Electrochemical impedance spectroscopy and corrosion point counting on metal sheet edges with different cathodic dip coat materials

摘要

>Edge coverage with organic coatings is a very important but insufficiently investigated topic in the automotive industry. Several examinations in other scopes show an influence of different coating materials as well as the metal edge radii. For an improved understanding, the edge coating coverage of defined steel sheet edges is investigated regarding its corrosion protection potential in automotive use. Therefore, four different cathodic dip coat (CDC) materials are applied in different Mercedes‐Benz plants on well‐defined and topological analyzed edges. The coating thickness and edge coverage are determined in a non‐exposed state before a 7‐days exposure in a neutral salt spray (NSS) test. To quantify the behavior of the different materials edge coverage under corrosive load, electrochemical impedance spectroscopy and corrosion point counting are performed. The results demonstrate that the type of applied CDC‐material has a great influence on edge coating coverage as well as corrosion protection. A higher edge coverage causes a higher and more stable impedance and subsequently less counted corrosion points over the whole exposure time frame.