The Preparation And Corrosion Resistance Of Superhydrophobic ZrO₂(TiO₂)-MAO Film On Magnesium Alloy

Magnesium(Mg)alloys have attracted increasing attention in the fields of automobile,aerospace,biomedical and electronics owning to their excellent properties such as high strength-weight ratio,excellent electromagnetic shielding and machinability.Nevertheless,the high electrochemical reactivity of magnesium alloys implies that they are easily oxidized and are susceptible to corrosion at room temperature,which has seriously limited their engineering application.ZrO2 and TiO2 are a class of chemically stable oxide ceramic materials.The superhydrophobic surface can form an air film between the metal substrate and the corrosive solution and effectively hinder the diffusion of corrosive media to the substrate.The construction of superhydrophobic ZrO2/TiO2 layer on AZ31B Mg substrate is expected to significantly improve the corrosion resistance of magnesium alloy.This paper prepared superhydrophobic ZrO2-MAO composite films and TiO2-MAO composite films on micro-arc oxidized(MAO)AZ31B Mg substrate by deep ultraviolet(DUV)assisted low-temperature sol-gel method.The organic combination of the three anti-corrosion technologies of MAO,the deposit of ceramic oxide and the construction of superhydrophobic surface significantly improves the corrosion resistance of Mg alloy.We eventually developed a new method to improve the corrosion resistance.The main research work was as follows:(1)ZrO2 sol was obtained with sensitive good ultraviolent sensitivity using zirconium n-butoxide as raw material,acetylacetone as a photosensitive chelating agent.The best process for the ceramic transformation of ZrO2 sol under DUV light was studied.The results showed the ZrO2 gel film had the strongest absorption at the wavelength of 304 nm;and that the organic in the ZrO2 gel film could be completely decomposed and ZrO2 film was completely transformed into an amorphous ZrO2 film under the DUV light of 120 min at 150?.(2)ZrO2-MAO composite films were prepared on the Mg alloy substrate by MAO and DUV-assisted low-temperature sol-gel method in sequence.The effect of annealing temperature on the microstructure,surface morphology and corrosion resistance of the ZrO2-MAO composite films was studied,and the corrosion resistance of magnesium substrate,MAO and ZrO2-MAO at different annealing temperatures was compared.The results showed when the annealing temperature was 400?,that the ZrO2 film had crystallized into a tetragonal phase structure;and that the surface of the ZrO2-MAO composite films was compact without cracks;and that the corrosion current density(icorr)of the ZrO2-MAO composite films was from 1.69×10-4 A/cm2 decreased to 9.77×10-8 A/cm2,impedance modulus(|Z|f?0)increased from?102?·cm2 to?105?·cm2 compared with the Mg substrate.The corrosion resistance increased by nearly 3 orders of magnitude,indicating that the corrosion resistance of the ZrO2-MAO composite films was significantly enhanced.(3)With using 1H,1H,2H,2H-perfluorooctyltrichlorosilane(FAS)as a chemical modifier,the FAS/ZrO2-MAO composite films with superhydrophobic properties were prepared by chemically modification.The FAS/ZrO2-MAO composite films were characterized by the surface chemical composition,wettability and corrosion resistance.The results showed the FAS organic molecular layer was uniformly immobilized on the surface of the composite films;and that the ZrO2-MAO composite films had a micro-nano rough structure,and that the WCA of the ZrO2-MAO composite films was less than 5°,showing excellent superhydrophilic,while the FAS/ZrO2-MAO composite films modified with low surface energy had a WCA of 162°,which was excellent superhydrophobic;and that compared with ZrO2-MAO composite films,icorr of FAS/ZrO2-MAO composite films was reduced from 9.16×10-7 A/cm2 to 2.75×10-9 A/cm2,|Z|f?0 from?104?·cm2 increased to?105 ?·cm2,and the corrosion resistance was improved by nearly one order of magnitude.(4)A TiO2 photosensitive sol was prepared by using n-butyl titanate as raw material.TiO2-MAO composite films were prepared by a process similar to ZrO2-MAO composite films.The changes on surface microstructure,surface chemical composition,wetting and corrosion resistance of the TiO2-MAO composite films before and after modification were discussed.The results showed the FAS modifier had little effect on the surface morphology of the TiO2-MAO composite film,which was immobilized on the surface of TiO2 film by the reaction of the Si-OH groups and the-OH groups on the surface of the TiO2 film,forming CF3(CF2)5(CH2)2Si(OTi)3;and that the WCA of the TiO2-MAO composite films were 8°,while the FAS/TiO2-MAO composite films had excellent hydrophobicity,and its WCA reached 160° because of the combined effect of the rough structure and the FAS hydrophobic layer.Compared with TiO2-MAO composite films,icorr of the FAS/TiO2-MAO composite films decreased from 1.64x10-7 A/cm2 to 1.31×10-9 A/cm2,|Z|f?0 value increased from?2.5×105 ?·cm2 to?107 ?·cm2,the corrosion resistance had increased by an order of magnitude.It could be seen that the superhydrophobic FAS/TiO2-MAO composite films can effectively hinder the interaction between corrosive media and the substrate,which further improve corrosion resistance of ZrO2-MAO composite films to Mg alloy.