A new technique of filling friction stir welding (FFSW) relying on a semiconsumable joining tool has been developed to repair the keyhole left at the end of friction stir welding (FSW) seam. The conventional nonconsumable tool of FSW was transformed, and a semiconsumable joining tool consisting of alloy steel shoulder and aluminium alloy joining bit was designed to create a solid state joint. Using the combined plastic deformation and flow of the consumable joining bit and the wall of the keyhole, the FFSW process is able to repair the keyhole with both metallurgical and mechanical bonding characteristics, and the FSW seam can be achieved without keyhole or other defects. The relative tensile strength and elongation of the FFSW joint are 84?3 and 98?9% of the base weld without defects respectively.

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Dissimilar alloys of Ti-6Al-4V and 5A06 Al were butt joined by Al based fillers using a novel TIG welding process, referred to as keyhole arc welding-brazing. The flow behaviour of weld pool was introduced, which was characterised by the formation of a keyhole under the tungsten electrode. It was found that porosity tended to be produced in the middle of the fusion line, while adding elements prevented its formation. At brazing interface, interfacial reaction at root face was enhanced, and a uniform serrated layer, identified as TiAl 3 , was obtained by pure Al fillers. When Al-Cu-La fillers were used, block Ti 2 Al 20 La phases appeared at the interface between the TiAl 3 layer and the brazed seam. Compared to joints brazed by pure Al fillers, the formation of Ti 2 Al 20 La reduced the hardness of the interfacial layer by more than half, while Al 2 Cu increased that of the brazed seam by y50%. The tensile strength of Ti/Al joints reached 270 MPa.