Study on weld formation and its mechanism in laser-TIG hybrid welding with filler wire of a titanium alloy

A series of laser-tungsten inert gas hybrid welding with filler wire experiments were performed on the TA15 titanium alloys to investigate the effect of welding parameters, such as the distance between the axis of the laser beam and the tip of the tungsten electrode (Dla), the defocused distance of the laser beam, and its CO2 concentration in the shielding gas, on the weld appearance and dimension. The mechanism of the weld formation was then analyzed. The results demonstrated that by adjusting space position between the heat sources and protecting the shielding gas content, the undercut defect could be suppressed effectively in the hybrid welding process. With the increase in the Dla, defocused distance, and CO2 concentration, the width of the top weld presented an increasing trend, while the width and reinforcement of the backside showed a decreasing trend. The ridgelike appearance may be effectively suppressed if the Dla, defocused distance of the laser beam, and CO2 concentration in the argon shielding gas were more than 2 mm, 4 mm, and 2%, respectively, because the Dla, defocused distance, and CO2-determined energy concentration, surface tension, and Marangoni convection determine the molten metal flow direction.