Towards understanding double extension twinning behaviors in magnesium alloy during uniaxial tension deformation

Multiple {101¯2} twin variants can be activated when the external tension loading is parallel to the normal direction of magnesium alloy plate. In the current work, we report that in addition to abundant primary {101¯2} twins, an atypical double twinning sequence, i.e. {101¯2}-{101¯2} double twin can also occur during uniaxial loading. The results of electron backscatter diffraction (EBSD) observation indicate that these secondary twins prefer to be formed at the regions where two primary {101¯2} twins belonging to different twin variant pairs interact with each other. Meanwhile, abundant dislocations activated can also be found within the primary twin containing secondary {101¯2} twin. Accordingly, the possible formation mechanisms of such secondary {101¯2} twin are proposed and discussed based on the local strain accommodation evaluated by a combination of geometrical compatibility parameter (m’) and Schmid factor. The analysis results suggest that the formation of these secondary twins may be closely related to the minimization of local strain incompatibility at the twinning boundary caused by the basal dislocation within the primary twins.