Carbon fiber reinforced epoxy and nylon were measured by means of potentiodynamic polarization, potentiostatic polarization and AC electrochemical impedance spectroscopy (EIS) in a solution containing 0.9wt% NaCl, 0.1wt% CaCl 2 and 0.075wt% NaHCO 3 . Their microstructures were examined by SEM. The results showed that these two types of carbon fiber reinforced polymers (CFRPs) were electrically conductive and electrochemically noble, and exhibited different EIS characteristics. Strong anodic and cathodic polarization could damage their surface polymer layers. Based on their different microstructures and electrochemical behaviors, a surface polymer layer model was proposed for these CFRPs. and aerospace 16 industries due to its light weight, high stiffness, high strength, good anti-fatigue performance and excellent corrosion resistance. Many investigators have been attracted to pursue better mechanical properties for different types of CFRPs. [17][18][19][20][21] CFRPs are often used together with other engineering metals, such as steels, Al alloys, Mg alloys and Ti alloys in industry. 14,15,22,23 As carbon has an open-circuit-potential (OCP) more positive than most engineering metals, strong galvanic cells can be formed between CFRPs and these metals in aggressive service environments, 24-27 thus galvanic corrosion of the coupled metals has been always a big concern.In the past decades, many studies have been focused on the galvanic effect of CFRPs on the coupled metals, including the influence of metallurgical and environmental factors on the galvanic corrosion. 10,25,[28][29][30][31] These have led to some common knowledge. For example, it has been generally accepted that, apart from the wellknown galvanic corrosion of steels caused by CFRPs, aluminum alloys with good general corrosion resistance, can also suffer from galvanic corrosion if they are coupled with CFRPs. 24,32 The galvanic corrosion of magnesium alloys coupled with CFRPs is more severe than any other engineering metals.26 Titanium alloys are stable in most aggressive environments and not attacked by galvanic corrosion if they are in contact with CFRPs. 27,33 However, most of these studies simply measured or estimated the corrosion damage of metals. They ignored the detailed electrochemical behavior of the coupled CFRPs. 26,32,34 In fact, the metal in contact with a CFRP may deteriorate more severely due to crevices formed in the joint than that simply caused by galvanic effect. On the other hand, the CFRP in a galvanic couple may also degrade and its electrochemical properties may vary with time while the coupled metal is being corroded, as the corrosion products from the coupled metal may in return affect the electrochemical performance or even accelerate the degradation of the CFRP. This kind of possible degradation of a CFRP in a galvanic couple, as well as the detrimental effect of the CFRP degradation on the galvanic corrosion of a coupled metal, has not been systematically investigated.In fact, CFRP can degrade in a corrosive medium chemical...