| The 6061 aluminum alloy battery pack located in the vehicle chassis faces problems such as battery heating,scuffing and snow-melting agent corrosion during service,which seriously affects the battery pack longevity and battery safety.In order to solve the above problems,this paper used simulation methods to guide the micro-arc oxidation（MAO）process parameters to prepare composite coatings with Si C and Si O2nanoparticles added and a ordinary MAO coating respectively.The strength of macroscopic corrosion resistance for the different coatings were investigated,and the annual corrosion thinning amount of the coatings was also predicted.The local electrochemical impedance of different coatings before and after scuffing was investigated by means of micro-area electrochemical testing,and the service performance of the coatings after scuffing had been clarified.Based on the above study,a corrosion process model was established to investigate the corrosion expansion mechanism of the coating after local damage.The main results are as follows:（1）Optimisation of coating preparation parameters and coating characterisationA COMSOL simulation program based on the Nernst-Planck equation was developed to simulate the micro-arc oxidation process and guide the laboratory preparation of coatings.The optimum MAO preparation time of 10 min was selected by simulation,and the MAO coating,Si O2/MAO composite coating and Si C/MAO composite coating were prepared.The Si C/MAO composite coating had the lowest surface porosity and the highest thickness.The addition of nano-Si C had a certain sealing effect and reduced the number of micropores in the MAO coating.（2）Coating macroscopic corrosion resistance experiments and annual corrosion thinning amount simulation predictionThe results of macroscopic electrochemical experiments showed that the Si C/MAO composite coating had the strongest corrosion resistance,the maximum corrosion current density of MAO coating can be reduced by 80.4%,but the corrosion resistance of all samples tested decreased with the increase in corrosion temperature and the corrosion products were all Al（OH）3.The long-cycle corrosion simulation results showed that the corners of the sample had the highest corrosion current density and corrosion thickness reduction,but the Si C/MAO composite coating had the lowest corrosion current density compared to the other samples.The simulation predicted that the Si C/MAO composite coating had the slowest corrosion reduction rate of 8.453 nm/a.（3）Study of the local corrosion mechanism of Si C/MAO composite coatings with prefabricated defectsResults of micro-area electrochemical experiments showed that the sealing effect of nano-Si C results in the highest local impedance value,the corrosion expansion rate of MAO coating can be slowed down to the maximum.Combining experimental and characterization analysis,the innovative model of corrosion mechanism for Si C/MAO composite coating in"cavity-fracture collapse"mode was proposed to provide a theoretical reference for the study of the causes of localised corrosion of micro-arc oxide composite coatings on the surface of electric vehicle battery packs and the formulation of corresponding corrosion prevention strategies. |
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