Characteristics and grain refinement of the weld bead by the GTAW with the alternating current on the filling wires

To control the formation and grain structural characteristics in the welding process, an alternating current (AC)-assisted double-wire feeding strategy was applied to a traditional gas tungsten arc welding (GTAW) process. During this process, two filler wires were connected to AC power and fed to the molten pool in a nonplanar and symmetric manner from one side. The influences of the AC, AC frequency, and arc current on various parameters, including the molten droplet size, droplet transition frequency, and deposited bead formation, were evaluated. The research revealed that this method could be implemented to effectively achieve a well-formed weld bead, especially at high ACs. Microstructural analysis indicated that the grain size decreased with increasing AC frequency. Finally, the underlying mechanism of grain refinement resulting from the addition of AC to the double filler wire was discussed.