Study On The Failure Of Organic Coating Protective Systems Caused By Environmental Stress

With the continuous expansion of the practice scope for human society,the development of industrial technology towards the field of deep space,deep sea and deep blue will face even harsher environmental conditions.The service environment of engineering structures which are protected by organic coatings is more severe and challenging,and makes the failure mode of organic coating protective systems more various and the failure mechanism more complex.Thus,a lot of research work related to coating failure has been done in relevant fields.However,the effect of mechanical factors,especially the interaction between mechanical factors and environmental factors,was still in its infancy.Although the failure and comprehensive evaluation of organic coating protection systems after accelerated test raise more concern in related domain,there is a few papers on the degeneration of mechanical properties to organic coating systems.Therefore,In this study the degeneration process and failure law of aluminum alloy,anodized aluminum alloy and anodized aluminum alloy with organic coatings had been studied systematically under the respective action of corrosion factors,mechanical factors and its synergistic/alternating effects through accelerated test.Based on electrochemical impedance spectroscopy technology and macro/micro morphology characterization technology,the mechanical property evolution and comprehensive evaluation using the analytic hierarchy process(AHP)of the organic coating protective systems also were investigated after the environmental simulation acceleration test.The conclusions were obtained as follows:1.Under the effect of corrosion factors,the corrosion resistance of 2024 aluminum alloy was very poor.But the corrosion resistance of aluminum alloy after anodic oxidation became higher,the barrier layer of anodic oxide film played a main shielding effect,the corrosion resistance of anodized aluminum alloy with organic coatings was higher than anodized aluminum alloy.Different membrane layer of organic coating system played a leading role in shielding solution under different immersion time.The time constant of the impedance spectra increased from one to three while the solution corrosive media transported to the interface of organic coating and anodic oxide film gradually.When the first corrosion point had appeared on the surface of the coatings,the impedance of the organic coating protective systems was getting low after immersion for 106 days.In this case,the impedance of the anodized film remained at a high level,2.Under the action of stress factor,the damage degree of coatings was related to the maximum stress value.Under the condition of constant tensile stress loading,both electrochemical impedance spectroscopy and microstructural morphology of the coating protective systems showed that the degeneration degrees were induced which could be ranked as:Plastic lower limit zone>Elastic limit zone>Perfectly elastic region;the degeneration of coatings was related to the maximum stress amplitude and cycle times under cyclic stress loading.3.Under the synergistic action of corrosion and stress,the electrochemical behavior of the coating systems was similar to the single factor action of stress,but the failure process of the coating system was greatly accelerated.This was directly reflected by the appearing time of corrosion points on the organic coating.In addition,the alternating effect is obviously weaker than the synergistic effect.4.After the marine atmosphere environment simulation accelerated test,the impedance spectra of organic coating protection systems with different substrates had different variation rules,showing different corrosion-resistance to humidity and heat,mold and salt spray.The evaluation obtained by using the comprehensive evaluation model was corresponding with the resistance,but the plasticity index of the anodized 2024 A1 alloy coating systems decreased.