Preparation of inorganic-organic composite film on AZ31B magnesium alloy by chemical conversion and its properties
[Introduction]Magnesium alloys feature excellent workability,shock resistance,and electromagnetic shielding performance.However,the poor corrosion resistance often limits their service lives.Therefore,effective anticorrosive surface treatment is very important for magnesium alloys.[Method]An inorganic-organic composite film was prepared in-situ on the surface of AZ31B magnesium alloy by chemical conversion.The conversion bath composition was firstly optimized by orthogonal test.The effect of conversion time on the morphology and corrosion resistance of conversion film was then studied.The composition of the conversion film prepared under the optimized conditions was also analyzed by X-ray photoelectron spectroscopy(XPS).[Result]The conversion bath composition and parameters were optimized as follows:sodium phytate 3 g/L,hexafluorozirconic acid 3 g/L,temperature 25 ℃,and treatment time 40 s.The conversion film obtained thereunder was mainly composed of MgO,MgF2,ZrO,and organofluoride,and exhibited uniform color,moderate thickness,compact structure,and excellent corrosion resistance.[Conclusion]The inorganic-organic composite conversion process developed in this paper can significantly improve the corrosion resistance of magnesium alloys.
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