Lifetime Prediction for Organic Coatings on Steel and a Magnesium Alloy Using Electrochemical Impedance Methods
- 1 September 1994
- journal article
- Published by Association for Materials Protection and Performance (AMPP) in Corrosion
- Vol. 50 (9) , 705-716
- https://doi.org/10.5006/1.3293547
Abstract
Electrochemical impedance studies were conducted on an epoxy polyamide-coated AISI1010 steel (UNS G10100) and an epoxy/chromate conversion-coated magnesium (Mg) alloy ZE41A-T5 (UNS M16410). Results were compared to evaluate the general applicability of various impedance-derived measures of coating performance for radically different metal substrates. Both coating systems were immersed in room-temperature aqueous sodium chloride (NaCl) solution of near neutral pH. Correlation of impedance parameters obtained early in exposure with long-term visual appearance demonstrated that low-frequency impedance (< 10 mHz), coating resistance, breakpoint frequency, phase angle minimum, and saddle frequency associated with the phase angle minimum forecasted the long-term performance of both systems. Impedance-based parameters adequately estimated the defect areas associated with corrosion sites that penetrated the organic coating but were unable to estimate the areas associated with coating blisters. More conse...Keywords
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