How does corrosion typically begin on an airframe made of aluminum?

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Multiple Choice

How does corrosion typically begin on an airframe made of aluminum?

Moisture and chemical exposure at joints and cutouts lead to pitting and intergranular corrosion. Aluminum’s protective oxide can be damaged or breached at these areas—where fasteners, sealants, and gaps create crevices—so electrolytes like moisture and salts remain in contact with the metal. This localized exposure initiates small pits and can strip along grain boundaries, especially if heat-treated areas or repairs have altered the microstructure. Paint damage or saltwater can accelerate the process, but the usual starting point is moisture plus chemicals at exposed joints and cutouts, not heat alone or random scrapes elsewhere.

Moisture and chemical exposure at joints and cutouts lead to pitting and intergranular corrosion. Aluminum’s protective oxide can be damaged or breached at these areas—where fasteners, sealants, and gaps create crevices—so electrolytes like moisture and salts remain in contact with the metal. This localized exposure initiates small pits and can strip along grain boundaries, especially if heat-treated areas or repairs have altered the microstructure. Paint damage or saltwater can accelerate the process, but the usual starting point is moisture plus chemicals at exposed joints and cutouts, not heat alone or random scrapes elsewhere.

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