Strain localisation and failure of dissimilar magnesium-based alloy friction stir welds

Dissimilar butted combinations of magnesium alloys AZ31, AZ61 and AZ80 were friction stir welded and transverse tensile tested until failure. Strain mapping across the deforming weld nugget and interfaces was carried out to correlate the deformation to the local microstructures. Mechanical performance was found to be highly dependent on the spatial distribution of alloys within the nugget and thus highly sensitive to changes in the tooling geometry. Process control requirements for repeatable, high-quality dissimilar friction stir welds will therefore be far more rigorous and challenging than those of similar welds of these alloys. In addition, proximity to the tool insertion point was found to decrease tensile performance, likely due to changes in tooling temperature.