Deformation structure after fracture-toughness test of Mg–Al–Zn alloys processed by equal-channel-angular extrusion

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Abstract
Fracture toughness and deformation structures have been investigated using an AZ31 magnesium alloy processed by equal-channel-angular extrusion (ECAE). The ECAE-processed alloy (as-ECAE) was annealed at 573 K for 24 h (annealed-ECAE). The average grain sizes of as-ECAE and annealed-ECAE alloys were 4.0 and 16.3 µm, respectively. The plane-strain fracture toughness K IC, obtained by stretched-zone analysis in as-ECAE and annealed-ECAE, were estimated to be 27.3 and 23.5 MPa/m1/2, respectively. From optical microstructural observations in samples after the fracture-toughness tests, deformation twins were observed in annealed-ECAE. No deformation twins were observed in as-ECAE. In addition, dislocations on basal planes, as well as on non-basal planes, were activated in as-ECAE. It is 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.