Improving the strength of friction stir welded joint by double side friction welding and varying pin geometry

Friction Stir Welding (FSW) is a candidate to overcome problems traditionally encountered when conventional fusion welding methods are applied to join low weldability metals. Moreover, FSW shows greater performance than conventional fusion welding in joining materials with dissimilar welding characteristics. However, since FSW is still a relatively new technique, more research is needed to improve the methodology and achieve a better understanding of the physical phenomena that occur during the FSW process. The focus of this paper is the role that the pin's shape plays on the achievable tensile strength. To this aim, three pin's shapes are considered, namely circular (baseline), square, and triangular. The effects of the pin's shape is studied by mean of experiment and numerical methods. The effect of pin geometry on double side stir welding (DSFSW) is also experimentally studied. It is proven that a modified pin geometry can indeed improve the tensile strength of FSW joints obtained with a cylindrical pin. DSFSW significantly improves the joint quality since it provides strain hardening in the interference zone and better mixing when the second pass is applied.