Studies Of Corrosion Behavior And Protective Measures Of 2A12 Aluminum Alloy In Coastal Atmospheric Environment

In this dissertation,the coastal atmospheric environment was simulated by neutral salt spray accelerated corrosion test.The corrosion law and corrosion mechanism of 2A12 aluminum alloy,the properties of organic composite coatings and modified acrylic polyurethane coatings,and the effect of CeO₂/Y₂O₃ rare earth oxides on the properties of micro arc oxidation coatings were studied by using mass loss method,X-ray diffraction（XRD）,scanning electron microscope（SEM）,energy dispersive X-ray spectrometer（EDS）,electrochemical tests and Fourier transform infrared spectroscopy（FT-IR）.In the first part of the dissertation,the corrosion characteristics of aluminum alloy in marine atmosphere were reviewed,the main influence factors of marine atmospheric corrosion had been overviewed,and the research progress,advantages and disadvantages of the corrosion protection methods of aluminum alloy in marine atmosphere were also summarized.Based on the above work,the purpose and significance of the dissertation have been pointed out.The corrosion law and corrosion mechanism of 2A12 aluminum alloy in coastal atmospheric environment were studied.The results show that the relationship between corrosion mass loss and corrosion time was in accordance with power rule.At initial corrosion stage,because of pitting corrosion,granular corrosion products emerged and gathered together to form a loose corrosion product layer,then pitting corrosion turned to be overall corrosion,and a large amount of Al（OH）3 formed by electrochemical corrosion thickened the loose corrosion product layer.During medium and later corrosion stage,outer corrosion product fell off and residual corrosion product layer became compact.The results of electrochemical tests were achieved.With corrosion time increasing,corrosion current density decreased firstly,then increased and finally decreased.In the meantime,capacitive reactance arc shrunk firstly,then expanded,finally shrunk slightly.Using fluorocarbon paint,acrylic polyurethane paint,epoxy glass flake paint,acrylic polyurethane paint,anti-corrosion primer and specific paint for aluminum alloy as ingredients,organic composite coatings were prepared on the surface of 2A12 aluminum alloy,and the modified acrylic polyurethane coating was prepared by adding nano graphite sheet and CeO₂/Y₂O₃ rare earth oxide.The properties of each organic composite coating and modified acrylic polyurethane coatings were studied.The result showed that the organic composite coating consisted of fluorocarbon paint,epoxy glass flake paint and anti-corrosion primer had the best corrosion resistance.Compared with 2A12 aluminum alloy,the corrosion current density decreased by 3 orders of magnitude,the polarization resistance increased by 3 orders of magnitude and the impedance value roughly enhanced by 2 orders of magnitude.Adding 0.5wt% nano graphite sheet and 1wt% CeO₂/Y₂O₃ rare earth oxide did not change the chemical structure of acrylic polyurethane coating,but improved the physical shielding effect,so the corrosion current decreased to 1/3 of the original coating,and the impedance value increased by about 1 order of magnitude.After adding CeO₂/Y₂O₃ rare earth oxides into the electrolyte,the micro arc oxidation film of 2A12 aluminum alloy became smooth and compact,and the number of micropores decreased.When the concentration was 3g/L and the ratio was 1:1,the corrosion resistance of micro arc oxidation film was the best.Compared with micro arc oxidation film,the corrosion current decreased by 1 order of magnitude,and the impedance value increased by 1 order of magnitude.