Effect of deformation temperature on the dynamic recrystallization mechanism and dynamic precipitation behavior of Mg-Gd-Nd-Zr alloy

Abstract

The deformation temperature is an important factor influencing the thermal deformation behavior of alloys. In this paper, thermal compression tests of Mg-Gd-Nd-Zr alloy were carried out at 350 ∼ 500 °C using the Gleeble-3800 thermal simulator, and the dynamic recrystallization (DRX) mechanism and microstructure evolution of the alloy were investigated by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results show that the basal slip a and pyramidal slip a+c were consistently high activity at the test temperatures. As the temperature increased, the pyramidal slip a was gradually activated. At 350 °C, monolayer necklace-like dynamic recrystallized (DRXed) grains were formed around the initial grains via discontinuous dynamic recrystallization (DDRX). At 400 ∼ 450 °C, the monolayer DRXed grains expanded into the initial grain via continuous dynamic recrystallization (CDRX) to form multilayer necklace-like DRXed grains. However, at 500 °C, no necklace-like structure was formed around the initial grains. The initial grains were split into subgrains by low angle grain boundaries (LAGBs), which continuously absorbed dislocations and rotated for DRX. In addition, at 350 ∼ 400 °C, the alloy produced significant precipitation bands (mainly β phase). Above 450 °C, the dynamic precipitation was significantly attenuated. Precipitates greater than 200 nm could well impede dislocation movement and induce DRX nucleation. Nevertheless, the precipitates at the grain boundaries of the DRXed grains in turn pined the grain boundaries, refining the DRXed grains.