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Hot-dip galvanized steel is well suited for use in a variety of environments and fabrications, and sometimes is placed in contact with different metals including, among others, stainless steel, aluminum, copper and weathering steel.

When two different metals are in contact in a corrosive environment, one of the metals experiences accelerated galvanic corrosion while the other metal remains galvanically protected.

Metals near each other in the galvanic series have little effect on each other. Generally, as the separation between metals in the series increases, the corroding effect on the metal higher in the series increases as well.

Relative surface areas of contacting dissimilar metals is also relevant in determining which metal exhibits accelerated corrosion. It is undesirable to have a large cathode surface in contact with a relatively small anode surface.

Galvanic corrosion occurs when two different metals are in contact in a corrosive environment: one of the metals experiences an accelerated corrosion rate. The contacting metals form a bimetallic couple because of their different affinities (or attraction) for electrons. These different affinities create an electrical potential between the two metals, allowing current to flow.


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Comments

Michael mifkovic, California Department Of Transportation

If a galvanized #6 reinforcement bar is in contact with a smaller #5 carbon steel bar in a concrete footing for a bridge structure (non corrosive soils), what sort of galvanic effects will occur to the black bar. Will accelerated corrosion occur in either of the bars (due to galvanic effects) if the alkalinity of the concrete lowers over time, or chlorides are introduced from the outside environment?

Alana Hochstein

Yes, galvanic corrosion can still be a concern when hot-dip galvanized rebar and black rebar are embedded in concrete, but there are several methods to prevent it. For more information on this topic and how to limit the effects of galvanic corrosion in concrete, we have the following article on our website: https://galvanizeit.org/education-and-resources/resources/technical-faq-dr-galv/dissimilar-metals-in-concrete

Joseph Moser

If galvanized angles and bolts are used to reinforce and replace members on a weathering steel lattice tower that has fairly severe corrosion, is there a concern of accelerated corrosion of the galvanized items at the contact points?

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