Structural Role of CaF2 Upon Welding Flux Viscosity

Flux viscosity affects weldability and alloying element transfer behaviors during submerged arc welding of grades of thick shipbuilding steel. It is widely accepted that viscosity is intrinsic to F-related bond structures. However, a validated relationship of the interplay remains at large. This investigation demonstrates the structureviscosity correlation by employing experimental measurements coupled with molecular dynamics calculations. The results showed that the maximum viscosity at 1500°C decreased from 4.53 to 0.375 Pa·s as the CaF2 content increased from 20 to 40 wt-%. Such a reduction could be partly attributed to the structures’ dilution effect and the highly polymerized units’ inhibition. Furthermore, CaF2 additions introduced Ca2+ and F– with high migration rates and promoted void formations among polyhedra, thereby significantly enhancing the overall diffusion coefficients from 0.25 to 2.47 Å2/ns. It was also found that F– tends to be incorporated into [AlOn ] polyhedra, with Ca2+ providing prominent structural compensation in Al2 O3-rich environments. Moreover, CaFn clusters were more favored than MgFn clusters across all involved compositions. The findings corroborated the relationship between structural features and fluoride content. Such insights could enrich our understanding of CaF2-induced viscosity behaviors and offer viable strategies for designing welding fluxes from an intrinsic structural perspective.