AMT Corrosion Control and Treatment 2 — Questions and Answers
Question 1: Which type of corrosion is most commonly found between mating surfaces of dissimilar metals?
- Uniform surface corrosion
- Galvanic corrosion (Correct answer)
- Intergranular corrosion
- Exfoliation corrosion
Correct answer: Galvanic corrosion
Galvanic corrosion occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte, causing the less noble metal to corrode.
Question 2: What is the primary purpose of alodine (chromate conversion coating) treatment on aluminum?
- To increase structural strength
- To provide a decorative finish
- To provide corrosion protection and improve paint adhesion (Correct answer)
- To seal existing corrosion products
Correct answer: To provide corrosion protection and improve paint adhesion
Alodine (MIL-DTL-5541) creates a chemically bonded chromate layer on aluminum that resists corrosion and serves as an excellent primer bonding surface.
Question 3: Intergranular corrosion in aluminum alloys is most dangerous because it:
- Produces visible staining on the surface
- Attacks along grain boundaries beneath the surface with little external evidence (Correct answer)
- Only occurs in tropical climates
- Is easily detected by visual inspection
Correct answer: Attacks along grain boundaries beneath the surface with little external evidence
Intergranular corrosion progresses along grain boundaries beneath the metal surface, making it difficult to detect visually until significant structural damage has occurred.
Question 4: When removing corrosion from an aluminum aircraft structure, which abrasive should NOT be used?
- Aluminum oxide abrasive cloth
- Non-woven abrasive pads rated for aluminum
- Steel wool or steel wire brushes (Correct answer)
- Fine-grit wet/dry sandpaper
Correct answer: Steel wool or steel wire brushes
Steel wool or steel wire brushes embed steel particles into the aluminum surface, creating galvanic corrosion sites that accelerate future corrosion.
Question 5: What does the term 'anodic' mean in the context of the galvanic series?
- The metal is more noble and resists corrosion
- The metal is less noble and will corrode preferentially (Correct answer)
- The metal is immune to corrosion
- The metal acts as a cathode in the reaction
Correct answer: The metal is less noble and will corrode preferentially
Anodic metals are less noble (more active) in the galvanic series and will corrode preferentially when coupled with a more cathodic (noble) metal.
Question 6: Which corrosion type produces a white or gray powdery deposit on aluminum surfaces?
- Crevice corrosion
- Filiform corrosion
- Uniform surface corrosion (oxidation) (Correct answer)
- Stress corrosion cracking
Correct answer: Uniform surface corrosion (oxidation)
Uniform surface corrosion on aluminum produces aluminum oxide, which appears as a white or gray powdery or chalky deposit on the metal surface.
Question 7: Before applying a corrosion-inhibiting compound (CIC) to an aircraft structure, the technician must ensure the surface is:
- Wet with water to activate the compound
- Clean, dry, and free of active corrosion products (Correct answer)
- Primed with zinc chromate regardless of metal type
- Heated to at least 150°F to open the pores
Correct answer: Clean, dry, and free of active corrosion products
CICs must be applied to clean, dry surfaces free of active corrosion; moisture or corrosion products prevent proper adhesion and reduce effectiveness.
AMT Corrosion Control and Treatment 2
Which type of corrosion is most commonly found between mating surfaces of dissimilar metals?