FAA Aviation Mechanic General (AMG)Materials, Hardware and ProcessesMedium
A repair facility processes aluminum wing skins through a chromic acid anodizing bath prior to painting. What is the primary purpose of this process?
- ATo completely remove the alclad protective coating before priming
- BTo significantly increase the hardness and wear resistance of the surface
- CTo improve the electrical conductivity of the aluminum surface
- DTo improve corrosion resistance and provide a better surface for paint adhesion
Show answer & explanationAnswer & explanation
Correct answer: D. To improve corrosion resistance and provide a better surface for paint adhesion
Chromic acid anodizing forms a thin, protective oxide layer on aluminum that increases corrosion resistance and provides an excellent bonding surface for primers and paint, while having minimal effect on fatigue strength compared to sulfuric acid anodizing.
Why the other options are wrong
- A. Anodizing does not intentionally remove alclad; it forms a protective oxide on the surface.
- B. The oxide layer is thin and offers little wear resistance compared to hard anodizing processes.
- C. Anodized oxide layers are actually electrical insulators, not conductors.
Chromic Acid Anodizing
An electrochemical process that forms a protective aluminum oxide layer on aluminum parts to improve corrosion resistance and paint adhesion.
- Produces thin, corrosion-resistant oxide film
- Improves paint/primer adhesion
- Causes less fatigue strength reduction than sulfuric anodizing
- Commonly used on aircraft aluminum structural parts
Memory trick: "Chromic coats to keep corrosion out and paint stuck on."