FAA Aviation Mechanic Airframe (AMA)Airframe StructuresMedium
A technician is preparing bare aluminum structural parts for painting and applies a yellow-green coating before the topcoat. What is the primary purpose of this zinc chromate primer coat?
- ATo improve aerodynamic smoothness of the skin
- BTo inhibit corrosion and provide a bonding surface for the topcoat
- CTo provide the final decorative color for the aircraft
- DTo add structural strength to the aluminum skin
Show answer & explanationAnswer & explanation
Correct answer: B. To inhibit corrosion and provide a bonding surface for the topcoat
Zinc chromate primer is applied to bare aluminum as a corrosion-inhibiting undercoat. It chemically passivates the metal surface and provides a good bonding base for subsequent topcoats, but it is not a decorative finish, does not add strength, and has no effect on aerodynamic smoothness.
Why the other options are wrong
- A. Primer thickness has no meaningful aerodynamic smoothing function.
- C. Zinc chromate is a primer, not the final color coat; a topcoat is applied over it.
- D. Primer coatings do not add structural strength to the base metal.
Zinc Chromate Primer
A yellow-green corrosion-inhibiting primer applied to bare metal aircraft structure before painting, providing corrosion protection and a bonding surface for topcoats.
- Distinctive yellow-green color
- Chromate ions passivate the metal, inhibiting corrosion
- Must be applied over clean, properly prepared bare metal
Memory trick: 'Yellow-Green Means Corrosion is Seen (and stopped)' — zinc chromate protects bare metal.