Deformation Mechanism of Mg-Gd-Y-Zn-Zr Alloy Containing Long-Period Stacking Ordered Phases During Hot Rolling

The orientation-dependent deformation mechanisms including {101 over bar 2}twinning, prismatic < a & rang; slip and kink in hot rolling of a Mg-5.5Gd-4.4Y-1.1Zn-0.5Zr (wt pct) alloy containing long-period stacking ordered (LPSO) phases were examined in this study. For grains with c-axes close to the rolling direction, {101 over bar 2} twinning is the major deformation mode. As for grains with c-axes close to the transverse direction, prismatic < a & rang; slip and kink dominate the plastic deformation. Kink serves as a supplementary of prismatic < a & rang; slip and only appears at a larger rolling reduction. The close value of CRSS for prismatic twinning was identified to be the cause of the competitive relationship between the two deformation modes at the temperature of 450 degrees C. The influence of LPSO phases on twinning was further evaluated by TEM. Twinning generally occurs in the lamellar matrix between LPSO phases with thickness above 100 nm and vanishes in the lamella with a very small thickness, such as 42 nm. Therefore, the occurrence of twinning is dependent on the thickness of the lamellar matrix between adjacent LPSO phases. As the distribution of LPSO phases in the tested material is relatively sparse, the activation of {101 over bar 2twinning deformation cannot be suppressed effectively.