Role of hybrid tool pin profile on enhancing welding speed and mechanical properties of AA2219-T6 friction stir welds

The friction stir welds o thick precipitation-hardenable aluminum alloys suffer from reduced joint strength due to dissolution/coarsening of the strengthening precipitates. The article portray hybrid pin profiled tool that enables sound welds at speeds 7-times faster than a conventional tool (a conical threaded tool), without pin breakage. The conical threaded and triangular cross-section in the upper and lower pin half-lengths of the hybrid tool facilitate material flow in a downward direction and shear deformation at a faster rate, respectively. The paper brings out the process mechanism responsible for the enhanced welding speed and mechanical properties obtainable with the hybrid tool through a case of 13-mm thick aluminum alloy AA2219-T6. The hybrid tool facilitates a 26% improvement in weld strength by reducing TMAZ softening, as evidenced by the microhardness and mechanical properties and supported by microstructural investigation and fractography.