AMT Corrosion Control and Treatment Questions and Answers 1 — Questions and Answers
Question 1: An aircraft operating in a coastal, high-humidity environment is undergoing a detailed inspection. The technician notices worm-like tracks and bubbling under the paint on an aluminum skin panel. What type of corrosion is most likely present?
- Intergranular corrosion
- Fretting corrosion
- Filiform corrosion (Correct answer)
- Galvanic corrosion
Correct answer: Filiform corrosion
Filiform corrosion is characterized by its worm-like appearance as it forms tunnels of corroded material underneath a paint film. It is common on aluminum surfaces in high-humidity environments where the paint coating has been compromised.
Question 2: A technician is treating an area of surface corrosion on an aluminum alloy fuselage. After mechanically removing the corrosion products, what is the primary purpose of applying a chemical conversion coating like Alodine before priming?
- To increase the surface hardness and wear resistance.
- To provide a sacrificial layer that is more anodic than the aluminum.
- To restore the material lost to corrosion.
- To form a passive oxide film that inhibits further corrosion and promotes paint adhesion. (Correct answer)
Correct answer: To form a passive oxide film that inhibits further corrosion and promotes paint adhesion.
Chemical conversion coatings, such as Alodine, are used to create a passive, corrosion-resistant film on the aluminum surface. This film inhibits new corrosion from forming and also serves as an excellent adhesive base for the subsequent primer coat.
Question 3: During an inspection of a high-time aircraft's wing structure, a technician discovers evidence of corrosion that appears to be attacking the metal along the grain boundaries. This has led to a lifting or flaking of the metal surface. This describes which form of corrosion?
- Pitting corrosion
- Exfoliation corrosion (Correct answer)
- Uniform surface corrosion
- Crevice corrosion
Correct answer: Exfoliation corrosion
Exfoliation corrosion is an advanced form of intergranular corrosion where the corrosive attack along the grain boundaries causes the surface layers of the metal to lift up and flake off. This type of damage is particularly severe as it delaminates the material, compromising its structural integrity.
Question 4: Fretting corrosion is most likely to be found in which of the following locations on an aircraft?
- In the bottom of the bilge area where water may collect.
- On a magnesium skin panel with chipped paint.
- Between two aluminum sheets in a lap joint under a loose rivet. (Correct answer)
- On a stainless steel firewall.
Correct answer: Between two aluminum sheets in a lap joint under a loose rivet.
Fretting corrosion occurs at the interface of two highly loaded surfaces that are subject to slight relative motion or vibration. A loose rivet in a lap joint allows for micro-movements between the aluminum sheets, which wears away the protective oxide layer and initiates corrosion.
Question 5: When inspecting a piano-type hinge on a control surface, a technician finds white powdery deposits and notices the hinge is stiff. What is the most appropriate initial maintenance action?
- Replace the entire hinge assembly immediately.
- Apply a water-displacing lubricant and cycle the hinge until it moves freely.
- Clean the hinge thoroughly, remove the corrosion, and lubricate before re-evaluating. (Correct answer)
- Paint over the affected area to seal out moisture.
Correct answer: Clean the hinge thoroughly, remove the corrosion, and lubricate before re-evaluating.
The standard procedure for a corroded piano hinge involves thorough cleaning and removal of the corrosion products to allow for a proper inspection of the damage. After cleaning and light corrosion removal, the hinge should be lubricated and actuated to work the lubricant in and ensure it operates freely. Replacement is only necessary if the corrosion is severe and has compromised the part's integrity.
Question 6: Which of the following is an essential requirement for galvanic corrosion to occur?
- The presence of a high-tensile stress on one of the metals.
- Two dissimilar metals in contact and the presence of an electrolyte. (Correct answer)
- An acidic environment with a pH below 5.0.
- Repetitive microscopic movement between two surfaces.
Correct answer: Two dissimilar metals in contact and the presence of an electrolyte.
Galvanic corrosion, or dissimilar metal corrosion, is an electrochemical process that requires three conditions: two different metals (anode and cathode) must be in electrical contact, and they must both be immersed in a conductive liquid (an electrolyte).
AMT Corrosion Control and Treatment Questions and Answers 1
An aircraft operating in a coastal, high-humidity environment is undergoing a detailed inspection.
The technician notices worm-like tracks and bubbling under the paint on an aluminum skin panel.
What type of corrosion is most likely present?