Influence of tool design on mechanical properties of AZ31 friction stir spot welds

The influence of tool design on the energy output, microstructural features and overlap shear strength properties of friction stir spot welds made of AZ31 base material is examined. The mechanical properties of AZ31 friction stir spot welds made using three-flat/threaded tools are superior to those in joints made using a tool with a threaded pin at all tool rotational speed settings. It is proposed that the failure load properties are optimised when the friction stir spot welding operation is carried out in such a manner that it produces a large bonded width, a small v/ t ratio (the height of the hook region above the sheet intersection divided by the thickness of the upper sheet) and a hook region, which is curved outwards from the tool axis.