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International Journal of Corrosion
Volume 2014, Article ID 819476, 12 pages
Research Article

Simulation of the Relaxation Potential Profile of an ac-dc-ac Test

1Department of Materials Science and Engineering, Boise State University, Boise, ID 83725, USA
2Boeing Research & Technology, P.O. Box 3707, M/C 19-LX, Seattle, WA 98124, USA

Received 3 December 2013; Accepted 4 March 2014; Published 3 April 2014

Academic Editor: Ramana M. Pidaparti

Copyright © 2014 Kerry N. Allahar et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The relaxation period of the accelerated ac-dc-ac test for coatings is associated with the transient electrochemistry that occurs when the immersed coated system is allowed to return to a stable open-circuit condition after being subjected to a cathodic potential. A mathematical model of the transient electrochemistry that occurs during this relaxation period is presented for coated aluminum. Expressions for the corrosion potential and corrosion current as functions of the local pH at the metal-coating interface were developed using reported experimental results. These expressions enabled the simulation of the transient electrochemistry under the constraint of balanced anodic and cathodic current densities. Regression of the transient relaxation potential profiles to exponential decay functions provided time-constant characterization of the profiles. Simulated results are presented that demonstrate the influences of the coating's porosity and thickness, the applied dc potential and the metal-coating interface condition on the time-constants associated with the relaxation profile. Interpretation of experimentally reported relaxation potential profiles supported the analysis of the simulated results.