Dynamic recrystallization mechanisms of as-forged Al–Zn–Mg-(Cu) aluminum alloy during hot compression deformation

The thermal deformation behavior of as-forged Al–Zn–Mg-(Cu) aluminum alloy at strain rate 0.001–1 s−1, temperature 663–783 K and deformation degree 0–60% was studied by isothermal compression test, and an accurate strain-compensated Arrhenius constitutive equation was established. Based on the microstructure characteristics of compressed specimens, the effects of strain rate, temperature and strain on dynamic recrystallization (DRX) behavior and substructure evolution were determined. The results show that the alloy undergoes discontinuous dynamic recrystallization (DDRX), continuous dynamic recrystallization (CDRX) and geometric dynamic recrystallization (GDRX) simultaneously at high temperature and low strain rate (743 K, 0.001–0.01 s−1), where CDRX includes microshear band assist (MSBA), homogeneous increase of misorientation (HIM) and progressive lattice rotation near grain boundaries (LRGB). However, with decreasing temperature and increasing strain rate, GDRX basically disappears, and DDRX becomes the main DRX mechanism. At medium to high strain rate (0.1∼1 s-1), high-density dislocations accumulate at the grain boundaries and numerous microshear bands form inside grains during the early deformation stage. The misorientation angles of these pre-existing geometrically necessary boundaries gradually increase with temperature and strain, ultimately transforming into subgrains and DRX grains.