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

This study investigates the protective properties of an epoxy coating that was cataphoretically deposited on a steel substrate modified by electroplated Zn–Mn alloy with varying chemical contents. The primary objective was to analyze the corrosion resistance and performance of the coating when immersed in a 0.5 mol dm−3 NaCl solution over a period of 60 days. Electrochemical impedance spectroscopy (EIS) was employed to evaluate the coating's effectiveness, revealing that the pore resistance of the epoxy on Zn–Mn alloy with 16 at.% Mn was significantly higher, while the capacitance values were substantially lower compared to those on substrates containing 5 and 8 at.% Mn. This observed disparity is attributed to the dissolution of the metallic substrate during the deposition process, driven by the high pH level of 12.9. Energy dispersive X-ray spectrometry (EDS) further supported these findings, indicating a decrease in zinc release from the coating as the manganese percentage in the alloys increased. The results highlight the crucial role of the substrate composition on the electrochemical behavior and protective efficiency of epoxy coatings.