| Micro-arc oxidation technology,refers to the formation by in situ growth of ceramic coating on the valve metal(such as titanium,magnesium,aluminum,etc.)with the metal matrix firm,compact structure,excellent corrosion resistance,abrasion resistance,high temperature and electrical insulation properties,is one of the commonly used technologies in the field of corrosion and protection of Mg-Li alloys at present.However,the micro-arc oxidation coating is composed of many micro-nano-size porous structures.The existence of the porous structure makes the corrosion medium more accessible to the metal substrate.Therefore,the preparation of composite coating technology is the focus of current micro-arc oxidation technology research.In this paper,magnesium-lithium alloy is the object of study.Based on the micro-arc oxidation film,we prepared a good corrosion resistance composite coating using different treatment methods in the magnesium-lithium alloy.XRD,EDS,SEM and FT-IR analytical techniques were used to characterize the composition and morphology of different layers.The static contact angles,potentiodynamic polarization curves and electrochemical impedance spectroscopy were used to discuss the wettability of composite coatings and the corrosion resistance performance.Micro-arc oxidation/stannate conversion coating was prepared on Mg-Li alloy substrates using micro-arc oxidation and chemical conversion composite techniques.Through the characterization test,it was observed that the surface of the composite coating was formed by stacking many white magnesium stannate crystals.The electrochemical performance test showed that the corrosion resistance of micro-arc oxidation/stannate conversion composite coating was better than that of micro-arc oxidation coating,and the corrosion resistance of magnesium-lithium alloy substrate was improved,its impedance modulus was that of magnesium-lithium alloy substrate 100 times and 30 times,respectively.Through long-term immersion experiments.The changes in morphological and the electrochemical tests after immersion at different times indicate that the stannate conversion membrane has excellent self-healing properties in 3.5wt.%NaCl solution.The self-healing property of the layer is due to the dissolution and reprecipitation of magnesium stannate crystals.After the sample was soaked for 33 days,the impedance film value could still reach 5000?cm~2.An superhydrophobic composite coating was prepared by self-assembly of the amphiphilic dodecylphosphonic acid dodecylphosphonic acid onto the surface of the microarc oxidation/stannate conversion composite coating.By the analysis of the FT-IR spectra,a comparison of the characteristic peaks of the synthetic dodecylphosphonic acid and self-assembled phosphonic acid film.demonstrates that dodecylphosphonic acid is assembled on the substrate in a P-O-Me bonded manner.Material surface.Optimizing the technological conditions for the self-assembly of phosphonic acid layer,the higher the polarity of the self-assembly solvent,the higher the coverage of self-assembled molecules on the surface of the film,and the best corrosion resistance of the film;the self-corrosion of the film at the assembly time of 24 hours.The lowest current density and the largest static contact angle demonstrated that the higher the hydrophobicity of the membrane,the better the corrosion resistance.The contact angle and electrochemical test were used to evaluate the wettability and corrosion resistance of the film.The results showed that the static contact angle of the ultra-sparse coating was greater than 130°in different pH solutions,and the self-assembled layer had good Chemical stability:The super-sparse composite coating has a resistance film value that is 40 times that of a magnesium-lithium alloy substrate and reaches 700,000?cm~2,and the corrosion resistance is greatly improved because the super-hydrophobic surface effectively blocks the direct corrosion of the etching solution and the metal substrate.contact.Through a week of immersion experiments,the ultra-sparse composite coating had a reduced impedance film value of 30000?cm~2,which is still higher than the un-corroded impedance film value of the micro-arc oxidation/stannate conversion composite coating.Through the layer-by-layer self-assembly method,the aromatic ring was successfully connected to the end of the amphiphilic organic phosphonic acid group to prepare a micro-arc oxidation/self-assembled composite coating.In the first layer,11-hydroxyundecylphosphonic acid was in-situ bonded to the micro-arc oxidation film by a self-assembly technique,and then a pyridine ring was grafted at the hydroxyl end through an esterification reaction to study the film having a pyridine ring at the tail end.The effect of the layer on the wetting and corrosion resistance of the self-assembled layer was investigated,and the bonding method of the organic phosphonic acid on the substrate was discussed.The results showed that the organic phosphonic acid was bonded with PO-Me on the metal substrate,and the self-assembled films were highly ordered.The contact angle of the self-assembled layer to the neutral and weakly acidic and alkaline droplets was higher than 150°,indicating super-hydrophobicity.Sex.The self-assembled films were electrochemically tested.The results show that the self-assembled films have excellent corrosion resistance in corrosive media,and the corrosion resistance is much higher than that of the micro-arc oxidation coatings themselves.Compared with the self-assembled dodecylphosphonic acid composite coating,the film with terminal pyridine ring can enhance the compact arrangement of self-assembled molecules throughπ-πconjugation,and the corrosion resistance is higher than that of intermolecular van der Waals force.Self-assembled dodecylphosphonic acid monolayers have an impedance film value 10 times that of the alkyl chain layer. |
PDF Full Text Request