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The corrosion behaviour of the hard anodic coatings prepared by three different methods viz., conventional hard anodizing (C-HA), pulse hard anodizing (P-HA) and low voltage room temperature pulse hard anodizing (LVP-HA) on AA 6061 was compared using electrochemical impedance spectroscopy (EIS) and linear polarisation. Scanning electron microscope (SEM) was used to study the surface morphology before and after corrosion. EIS data revealed that no significant difference in corrosion resistance was observed among three types. R p , I corr and E corr were found to be highly stable over the exposure period up to 72 h which confirms the excellent corrosion resistance. The studies indicate that the corrosion resistance of LVP-HA and P-HA, which are processed at lower voltage and at relatively higher temperatures, are comparable to that of C-HA which is processed at sub-zero temperatures and high operating voltages. The corrosion resistance of all coatings was found to be improved after hydrothermal sealing.

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