Marangoni convection and welding penetration in A-TIG welding

Abstract

The activated flux TIG (A-TIG) welding process is now considered as a feasible alternative to increase the process productivity using a thin layer of an active flux that results in a significant increase in weld penetration. The mechanisms by which five single oxide fluxes, Cu2O, NiO, SiO2, CaO and Al2O3, exert their effects on depth/width ratios in SUS304 stainless steel are studied. The oxygen dissolved in the weld plays an important role in altering the liquid pool surface tension gradient, the Marangoni convection mode and hence the weld penetration. The effective range of oxygen in the weld is between 70 to 300 ppm. Too high or too low oxygen content in the weld pool does not increase the depth/width ratio. The change in the surface tension of the molten pool is considered to be the principal mechanism for increased penetration. The decomposition of the flux significantly depends on the flux stability.