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Welding Journal | June 2016

2) The typical droplet transfer mode during this underwater welding experiment was classified as repelled globular transfer with large droplets and low frequency. Under the given condition, the metal transfer frequency was obviously lower than the bubbles’ evolution frequency. This may have caused the extra forces on the droplets due to the unstable gas flow of the evolving bubbles. The big volume molten droplets were repelled by the complex forces, among which the cathode jet force and gas flow drag force may have contributed. 3) The arc cathode spot was captured drifting on the substrate intensively and continuously with very high frequency and speed. This behavior was negative for maintaining a stable welding process and made the forces on the droplets more complicated. The authors deduced that the oxide distribution and cold cathode substrate caused this phenomenon. Adding more oxides in the flux was considered a feasible method to reduce the arc drifting and deviation. 4) Under the impact of the water environment, the average electric potential gradient of the arc column was apparently much higher than other conventional GMAW methods. The special arc burning atmosphere, including hydrogen, oxygen, and vapor, caused the higher thermal conductivity and consequently higher electric potential gradient. The welding arc current density increased significantly due to the compression by the environment. 5) The asymmetric weld appearance and uneven surface with distortions were closely concerned with the complicated physical welding process. High-frequency evolving bubbles, lowfrequency droplet transfer, and drifting arc were the main factors influencing the welding process stability. The repelled large droplet transfer mode especially caused random transfer paths, uncertain landing locations, and intense fluctuation of the weld pool. 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Welding Journal | June 2016
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