Which protective method is commonly used to prevent corrosion on structural aluminum alloy?

• A. Plain water immersion.
• B. An oxide coating or aluminum cladding.
• C. High-temperature annealing.
• D. No protective coating.

Answer: (B)

Protecting aluminum structural alloys hinges on creating a barrier that keeps moisture, oxygen, and electrolytes from reaching the metal surface. Aluminum naturally forms an oxide film, but a thicker, more durable protective layer is achieved with an oxide coating (anodizing) or by cladding the surface with pure aluminum (alclad). This barrier greatly slows or stops corrosion in demanding environments like aviation, where exposure to humidity and salts is common. Immersing in plain water isn’t protective and can promote corrosion, especially with electrolytes present. High-temperature annealing changes the metal’s structure and properties but does not provide the robust barrier needed for corrosion protection. Leaving the surface uncoated leaves it vulnerable to corrosion in service. An oxide coating or aluminum cladding is the commonly used protective method.