Investigation on Properties of Fluorine‐Free Mold Fluxes Based on CaO–Al 2 O 3 –B 2 O 3 System

Fluorine‐free mold flux has received ever increasing attentions due to environmental problems cause by fluorine in casting. Fluorine‐free mold fluxes based on CaO–Al 2 O 3 –B 2 O 3 systems are developed in the present work. The melting temperatures, viscosities, and crystallization behaviors of CaO–Al 2 O 3 –B 2 O 3 based mold fluxes are investigated. The results show that the melting temperatures decrease with the increasing B 2 O 3 and Na 2 O content, while the melting temperatures of mold fluxes first increase with increasing CaO/Al 2 O 3 mass ratios, and then decrease with further increasing CaO/Al 2 O 3 ratios. The viscosity values of mold fluxes decrease with increasing of B 2 O 3 , Na 2 O content, and CaO/Al 2 O 3 ratio. The crystallization temperatures of mold fluxes decrease with the increasing B 2 O 3 and Na 2 O, while the crystallization temperature of mold fluxes first increases with increasing CaO/Al 2 O 3 mass ratios, and then decreases with further increasing CaO/Al 2 O 3 ratios. XRD and SEM are used to analyze the sequence of crystallization. Ca 3 Al 2 O 6 crystals are precipitated at first, followed by LiAlO 2 during continuous cooling for all samples, and Ca 3 B 2 O 6 is precipitated finally. It is shown that CaO–Al 2 O 3 –B 2 O 3 based mold flux has a potential to be applied as a kind of F‐free mold flux.