DEGRADATION OF STRAINED ORGANIC COATINGS

摘要

The degradation of uniaxially and biaxially strained coil-coated electrogalvanised steel was studied. The samples were exposed to 5% NaCl aqueous solution and the loss of protective properties was assessed by Electrochemical Impedance Spectroscopy (EIS). Monitoring the coating resistance and the double layer capacitance have shown that protection rapidly decreases with strain. Scanning electron microscopy (SEM) was able to explain the electrochemical measurements by revealing defects introduced by strain in both substrate and organic coating. The electroplated zinc crystals became shifted from their original position, whereas the phosphate layer cracked perpendicularly to the sliding direction of zinc. The paint, in turn, showed defects nucleated in the vicinity of pigments.