The activation of compression twin pairs and plasticity improvement of directionally solidified Mg alloy

The <112¯0> orientated Mg-4.70Zn-0.38Y-0.14Zr alloy with high product of strength and elongation (PSE = 5346 MPa•%) was prepared using directional solidification technology. Electron Back Scatter Diffraction (EBSD) and High Resolution Transmission Electron Microscopy (HRTEM) were applied to explore the deformation mechanism and plasticity improvement of experimental alloys. Experiment results showed that the dominant deformation systems were non-basal slipping systems and compression twin pairs (CTPs). High critical resolved shear stress (CRSS) of non-basal slipping system increased the yield strength (180 MPa) and tensile strength (198 MPa). The CTP followed the geometrical relationship of TP1 (twinning plane of variant1)∥TP2 (twinning plane of variant2) and appeared in a wider misorientation range than tensile twin pair which was classified as twinning shear transmission and had high geometric coordination factor (m’). Calculation results showed that the stress concentration at the junction of CTP and grain boundaries was the same as inside the compression twin. 60% of x/<11 2¯ 0> (0°≤x < 180°) grain boundaries in experimental alloy satisfied this geometrical relationship, leading to the general activation of CTP and plasticity improvement (elongation is 27%).