Hot-Dip Galvanized Steel in Contact with Other Metals
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. 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.
© 2023 American Galvanizers Association. The material provided herein has been developed to provide accurate and authoritative information about after-fabrication hot-dip galvanized steel. This material provides general information only and is not intended as a substitute for competent professional examination and verification as to suitability and applicability. The information provided herein is not intended as a representation or warranty on the part of the AGA. Anyone making use of this information assumes all liability arising from such use.
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 (AGA)
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?