2.77 × 107 s−1, the mechanism is DDRX and HAGB% is larger than 41%. For isothermal compression at 5 × 10−6 s−1 and a temperature of 350 °C or 400 °C, a large number of fine grains are formed for the growth of these recrystallized grains were hindered, because of the presence of Al3Zr particles, which precipitate during isothermal compression.