Hot deformation behavior and microstructure evolution of Mg–Gd–Sm(–Zn)–Zr alloy

The dynamic recrystallization (DRX) and dynamic precipitation of Mg–5Gd–3Sm(–1Zn)–0.5Zr alloy after hot compression deformation were analyzed by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) techniques. Furthermore, the DRX mechanisms were investigated by calculated the deformation activation energy, established the constitutive equation, and created a critical strain model. The results indicate that the presence of Zn element enhanced the production of DRX, considerably reduced the strength of 0001 plane texture, and boosted the Schmidt factor of nonbasal plane slip. The Mg–5Gd–3Sm–0.5Zr alloy had a low degree of DRX, manifested as a monolayer of DRX grains at the grain boundaries and dominated by the discontinuous DRX mechanism. However, the Mg–5Gd–3Sm–1Zn–0.5Zr alloy had a high degree of DRX, which occurred in the form of multilayered DRX grains by the main mechanism of continuous DRX. Compared with the Mg–5Gd–3Sm–0.5Zr alloy, in addition to the Mg₅(Gd,Sm) phase, the Mg–5Gd–3Sm–1Zn–0.5Zr alloy also introduced a new dynamic precipitation phase called (Mg,Zn)₃(Gd,Sm) phase. The dynamic precipitation phase prevented grain boundary migration and dislocation motion, which promoted DRX nucleation and prevented the growth of recrystallized grains.