Evaluating the Influence of Tool Materials on the Performance of Refill Friction Stir Spot Welding in Aluminum-Lithium Alloys

Joining high-strength 2xxx series aluminum is difficult, and these alloys are traditionally considered non-weldable for fusion technologies. Refill friction stir spot welding (RFSSW) is a solid-state process invented in the early 2000s that produces spot welds that are strong, lightweight, flush, and hermetic. As a solid-state joining process RFSSW is capable of effectively welding 2xxx series aluminum alloys. While the process is amenable to joining 2xxx series alloys, the selection of tool materials plays a role how effective the process interacts with these high-strength aluminum alloys. An evaluation was made of a 9mm diameter tool set made from various tool materials including tungsten carbide, H-13 tool steel, and a creep-resistant MP159 alloy often used in linear friction stir welding. Properties of these materials are investigated as a means of understanding how they influence weld properties in the RFSSW process. A comparison of parameters, weld consolidation, and the size of the heat-affected zones is made to understand the influence of tool material on the RFSSW when joining 2xxx series aluminum alloys.