| T he problem of poor corrosion resistance seriously restricts the application of magnesium alloy in many conditions.Micro-arc oxidation treatment of magnesium alloy can significantly improve the corrosion resistance of magnesium alloy.Due to the hydrophilic characteristics of micro-arc oxidation ceramic layer,its corrosion resistance is greatly reduced in humid environment.The preparation of hydrophobic film on the surface of micro-arc oxidation ceramic layer is an effective way to solve this problem.At present,in the study of preparing hydrophobic film on the surface of micro-arc oxidation ceramic layer,the hydrophobic film is mainly used to completely cover and fill the structure of micro-arc oxidation ceramic layer.However,studies have shown that hydrophobic membranes with appropriate three-dimensional structures exhibit better hydrophobicity than those with planar structures.Therefore,in this work,a rough surface was constructed by micro-arc oxidation and a hydrophobic surface with three-dimensional structure(rough structure)was constructed based on the rough surface to further improve the corrosion resistance of magnesium alloy micro-arc oxidation surface.At present,the hydrophobic surface with three-dimensional structure is constructed by micro-arc oxidation,and the relationship between the rough structure and the hydrophobicity of the hydrophobic film is rarely reported.In this paper,AZ31B magnesium alloy was selected as the substrate,and micro-arc oxidation ceramic coatings with different rough structures were prepared on the surface of magnesium alloy by controlling the current density of micro-arc oxidation.Then,the surface of micro-arc oxidation ceramic coating was modified by dimethyl silicone oil,stearic acid and perfluorodecyl triethoxysilane to obtain a hydrophobic coating with three-dimensional structure(rough structure).The microstructure,wettability and corrosion resistance of the coatings were studied by scanning electron microscope and energy dispersive spectrometer,optical contact angle measuring instrument,laser confocal microscope and electrochemical workstation.The findings are as follows:(1)When the micro-arc oxidation ceramic layer was hydrophobically modified by dimethyl silicone oil,the thickness of the hydrophobic film increased with the increase of the hydrophobic modification time.When the modification time was 2h,the surface hydrophobic film was continuous and uniform without changing the rough structure of the micro-arc oxidation ceramic layer.After the modification time reaches 10h,the micropores of the micro-arc oxidation ceramic layer are completely filled,and the morphological characteristics of the micro-arc oxidation completely disappear.The results of hydrophobicity and corrosion resistance tests show that the hydrophobic film with micro-arc oxidation rough structure obtained by modifying 2h has better hydrophobicity and corrosion resistance than the smooth hydrophobic film with micro-arc oxidation rough structure completely covered by the hydrophobic film obtained by modifying 10h,indicating that the rough structure can significantly improve the hydrophobicity and corrosion resistance of the hydrophobic film.(2)The rough structure of micro-arc oxidation ceramic coating is affected by the current density of micro-arc oxidation.In this paper,micro-arc oxidation ceramic coatings with different rough structures were prepared by using current densities of 1A/dm2,1.5A/dm2,2A/dm2,2.5A/dm2,3A/dm2,respectively.On this basis,the hydrophobic film with corresponding microarc oxidation rough structure was prepared after modification for 2h,and the effect of micro-arc oxidation rough structure on the water contact angle of hydrophobic film was analyzed.The results show that there is no correlation between single height parameter and volume parameter and hydrophobicity,but the ratio of volume Vmp of micro-arc oxidation rough structure peak to volume Vm of rough structure is positively correlated with the water contact angle of hydrophobic film,that is,the larger Vmp/Vm is,the larger the water contact angle is.(3)Based on the preparation of hydrophobic film with rough structure on the surface of the same micro-arc oxidation ceramic layer,the effects of three hydrophobic film materials,dimethyl silicone oil,stearic acid and perfluorodecyl triethoxysilane,on hydrophobicity were analyzed.The results show that the perfluorodecyl triethoxy silane layer has the best hydrophobicity,its water contact angle can reach 153.9°,and the surface of the hydrophobic film shows superhydrophobicity.The electrochemical analysis of the hydrophobic film shows that the corrosion current density of the perfluorodecyl triethoxysilane hydrophobic film is four orders of magnitude lower than that of the micro-arc oxidation ceramic layer,which greatly improves the corrosion resistance of the micro-arc oxidation ceramic layer of magnesium alloy. |
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