Tailoring microstructural evolution and fracture damage behavior of a Mg–Y–Zn alloy during hot tensile deformation

Abstract

Hot tensile tests are employed herein to explore the microstructural evolution and fracture damage of a hot–extruded Mg-9.1Y-1.8Zn (wt%) alloy at deformation temperatures of 250–400 °C and strain rates of 0.005–0.1 s−1. The deformed microstructure and fracture morphology are systematically studied using electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The flow stress tends to decline with increasing tensile temperature or decreasing strain rate. Under all the tested conditions, discontinuous dynamic recrystallization (DDRX) is characterized by a bulged grain boundary and plays a critical role. Particle-stimulated nucleation (PSN) induced by the twisted long-period stacking ordered structure (LPSO) is another essential nucleation mechanism for DRX, especially at low strain rates. Since DRX is more straightforward at high temperatures, the fracture mechanism can be easily observed to change from intergranular to transcrystalline at tensile temperatures exceeding 250 °C. However, the effects of strain rate on the fracture mechanism seem inconspicuous at strains rates of 0.005–0.1 s−1. Based on the Oyane-Sato criterion, a fracture damage model is established based on the experimental and numerically simulated results. The results signify that the developed damage model can accurately forecast fracture damage during hot tensile deformation, which is valuable for optimizing the hot forming processing of the tested Mg-RE alloy.