Effect of MgO on the viscous behavior of CaO-SiO₂- Al₂O₃-MgO welding flux system

The viscosities of CaO-SiO₂- Al₂O₃-MgO flux were measured under the condition of CaO/SiO₂ = 1.0-1.3 and 5.0 wt%MgO. Submerged arc welding flux with 5 wt%Al₂O₃ content had the lowest critical temperature and widest solid-liquid coexisting region at about 5 wt%MgO. It indicateds that both critical temperature and viscosity depend on the kind of primary phase of molten flux. Viscous behavior of the molten flux at 1773 K was analyzed in the view of silicate structure changed by FT-IR spectroscopy. Based on the critical temperature and the behavior of viscosity at a fixed temperature, it could be proposed that the contents of MgO and Al₂O₃ in SAW flux show a ronounced effect on preventing contamination in maintaining the liquid phase flux after welding process.