The influence of steel surface modification by electrodeposited Zn-Fe alloys on the protective behaviour of an epoxy coating

The electrochemical and transport properties of epoxy coatings electrodeposited on steel and steel modified by Zn-Fe alloys were investigated during exposure to 3% NaCl. The Zn-Fe alloys were deposited on steel surface from alkaline bath galvanostatically using different current densities. From the time dependence of pore resistance of epoxy coating (impedance measurements), diffusion coefficient of water through epoxy coating (gravimetric liquid sorption measurements) and water content in the epoxy coating (thermogravimetric analysis), it was shown that Zn-Fe sublayer could improve the corrosion stability of the protective system based on epoxy coating. The values of the pore resistance were almost unchanged over the long period of immersion time for epoxy coating on steel modified by Zn-Fe alloy deposited by 4 A dm(-2), indicating the great stability of this protective system. The values of diffusion coefficient of water through epoxy coating on this alloy and water content inside the epoxy coating were the smallest, indicating the low porosity of the coating. (C) 2003 Elsevier Science B.V. All rights reserved.