Influence of shoulder geometry and coating of the tool on the friction stir welding of aluminium alloy plates

Friction Stir Welding (FSW) has demonstrated a significant potential for joining low melting point non-ferrous metals in several joint configurations. During FSW metals are joined in the solid state due to the heat generated by the friction and flow of metal by the stirring action of a pinned tool. This paper reports an experimental investigation on the effects of geometry and surface coating of the tool shoulder on the defectiveness, the microstructure and the microhardness of a 3 mm thick 5754H11 aluminium alloy butt weld. During the experiments the diameter and slope of the shoulder varied. Moreover a tungsten carbide coated was tested. The pin geometry and dimensions were kept constant. Four different tools for shoulder geometry and coating condition were tested. The weld was characterized in terms of the bead morphology and the grain size. The weld microhardness profile was measured for all the microstructural zones of the friction stir welding process. The obtained results provide a deeper knowledge of the effect of the tool shoulder geometry and surface condition on the aluminium alloy weldability.