Role of slip and {10-12} twin on the crystal plasticity in Mg-RE alloy during deformation process at room temperature

The deformation mechanism of slips and twins has a considerable influence on the plasticity of magnesium alloys. However, the roles of slips and twins in the room-temperature deformation of Mg-rare earth (Mg-RE) alloys with high contents of rare earth elements is rarely investigated. Here, the microstructural evolution and deformation mechanism of an aged Mg-5Y-2Nd-3Sm-0.5Zr alloy during uniaxial compression at room temperature were systematically investigated using in-situ electron-backscattered diffraction and transmission electron microscopy. The results indicated that in the early stage of deformation, the Mg-RE alloy was mainly controlled by the slip of <a> dislocations in the basal plane and the coordinated c-axis strain of the {10-12} twin. With an increase in the strain, the grain orientation became more suitable for the initiation of pyramidal II <c + a> dislocations in the later stage of deformation; these dominated the deformation mechanism. In the twin evolution of the Mg-RE alloy, there were three types of twin-twin interaction behaviors: (i) single twin variant ‘parallel’ structure, (ii) single twin variant ‘cross’ structure, and (iii) multi twin variant ‘cross’ structure. In addition, three types of twin-grain boundary interaction behaviors were summarized: (i) twin ‘refracting through’ grain boundary, (ii) twin ‘parallel through’ grain boundary, and (iii) twin ‘fusing through’ grain boundary, which are expected to act as new means and solutions for the twin strengthening of magnesium alloys.