The ductile fracture mechanism in a fine-grained magnesium alloy was investigated by transmission electron microscopy-focused ion beam techniques. In coarse-grained or conventional magnesium alloys, twins form at the very beginning of the deformation process, and crack propagation occurred through the twin boundaries. However, in the alloy used here, sub-grain structures were found instead of twins at the crack tip. Nanoscale twins formed subsequently owing to large stress in the crack propagation route. The fine-grained alloys showed high fracture toughness resulting from resistance to the twins at the beginning of the deformation.

Ductile Fracture Mechanism in Fine-Grained Magnesium Alloy. H.Somekawa, K.Nakajima, A.Singh, T.Mukai: Philosophical Magazine Letters, 2010, 90[11], 831-9