Oxidation behavior of molten magnesium alloy AZ91D in different atmospheres containing sulfur and fluorine

Abstract In the magnesium alloy melting process, the implementation of anti-burning technology is imperative. This study investigates the oxidation resistance of AZ91D magnesium alloy melting at 730 °C in an open environment under a mixed gas atmosphere, where sulfur is decomposed by pyrite (FeS 2 ) and fluorine is generated from 1,1,1,2-tetrafluoroethane (HFC-134a). By changing the proportion of sulfur and fluorine in the protective atmosphere, it is possible to alter the composition and structure of the protective film. Compared with a single atmosphere protection, a complete and compact protective film was obtained when a mixed protective atmosphere was employed. The optimal effectiveness, density of protective film PBR (Pilling-Bedworth Ratio) = 1.18, was achieved with 0.1% HFC-134a and 0.5 g FeS 2 added at 30 min intervals. The morphology of the surface film was analyzed by scanning electron microscope, the composition by energy-dispersive x-ray spectroscopy, the phase by x-ray diffraction and the film layer composition and the valence states by x-ray photo-electron spectroscopy. The thermodynamic properties and the mechanisms of protective film formation were also analyzed. The established correlations between protective film composition and formation mechanisms contribute valuable knowledge to the field, providing a foundation for advancements in alloy processing and application.