Mis-layered structure of twin-twin interface with 7.4°<-12-10> misorientation relationship in Mg alloy

Twin-twin interfaces have long been thought to be responsible for strain hardening during twinning because of their roles on blocking the motion of twinning dislocations and forming boundary dislocations. However, there is still the lack of experimental observation of interface structure due to the great stress concentration on the boundaries. The 7.4° twin-twin interfaces bonding the prismatic planes of both twins in the deformed AZ31 Mg alloy were investigated combining transmission electron microscopy (TEM) observations and theoretical analysis. Mis-layered structure of {0001} planes, i.e. the basal A layer of one twin connecting the basal B layer of another twin, is found in the interface. Modeling analysis indicates that twin-twin interaction mode with the basal mis-layered connection is more energetically favorable than that without it. Meanwhile, misfit dislocations are observed in the interface. This interfacial crystal structure may result in annealed strengthening of detwinning in Mg alloy.