Microstructural evolution and characteristics of weld fusion zone in high speed dissimilar welding of Ti and Al

The joining or welding of dissimilar metals is one of the effective measures to reduce structures weight of the production or to save rare metals and to save a manufacturing cost. In the weld fusion zone of Ti and Al, intermetallic compounds such as Ti3Al, TiAl, TiAl2 and TiAl3 are easily formed, and especially, brittle TiAl2 and TiAl3 makes such dissimilar metals joining very difficult. However, it was clarified that an ultra-high speed welding could suppress the formation of intermetallic compounds in the previous study.(1) Full penetration dissimilar lap welding of Ti and Al with single-mode fiber laser was tried at ultra-high welding speed in this study, and the microstructure of the welded zone, interface zone and base metals in the dissimilar Al and Ti weld bead was investigated. To confirm the formation of intermetallic compounds in the weld fusion zone, welded interface areas were observed and analyzed using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and micro-probe X-ray diffractometer (XRD). Especially microstructural phases of Ti and Al dissimilar welds were confirmed using transmission electron microscopy (TEM) with EDX. It was consequently found that Ti3Al intermetallic compound phase existed in all the weld fusion zones produced under any conditions, but the formation areas of such intermetallic compounds could be reduced by the ultra-high welding speed of 50 m/min.