Direct observation of twinning-detwinning-retwinning on magnesium single crystal subjected to strain-controlled cyclic tension-compression in [0001] direction

Cyclic deformation of magnesium single crystal under fully reversed tension-compression along the [0 0 0 1] direction at a strain amplitude of 0.5% was investigated in ambient air. In situ light microscopy of {10 (1) over bar2} twins was conducted on the (10 (1) over bar0) prismatic plane. Fundamental morphology evolution of twinning-detwinning-retwinning was characterized in situ. The critical resolved shear stress of {10 (1) over bar2} twinning was found to be similar to 2.4 MPa. With increasing loading cycles, the activity of twinning-detwinning-retwinning exhausted and the residual twins accumulated. During detwinning at each loading cycle, the residual twins were observed to form on the vicinities of twin boundaries which had been fully expanded at the previous tensile peak. Microcracks were found on the boundaries of residual twins and the basal slip bands.