Effects of helium gas flow rate on arc shape, molten pool behavior and penetration in aluminum alloy DCEN TIG welding

Helium arc bead-on-plate welding has been observed using a high-speed video filming technique. Both the arc diameter and area were compressed with increasing gas flow. The arc compressed in the radial direction and stretched in length, causing a voltage increase. There was no negative-pole atomization in the direct current electrode negative (DCEN) mode, and the helium arc could tear the oxidation film on Al alloys. The broken oxidation film flowed on the molten pool under various forces. The arc shear force and arc pressure component are the dominant driving forces to tear the oxidation film. The ability of the helium arc to tear the oxidation film decreased with gas flow rate varying from 5 to 20 L/min. Penetration increased with gas flow because of the compression effect.