محمد امامی

The present work evaluates the mechanisms that cause the weld geometry to change in activating flux TIG (A-TIG) welding. For this purpose, an austenitic 316 stainless steel and ferritic A516 steel in conventional TIG and A-TIG welding were compared and evaluated under the same process parameters. Al2O3, Fe2O3, MnO2, SiO2, and TiO2 powders were used as activating fluxes. The depth of penetration and width of the beads were measured metallographically. In conventional TIG, the welds of carbon steel and stainless steel had a thickness of about 2.2 mm and 1.7 mm, respectively. A-TIG welding of 316 SS using TiO2, MnO2, and Fe2O3 led to a 75% increase in the weld depth. In the case of Al2O3 and SiO2 the weld depth increased 50% and 9%, respectively. However, in A516 steel, less thermodynamically stable oxide fluxes such as MnO2, and Fe2O3 had a smaller effect i.e., 9-22% increases. More stable oxides like Al2O3, SiO2, and TiO2 caused a decrease of about 30% in the weld depth compared to the conventional TIG weld. It was proposed that when the penetration increases, reverse Marangoni is dominant. This mechanism is mainly associated with viscosity and surface tension that vary by the dissolution of oxygen in the melt. Regarding penetration reduction, as in the case of more stable oxides like SiO2, the energy dissipation by the flux through heating and dissociation of the oxide and barrier effect of the undissolved oxide dominate.