Study On Preparation And Properties Of Micro-arc Oxidation Coating On Boron-containing Low Carbon Steel

In order to overcome the defect of low corrosion resistance of boron-containing low carbon steel and improve its surface properties,micro-arc oxidation technology was used to treat the surface of boron-containing low carbon steel.Micro arc oxidation?MAO?is an environmental-friendly metal surface film technology.The main factors affecting the performance of the film are the material itself,electrochemical parameters and electrolyte composition.Al₂O₃ ceramic film was prepared on the surface of 10B21 boron-containing low carbon steel by exploring suitable MAO process parameters.After determining the appropriate process parameters,Na₂CO₃ and Na₂B₄O₇ were used as additives to optimize the electrolyte,and?-Al₂O₃ ceramic film with good crystallinity,compact morphology and excellent performance was successfully prepared.In order to further enhance the protective performance of the film layer on low carbon steel,adding?-Al₂O₃ is adopted to reduce the number and size of holes in the film layer and increase the content of?-Al₂O₃ on the surface of the film layer.Through the characterization and performance test of the film layer,the research results show that:1.The process parameters of low carbon steel MAO were investigated.The Al₂O₃ ceramic film layer was formed in situ on the surface of 10B21 boron-containing low carbon steel.The microstructure and properties of the ceramic film layer were studied.It was found that the MAO process parameters have a significant effect on the phase composition,microstructure and film properties of the film.The experimental results show that when the process parameters are:forward voltage 550 V,frequency 1500 Hz,duty cycle 20%.The low carbon steel MAO film layer prepared by the process parameters has the most compact microstructure and the best film performance.2.Na₂CO₃ and Na₂B₄O₇ were added as additives to the MAO electrolyte solution.When the concentration of both in the solution was 3 g/L,the highest content of?-Al₂O₃ was present in the film layer,and the electrochemical corrosion behavior of the film was the best.The chemical self-corrosion current is 2.7?A/cm²,and the AC impedance is about 1900?·cm².After 7 days of neutral salt spray test,the corrosion rate was 50 g·m^-2·d^-1,and the corrosion rate was significantly lower than that of other layers.Based on the microscopic morphology and properties of the film,the optimization mechanism of Na₂CO₃ and Na₂B₄O₇ on MAO electrolyte was investigated.It was found that Na₂CO₃ had a significant effect on the size and number of pores in the film.The addition of Na₂B₄O₇ promotes the conversion of Al₂O₃ to the?phase in the film layer,and it inhibits the formation of ferrite in the film layer and increases the content of?-Al₂O₃ in the film layer.3.The sealing process of?-Al₂O₃ as the low carbon steel MAO film layer is adopted.When the concentration of?-Al₂O₃ is 3 g/L,the pore diameter of the film layer is the lowest?1-2?m?.The electrochemical corrosion behavior is excellent,the chemical self-corrosion current is 0.2?A/cm²,and the AC impedance is about 5500?·cm².After 7 days of 5%NaCl neutral salt spray test,the corrosion rate was 20 g·m^-2·d^-1,and the corrosion resistance was significantly improved.The sealing mechanism of?-Al₂O₃ was analyzed.The good sintering performance of?-Al₂O₃ promoted the pore filling of MAO film layer,and induced the transformation of amorphous Al₂O₃ to?phase.The microstructure and phase composition of the film layer are significantly optimized.