Generation of fine extension twins in rolled magnesium alloy AZ31B at room temperature by simple shear

•Extension twinning in Mg alloy under multi-axial stress was statistically studied.•Thin twins with a mode thickness value below 1.5 μm persisted in ND45 simple shear.•ND45 simple shear suppresses twin growth while brings sustained twin nucleation.•Twinning CRSS can be determined via statistical analyses as in the present study.•Dense and fine twins can form in Mg alloy under appropriate multi-axial stress.