Plastic deformation and fracture mechanisms of rolled Mg-8Gd-4Y-Zn and AZ31 magnesium alloys

[Display omitted] •After detwinning, some twins re-nucleate in the original position, and the re-selection of twin variants is related to the change of the local stress field.•The occurrence of cracks in Mg-8Gd-4Y-Zn and AZ31 alloys can be evolved from ledges, but the positions of ledges are different.•Cracks in AZ31 alloy tend to occur around grains with severe dislocation accumulation due to twinning and a few adjacent grains with incompatible strains.•The ledges in rare earth magnesium alloys may be caused by penetration slip and may also arise in adjacent grains of the matrix with twinning activity. The wrought rare-earth and rare-earth-free magnesium alloys exhibit differences in plasticity due to different slip and twinning behaviors. In this paper, the microstructure evolution and plastic deformation mechanism of as-rolled rare earth (Mg-8Gd-4Y-Zn) and rare earth-free (AZ31) magnesium alloy sheets during room temperature deformation were investigated by in-situ tensile EBSD observations. The results show that the tensile twin in AZ31 alloys exhibits various evolutionary behaviors to adapt to crystal deformation, however, the twin boundaries in Mg-RE alloys cannot move during deformation due to the pinning effect of the precipitates. In addition, the slip between adjacent grains in Mg-RE alloys is difficult to transmit and multiple penetrating slips are prone to occur in the same grain, resulting in the generation of ledges. In AZ31 alloys, the slip variants between adjacent grains are strain compatible, and in addition to the contribution of twinning to coordinated plastic deformation, twinning stimulates the generation of slip to coordinate deformation. Cracks in AZ31 alloys tend to occur around grains with severe dislocation accumulation due to twinning and a few adjacent grains with incompatible strains, and crack in Mg-RE alloys are easily generate at the strain incompatibility between grains with multiple penetration slips and adjacent grains.