Oxides as one of the commonly activating fluxes used in active tungsten inert gas welding (A-TIG welding) can dramatically increase the penetration depth to 2–4 times that of conventional welding. Using the oscillation principle of inviscid fluid, a robust method is developed to measure the average surface tension of molten metal during A-TIG welding for four different oxide activating fluxes of B2O3, TiO2, SiO2, and MgO. The experimental results suggest that the oxygen released from the decomposition of oxides is the dominant factor contributing to the change of the surface tension, which can result in the change of the temperature coefficient from negative to positive and alter the Marangoni convection, leading to the increase in the penetration depth. However, oxygen of small amount or large amount has a negligible effect on the sign change of the temperature coefficient. For oxides of low melting points, the interaction between the electrons outside the arc and the neutral particles (atoms and molecules) formed from the dissolution of the oxides causes the constriction of the arc; for oxides of high melting points, the decrease of the spot area in the anode due to high resistivity of the oxides leads to the constriction of the arc.

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Published in RSC Advances, v. 7, issue 85, p. 53941-53950.

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This work was supported by National Natural Science Foundation of China (#51765037), State Key Laboratory of Advanced Processing and Recycling of Nonferrous Metals of China (SKLAB 020114208), the Hong Liu outstanding Talent Training Plan of Lanzhou University of Technology of China (#J201201), Plan for Basic Research Creative Group of Gansu Province (17JR5RA107) and Outstanding Students Overseas Exchange Foundation of Lanzhou University of Technology of China, and Project for Collaborative Innovation Team of Universities in Gansu Province (2017C-07).