In a galvanic couple formed by carbon steel and aluminum exposed to ocean spray, which metal acts as the anode?

• A. Aluminum
• B. Carbon steel
• C. Concrete
• D. Glass

Answer: (A)

In a galvanic pair exposed to an electrolyte like ocean spray, the more active metal acts as the anode and corrodes, while the more noble metal acts as the cathode and is protected. Between aluminum and carbon steel in marine conditions, aluminum is the more active metal, so it becomes the anode and undergoes preferential corrosion. Carbon steel serves as the cathode and remains comparatively protected. Nonmetal materials such as concrete or glass don’t form this metal-to-metal galvanic connection in the same way, so they don’t act as the anode.