Corrosion Resistance of Painted Zinc Plated Steel in Sodium Chloride Solution

Abstract

A series of immersion tests were carried out by using coupled samples to accelerate deterioration of painted specimens in 5%NaCl solution. Coupled samples consisted of two electrically conected pieces aselectrodes. One was a painted specimen and the other was unpainted. The time dependence of galvanic current on coupled samples coresponded to the accumulation of alkali in the underfilm solution of paintedspecimens. Adhesion strength correlated to the amount of galvanic current. The corrosion resistance of painted specimens(Rt) in 5%NaCl can be calculated from the frequency response of AC-impedance measurements. The effects of chemical conversion coating against underfilm corrosion were also analyzed by electrochemical techniques.