Weld formation, arc behavior, and droplet transfer in narrow-gap laser-arc hybrid welding of titanium alloy

In this study, the weld formation, arc behavior, and droplet transfer in the narrow-gap laser-arc hybrid welding of 16 mm-thick TC4 titanium alloy were investigated. The penetration depth was mainly affected by the laser power and welding speed while the filler metal height and sidewall penetration were proportional to the wire feeding speed. The weld cross-sectional morphologies can be classified into three types, namely inclined, concave, and convex shapes. By optimizing the laser power and wire feeding speed, the standard deviation σ of the arc deflection angles was reduced by approximately 73.7 % and 77.9 %, respectively. This indicates that arc stability was enhanced. Increasing the welding speed from 14 to 20 mm/s caused σ to increase by approximately 343.6 %, indicating that arc stability was weakened. An inclined weld was obtained when droplet transfer deviated from the welding wire axis. A convex weld was formed due to insufficient spreading of the excessively converged molten metal in the middle of the molten pool surface. A concave weld was produced when there was sufficient spreading of the converged molten metal in the middle of the molten pool surface.