Study on the activating flux laser welding of titanium alloy

The CO₂ laser was conducted to investigate the effect of activating flux on laser welding of TA15 titanium alloy with 2.5mm thickness in this paper, which originally developed to improve the penetration depth and reduce the weld porosity for TIG welding of titanium alloy. Results show that the activating flux can eliminate weld undercut defect, and increase the weld depth with the same laser welding parameters. It was also found that the activating flux can improve the back width to surface width ratio (Rw) of weld, and reduce the weld surface width for full penetration laser welding, but overlarge laser power and low welding speed will result in the Rw decreasing and surface width widening. As a result, it could be assumed that the activating flux decrease obviously both laser energy density and heat-input thresholds that penetration laser welding occurs for titanium alloy, because it can improve titanium alloy absorbing laser energy derived from higher laser absorption of activating flux and weakening screening efficiency of plasma plume. By means of a high speed camera, the effect of activating flux on the CO₂ laser welding plasma/metal vapor plume behavior can be observed. The overlarge laser energy density and heat-input will produce intensive evaporating of metal and activating flux. It would be a reason that the activation flux could not play its role in this case. According to the activating flux action mechanism, it would also be responsible for improving the weld quality of titanium alloy that it can modify surface tension and change Marangoni fluid flow in pool.