Corrosion Behavior And Life Prediction Of Copper Aluminum Composite Plate

The copper-aluminum layered composite can significantly reduce the material cost and the weight of the transmission system by replacing pure copper as the conductor.However,when it is used in important equipment or engineering,the performance changes and life problems caused by corrosion during service have not been systematically studied,which directly restricts the expansion of its application scope.As a conductor,corrosion is the main reason for its performance change and failure.Due to the structural characteristics of copper-aluminum layered composite,the corrosion behavior is quite different from pure copper and pure aluminum.However,the research work in this field is not deep enough,especially the impact assessment and life prediction of corrosion on the performance of materials in service are missing.Therefore,the research work on copper-aluminium layered composites for conductive purposes was carried out in this paper.The corrosion behavior of AC and DC current in service was systematically studied by the accelerated corrosion test of copper-aluminium composites.The mechanism of current influence is discussed.The service life prediction model under corrosive conditions was built and the corrosion prevention technology for improving the corrosion life of copper-aluminum composite plates was studied.The results show that the corrosion of copper-aluminum composite plate occurs on one side of the aluminum base,including galvanic corrosion at the interface and pitting on the aluminum base.The corrosion products mainly include Al₂O₃,Al(OH)₃and Al O(OH).Only oxygen reduction reaction occurs on the copper surface,which provides sufficient OH^-ions for the aluminum anode,and copper does not corrode itself.The galvanic corrosion leads to the corrosion resistance of copper-aluminum composites which is lower than that of pure aluminium and pure copper.The common influence mechanism of AC current and DC current on copper-aluminum composites is the synergistic effect of accelerated corrosion of materials caused by current on electrochemical parameters and corrosion inhibition of materials caused by current temperature effect.Therefore,the corrosion rate and corrosion degree of materials increase first and then decrease with current.The difference is that AC current affects the corrosion behavior of material by changing the mobility of Cl-ions in electrolyte liquid film on material surface.The higher the mobility of Cl^-ions is,the worse the adhesion on material surface and the lower the corrosion rate and degree.However,AC current has no effect on the formation of corrosion products.DC current influences the corrosion behavior of the material by causing the directional migration of ions on the surface of the liquid film.A large number of Cl^-ions and OH^-ions accumulate on the positive surface of the sample under the action of electric current,resulting in more serious corrosion on the surface of the positive than that on the negative.Meanwhile,the corrosion products formed on the surface of the two poles ends of the sample are different.The surface corrosion products of positive are mainly composed of Al(OH)₃and the negative are mainly Al O(OH).The heat effect of DC current is more obvious than that of AC current,so under the same current value,the corrosion rate and degree of material are lower than that of AC current.A prediction model for service life of copper-aluminium composite under extreme conditions was established based on 0-7 days salt spray corrosion weight loss data at 5 salt spray concentrations,and the current influence coefficient of the model was corrected by using salt spray corrosion weight loss data under 50A AC current value energized state with3 salt spray concentrations.The relationship between the change of conductive area of conductor caused by corrosion and temperature rise during stable operation was proposed.Based on the conductor standard,the electrical failure criterion of copper-aluminum composite plate was established.The physical and mathematical model for service life prediction of copper-aluminum composite plate under extreme conditions was established by using the relationship between thermal balance and electrothermal effect.According to this model,when the conductive cross-section area of copper-aluminium-copper laminated composite plate(copper layer thickness 1mm and aluminium layer thickness 8mm)caused by corrosion decreases to 37.5%,the temperature rise will exceed the standard due to the enhanced electrothermal effect,thus causing failure.In the service environment with 0.2%(far sea area),0.4%(near sea area)and 1.5%(polluted area)salt mist concentration,the lifetime of the material is 2539 days,1311 days and 273 days respectively,but in non-marine climate(0.05%salt mist concentration),the lifetime of the material can reach 13128 days.In order to improve the corrosion resistance of copper-aluminium composites,a hydrophobic coating of organosilicon modified resin and a superhydrophobic coating of fluorosilicon copolymer nano-Si O₂ rough surface were synthesized.The anticorrosive coating was prepared on the basis of copper-aluminium composites.The average contact angle of water droplets on the surface of the two coatings is 103.7 degrees and 154.6 degrees respectively;both coatings have excellent corrosion resistance at the initial stage of corrosion,with corrosion inhibitory rate of over 98%,but modified resin coatings have more effective corrosion protection.The increasing time of weight loss of materials in 5%salt mist environment is 15 days and 3 days respectively.Modified resin substrate provides better mechanical stability and wear resistance for the coating,and its wind and sand erosion resistance is generally better than that of fluorosilicone copolymer substrate of superhydrophobic coating.Non-fluorinated synthetic materials make the modified resin coating environmentally friendly.Resin hydrophobic anticorrosion coating can improve the service life of copper-aluminum composite plate conductors in offshore areas to over 70years.Although superhydrophobic anticorrosive coating also has high corrosion resistance,its durability is not as good as that of resin coating and its application is limited.Therefore,modified resin anticorrosive coating is more suitable for corrosion and protection of copper-aluminium layered composites in service.