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

Magnesium alloy is the lightest metal structural material,with high specific strength,specific stiffness,noise reduction,electrical conductivity,heat conduction and other characteristics,and has broad application prospects in the fields of communication electronics,automobile manufacturing,and aerospace.However,because magnesium has high electronegativity and the porous Mg O and Mg（OH）₂films are easily formed on the surface,the corrosion resistance of magnesium alloys is poor,which limits its practical applications.Although the traditional anti-corrosion coatings can effectively separate the corrosive medium from the magnesium alloy,they are in direct contact with the corrosive medium.During the service process,the corrosive medium will gradually penetrate the coating,which will lead to severe corrosion of the magnesium alloy.Superhydrophobic and superamphiphobic coatings can effectively reduce the contact area and contact time between the corrosive medium and the coating.So,they have received great interest.However,the conventional superhydrophobic and superamphiphobic coatings have some problems such as poor stability,poor salt spray corrosion resistance,and complicated preparation methods.Therefore,in this study two magnesium alloy anti-corrosive coatings with excellent performance have been prepared by the combination of the attapulgite superamphiphobic coating or carbon nanotube superhydrophobic coating with the shape memory polymer.The main research contents and results are shown below.First,by combining the shape memory polymer（SMP-BTA）dispersed with the corrosion inhibitor and the attapulgite superamphiphobic coating（fluoro ATP）,a bi-layer self-healing superamphiphobic coating for long-term corrosion protection of magnesium alloys was prepared.coating.The coating has excellent superamphiphobicity(CA_{3.5 wt%NaCl}=160.4°,SA_{3.5 wt%NaCl}=1.8°,CA_n-hexadecane=154.7°,SA_n-hexadecane=10.1°),which can resistant to immersion corrosion in 3.5 wt%NaCl solution for 80 days and resistant to 5 wt%NaCl salt spray corrosion for 54days.It exhibits excellent long-term corrosion resistance and is resistant to various serious physical damages（such as 10 cycles of scratching/self-healing,hexagonal star scratching and grid scratching）.In addition,the repaired coating can still withstand immersion corrosion in 3.5 wt%NaCl solution for 60 days and 5 wt%NaCl salt spray corrosion for 30 days,showing excellent self-healing performance.Second,the superhydrophobic long-term anti-corrosive coating with photo-thermal self-healing ability was prepared by combining superhydrophobic carbon nanotubes（PF-POS@MWCNTs）and shape memory polymers dispersed with corrosion inhibitors（SMP-BTA）.The coating showed excellent superhydrophobicity(CA_{3.5 wt%NaCl}=155.4°,SA_{3.5 wt%NaCl}=4°).In addition,the coating has excellent photo-thermal self-healing properties for both chemical damage and physical damage.After O₂plasma etching treatment,the surface becomes superhydrophilic(CA_{3.5 wt%NaCl}=0°),but its superhydrophobicity can be fully restored after exposure to 1 sun for10 min(CA_{3.5 wt%NaCl}=155.4°,SA_{3.5 wt%NaCl}=4°).The logarithmic value of the low-frequency impedance modulus of the sample after physical damage is reduced to5(log|Z|_0.1Hz=5),but was completely restored to the original coating state(log|Z|_0.1Hz=10)after exposure to 1 sun for 10 min.The original intact coating is resistant to salt spray corrosion for 50 days,while the coating photo-thermally self-healed from O₂plasma etching and scratch damage is still resistant to salt spray corrosion for 50 days and 25 days,respectively.This study provides a new approach to solve the poor durability and salt spray corrosion resistance of superhydrophobic and superamphiphobic anti-corrosion coatings,and develops a useful preparation technology of anti-corrosion coatings.