Local electrochemical impedance at the cut-edge of coil-coated galvanized steel after corrosion testing

The cut edge corrosion of polyester-coated galvanized steel was investigated using electrochemical impedance spectroscopy. Measurements were performed on specimens which had been tested in an accelerated atmospheric corrosion test. The samples were subjected to 208 wet and dry cycles in an exposure cabinet (26 days) with an artificial acid rain solution. Subsequently, the local impedance response of 50.3 mm(2) areas of coated material was measured and evaluated as a function of distance from the cut edge. The results indicate that the coating performance varies from the cut edge into the sheet. Thus, the coating resistance was too large for impedance measurements to be obtained further away than approximately 40 mm from the cut edge. At 34-40 mm from the cut edge the coating resistance had dropped significantly and an RC response was obtained. Less than 32 mm from the edge the impedance was either a modified response with further reduced coating resistance or a response indicative of a coating failure. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.