In a galvanic couple consisting of a steel fastener and an aluminum alloy plate in the presence of an electrolyte, which metal would corrode preferentially?

In a galvanic couple consisting of a steel fastener and an aluminum alloy plate in the presence of an electrolyte, which metal would corrode preferentially?

• A. Aluminum
• B. Steel
• C. Both equally
• D. Neither

Answer: (A)

Galvanic corrosion happens when two dissimilar metals are electrically connected in an electrolyte. The metal that is more anodic (less noble) will oxidize and corrode first, while the more cathodic (nobler) metal is protected. In this pair, aluminum is more active than steel, so aluminum acts as the anode and corrodes preferentially. The steel plate becomes the cathode and is relatively protected, though conditions can still allow some corrosion if the environment is aggressive or coatings fail. The oxide film on aluminum doesn’t stop the galvanic tendency; it affects rate but not the direction of the attack.

Galvanic corrosion happens when two dissimilar metals are electrically connected in an electrolyte. The metal that is more anodic (less noble) will oxidize and corrode first, while the more cathodic (nobler) metal is protected. In this pair, aluminum is more active than steel, so aluminum acts as the anode and corrodes preferentially. The steel plate becomes the cathode and is relatively protected, though conditions can still allow some corrosion if the environment is aggressive or coatings fail. The oxide film on aluminum doesn’t stop the galvanic tendency; it affects rate but not the direction of the attack.