Oxide flux quantity and size effects on the penetration depth in A-TIG welding

Abstract

Four single oxide fluxes, Cu2O, NiO, SiO2 and TiO2, were used to investigate the effect of active flux on the depth/width ratio in SUS304 stainless steel. Flux quantity, and particle size effects on the weld pool shape and oxygen content in the weld after welding were studied systematically. The results showed that the depth/width ratio of the weld pool was closely related to the oxygen content in the pool. The oxygen content in the weld metal increases with the quantity of fluxes for Cu2O, NiO and SiO2. However, for the TiO2 oxide flux, the highest oxygen content in the weld metal is below 200 ppm. As the oxygen content in the weld metal is in a certain range, the depth/width ratio increases to 1.5 to 2.0 times. Too low or too high oxygen content in the pool does not increase the depth/width ratio. The oxygen from the decomposition of the flux in the welding pool alters the surface tension gradients on the weld pool surface, and hence, changes the Marangoni convection direction and the weld pool penetration depth. The decomposition of the flux strongly depends on the flux particle size. TiO2 flux and SiO2 flux with small particle size (0.8 micrometer or 4 micrometer) is a highly recommended active flux for deep penetration for real GTAW applications.