Mechanism of the oxidation film tearing by DCEN-TIG helium welding of aluminum

Oxidation film tearing under different helium flow during DCEN-TIG welding of aluminum was observed via high-speed photography. The results showed that helium flow reduced the oxidation film tearing, but it increased the deep-to-width ratio of the weld pool and arc energy efficiency. The enhanced power of the positive pole of helium welding weakened the chemical bond of the oxidation film and leaded to the tearing of oxidation film. Based on the static equilibrium equation, differential equation of the intersection line between the surface of molten pool and the electrode plane was derived, which explained that the depression of molten pool increased with the increase of helium flow, and the surface tension from the center to the edge of the molten pool also decreased with the increase of helium flow. Both factors work together to make the tearing degree of oxidation film decreased with the increase of helium flow.