Research Of Corrosion Resistance And The Construction Of Hydrophobic Composite Coating On Magnesium Alloy Surface

Magnesium alloys are widely used because of their high specific strength/specific stiffness,good electrical and thermal conductivity,light weight and good electromagnetic shielding performance.However,the high chemical reactivity makes it extremely easy to be corroded in humid or acidic environments,resulting in component failure,which seriously limits their large-scale application in the industrial field.Therefore,it is imperative to improve the corrosion resistance of magnesium alloys.Surface coating technology is an effective means to improve the corrosion resistance of metals and alloys.Epoxy resin（EP）has good corrosion resistance and low price,so it is widely used as anti-corrosion coating.However,it has a large brittleness,and defects such as cracks can occur during curing,so a single epoxy resin can’t provide effective protection for magnesium alloy.In this paper,epoxy resin is used as a film-forming substance,starting from improving the hydrophobicity and extending the corrosion path of the coating,by characterizing and testing the microstructure,wettability and corrosion resistance of coatings with different structures,in order to improve the long-term protection ability of epoxy-based coating against magnesium alloy.The main research contents and results are as follows:（1）Using NH₂-PDMS-NH₂ as the modifier,the epoxy resin（EP）was hydrophobically modified,and the PDMS-EP coating（P-EP）was prepared by spraying process.Compared with pure EP coating,the surface of this coating has no defects such as cracks,which improves the surface quality of the coating.The water contact angle has been increased from 88°to 118°,and the coating has been transformed from a hydrophilic surface to a hydrophobic surface,reducing the contact area with corrosive solutions.The results of the potentiodynamic polarization curve show that the corrosion current density of P-EP coating is reduced by 6 and 4 orders of magnitude compared with magnesium alloy and pure EP coating,respectively,and the corrosion resistance is significantly enhanced.By immersing pure EP coating and P-EP coating in 3.5%Na Cl solution for 7 days,the corrosion resistance of P-EP coating is still better than that of pure EP coating,showing better durability.（2）Using graphene oxide（GO）as filler,EP-GO coating was prepared by spinning coating process,and nano-silica was modified by Perfluororooctyltriethoxy-silane（PFOTES）to prepare hydrophobic silica solution,and silicon-based superhydrophobic surface was prepared on the surface of EP-GO coating by spraying-assisted self-assembly technology to obtain EP-GO/Si O₂ coating with double-layer structure.The water contact angle of the composite coating reaches 158°,and the contact area with the corrosive liquid is only 10%,which has good mechanical and chemical stability and good self-cleaning performance.The EIS test results show that the hydrophobic coating of the double-layer structure has the best corrosion resistance.By immersing pure EP coating,EP-GO coating and EP-GO/Si O₂ coating in 3.5%Na Cl solution for 21 days,the corrosion resistance of EP-GO/Si O2 coating was always maintained at the best and showed good durability.（3）EP-ZnO/ZnO-SHS coating was prepared by spin-coating-hydrothermal in-situ growth method,and EP-ZnO/ZnO-SLIPS coating was prepared by perfluoropolyether lubricant（PFPE）as the substrate,the water contact angles of the two coatings were 157°and 120°,respectively,both with good hydrophobicity,and the friction test results showed that the EP-ZnO/ZnO-SHS coating had good mechanical stability and maintained superhydrophobic characteristics after friction of 240 cm.This lays the foundation for stable storage of the lubricant.The soaking results in 3.5%Na Cl solution showed that the chemical stability of EP-ZnO/ZnO-SLIPS coating was much better than that of EP-ZnO/ZnO-SHS coating.The results of the potentiodynamic polarization curve show that the corrosion current density of EP-ZnO/ZnO-SLIPS coating is reduced by 7 and 1 order of magnitude compared with magnesium alloy and EP-ZnO/ZnO-SHS coating,respectively,and has the best corrosion resistance.The two coatings were immersed in 3.5%Na Cl solution,and the corrosion resistance of EP-ZnO/ZnO-SHS coating was close to that of magnesium alloy after one week,while the EP-ZnO/ZnO-SLIPS coating still had high corrosion resistance after 70 days of immersion,showing good long-term serviceability.