Effect Of Anodizing On The Corrosion Resistance Of CFRP/ Aluminum Alloy Bolted Joints

T300 carbon fiber reinforced polymer(CFRP)are increasingly used in high-speed trains due to their high strength,light weight,shock resistance,and corrosion resistance.In the engineering application of CFRP,it is usually necessary to be connected with metals such as5083P-O aluminum alloy(5083P-O Al),which is mainly used in high-speed train bodies to form a composite structure.The galvanic effect between the CFRP and the 5083P-O Al will accelerate the corrosion rate of the aluminum alloy and cause effective damage in a short time.The anodizing process of the aluminum alloy can improve the corrosion resistance of the aluminum alloy in the connector.In this paper,the 5083P-O aluminum alloy is anodized with different parameters.The electrochemical impedance test method is used to analyze the corrosion performance of the aluminum alloy under each anodization process parameter.The CFRP is bolted to the anodized aluminum alloy with the best corrosion performance and the unanodized aluminum alloy.Combination with acid salt spray test and electrochemical test,the corrosion resistance of CFRP/5083P-O Al bolted joints with and without anodizing was investigated.This article focuses on the study of the influence of anodizing process on the corrosion resistance and mechanical properties of T300 carbon fiber composite/5083P-O aluminum alloy bolt connectors.The results show:As the salt spray corrosion time increases,the surface damage of the unanodized aluminum alloy gradually increases.Due to accelerated galvanic corrosion,the corrosion of the cross section and bolt holes of the unanodized aluminum alloy is relatively serious.No obvious corrosion occurred on the surface of aluminum alloy anodized in 225 g/L H₂SO₄+8 g/L H₃BO₃ solution for 60 min.Anodizing reduces the weight loss rate of aluminum alloy,after 1000 hours of corrosion,the weight loss rate of the unanodized aluminum alloy is 2.45%,which is 49 times that of the anodized aluminum alloy.Galvanic corrosion and anodizing do not affect the hygroscopicity of CFRP.Under the same corrosion cycle,the moisture absorption rate of the CFRP in the anodized connection piece and the CFRP plate in the unanodized connection piece and the unconnected CFRP base material is basically the same.With the increase of corrosion test time,the weight gain rate per unit mass continues to increase,but the weight gain rate decreases slowly.Anodizing improves the tensile properties of the connector and slows down the rate of decrease in the tensile strength of the connector after increased corrosion time.The tensile strength of the anodized connector pre-corroded for 1000 h is 16467.03 N,which is only 0.8%lower than that of the uncorroded sample.The tensile strength of unanodized bolted joints decreases faster with the increase of corrosion time.After 1000 hours of pre-corrosion,bolted joints decreased by 4.4%compared with uncorroded bolted joints.Observing the fracture of the sample,salt spray corrosion affects only a small part of the outermost layer of the sample,and the internal structure of the material has not changed significantly.Salt spray corrosion has no effect on the tensile fracture mechanism of unanodized and anodized connectors.Fatigue test results show that anodizing in a corrosive environment can improve the fatigue strength of carbon fiber composite/aluminum alloy bolted joints.The fatigue limit of uncorroded original connectors is 59.80MPa.The anodized treatment reduced the fatigue limit of the bolted joint to 58.56MPa,a decrease of 2.07%.After 1000 hours of pre-corrosion,the fatigue limit of the unanodized bolted joint specimen and the anodized bolted joint specimen were 33.10 MPa and 54.51 MPa,respectively,and the fatigue limit decreased by 8.85%and44.65%,respectively.In a corrosive environment,anodizing treatment can improve the fatigue strength of CFRP/Al bolt connections.Fracture analysis found that the uncorroded unanodized connectors and the anodized connectors(before and after corrosion),main fatigue damage were caused by stress concentration at the bolt holes,and the fatigue failure after unanodized connectors corroded was mainly caused by corrosion pits,thereby reducing the fatigue limit.