Effects of accumulative rolling reduction on the microstructure characteristic and mechanical properties of Mg-Gd-Y-Zn-Zr sheets processed by hot rolling

Abstract

The Mg-Gd-Y-Zn-Zr sheets with different accumulative rolling reduction were successfully prepared through the multi-passes hot rolling process. The accumulative rolling reduction significantly affects the mechanical properties of the resulting sheets through altering the fraction of dynamic recrystallization (DRX) grains and distribution of the broken interdendritic 14H-LPSO phase. In addition, the precipitated equilibrium β phase at grain boundaries can facilitate the DRX process through the particle-stimulated nucleation (PSN) mechanism. The sub-grain boundaries formed in the vicinity of the grain boundaries and within the coarse deformed grains, and then transformed into the high-angle grain boundaries (HAGBs) through incorporating the adjacent dislocation. The coarse deformed grains were also divided into several grains by the formation of HAGBs and the DRX grains at grain boundaries also spread into the coarse deformed grains, and thus the fraction of the DRX grains improved with the increase of the accumulative rolling reduction. The ambient temperature tensile strength anisotropy of the resulting sheets increases with further accumulative rolling reduction. The effectively broken interdendritic 14H-LPSO phases, which acts as the reinforcing short-fiber, significantly strengthen the tensile yield strength along the RD due to its decreased aspect ratio (d/l) and more dispersed distribution aligned along the RD. Thus, the tensile yield strength along the RD demonstrated the higher increment than that along the TD and 45° with increasing accumulative rolling reduction. The broken interdendritic 14H-LPSO phases aligned along the RD also contribute to the higher fracture elongation along the 45° due to its alignment parallel to the resolved maximum shear stress during tension. Furthermore, the larger accumulative strain is conducive to decreasing the tensile anisotropy of the resulting sheets at elevated temperature.