Investigation on TIG arc welding-brazing of Ti/Al dissimilar alloys with Al based fillers

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 ₂Al ₂₀La 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 ₂Al ₂₀La reduced the hardness of the interfacial layer by more than half, while Al ₂Cu increased that of the brazed seam by ~50%. The tensile strength of Ti/Al joints reached 270 MPa.