Elucidating the effect of Al2O3/SiO2 mass ratio upon SiO2-MnO-CaF2-Al2O3-based welding fluxes: Structural analysis and thermodynamic evaluation

The effect of Al2O3/SiO2 mass ratio has been fully investigated upon SiO2-MnO-CaF2-Al2O3-based fluxes by examining weld metal and slag shell morphologies. It has been documented that flux viscosity could be significantly diminished by elevating the Al2O3/SiO2 mass ratio from 0.1 to 0.6, after which only negligible changes are observed. The compositional dependence of flux behaviors has been elaborated by means of structural analysis via Fourier Transform Infrared spectroscopy, Raman spectroscopy and molecular dynamics simulation. The formation of [AlO4]-tetrahedral units and Al-O-Si with weaker bond energy are encouraged, which is accompanied by the increased NBO/Si (non-bridging oxygen per [SiO4] units) and decreased Q3/Q2 (X3/X2) to establish a depolymerized aluminosilicate network. Thermodynamic evaluations have also been performed, showcasing activity and excessive free energy variations to enrich the structural analysis. Gaining an insight into the physicochemical properties of fluxes from structural and thermodynamic analysis view is essential to empower fundamental understandings towards quality manufacturing.