Effect of wire feed rate on microstructure and properties of laser welded Ti-3Al-6Mo-2Fe-2Zr joints with filler wire

The Ti-6Al-4V(TC4) filler wire was used to join 2 mm thick Ti-3Al-6Mo-2Fe-2Zr titanium alloy during laser welding process. Investigations concerning the influence of wire feeding rate on microstructure and tensile properties were conducted on laser welded Ti-3Al-6Mo-2Fe-2Zr joints with filler wire by optical microscope, scanning electron microscope, and X ray energy spectrometer and other analytical testing methods. The results show that, due to the decreasing heat effect from fusion line to base metal, the microstructure of the heat affected zone is divided as follows: single β region, primary α + matrix β region, and primary α + retained secondary α + matrix β region. Acicular α' phase is formed in the fusion zone, and the distribution is not uniform. As the wire feed speed increases, the number and size of acicular α' phase increases. The tensile strength and elongation of laser welded joints with filler wire are lower than those of the base metal. With the increase of wire feeding rate, the tensile strength of the joint increases and the elongation decreases. The reason is attributed to that, as the wire feeding rate increased, the Mo_eq in the fusion zone decreased correspondingly, which led to the increment in the number and size of α' phase. When the wire feeding rate was higher than 1.0 m/min, the fracture location changed from fusion zone to heat affected zone because of the strengthening effects of α' phase.