Deformation mechanism near crack-tip by finite element analysis and microstructure observation in magnesium alloys

The effects of microstructural factors, i.e., grain size and texture, on the deformation behavior near the crack-tip region during the fracture toughness test were investigated using wrought Mg–3 wt.%Al–1 wt.%Zn alloys, which were produced by extrusion or equal-channel-angular extrusion (ECAE). The stress distributions related to deformation twins were predicted by finite element analysis (FEA), and the microstructural evolutions were confirmed by experiment. Deformation twins were formed at the beginning of the fracture toughness test due to the creation of a large stress field near the crack-tip region. The formation region of deformation twins became small with grain refinement due to the changes in the dominant plastic deformation mechanisms. The results from microstructure observations showed similarities to the stress distribution, which used simple stress–strain relations that assumed a mechanical asymmetry following the Hill's potential function. The texture, i.e., basal plane distribution, also affected the formation of deformation twins. The formation region of deformation twins in the ECAE-ed alloy was predicted to be smaller than that in the extruded alloy by FEA, and this tendency was very similar to that in the microstructural observations of the deformed samples. These results can be used to predict the macroscopic deformation features near the crack-tip, and could be helpful for developing magnesium alloys with high performance mechanical properties.