Investigation on Properties of Fluorine‐Free Mold Fluxes Based on CaO–Al2O3–B2O3 System

摘要

> 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.