FSW welding of Al-Mg alloy plates with increased edge roughness using square pin tools of various shoulder geometries

In the paper, the influence of tool shoulder geometries on the mechanical properties and weld surface roughness of an Al-Mg alloy was studied. Different types of tools were used: with straight and concave profiles. Three concave-shoulder types were applied, with volume ratios of 0.5 and 0.9 of the square pin to the shoulder reservoir and one with three concentric semi-toroidal reservoirs with a volume ratio of 0.5 of the pin to the shoulder reservoir. The tensile and bend properties, hardness profiles and macro-features of welds were examined. It was found that the optimum tensile and bending properties were obtained when applying the tool with concentric reservoirs and the lowest welding speed. In this way, the widest nugget zone at the plate axis is obtained, as well as the thickest nugget-zone layer under the specimen surface, covering the thermomechanical and heat-affected zones. The overlapping of the nugget zone with the thermomechanical and heat-affected zones enables higher proof and ultimate tensile strengths compared to the base material. The surface-roughness parameters of the weld face are lower for the specimens welded with the tools with reservoirs and considerably lower than the base-material edge-surface roughness.