Preparation And Properties Of Superamphiphobic Coatings For Anti-corrosion Of Mg Alloy

Magnesium（Mg）alloys,the lightest structural alloys,have many unique properties and thus are widely used in various fields,such as 3C products,automobiles,aerospace components and biomedical,etc.However,they are extremely susceptible to corrosion when exposed to the environment.This is because of highly electronegative potential of Mg and the naturally formed MgO/Mg（OH）₂ layer on Mg alloys is highly porous.In recent years,bioinspired super anti-wetting coatings have received great interest in the fields of anti-corrosion,self-cleaning,anti-fouling and anti-icing,etc.Therefore,two superamphiphobic coatings for the anti-corrosion of the Mg alloy were developed in this study.The wettability and corrosion resistance of the coatings were also studied,and the anti-corrosion mechanism was revealed.The main research contents and results are shown below.First,the superamphiphobic coating for anti-corrosion of the Mg alloy was successfully prepared by combining a conventional epoxy resin adhesive layer and the perfluorodecany polysiloxane modified SiO₂ superamphiphobic coating.The coating showed excellent superamphiphobicity(CA _water=166°,SA _water=1°,CA _n-hexadecane=163°,SA _n-hexadecane=3°)and corrosion resistance.The corrosion current density and the impedance modulus at low frequency are 7.154×10^-1212 A cm^-2 and 10¹00 ohm,respectively.Moreover,the coating can withstand corrosion of the 3.5 wt%NaCl solution immersion test for 70 d or the salt spray test for 35 d.This is owing to high superamphiphobicity and“synergistic effect”of the bi-layer structure.In addition,in the long-term 3.5 wt%NaCl immersion test and the salt spray test,it was found that the anti-corrosion performance of the superamphiphobic coating is superior to the superhydrophobic coating with similar microstructure.This is because the superamphiphobic coating maintained excellent superamphiphobicity in the corrosion tests owing to high chemical stability of the C-F bonds.Furthermore,compared with the superhydrophobic coating,the superamphiphobic coating has better superhydrophobicity for microdroplets.Hence,the contact area and contact time of NaCl drops on the coating are limited,and the diffusion of corrosive media was effectively blocked,which provides long-lasting efficient protection for the Mg alloy.In addition,another self-healing superamphiphobic coating for anti-corrosion of the Mg alloy was successfully prepared by combining a shape memory epoxy resin coating with the perfluorodecyl polysiloxane modified SiO₂ superamphiphobic coating.The coating showed excellent superamphiphobicity(CA _{3.5 wt%NaCl}=165.8°,SA 3.5 wt%NaCl=1°,CA n-hexadecane=160°,SA n-hexadecane=3.4°)and corrosion resistance.The corrosion current density and impedance modulus at low frequency are 5.971×10^-1212 A cm^-2 and 10^10.7 ohm,respectively.Meanwhile,the coating showed excellent self-healing performance for the damage caused by physical scratch.The impedance modulus at low frequency of the healed coating completely recovered to the original coating,and the healed coating had excellent corrosion resistance.This is because the shape memory self-healing epoxy resin layer could effectively drive repair of microstructure of the superamphiphobic layer.With the repair of microstructure,the superamphiphobicity and anti-corrosion performance of the coating were completely restored.Therefore,the repaired coating still had excellent anti-corrosion performance.This study provides a new approach to solve the corrosion problem of various metals and alloys,and forms promising preparation techniquies of anti-corrosion coatings.