Study of different ageing tests and EIS evaluation of automotivecataphoretic epoxy primers

摘要

Owing their barrier properties against corrosive species, organic coatings are often usedto protect metals against corrosion. This protection is however guaranteed only if goodadhesion properties are reached between the metal and the coating. Acceleratedcorrosion tests are commonly used to evaluate coatings in a reasonable lapse of time.Many ways of degradation are accessible such as immersion, exposure to humidity or insalt fog chamber. Cyclic corrosion tests combining different exposures (humidity, saltfog) and drying steps are also increasingly used. Unfortunately the correlation betweenthe results of the accelerated tests and the 'natural' degradation in field is not alwaysclear. If not combined to EIS, the accelerated tests generally provide poor informationon the degradation mechanisms. Furthermore, it is not always clear whether the methodused to accelerate corrosion generates degradation mechanisms comparable to 'natural'degradation.In this work we compared different ageing tests (salt spray, ECC1 Renault Test,immersion) for the evaluation of the corrosion resistance of lead-free epoxy primersused in the automotive industry and cataphoretically deposited on pre-treatedaluminium 6016 and electroplated steel. These tests were compared to accelerateddegradations obtained by means of different techniques such as cathodic disbonding anda combination of AC and DC polarizations. The evaluation of the degree of degradationwas carried out by EIS with intact and scratched samples in NaCl 3.5 %.