The effect of activating fluxes on the cathode spots in the activating TIG welding

The cathode spots are a common phenomenon in the TIG (tungsten inert gas) welding process. However, it is rarely observed in the activating TIG welding process. This research is mainly focused on the effect of activating flux on cathode spots in the activating TIG welding. The characteristics and behaviors of cathode spots were investigated in activating TIG welding by the high-speed camera and the spectrograph. Three kinds of oxide (TiO₂, SiO₂, MnO₂) and two halide (MnCl₂, CaF₂) activating fluxes are used in the activating TIG welding process. The results show that differ from the TIG welding, the oxide activating flux increases the number of cathode spots and decreases the velocity. The effect is the opposite for the halide activating flux. Moreover, the number of spots no longer varies with the current except TiO₂ activating flux. As the temperature of the weld pool surface increases the spot moves away from the center. But this rule is not valid when silica and manganese compounds activating fluxes are used. The variation of cathode spots is caused by the oxide film reformed and the distribution of weld slag. The formation mechanism of cathode spots might be the impact of ions on the cathode surface and the strong electric field formed near the cathode surface.