Effect of Active Gas on Weld Shape and Microstructure of Highly Efficient TIG Welded A516 Low Carbon Steel

Abstract

A highly efficient TIG welding method was performed to increase the weld penetration and compared with the conventional TIG welding process. A double-shielded gas flow system was designed to apply Ar + CO2 mixed gas as the outer layer, while the inner layer remained pure argon to impede oxidation of the electrode. The results demonstrate that the addition of the active gas to the molten pool controls the Marangoni convection on the liquid pool surface so that the weld shape changes from a shallow shape to a deep and narrow weld pool owing to the change in direction of Marangoni convection. The increase in CO2 content from 0.5 to 2 % leads to the reduction in the weld depth which is due to the formation of a thick oxide layer on the weld pool surface and reduction in the interface between the shielding gas and the weld pool. Moreover, Preheating of the samples causes the formation of deeper fusion zone profiles which can be attributed to the slow cooling rate and the increase of heat concentration in the weld pool.