Arc characteristics in double-pulsed VP-GTAW for aluminum alloy

This paper studied the variation in arc profile and arc macroscopic electromagnetic force with double-pulsed variable polarity gas tungsten arc welding (DPVP-GTAW) for aluminum alloy, using a synchronous acquisition and analysis system. The arc shapes were regionalized into arc edge region and arc core region by image processing method based on the gray level of the arc images. The arc characteristic size such as arc electrode end diameter DE, arc workspace end diameter DB and arc length L were measured and analyzed in the arc core region. In variable polarity pulse phase, DE and DB decreased, while L increased when welding current switched from negative polarity to positive polarity. DE, DB and L were all much larger in low-frequency pulse on tp compared with those in low-frequency pulse off tb. The size of arc profile changed periodically between tp and tb throughout the welding process. The arc macroscopic electromagnetic force Fz and arc pressure Pz oscillated in cycles with the variation of arc profile, inducing the refinement of weld zone grain structure.