FAA Aviation Mechanic Airframe (AMA)Airframe StructuresHard
A technician is preparing an aluminum landing gear strut component for corrosion protection prior to painting. The specified process involves submerging the part in an electrolyte bath and passing an electric current through it, with the part acting as the anode, to build up a hard protective oxide layer on the surface. What process is being performed?
- ACadmium plating
- BAnodizing
- CParkerizing
- DAlodine (chromate conversion) coating
Show answer & explanationAnswer & explanation
Correct answer: B. Anodizing
Anodizing is an electrochemical process in which the aluminum part is made the anode in an electrolytic cell, causing a controlled, hard oxide layer to form on its surface. This differs from Alodine, which is a chemical (non-electrolytic) conversion coating, and from cadmium plating, which deposits a different metal via electrodeposition.
Why the other options are wrong
- A. Cadmium plating deposits cadmium metal onto steel parts and is typically used on steel, not aluminum oxide formation.
- C. Parkerizing is a phosphate conversion coating process used on ferrous (steel) parts, not aluminum.
- D. Alodine is a chemical conversion coating that does not require an electric current or anodic reaction.
Anodizing
An electrochemical surface treatment in which an aluminum part serves as the anode in an electrolytic bath (chromic or sulfuric acid), building up a hard, corrosion-resistant oxide layer that also improves paint adhesion.
- Part is made the anode; current passes through an acid electrolyte bath.
- Chromic acid anodizing is common on aircraft structural aluminum parts.
- Produces a harder, more durable oxide layer than chemical conversion coatings like Alodine.
Memory trick: Anodizing = 'Anode' + 'Oxide' building up under electric current