A comparative evaluation of corrosion protection of sol–gel based coatings systems
By Lafront, A.-M.; Zhang, W.; Jin, S.; Tremblay, R.; Dubé, D. & Ghali, E.
Published in Surface and Coatings Technology
2001
Abstract
Sol–gel technology offers a wide choice of chemistries and is currently perceived as a potential replacement for current chromate treatments. The corrosion prevention behavior of a commercially available sol–gel surface pretreatment with six different primers was evaluated using electrochemical impedance spectroscopy. Eighteen different coatings systems were selected for evaluation. The test panels were prepared in three separate treatment groups of deoxidization only, Alodine 1200 chromate conversion treatment, and Lord Aeroglaze sol–gel 110 non-chromate surface treatment, followed by six different primer coatings, and a polyurethane top coat. A variety of environmental conditions were generated based on Harrison's solution, salt fog and UV light exposure. Electrochemical impedance measurements were obtained from panels exposed to continuous immersion, alternate immersion in Harrison's solution and an alternate cycle of salt fog and UV chamber. The corrosion behavior of sol–gel based coatings was compared to that of chromate conversion coatings and de-oxidized samples. Scribed panels were also tested to evaluate the corrosion resistance behavior of scratched or cracked coatings. Of all the 18 coatings systems investigated, the E-coat based system showed the best corrosion resistance performance. The sol–gel treated E-coat provided an acceptable corrosion protection level, a barrier resistance of over 108 Ω and performed similar to the conventional chromate system, as seen from the results of unscribed panels. However, the scribed panel data clearly demonstrates the superior performance of the Alodine 1200 treated systems over the sol–gel based coating systems. Cyclic salt fog/UV exposure did not provide clear discrimination over the alternate immersion test. The scribed panel, on the other hand, did provide a higher degree of discrimination in a short time.