Study On Preparation And Properties Of Magnesium Alloy SiO₂/PVDF Superhydrophobic Polymer Composite Coating

As the lightest structural materials,magnesium alloys possess advantages of low density,high specific strength,high stiffness strength,good electrical conductivity,and excellent electromagnetic-shielding properties,Therefore,magnesium alloys have been widely used in many fields,such as automobile industry,electronic industry,aerospace,computer manufacturing,optical equipment,and etc.However,the corrosion resistance of magnesium alloys is extremely poor,which restricts the wide application of magnesium alloys in practice.Forming a superhydrophobic coating on the magnesium alloy can reduce the direct contact between the substrate and the corrosive medium,Thus,the corrosion resistance of the magnesium alloy can be effectively improved.In addition,the special characteristics of the superhydrophobic surface can also further expand the application of the magnesium alloy in practice.In this paper,different superhydrophobic coating on AZ31B magnesium alloy were fabricated via spraying,using SiO₂ nanoparticles and polyvinylidene fluoride(PVDF).SEM,AFM,BET,XPS and other analytical methods were utilized to study their morphology,structure and chemical composition and their combination with the magnesium alloy matrix,the electrochemical polarization test was used to analyzes the corrosion resistance of superhydrophobic coating.The specific research content is shown as follows:1.Fluorinated modification of 15 nm silica(SiO₂)and 500 nm silica(SiO₂)with1H,1H,2H,2H,-trimethoxytridecylfluorooctylsilane with low surface energy.Fluorinated silica(SiO₂)and polyvinylidene fluoride(PVDF)were used to construct the super-hydrophobic coating on the surface of magnesium alloy by spraying method.The changes in the syrface wettability of superhydrophobic coatings fabricated with different ratios were studied.The results indicate that the surface hydrophobicity of the coating prepared by 500nm SiO₂ is not very good.With increasing of 15 nm SiO₂ content,the surface wettability of the coating prepared by 15 nm SiO₂ showed the trend of first increasing and then decreasing.When the ratio of 15 nm SiO₂ to PVDF is 1:3,the contact angle of the coating is 151.8°,presenting good surface superhydrophobicity.According to electrochemical polarization curves,the corrosion current density decreases by an order of magnitude,indicating that the coating exhibits excellent corrosion resistance.As for the adhesion and friction test of the coating,the adhesion between the coating and the magnesium alloy reaches level 1,showing good adhesion and wear resistance.2.In order to construct a rough surface with different scale structure,the above-mentioned fluorinated SiO₂ nanoparticales were mixed with different particles having different diameters,so that a micro/nano rough surface can be fabricated on the magnesium alloy.The effect of ratios of 15 nm SiO₂ and 500 nm SiO₂ on the surface wettability of the coating and its changing trend were discussed.The results show that when the ratio of SiO₂ at 500 nm to SiO₂ at 15 nm is 4.5,the rough structure presents good surface hydrophobicity and the contact angle is about150°.Form electrochemical polarization curves,the corrosion current density decreases,and the coating shows good corrosion resistance.The adhesion between the coating and the magnesium alloy reaches level 0,showing excellent adhesion quality,Besides the coating presents good self-cleaning performance.3.Due to the ultraviolet light-sensitive characteristics of titanium dioxide(TiO₂),it is often used as a functional material for the preparation of surface wettability conversion.Therefore,the rough structure of the composite nano-system was constructed on the surface of magnesium alloy by spraying method using hydrophilic TiO₂ and hydrophobic SiO₂ .The effects of TiO₂ and SiO₂ on the surface wettability of the coating were explored separately.The surface hydrophobicity of the coating increases first and then decreases as the content of the two nanoparticles increases,achieving a reversible conversion of the wettability of the coating.The prepared coating showes good surface superhydrophobicity,and the contact angle is approximately 150°.In addition the coating exhibits self-cleaning performance.The adhesion between the coating and the substrate reaches level 0,indicating that the coating has excellent adhesion.