Dejia Liu

Fracture localisation in retreating side of friction stir welded magnesium alloy

Abstract Friction stir welding was successfully applied to joint Mg–3Al–1Zn alloy sheets. Serious strain localisation was observed during transverse tensile tests of the welds. Fracture was initiated from the interface of thermal–mechanical affected zone and stir zone in retreating side. The reasons for such localised fracture behaviour were explained by analysing the texture, Schmid factor, grain size and strain localisation characteristics in retreating side and advancing side. The results suggest that the coarser grain size and higher Schmid factor resulted in the easier activation of basal slip in retreating side than advancing side, which caused more serious strain localisation and stress concentration, and hence promoted fracture initiation from the interface of thermal–mechanical affected zone and stir zone in retreating side.

Microstructural investigation and mechanical properties of dissimilar friction stir welded magnesium alloys

Abstract Dissimilar joints of magnesium alloys were obtained by friction stir welding. Detailed microstructure and texture examinations were performed on the joints. Significant difference in microtexture distribution and microstructural features is observed between crown and stir zones in the dissimilar joints. However, an overall effect of these factors on mechanical properties of layered joints is not obvious as both the up and middle samples present quite similar yield strength and strain hardening behaviour. Moreover, both samples fracture in the Mg–3Al–1Zn alloy side. The fracture of the middle sample starts at the boundary of transition and stir zones, while the up sample starts in the crown zone side.