| 2024 aviation aluminum alloy is widely used in aviation due to its high strength,good heat resistance and processing performance,and good damage tolerance performance.However,it is easy to cause intergranular corrosion and pitting because of its poor corrosion,which seriously affects the safety of aircraft.Therefore,it is essential to research and develop high-performance anti-corrosion coatings for the corrosion protection of aircraft.Montmorillonite(MMT)has great potential for nanocomposite anticorrosion coating applications because of its high aspect ratio,special layered structure,and easy intercalation.In this thesis,we study the electrochemical behavior of a double-layer coating composed of polypyrrole/montmorillonite nanocomposite epoxy coating(PPy-MMT/EP)and a Ce3+loaded montmorillonite epoxy coating(Ce-CS-MMT/EP)in the corrosion protection of 2024 aerospace aluminum alloy.Also,a flower-like zinc oxide/epoxy hydrophobic layer(Zn O/EP)was prepared on the surface of the double-layer coating in order to improve the mechanical durability and hydrophobicity of the coating.The main studies are as follows:(1)PPy-MMT nanocomposites were prepared by intercalation polymerization method,and the effects of different Py content and PPy-MMT additive content on the anti-corrosion performance of the coatings were investigated.It was shown that the cytosolic PPy particles were successfully inserted into the interlayer of MMT,and the interlayer spacing of MMT was expanded from 1.241 nm to 1.838 nm.The corrosion potential of the doped 5 wt%PPy-MMT(Py:MMT=3:1)nanocomposite coating was the largest at-0.661 V,and the corrosion current was the smallest at 1.801×10-8 A·cm-2.The protection rate reached 99.28%.The PPy-MMT/EP coating had a larger impedance arc and better corrosion protection than other coatings.(2)Ce-MMT and Ce-CS-MMT nanocomposites were prepared by cation exchange method,and the corrosion inhibition behavior of cerium ions on aluminum alloy and the anti-corrosion performance of the coating were investigated.It was shown that the Ce-MMT morphology changed from obvious agglomeration to irregular shape.The chitosan molecules were located on the MMT lamellar surface,which made the MMT lamellar surface uneven,and more Ce3+could be obtained between the MMT layers after chitosan pretreatment,and the interlamellar spacing of MMT was expanded from 1.241 nm to 1.577 nm.The electrochemical analysis of aluminum alloy in cerium-containing solution showed that the corrosion potential of aluminum alloy in Na Cl solution containing Ce-MMT extract was the largest(-0.636 V),the corrosion current was the smallest(2.059×10-6 A·cm-2).The corrosion inhibition efficiency reached 95.52%and the impedance arc was the largest with the best corrosion inhibition effect.The corrosion study of the coating showed that the corrosion potential of the Ce-CS-MMT/EP coating was the largest at-0.636 V and the corrosion current was the smallest at 1.049×10-7 A·cm-2.The protection rate reached 95.82%.Ce-CS-MMT/EP coating impedance arc was the largest,the greater the resistance of charge transfer,the better the shielding effect for electrolyte corrosive ions,and the best anti-corrosion performance.(3)Double-layer coatings of different thicknesses and sequences of Ce-CS-MMT/EP and PPy-MMT/EP were prepared by coating method to study their anti-corrosion and hydrophobic properties.The AC impedance spectra showed that the bilayer coating with 100?m Ce-CS-MMT/EP on the upper surface and 50?m PPy-MMT/EP on the lower surface had the largest Rp value,the smallest Cdl value and better corrosion resistance.The impedance modulus value of the bilayer coating structure was about 1000 times that of PPy-MMT/EP and about 100 times that of Ce-CS-MMT/EP,and the double coating had excellent corrosion resistance.It was shown that the hydrophobic coating surface was nanoscale flower-like,that acetic acid and stearic acid modified the Zn O/EP coating with a contact angle of 152.5°,adapted to a wide p H range,with excellent wear resistance.Moreover,after re-immersion in 20 ml of stearic acid(5wt%)and 2 M acetic acid/ethanol solution,the coating regenerated its hydrophobicity with a contact angle of 150±2°,while the hydrophobic double layer coating was found to have strong adhesion and excellent corrosion resistance. |
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