Posted Treatment Of Microarc Oxidation Film On Al Alloy And Its Corrosion Performance

Microarc oxidation(MAO)films are widely used in aerospace,ship and machinery manufacturing as its excellent wear resisitance and electrical insulation.However,the corrosion problem is still restricts the application of MAO film in the corrosive environment,due to the structure defects of micropore and microcrack formed during the MAO process.In this paper,in order to improve the density of MAO film,in situ growth of layered double hydroxide(LDH)and silanization treatment were used to modify the MAO treated Al alloy.The insitu growth of LDH on the surface of MAO film was attempted to seal the defects in MAO film.And then,the process of silanization of MAO film was optimized by dipping method.On this basis,the reinforcement of hydroxylation pretreatment and electrochemical assisted deposition on the silanization of MAO film was discussed.Microstructure of film was observed and analyzed using SEM,XRD,XPS,etc.Corrosion resistance and corrosion behaviors of the films were evaluated by electrochemical test,salt spray test and salt immersion test.NiAl-LDH,ZnAl-LDH and MgAl-LDH were fabricated on MAO treated Al alloys via an insitu growth method.The results showed that the growth of the LDH on MAO film is largely determined by the specific area,chemical composition,crystalline structures of the alumina phase of the MAO film and the type of metal ions in LDH solution.More importantly,LDH nanoplates can grow into the micropores and microcracks in MAO film,and then gradually seal these structural defects.The anti-corrosion performance of MAO film during long-term immersion in NaCl solution also can be improved greatly via LDH treating because the defect-sealing effects of LDH can enhance the barrier property of both the porous and dense layers of MAO film,and then restrain the penetration of corrosive agents through the MAO film to the metal substrateThe effects of silanization on the corrosion resisitance of MAO film were studied using dipping method.The results showed that a silane film fabricated on the surface of MAO film after silanization treatment,the defects in the MAO film defects were sealed by silane effectively,and then the corrosion resistance of MAO film is improved significantly.The anti-corrosion performance of MAO film during long-term immersion in NaCl solution also can be improved greatly via silanization treatment because the defect-sealing effects of silane can enhance the barrier property of both the porous and dense layers of MAO film,and then restrain the penetration of corrosive,so as to improve the long-term corrosion resistance of micro-arc oxide film.In addition,DTMS films displayed the highest barrier properties and corrosion resistant performance during the three kinds of silane in this paper due to the presence of long hydrophobic dodecyl chain in bone structure.The effects of hydroxylation pretreatment on the silanization of MAO film were studied by hydrothermal treatment.The results showed that the amount of hydroxyl on the surface of MAO film increased significantly after hydroxylation pretreatment,which improved the formation of silane film dramatically,and further improved the corrosion resistance of the MAO film.The effects of electrochemical assisted deposition on the silanization of MAO film were discussed.The results showed that the "alkalize catalylic effect" of electrochemical assisted deposition would facilitate the deposition of silane in the micropores of MAO film,improve the sealing effect of silane on the micropores,and then further improve the corrosion resistance of the film.The study also found that the effect of electrochemical assisted deposition was significantly influenced by the structure of MAO film and electrodeposition parameters.The diffusion ability of O2 in the micropore of MAO film decreases and the effectiveness of "alkalize catalylic" decreased with increasing the thickness of MAO film.The effectiveness of "alkalize catalylic" initially increased and then remained at this level with increasing the deposition time or decreasing the deposition potential.