Arc characteristics and metal transfer behavior on weld quality in rotating arc ultra-narrow gap GTAW of thick plates

Manufacturing industries are facing problems related to joining thick plates using narrow gap welding, such as sidewall incomplete fusion, arc climbing, etc. The current research provides an outlook to address the above issue by utilizing an innovative approach, i.e., rotating arc ultra-narrow gap (i.e., 5 mm) with gas tungsten arc welding (GTAW). This method utilizes the infinite rotation of the non-axisymmetric tungsten electrode tip to make the arc rotate periodically and burn evenly at the bottom and sidewall of the groove. So, reliable sidewall penetration and good weld formation can be obtained. A detailed comparative analysis of arc dynamic behavior, droplet transfer characteristics, and weld cross-section formation is examined for ultra-narrow gap (5 mm) and narrow gap (8 mm) welding of 16 mm thick plates. Besides this, the microstructural and mechanical behavior of the welded joints are also analyzed. The results show that a smaller stable elliptical arc appears during ultra-narrow gap welding due to the constraint effect of the sidewall. Moreover, the rotation speed of the tungsten electrode is consistent with the rotating arc. The more stable droplet transfer is observed during ultra-narrow gap welding. The weld cross-section formation shows the enhancement in the sidewall penetration depth with the reduction in the heat-affected zone (HAZ) due to the strong stirring effect of the rotating arc. Furthermore, reducing heat input during ultra-narrow gap welding improves the weld quality. The ultra-narrow gap welded joints exhibit a maximum tensile strength of 531 MPa, exceeding that of the base metal, together with improved plasticity and excellent impact toughness. Hardness measurements indicate enhanced hardness in the weld zone (200–300 HV) compared with the base metal (160–180 HV), which is attributed to microstructural refinement induced by the rotating arc process. The present study proposes improving the properties of thick plate joints for high-performance components by utilizing rotating arc narrow gap welding.