Filling friction stir weld keyhole using pin free tool and T shaped filler bit

A keyhole produced by friction stir weld bead on plate (4·7 mm thick 1060 Al plate) technique was filled using a method like rotational extrusion process, in which a pin free tool and a T shaped filler bit was used. As compared with the case using a simple cylindrical filler bit, in which all of the filled samples fractured at the initial periphery interface, the beneficial effect of T cap on improving filling quality was demonstrated by higher and more stable fracture load and fracture location away from initial periphery interface, although small gaps were present at the lower periphery interface and the bottom interface. To further eliminate the small gaps mentioned above with liquid phase, Zn braze foil was preplaced at the bottom of the keyhole. As expected, with the aid of the extruding and torquing effects of the pin free tool, intimate contact was achieved well by filling and alloying effects of molten Zn.