Strain localization in friction stir welded magnesium alloy during tension and compression deformation

As a solid-state process, friction stir welding can avoid solidification problems and therefore has great potential in welding of Mg alloys. However, strong texture is usually formed in Mg welds, which results in localized plastic deformation, and significantly deteriorates the mechanical properties of welds. The present paper seeks to understand the characteristics of strain localization in deformed Mg welds and underline mechanisms. AZ31 Mg alloy sheets were friction stir welded and then were subjected to transverse tensile and compressive deformation. During the transverse deformation, severe and complex strain localization was observed in Mg welds during tensile and compressive deformation, which resulted in “concave-convex” appearances in longitudinal section. The largest strain corresponds to the region easy to activate basal slip for both kinds of deformed samples. Extension twinning contributed the strain in the side of stir zone for tension but in the center of stir zone for compression. The characteristics of strain localization were explained based on the activation of basal slip and extension twinning with respect to local texture.