Elucidating Electrical Conductive Mechanisms for CaF2–SiO2–Al2O3–MgO Welding Fluxes in Liquid and Crystalline States

Electrical conductivity of flux, particularly in a liquid state, plays significant roles in optimizing arc and molten pool behaviors pertinent to submerged arc welding. However, the effects of crystallization on flux electrical conductivity remain less clear. Here, the relationship between electrical conductivity of CaF₂–SiO₂–Al₂O₃–MgO fluxes with varying Al₂O₃/MgO ratios between 0.51 and 4.13 and crystallization characteristics have been established. It is demonstrated that, as a function of Al₂O₃/MgO ratio, liquid-state flux conductivity gradually decreases from 0.115 to 0.078 S/cm. Such results can be attributed to the reduced carrier number and impaired carrier diffusion. Furthermore, flux crystallization ability diminishes and then enhances as the Al₂O₃/MgO ratio increases in the range from 0.51 to 4.13. Crystals gradually shift from Mg-dominating phases to spinel, and ultimately to Al-dominating phases. When the Al₂O₃/MgO ratio is 0.51, coarse Mg-dominated crystals strongly inhibit conductivity. However, when the Al₂O₃/MgO ratio ranges from 0.97 to 1.85, scattered spinel phases showcase a minor impact on conductivity as the effective carrier number remains almost constant. This study sheds light on flux crystallization behaviors and also contributes to optimized flux design for desired electron transport capabilities.