FAA Aviation Mechanic Airframe (AMA)Airframe InspectionMedium
During a corrosion inspection, a technician finds a flaking, layered appearance on an extruded aluminum wing spar cap, with the surface lifting in thin layers parallel to the material's grain structure. This is characteristic of which type of corrosion?
- AExfoliation corrosion
- BGalvanic corrosion
- CFretting corrosion
- DUniform surface corrosion
Show answer & explanationAnswer & explanation
Correct answer: A. Exfoliation corrosion
Exfoliation corrosion occurs along grain boundaries in extruded or rolled aluminum, causing the metal to lift and flake in layers parallel to the grain, often appearing as a swollen, flaking surface.
Why the other options are wrong
- B. Galvanic corrosion occurs at dissimilar metal junctions due to electrochemical reaction, not grain flaking
- C. Fretting corrosion results from vibration/rubbing between mating surfaces, showing pitting not flaking layers
- D. Uniform surface corrosion is a general even etching, not layered flaking
Exfoliation Corrosion
A severe form of intergranular corrosion in extruded/rolled aluminum where corrosion products build up along grain boundaries, causing the surface to lift and flake in layers.
- Common in high-strength aluminum alloys with directional grain structure
- Appears as a blistered or flaking surface parallel to the grain
- Often requires structural repair or part replacement once detected
Memory trick: Exfoliation peels off in layers like old paint on a fence