Which metal combination presents the greatest galvanic corrosion risk when exposed to seawater spray?

• A. Aluminum and stainless steel
• B. Copper and brass
• C. Concrete and steel
• D. Carbon steel and aluminum

Answer: (D)

In seawater spray, galvanic corrosion happens when two dissimilar metals are electrically connected and an electrolyte is present. The metal that is more anodic (less noble) becomes the anode and corrodes faster, while the more cathodic metal is protected.

Aluminum is more anodic than carbon steel in salty water, so when they touch, electrons flow from the aluminum to the carbon steel. This drives rapid corrosion of the aluminum and can accelerate material loss where aluminum is exposed, especially if there is a large aluminum surface area in contact with the steel. The seawater spray provides the conductive path that makes this corrosion current flow continuously, making this pairing particularly risky.

Other pairings involve smaller potential differences or nonconductive contexts (like concrete and steel) that don’t promote the same strong galvanic cell in the spray environment, so they pose a lower galvanic corrosion risk.