The protective properties of epoxy coating electrodeposited on Zn-Mn alloy substrate

Abstract

The epoxy coating was cataphoretically deposited on steel and steel modified by electroplated Zn-Mn alloy of different chemical contents. The samples were immersed in 0.5 mol dm(-3) NaCl solution for 60 days. The electrochemical impedance spectroscopy (EIS) analysis showed that the values of pore resistance for epoxy coating on steel and Zn-Mn alloy with 16 at.% Mn were two orders of magnitude higher, while the capacitance values were two orders of magnitude lower than those for the epoxy coating on Zn-Mn alloy substrates with 5 and 8 at.% Mn. It was assumed that the main reason for such a difference was metallic substrate dissolution during cataphoretic deposition, due to high pH (12.9). This assumption was supported by energy dispersive X-ray spectrometry (EDS) measurements showing that the amount of released Zn in epoxy coatings decreased as Mn percent in the Zn-Mn alloys increased. In addition, Zn-Mn alloy coatings on steel, as well as bare steel, were immersed in 0.1 mol dm(-3) NaOH solution, pH 12.9, simulating conditions during cataphoretic deposition, and polarization resistance measurement in this solution indicated that Mn inclusions in Zn-Mn alloy substrate prevent Zn dissolution in alkaline medium.