Preparation And Characteristics Of Superhydrophobic Surface On AZ31B Magnesium Alloy

As one of the important structural metals,magnesium alloys have the advantages of low density,high specific strength,high stiffness strength,good electrical conductivity,and excellent electromagnetic shielding properties,and magnesium alloys have been widely used in many fields such as automobile industry,electronics industry,aerospace,computer manufacturing,optical equipment and etc.However,the corrosion resistance of magnesium alloys is extremely poor,which restricts the application of magnesium alloys in the industrial field.Preparing a superhydrophobic surface on magnesium alloy,which can reduce the direct contact between the anti-corrosion coating and the corrosive mediu,therefore,the corrosion resistance of the magnesium alloy and the stability of the anticorrosion coating can be effectively improved.In addition,the special function of the superhydrophobic surface can also further expand the application of the magnesium alloy in the industry.In this paper,we build different superhydrophobic films on AZ31B magnesium alloy via hydrothermal synthesis and spraying method.The SEM,EDS,XRD,FT-IR and other analytical methods were used to study the morphology,structure and composition of the various film products and the combination with the magnesium alloy matrix,and the electrochemical polarization test was used to analyzes the corrosion resistance of superhydrophobic film.The specific research content is as follows:1.The rough surface structure was constructed by hydrothermal alkali etching on the surface of magnesium alloy.The fluorinated silane modified by self-assembly technique was used to prepare the superhydrophobic magnesium alloy surface.The effects of different alkali concentrations on the surface morphology of magnesium alloy were studied.After silanization,the static water contact angle of the surface film reached 162.2°.The results of the electrochemical electrochemical polarization test results showed that the super-hydrophobic surface had a significant anti-corrosion effect.The results of friction test and adhesion test showed that the prepared superhydrophobic film did not have superhydrophobic properties after 6 times friction test,and the adhesion between superhydrophobic film and AZ31B Mg alloy substrate had achieved level 0.2.Superhydrophobic surfaces on AZ31B magnesium alloy were fabricated by a simple one-step hydrothermal method.SEM images showed that the prepared superhydrophobic surface was composed of petaloid and stripe layered micro-nano structures.The maximum contact angle of the superhydrophobic surface was 163.3°and the minimum sliding angle was 2.8°.Superhydrophobic surfaces showed good corrosion resistance when immersed in 3.5 wt.%NaCl solution.In addition,by controlling the hydrothermal reaction conditions,constructing a suitable roughness structure was a necessary condition for the formation of superhydrophobic.The results of friction test showed that the contact angle of the prepared superhydrophobic film was less than 150°after 2 times friction test,and the adhesion test results showed that the superhydrophobic film has poor adhesion with AZ31B Mg alloy substrate?level 5?.3.The superhydrophobic coating with microscale and nanoscale binary structure was constructed on the surface of magnesium alloy AZ31B.The corrosion resistance of the superhydrophobic surface was investigated,and its wettability to different liquids was studied comprehensively.The corrosion current density of the superhydrophobic film decreases by three orders of magnitude,and the contact angle of water increases from 32°to 155°.The corrosion property was obviously improved.The solution pH and the coexisting NaCl,MgCl₂,NaI and CH₃COONa salts had little effect on the wetting properties of the prepared superhydrophobic surface.However,ethanol?C₂H₅OH?,sodium oleate(C₁₇H₃₃COONa)or sodium dodecyl benzene sulfonate(C₁₈H₂₈NaO₃S)solution significantly affected the wetting properties.The wear test results show that after 10 times rubbing with sandpaper,the contact angle is maintained above 155°and the roll angle is less than 2°.The results of friction test showed that the contact angle was maintained above 155°and the sliding angle was less than 2°during 10 times friction testing process.The adhesion test showed that the adhesion between the coating and the magnesium alloy substrate reaches level 0.4.The superhydrophobic composite coating of Si O₂/MWCNTs/PFOTES was prepared by sparying a mixing ethanol solution contained tetrafluoroethane?TEOS?,multi-walled carbon nanotubes?MWCNTs?,fluorosilane?PFOTES?and ammonia?NH₃·H₂O?.The effects of TEOS,MWNTs,PFOTES and NH₃·H₂O dosage on the superhydrophobic coating properties were investigated.The corrosion resistance of the superhydrophobic coating was evaluated by electrochemical method,and the results showed that superhydrophobic coating surface with contact angle greater than 155°and rolling angle less than 2°.Compared with bare AZ31B magnesium alloys,the superhydrophobic surface corrosion current density droped by4 orders of magnitude,which showed that the superhydrophobic coating significantly improved the corrosion resistance of magnesium alloys.The results of friction test showed that the contact angle of the prepared superhydrophobic film was less than150°after 3 times friction test,and the adhesion test results showed that the superhydrophobic film has poor adhesion with AZ31B Mg alloy substrate?level 5?.5.The superhydrophobic composite coating of PVDF/PFOTES-SiO₂ with 163.1°of contact angle and 2.2°of rolling angle was prepared by fluorinated nano-silica particles introduced into polyvinylidene fluoride?PVDF?by a simple spray process.The results of friction test and adhesion test showed that the prepared superhydrophobic coating had good adhesion with the substrate and had good abrasion resistance.In addition,the results of Tafel curve test showed that the prepared superhydrophobic coating had good resistance corrosion performance.6.The corrosion resistance of prepared superhydrophobic surface was studied by salt spray corrosion and real brine immersion method.The results showed that the corrosion resistance of magnesium alloys was related to its surface hydrophobicity,composition and microstructure.The superhydrophobic coating with microscale and nanoscale binary structure showed superior corrosion resistance.