Towards understanding twinning behavior near fracture surface in magnesium

Abstract Deformation twin is one of the most important strain accommodation mechanisms and ultimately influences the mechanical properties for magnesium and its alloys. Especially, { 10 1 ¯ 1 } twin is usually thought to be closely related to the fracture or fatigue process of magnesium alloys. In the present work, the characteristics of microstructure near fracture region of deformed magnesium alloy have been investigated by a combination of electron back-scatter diffraction (EBSD) and transmission electron microscope (TEM). It has found that a large of deformation twins occur near fraction region, including { 10 1 ¯ 2 } and { 10 1 ¯ 1 } primary twins, { 10 1 ¯ 1 } - { 10 1 ¯ 2 } double twin and { 10 1 ¯ 1 } - { 10 1 ¯ 2 } - { 10 1 ¯ 1 } - { 10 1 ¯ 2 } quadruple twin. The actual boundaries of { 10 1 ¯ 1 } twins at atomic scale consist of { 10 1 ¯ 1 } coherent twinning boundaries (TBs) and parallel basal-pyramidal (BPy/PyB) planes. The tip of { 10 1 ¯ 1 } twin can even end up with BPy/PyB interfaces only. The experimental observations also reveal that when two { 10 1 ¯ 1 } twin variants sharing a common [ 11 2 ¯ 0 ] zone axis approach each other, the growth of one twin is usually hindered by the boundaries of the other twin. In addition, an apparent “crossing” phenomenon is also discovered when interaction of two { 10 1 ¯ 1 } twins takes place. According to these experimental observations, the possible underlying mechanisms behind such phenomena are proposed and discussed. These finding are expected to provide an insight into understanding the twinning behavior and the relationship between twin and fracture in magnesium and other materials with hexagonal structure.