Relationship between deformation twinning and surface step formation in AZ31 magnesium alloys

Rolled sheets of AZ31 Mg alloys were deformed at room temperature under tension along the rolling direction. A number of large surface steps were observed in the region near the fractured edge. Transmission electron microscopy showed the presence of twins under these steps. Crystallographic analysis indicated that the twins are of the {101̄1}-{101̄2} double twin type with their basal planes tilted by 37° with respect to the basal planes of the matrix, which is considered to make basal dislocation slip highly active within the twin. The localized deformation within the twins may lead to the formation of crack-like faults and to failure in a macroscopically brittle manner.