Originally published on July 10, 2018 by BNP Media through the Building Enclosure Blog.
The concept of “galvanic action” is confounding to many design professionals. In simple terms, galvanic action refers to the corrosive effect created when two electrochemically dissimilar metals are in direct contact with each other. Their contact creates a conductive path for electrons and ions to move from one metal to the other. As ions move from one metal to another, corrosion occurs. The remedy is to keep these dissimilar metals insulated from each other to drastically slow the corrosive effect.
We know it is unwise to play in an outdoor swimming pool when lightning is present. Generally, water creates a conductive path – especially salt water. Therefore, it is critical to keep dissimilar metals separated in wet conditions.
The Galvanic Series Chart
Cathodes are noble – or stable – metals, meaning they are less prone to corrosion. Historically, silver and gold have been preferred for jewelry and currency because they are less susceptible to gradually destruct while in one’s possession.
Anodes are less stable and more prone to corrosion. Zinc and aluminum a common metals with higher anodic properties.
The chart below exhibits several common metals and where their relative location in the galvanic series (Fig. 1). When two metals close in this chart are in contact, there is less galvanic action (corrosion of the more anodic metal). Conversely, if the two metals in contact are farther away on the chart, galvanic action is more likely to occur.
Figure 1: The Galvanic Series Chart. The order of the metals are general and meant to serve for referential purposes here. In application, these metals can exhibit a range of voltage potential relative to a reference electrode. This series of alloys assumes full submersion in flowing seawater. Figure by Daniel Overbey.