Studies On Superhydrophobic And Superoleophobic Coatings On Magnesium Alloys

For their low density,high strength and high specific strength,magnesium alloys are widely used in automotive,electronics,aerospace and other fields.However,the chemical property is so active that the application seriously compromised because of their high susceptibility to corrosion.The superhydrophobic and superoleophobic surfaces developed in recent years have the functions of anti-corrosion and self-cleaning property,which can not only provide protection for magnesium alloys,but also endow them with self-cleaning ability,which helps to expand the application field of magnesium alloys.However,the superhydrophobic and superoleophobic surfaces of magnesium alloys reported in the current literature have complicated preparation processes,substrate-dependence,and small-scale production.In particular,the poor durability of these surfaces seriously affects the application of magnesium alloys.In order to solve the above problems,in this paper,a simple one-step spray method was used to prepare a polymethyl methacrylate/zinc stearate(PMMA/Zn(C₁₇H₃₅COO)₂)superhydrophobic coating and aluminum phosphate/perfluorooctyl trichlorosilane（AP/PFOTS）superamphiphobic coating with superhydrophobicity and superoleophobicity on the surface of magnesium alloys with good durability.The wettability,micro-morphology and chemical composition of the coating were characterized by contact angle measuring instrument（CA）,scanning electron microscope（FESEM）,X-ray photoelectron spectroscopy（XPS）and Fourier infrared spectroscopy（FTIR）.The anti-corrosion performance,mechanical performance,chemical stability,light stability,high temperature resistance,natural environment adaptability and self-cleaning performance of the coating were tested through laboratory simulation experiments and actual natural environment experiments.Based on the characterization of various properties characterization and performance test results,the film formation mechanism and durability mechanism of the coating are discussed.And the main tasks as follows:1.Based on polymethyl methacrylate（PMMA）can form a network structure,Zn O modified with stearic acid（SA）can provide the idea of roughness and reduce surface energy,a superhydrophobic coating was prepared with a static contact angle of 157.0°and a rolling angle of 6.0°by spraying PMMA/Zn(C₁₇H₃₅COO)₂ suspension on the surface of magnesium alloys.The coating consists of laver-like micro-nano structures,whose main components are PMMA and zinc stearate.The long alkyl chain(C₁₇H₃₅-)of zinc stearate in the coating can significantly reduce the surface energy of the coating,making the coating superhydrophobic.Performance test results show that the prepared coating has excellent corrosion resistance（R_c=1.23×10⁵Ω·cm²）,self-cleaning property,sand impact resistance(1.0 g min^-1,≥20 min),water impact resistance（2drops per second,≥180 min）,friction and wear resistance（1.0 k Pa,≥1250 cm）,tape peel resistance（≥2.15 k Pa）,acid and alkali resistance（p H=1～13）,resistance to organic solvent immersion（≥24 h）and high temperature resistance（200°C,≥24 h）.Zinc stearate is embedded in the network structure formed by the polymer PMMA and is firmly fixed,so the coating shows good durability.2.Aluminum phosphate（AP）can react with magnesium alloys to form micro/nano structure at a certain temperature to enhance the binding force between the coating and the substrate,and perfluorooctyltrichlorosilane（PFOTS）can provide extremely low surface energy substance.Based on the above reasons,the superhydrophobic and superoleophobic coatings were prepared on the surface of magnesium alloys by spraying AP/PFOTS suspension The coating has a multi-layer network structure and many nano-protrusions are distributed on the network structure.The fluorine-containing functional groups in the coating give the coating extremely low surface energy.Performance test results show that the prepared coating has excellent impact resistance to sand particles(1.0 g min^-1,≥20 min),water impact resistance（2 drops per second,≥20 h）,and friction and wear resistance（1.0 k Pa,≥2500 cm）,acid and alkali resistance（p H=1～14）,resistance to organic solvent immersion（≥48 h）and light stability（≥672 h）,and natural environment testing further shows that the coating has good environmental adaptability.The coating has long-lasting self-cleaning performance on the pollution of inorganic particles and organic matter.Without additional nanoparticles adding,the coating is complete and uniform.The adhesive property of aluminum phosphate and the reaction with the magnesium alloy substrate enhanced the bonding force between the coating and the substrate,making the coating have excellent durability.