Corrosion Control and Prevention Flashcards

Which type of corrosion is characterized by a white or gray powdery deposit on aluminum aircraft structures?

Answer: Uniform surface oxidation (aluminum oxide formation)

When aluminum oxidizes, it forms aluminum oxide (Al₂O₃) — a white or gray powdery film. Unlike iron rust, aluminum oxide forms a tight adherent layer that can slow further corrosion, but the powdery appearance is a clear visual indicator of surface oxidation.

What condition must be present for galvanic corrosion to occur between two dissimilar metals?

Answer: The metals must be in electrical contact with each other in the presence of an electrolyte

Galvanic corrosion requires three elements: two dissimilar metals (separated in the galvanic series), a metallic electrical path connecting them, and an electrolyte (such as moisture, fuel, or salt water) completing the circuit. Remove any one element and galvanic corrosion stops.

Which fastener material used in aluminum aircraft skin would create the greatest risk of galvanic corrosion?

Answer: Uncoated carbon steel fasteners

Uncoated carbon steel and aluminum are far apart in the galvanic series, creating a large electrochemical potential difference that drives aggressive galvanic corrosion. Aluminum and titanium are much closer in the galvanic series, making titanium an acceptable fastener in aluminum structure.

What is the correct first step when active corrosion is discovered on an aircraft structure during inspection?

Answer: Remove all corrosion mechanically or chemically before applying any corrosion-inhibiting treatment or primer

Primer and sealant applied over active corrosion trap moisture and corrosion products against the metal, allowing the corrosion to continue undetected underneath. The corroded material must be fully removed first, the base metal restored, and then primer and protective coatings applied.

What non-destructive testing (NDT) method is most effective for detecting corrosion beneath the outer skin of an aluminum aircraft panel that shows no exterior symptoms?

Answer: Eddy current or ultrasonic testing

Eddy current and ultrasonic testing can detect material loss or density changes beneath the surface of aluminum panels without removing the skin. Dye penetrant requires a surface-breaking defect to be visible; magnetic particle inspection only works on ferromagnetic metals.

Intergranular corrosion is considered especially serious in aircraft structures because it:

Answer: Attacks along grain boundaries within the metal, causing severe strength loss that may not be apparent from the surface

Intergranular corrosion propagates along the grain boundaries inside the metal microstructure, physically separating the grains and reducing structural strength dramatically. Because the surface may look intact, the full extent of damage is hidden, making this one of the most dangerous corrosion forms for aircraft structures.