Abstract
The effect of tool geometry on microstructure and static strength in friction stir spot welds of 6061 aluminium alloy sheets was studied. Tools with three different shoulder diameters were evaluated. The weld microstructures varied depending on shoulder diameter, tool rotational speed and tool holding time. The tensile shear strengths at the fixed tool rotational speed were strongly dependent on tool holding time and shoulder diameter. The dependence of static strength on shoulder diameter and the fracture mechanisms were discussed based on observation of the microstructures.
