The hot-dip galvanized coating is primarily comprised of zinc and zinc alloys, but is sometimes placed in contact with different metals including stainless steel, aluminum, copper and weathering steel. When two different metals are in contact and exposed to a common electrolyte, one of the metals experiences accelerated corrosion while the other is protected. This type of accelerated corrosion between dissimilar metals is referred to as galvanic corrosion. Because galvanic corrosion can occur at a high rate under certain circumstances, it is important to evaluate the combination of galvanized steel with other metals to determine if galvanic corrosion is of concern.

Figure 1: Galvanic Series of Metals in Saltwater

All metals have different electrical potentials that can be quantified in the presence of a conductive medium such as moisture or saltwater. A Galvanic Series of Metals lists metals and alloys in decreasing order of electrical activity in a particular medium (see Figure 1 for saltwater).

Metals and alloys nearer the top of the series have a greater negative electrical potential than the more noble or stable metals below. When two metals of different electrical potentials are combined under the right conditions, a galvanic cell (Figure 2) is formed. //

Difference in electrical potential – Refer to Figure 3 for a Galvanic Series containing values for electrical potential of various metals in a saltwater application8. Generally, severity of corrosion increases when combining galvanized steel with metals far away from zinc in the galvanic series.