Study on Mechanism of Red Mud Doped Coatings for Improving High Temperature Anti-Oxidation on Surface of Billet

Red mud-doped coating was prepared by wet grinding with red mud, in which taking SiO₂, MgO and graphite powders as main raw materials. The peeling performance, anti-oxidation ability and mechanism of the coating on the surface of billets were analyzed. The microstructure, phase compositions and thermogravimetric properties of the coating were analyzed by SEM-EDX, XRD and TG-DSC.The results indicate that the peeling property of the coating is better than that of the commercial coatings.The coating can significantly improve the anti-oxidation performance of billets at high temperature.The anti-oxidation loss per unit area of coated billet at 900 ℃ is the best, which can be reduced 80.5%. In the process of heating the billet, the graphite powder in the coating reacts with O₂ to form a mixed gas layer of CO and CO₂, which prevents the invasion of external O₂ and slows down the oxidation rate of the billet.At 950 ℃, the MgFe₂O₄ spinel which in-situ formed can enhance the compactness of the coating and slow down the oxidation rate of the billet.