Influence Of Environmentally Friendly Sealing Process On Corrosion Resistance And Self-healing Properties Of6061 Aluminum Alloy Anodic Oxide Film

6061 aluminum alloy has been widely used in ships and marine equipment engineering due to its excellent comprehensive performance,but it is prone to corrosion in the marine atmosphere of high temperature,high humidity,and high salt spray.Therefore,the surface treatment of aluminum alloy is necessary to improve corrosion resistance.Anodizing is a common surface treatment method,but the generated micropores are easy to absorb corrosive media and corrode,so the micropores should be sealed.Traditional sealing technology is gradually replaced by new green sealing technology due to its disadvantages such as harmful to human body and environment.Although the research on compound sealing has gradually increased,whether the sealing film show a significant improvement in corrosion resistance in the harsh marine atmosphere remains to be studied.At the same time,this thesis explores whether the new sealing process can be used in the harsh marine atmosphere.There is a certain degree of"self-healing"and its self-healing mechanism in the environment.In this thesis,the green and environmentally friendly cerium salt and SiO₂ sol sealing are performed on the 6061 aluminum alloy anodic oxide film,and the optimal process parameters of the two are obtained through orthogonal experiments,and then the oxide film is composite sealed with the optimal process parameters of the two.This thesis selects unsealed,cerium salt sealing,SiO₂ sol sealing and composite sealing for corrosion resistance comparison,and selecting unsealed after scratches,new green cerium salt sealing,composite sealing and traditional chromium salt sealing is used for self-healing comparison,and the harsh marine atmospheric environment conditions and parameters are simulated in the periodic infiltration box,and each sample is studied of the corrosion behavior,self-healing behavior and its mechanism in harsh environments by means of scanning electron microscope,energy spectrometer,X-ray energy spectrum diffraction and electrochemical workstation testing.The results show that:Taking the corrosion resistance of the film as an indicator,the optimal process parameters for single cerium salt sealing are 40g/L cerium salt,and the sealing temperature and time are 65℃and 2h respectively;The optimal process parameters of single SiO₂ sol sealing are H₂O:TEOS molar ratio 1:1,heat treatment temperature and time are 100℃and2h.In the micro-morphology after sealing,the composite sealing cross-linked composite film is relatively flat and uniform,while the cerium salt has film cracks,and the SiO₂ sol has pit defects.From the perspective of self-corrosion potential,the self-corrosion potential of composite sealing is about 80-100m V higher than single sealing;From the perspective of corrosion current density,the corrosion rate of unsealed is the largest,and the corrosion rate of composite sealing is the smallest.The corrosion current density is several times or even hundreds of times that of the sealed sample.The performance of the sample’s corrosion resistance is:composite sealing>SiO₂ sol sealing>cerium salt sealing>unsealing.In the periodic immersion test,the main form of corrosion of each sample to the later stage is pitting.The unsealed pits are the most serious,and the composite sealing pits are the least,indicating that the composite sealing has a more protective effect on the film;Electrochemical tests show that in a harsh corrosive environment,the overall corrosion resistance of the sample film decreases with the extension of the corrosion time,but the corrosion resistance of the cerium salt sealing and composite sealing will be uprushed at a certain corrosion stage;However,the corrosion resistance of SiO₂ sol sealing continued to decrease,indicating that cerium salt is more time-sensitive than SiO₂ sol sealing.According to the self-healing behavior of the scratched sealing sample in the simulated marine atmosphere,it can be found that the self-healing mechanism of cerium salt sealing and chromium salt sealing is different.Among them,the cerium salt sealing is the Ce ion formed by the dissolution of the conversion film and migrate to the scratch,and form Ce（OH）₃ and Ce（OH）₄ precipitates with OH^-;While chromium salt sealing is the formation of CrO₄^2-formed by the dissolution of the passive film.After migration to the scratch,reduction and dehydration condensation reaction forms of Cr（OH）₃ and Cr₂O₃,Cr（OH）₃,Cr₂O₃,CrO₄^2-and Al³⁺react to form precipitates at the scratches;Among them,Cr has a strong migration force.The"self-healing"of the sealed samples gradually weakened with the extension of the corrosion time;the"self-healing"of the composite sealing film was the weakest.