Friction stir welding: Process, temperature, microstructure and properties

As an energy-efficient solid-state joining technique, friction stir welding (FSW) shows enormous advantages compared to conventional fusion welding methods. This work comprehensively reviewed the recent studies on FSW of commonly-used metals including Al, Mg, Fe, Ti and their alloys, with a particular focus on thermal cycles experienced during FSW. The role played by thermal cycles was comparatively summarised for different metals, trying not only to understand the physical effect of welding conditions on joints’ microstructural evolution and mechanical properties, but also provide a guide for engineers to take proper FSW strategies when facing different metals, which has not been discussed in detail in other reviews. Finally, several ideas were proposed for a possible advancement in FSW of the investigated metals.