Determination of active flux compounds suitable for A-TIG and FB-TIG welding techniques of 90/10 CuNi alloy

90/10 CuNi alloy, known as Cupronickel, is widely used in various industries such as defence, automotive, chemical, oil and gas, steelmaking, environmental technologies, marine and energy. This alloy is favoured for its outstanding mechanical properties, compatibility with various production methods and, significantly, its high resistance to corrosion and biofouling in seawater. Tungsten Inert Gas (TIG) welding is the primary joining method used to weld non-ferrous and stainless steels, producing high quality welds with lower investment. However, relatively shallow penetration capability and low productivity are the main disadvantages of TIG welding. In order to guarantee high productivity in addition to the superior weld quality provided by conventional TIG welding, new technologies such as A-TIG and FB-TIG using active fluxes have been developed. However, when the related literature and practical applications are analyzed, it is evident that there is a lack of comprehensive information on suitable active flux materials and related welding parameters recommended for A-TIG and FB-TIG welding of 90/10 CuNi alloy. In this study, the effect of different active fluxes on weld bead geometry and mechanical properties during welding of 8 mm thick 90/10 CuNi parts was investigated. Initially, a large number of active flux compounds were used in A-TIG and FB-TIG techniques for alloys of various thicknesses and different grades. The geometrical parameters of the weld beads obtained, depth of penetration (DOP) and the ratio of depth of penetration to weld width (DWR), were analysed in comparison with measurements obtained from conventional TIG welding. As a result of experimental studies, compounds such as AI₂O₃, Cr₂O₃, MgO, and 50% SiO₂ + 50% Cr₂O₃ emerged as prominent active fluxes. Each compound has different effects in different sets of experiments. While full penetration (DOP=8.36 mm) was achieved in FB-TIG welding with Cr₂O₃, full penetration (DOP=8.10 mm) was achieved in A-TIG welding with SiO₂+ Cr₂O₃ with a single pass. In comparison to the DOP of conventional TIG welding, DOP was observed to rise by 160% with AI₂O₃ in A-TIG welding and by 177% in FB-TIG welding; by 144% with MgO in A-TIG welding and by 130% in FB-TIG welding; by 161% with Cr₂O₃ in A-TIG welding and by 215% in FB-TIG welding; and by 181% with SiO₂ + Cr₂O₃ in A-TIG welding and by 151% in FB-TIG welding. In parallel with these results, it was also determined that the use of active flux improves the DWR of the weld, thus enhancing the weld geometry and mechanical properties.