Corrosion of enamel with and without CaF2 in molten aluminum at 750 °C

•Enamel coatings effective protect the 304 stainless steel served in molten-Al.•Fluorides segregation at the enamel coating surface reduces liquid-Al wettability.•Continuous mullite scale on F-containing enamel bulk slows down Al permeation rate.•Homogeneous cristobalite in F-containing enamel bulk ensures its uniform erosion.•Defective Al2O3 tends to grow along α-quartz on F-free enamel bulk in molten-Al. Coatings and bulks of enamel with and without CaF2 were prepared to investigate their corrosion behavior in molten Al at 750 °C. Enamel coatings provide high corrosion resistance to the 304 stainless steel against molten-Al. In the presence of 2.5 wt% CaF2, its corrosion resistance was further improved. Detail study on corrosion of the enamel bulks reveals that such role of CaF2 played on the corrosion behavior of enamel relies on the following two aspects: (1) Concentration of fluorides at surface reduces wettability; (2) Adding CaF2 changes crystallization of enamel, and different crystallites result in the varied corrosion resistance.