FAA Aviation Mechanic Airframe (AMA)Airframe InspectionMedium
During a corrosion inspection, a technician finds localized pitting corrosion occurring where an aluminum wing skin panel is fastened with stainless steel screws, in an area exposed to moisture. What type of corrosion is most likely present?
- AExfoliation corrosion
- BIntergranular corrosion
- CGalvanic corrosion
- DFiliform corrosion
Show answer & explanationAnswer & explanation
Correct answer: C. Galvanic corrosion
Galvanic corrosion occurs when two dissimilar metals (here, aluminum and stainless steel) are in contact in the presence of an electrolyte such as moisture, causing the more anodic metal (aluminum) to corrode preferentially.
Why the other options are wrong
- A. Exfoliation corrosion causes flaking/layered lifting in extruded aluminum, not dissimilar-metal pitting.
- B. Intergranular corrosion occurs along grain boundaries in heat-treated alloys, unrelated to dissimilar metal contact.
- D. Filiform corrosion appears as thread-like filaments under paint or coating.
Galvanic Corrosion
Corrosion that occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte, causing accelerated attack of the more anodic metal.
- Requires dissimilar metals, electrical contact, and an electrolyte
- Aluminum near stainless steel or copper is a common example
- Prevented by isolating dissimilar metals with sealant, primer, or non-conductive spacers
Memory trick: 'Galvanic = two metals shake hands and one gets hurt.'