Kinetic mechanisms for cut edge corrosion of coil coated architectural cladding

Abstract Cyclic dip testing of coil coated architectural claddings was carried out in order to understand the mechanisms of cut edge corrosion. Thus, a number of nominally identical materials from the same manufacturer, but with varying steel thickness (and, hence, zinc to steel area ratios at the cut edge) were examined. The degree of disbondment of the organic coating from the cut edge was measured after 1000 h. For a constant thickness of zinc coating, the results demonstrate a linear relationship between the degree of coating disbondment and the thickness of the steel substrate. Further, the trend line showed a positive amount of disbondment when ex trapolated to zero thickness of steel. It is concluded that the cathodic disbondment mechanism plays an important role in the initiation of organic coating failure at the cut edge. However, the kinetics of cut edge disbondment is dominated by the anodic undermining mechanism.