Abstract The corrosion performance of LY12 aluminum alloys/passivation film/epoxy coatings was characterized by electrochemical impedance spectroscopy (EIS) in NaCl solution. The results showed that with the increasing of immersion time, the impedances of composite electrodes continuously increased. In the beginning of immersion, the diffusion impedance emerged in the impedance spectroscopy of composite electrode, which was considered to result from the mass transport behavior of solving products of passivation film prepared on metal substrates. The observation of scanning electron microscope (SEM) suggested that the chromate conversion film presented the obvious crack morphology on metal substrates, which was favour for solving chromate to penetrate through the film and passivate the metal substrate surface. This may be the possible reason of the continuous increasing of impedance of composite electrodes.
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