Study On The Forming Mechanism Of Alumina Ceramic Film On Metal Surface

Steel material is the most widely used metal material at present,and plays a very important role in industries.The most failure of steel starts from its surface whatever owing to wearing or corrosion,and finally steel body is broken,will impact on the working life of metal materials.Forming ceramic films on steel surface is an effective way to improve the properties of base metal,it retains the mechanical properties of metal materials,also have a good corrosion and wear resistance of ceramic material,also can improve the performance and working life of metal materials.However,there is a big difference in thermal expanding coefficient between metal substrate and ceramic film,a large change in temperature will cause large thermal stress,resulting in binding broken and film peeling off.The thermal expanding coefficient of Fe-Al intermetallic compounds is between metal and ceramic,which can be used as the transition to relieve the difference between the film and the substrate.In this paper,Fe-Al intermetallic compounds were formed on Q235 steel by pack aluminizing The relationship among aluminizing temperature,time,agent composition and the layer thickness were studied.Moreover a new catalyst has been developed successfully,which can lower the reaction temperature and shorten the reaction time,effectively improve the efficiency of pack aluminizing.Al₂O₃ film was obtained in-situ on Fe-Al intermetallic compound surface by oxidizing at high temperature in the air.The feasibility of reaction was analyzed by the thermodynamics.The relationship between oxide film formation and oxidation temperature and time was analyzed from dynamics.The phase composition and microstructure of aluminized layer were analyzed before and after oxidation by means of XRD,SEM etc.The results show that a protective oxide film can be easier formed between 900℃¹000℃.The results show that,the surface hardness of ceramic film can reach more than 1000 HV,average friction coefficient is 0.32,in molten zinc at 460℃can keep stable for a long time,corrosion of 120 h in NaCl neutral salt spray environment,average corrosion rate is 0.0808g/m²·h.