Insight into the Viscosity–Structure Relationship of MnO–SiO2–MgO–Al2O3 Fused Submerged Arc Welding Flux

In this study, the influence of Al2O3 on the viscosity and structure of MnO–SiO2–MgO(–Al2O3) submerged arc welding fluxes was investigated. The results showed that the viscosity initially decreased and subsequently increased with increasing Al2O3 contents from 0 to 25 mass pct, which correlates well with the “V”-shaped variation trend of the activation energy. The enhanced (Q2 + Q3 + Al–O0)/(Q0 + Q1 + Al–O−) ratio indicated the continuous polymerization of the flux structure with higher Al2O3 contents, which was further confirmed by the distribution characteristics of various oxygen species. The variation trend may likely be attributed to the competing effects of the overall weakened bond energy and the enhanced degree of polymerization of the flux structure.