Investigation and modelling of edge corrosion of e-coated galvanized steel with respect to the spatial edge orientation

The effect of the spatial orientation of e-coated hot dip galvanized test sheets on edge corrosion is investigated. Therefore paint delamination from corrosion sample edges at different steps in time of samples at different angles relative to the horizontal during a corrosion test is analysed. Two general relations are found: Horizontally oriented edges exhibit significantly increased coating delamination compared with vertically oriented edges. This is due to increased exposure to the electrolyte, resulting from the pinning of electrolyte droplets along the upper edge. With increasing angular displacement relative to the ground, electrolyte exposure and edge delamination decrease. The edges of the upward-facing specimen side showed a higher delamination width compared with the downward-facing side at the same angle. These results are supported by electrochemical impedance spectroscopy and a wetting test. Ultimately, a semi-empirical model to numerically predict the edge delamination over time, incorporating electrochemical impedance spectroscopy and polarization curves, is presented.