Experimental observation of cleaning action of cathode spots in AC TIG welding of aluminum plates

Since it is indispensable to remove oxide layer on aluminum for realizing high quality weld joint in arc welding of aluminum plates, AC TIG welding is generally employed. In periods of EP (Electrode Positive) of AC TIG welding, the oxide layer is removed by cleaning action of cathode spots. In this paper, results on experimental observations of the cleaning action of the oxide layer by cathode spots in AC TIG welding of the aluminum plate with a high speed video camera will be reported. As a result, it was found that cathode spots moved slowly on the oxide layer and their averaged velocity was 26.1m/s. On the other hand, cathode spots near the center of the weld pool, where the oxide layer had been mostly removed, moved at high speed and their averaged velocity reached 121.9 m/s. Furthermore, the velocity greatly changed depending on the position of the cathode spot and exceeded 1 km/s at the maximum.