Fracture localisation in retreating side of friction stir welded magnesium alloy

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.