Galvanic Action Reference

I have looked at various resources for Galvanic action relationships between metals and they all are inconsistent. Any suggestions on what is the best reference to follow?

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Hey @molls808,

I’m not familiar with any of these resources, however @coachbryanhadley might be able to help us out here.

Hi @molls808,

Assume your question is pointed at best practices for preventing corrosion?

Think of galvanic action as battery science. It occurs when two electro-chemically dissimilar metals come into contact, and electrons essentially “hop” from one metal to the other, and cause corrosion to occur.

Below is a diagram taken from “Conservation of Architectural Ironwork” by David S. Mitchell showing the electro-chemical spectrum of common metals, from cathodes (negative charge) to annodes (positive charge):
image

Note that stainless steel 430 and aluminum are toward opposite ends of the spectrum, with stainless steel 430 being more cathodic (negatively charged) and aluminum being more annodic (positively charged). Now let’s say we have an architect that wants to clad a building in aluminum sheet metal. The architect has decided to specify stainless steel 430 fasteners. What will happen if these are placed in direct contact with the aluminum sheet metal? Well, galvanic action of course! Over time ions will have a tendency to jump from the aluminum from the steel, causing it to corrode. Further, during rain events there will be a tendency for some of that corrosion to be washed down and deposited on the side of the building, causing a staining effect that might not be desired.

What can the architect do?

One option is that the architect can specify metals of the same electro-chemical makeup. Going back to the electro-chemical spectrum the architect could select a fastener of a metal that is more similar to the aluminum, or consider a different metal for the siding. Depending on cost, aesthetics and durability of the materials this might not be viable.

Another option would be to use plastic spacers at fasteners.

This link to archtoolbox.com has a great, simple explanation: https://www.archtoolbox.com/materials-systems/metals/galvanicaction.html

Hope it helps.

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This is great! Thanks so much!

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