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

•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.