Electrochemical Behavior Of The Carbon Fiber Reinforced Polymers (CFRP) And The Galvanic Process Between CFRP And Typical Alloys

The electrochemical behaviors of carbon fiber(CF)and the reinforced polymers(CFRP)were investigated,and the galvanic corrosion processes between CFRPs and typical engineering alloys were analyzed in this dissertation.All materials used in this research were provided by the General Motor from the United States.The carbon fiber is PAN-based that named 50k.Two kinds of CFRPs(epoxy matrix noted as E-CFRP and nylon matrix noted as T-CFRP)and four alloys(Aluminum 6022,Magnesium AZ31,Zn coated DP590 steel and 1040 steel)were used in the study.Considering the practical application environments,GMW14872 solution(0.9wt.%NaCl+0.1 wt.%CaCl2+0.075wt.%NaHCO3,according to GM worldwide engineering standard)and 3.5wt.%NaCl were used.The basic electrochemical behavior of the CFRPs,as well as the effect of the CFRP microstructure,was systematically studied.The long-term galvanic corrosion currents and corrosion of the CFRP/metal couples were measured.A CFRP microstructural defect model was proposed to understand the electrochemical behavior and the galvanic process.The results show that the open circuit potentials(OCPs)of the two kinds of CFRP are very positive like noble metals Pt and Au.The difference in Ecrr between the CFRP and metals is obviously larger than 50mV.Thus,there will be a big risk of galvanic corrosion in a CFRP/metal couple in the aggressive environment.The number of micro defects inside the E-CFRP body is obviously higher than that in the T-CFRP.Thus,the E-CFRP reaches a relatively stable state relatively more slowly than the T-CFRP in the electrochemical measurements.As the number and distribution of defects in the two CFRPs are very different,their electrochemical behaviors vary differently with time.The galvanic currents of the metal/T-CFRPs started at a relatively high value and then reached stable quickly.The galvanic currents of metal/E-CFRP started at a relatively low value and kept increasing with time.Besides the galvanic corrosion,the effect of crevice corrosion is significant when a metal is coupled with a CFRP in practical applications.Especially in the salt spray environment,the effect of crevice corrosion and self-corrosion can significantly affect the behavior of the galvanic system.The most interesting scientific finding was that carbon fiber is electrochemically anisotropic.The cross-section of the CF is 2 orders of magnitude more active than the cylindrical surface.The study focused more on the cathode than the anode that was overlooked before.A microstructural model was proposed to get a better understanding on the electrochemical behavior of CFRP.The understanding on the corrosion behavior of CFRP/metal couples was improved.The knowledge on the effect of galvanic corrosion on the cathode CFRP was enriched.A new engineering method was proposed by using different kinds of joints to distinguish the contribution of galvanic corrosion,crevice corrosion and self-corrosion in the CFRP/metal couples.To improve the design and manufacture of the composites,to obtain a more reasonable joint,and to reduce corrosion damage,prevent such galvanic corrosion are the hot issues that should be focused in the practical applications.Preliminary investigation was made on the two-dimensional anisotropic electrochemical behavior of CF which provided a new direction on the future research of CF.