Gas tungsten arc welding of titanium using flux cored wire with magnesium fluoride

Grade 2 Ti - CP was gas tungsten arc welded using flux cored (FC) wires and flux pastes that contained various MgF2 contents. The effects of MgF2 on bead morphology, chemical composition and hardness of weld bead were investigated and interpreted. With an increase of MgF2 content in the flux paste, depth/ width ratio of weld bead increased gradually with little variation in interstitial element contents and hardness. Weld bead made with cold FC wire feed showed even deeper and narrower bead, indicating the greater effectiveness of wire feed than flux paste on weld penetration. While the 50% MgF2 FC wire produced complete slag coverage and smooth weld bead surface, 85% MgF2 wire resulted in incomplete slag coverage and rough weld surface. Arc spectroscopy revealed that the 50% MgF2 FC wire produced plasma spectrum with atomic and ionised titanium peaks, which is an indication of a high temperature arc and a larger amount of flux vapours in the arc. Therefore, it is believed that deep weld penetration associated with high MgF2 fluxes in this experiment is caused by arc constriction, resulting from the greater amount of flux vapours owing to high arc temperature.