Comparison of corrosion protection of normal and galvanised steel coated by cathodic electrocoatings using EIS and salt spray tests

Cathodic electrocoatings were applied onto phosphated normal and galvanised steel substrates with average dry film thicknesses of 20 and 12 μm. To evaluate the anticorrosion properties of the coatings, electrochemical impedance spectroscopy and salt spray tests were carried out on the samples. The results showed that, by increasing the curing temperature, the protective properties of electrocoated galvanised steel are improved to a higher extent compared to normal steel panels. This was indicated by a pore resistance of two orders of magnitude higher in the case of galvanised steel panels. At lower curing temperatures, the corrosion resistance of electrocoated normal steel panels is better than that of the galvanised steel, indicated by a two orders of magnitude higher pore resistance value. On the other side, the salt spray test could not recognise the difference between protective properties of different coating films on galvanised steel suitably, and this is one of the notable disadvantages of this test.