Development of a new joint geometry for FSW

Friction Stir Welding (FSW) is an emerging solid state joining technology that allows welding most aluminum alloys that otherwise are difficult to weld by using conventional fusion based technologies. The technology is of particular interest for transport applications, since welded structures are considered to offer cost and weight savings. From a point of view of the joint geometries, FSW is mature for simple configurations. Most work to date has concentrated on butt welds and, only to a certain degree, on overlap configurations. Different designs such as T-sections, corner welds, box sections... are then principally restricted to the use of butt weld configurations. However, it is necessary for FSW to be able to be applied to new geometries in order to spread its use to a wider range of applications. Present work explores the feasibility of producing corner fillet geometries using FSW. Although such a kind of geometry has traditionally been considered unfeasible for the process, it seems to have the greatest potential to be used for T-joint configurations, a recurrent design pattern in transport applications. In order to study the feasibility of the proposed new joint geometry, a specific tool has been developed and a set of welds has been produced with it. Microstructure of the produced welds has been analyzed. According to the obtained results, the proposed joint geometry seems to be feasible. Main problem pending to solve is how to avoid the formation of a tunnel defect in the weld centre line due to a suck effect of the tool on the stirred material. Further improvements are proposed to produce welds with acceptable quality.