FAA Aviation Mechanic General (AMG)Materials, Hardware and ProcessesMedium
A technician repairing 2024-T3 aluminum skin is careful not to sand through the thin, bright surface layer visible on the sheet. What is the purpose of this Alclad layer?
- AImprove rivet shear strength at fastener locations
- BIncrease the overall tensile strength of the sheet
- CProvide sacrificial corrosion protection for the base alloy
- DAct as a low-resistance electrical bonding path
Show answer & explanationAnswer & explanation
Correct answer: C. Provide sacrificial corrosion protection for the base alloy
Alclad is a thin layer of pure aluminum roll-bonded to the surface of high-strength aluminum alloys like 2024-T3. Because pure aluminum is more anodic than the copper-bearing alloy underneath, it corrodes preferentially and sacrifices itself to protect the base metal from corrosion. Sanding through this layer exposes the alloy to corrosion.
Why the other options are wrong
- A. Rivet shear strength depends on the rivet alloy and diameter, not the cladding layer.
- B. The pure aluminum cladding is actually softer and weaker than the core alloy, contributing little strength.
- D. Bonding paths are provided by separate bonding jumpers, not the Alclad coating.
Alclad Aluminum
A corrosion-resistant aluminum sheet made by bonding a thin layer of pure aluminum to the surface of a stronger, less corrosion-resistant aluminum alloy such as 2024-T3.
- Pure aluminum cladding is anodic, sacrificing itself to protect the core
- Must not be sanded/polished through during repairs or corrosion of the core alloy can begin
- Commonly used on exterior skins for corrosion resistance
Memory trick: 'Alclad is the sacrificial shield' - pure aluminum takes the corrosive hit first