Preventing Galvanic Corrosion with Coatings

Galvanic corrosion, also known as bi-metallic corrosion is a process in which one metal corrodes preferentially to another when both metals are in electrical contact and in the presence of an electrolyte. In layman’s term’s this mean there is a reaction between dissimilar metals or materials. The process is similar to corrosion of a single material, but generally happens at a much higher rate depending on the reactivity between the dissimilar metals. The accelerated corrosion rate could lead to premature failures causing expensive repairs.However, when coatings are utilized this alteration of corrosion rates can be prevented.

To learn more about galvanic corrosion reactions between specific metals refer to the “Anodic Index” or “Galvanic Series” at http://engineersedge.com/galvanic_capatability.htm. This tool can very useful as it lists different metals from most cathodic to most anodic, and the further from each other the metals are on the index, the more reaction there is between the metals.

For example, a common misconception is that stainless steel is the best option for corrosion resistance. However, when in contact with dissimilar metals, stainless steel can cause pitting or corrosion in the other metal. Choosing metals that have similar electropotentials is vital to preventing galvanic corrosion. Another example would be a carbon steel fastener coated with a zinc flake coating system that utilizes an aluminum rich top coat fastened to some aluminum panel or body.

How Do Coatings Help?
Coatings can isolate the metals from the environment to slow down or prevent galvanic corrosion (coating stainless fasteners going into aluminum or switching to a carbon steel fastener with a zinc flake/aluminum rich coating system). It is imperative to ensure your coatings manufacture has a comprehensive understanding of the application and has the ability to customize coatings specific to each end user and/or application.

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