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.

Synchrotron diffraction was used to construct the first 2D texture maps of entire magnesium AZ80 friction stir welds and showed that basal slip is favoured along most of the advancing side interface, and to a lesser extent on the retreating side interface. Zones of grains optimally oriented for basal slip are known to be a major contributor to strain localisation leading to failure during transverse tensile tests. Profilometry results confirm that the basal plane orientation dominates strain localisation. Microtexture maps traversing the weld interfaces were used to describe the material flow within the weld using scatter from the ideal shear texture fibre. The current results are highly applicable to modelling the strength and ductility of these joints under transverse loading.

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Research is currently being conducted on the feasibility of hydroforming extruded magnesium tubes to integrate multiple parts into a single hydroformed section. Among other applications, such sections would reduce the weight of both cars and planes, particularly when used in the vehicle frame. This would lead to either reduced fuel costs, or the ability to carry an increased payload. Magnesium generally has limited ductility, which in the case of the current extruded tubes is even further reduced at the extrusion seams. These are locations where the material flow separates and rejoins during extrusion and are unavoidable when a hollow profile die is used. When the tubes were stressed in a circumferential direction, tube ruptures consistently occurred along the extrusion seams of the tubes. This led to the current project, an inquiry into the exact cause of failure at these locations. The creation of irregularities at the seams, such as precipitate dispersions, local texture changes, grain size changes and entrained material, is discussed. These irregularities are considered together with their roles in producing the failures. The results are summarized and the most fruitful directions for future work are outlined.