Uncovering crystallization mechanisms of SiO2–MnO based welding fluxes

Understanding the crystallization mechanism of flux is critical to tailoring welding processes and thus improving welding performance. However, reproducing or directly observing the flux crystallization process during welding is not feasible due to technical limitations. We report a strategy capturing the crystallization features of SiO2−MnO based fluxes by analyzing post-welding slags. Crystallization mechanisms of the slags have also been elucidated by molecular dynamics simulations and thermodynamic approaches. Our findings reveal that the crystallization fraction is significantly enhanced from 0 to 100% with a substitution of TiO2 for SiO2, but is moderately reduced from 70.68 to 61.96% upon substituting MnO with CaO. Such distinct phenomena have been associated with the fact that crystal nucleation and growth are subjected to thermodynamic and kinetic factors, including degree of structural polymerization, bond distributions, and atomic diffusion capacity. These insights will facilitate tackling practical challenges pertinent to precisely controlling flux crystallization behaviors through compositional adjustment.