Fracture toughness and deformation structures were investigated using a Mg alloy processed by equal-channel-angular extrusion. The equal-channel-angular extrusion-processed alloy (as-equal-channel-angular extrusion) was annealed (573K, 24h). The average grain sizes of as-equal-channel-angular extrusion and annealed-equal-channel-angular extrusion alloys were 4.0 and 16.3µm, respectively. The plane-strain fracture toughness, KIC, obtained by stretched-zone analysis in as-equal-channel-angular extrusion and annealed-equal-channel-angular extrusion, were estimated to be 27.3 and 23.5MPa/m1/2, respectively. From optical microstructural observations in samples after the fracture-toughness tests, deformation twins were observed in annealed-equal-channel-angular extrusion. No deformation twins were observed in as-equal-channel-angular extrusion. In addition, dislocations on basal planes, as well as on non-basal planes, were activated in as-equal-channel-angular extrusion. It was concluded that the enhancement of the fracture toughness in the fine-grain structure was related to a reduction of deformation twins and dislocation movement in non-basal planes.

Deformation Structure after Fracture-Toughness Test of Mg–Al–Zn Alloys Processed by Equal-Channel-Angular Extrusion. H.Somekawa, A.Singh, T.Mukai: Philosophical Magazine Letters, 2006, 86[3], 195-204