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Alclad protective layer

Aviation Mechanic General (AMG) practice question 14 of 31 on Cleaning and Corrosion Control. ACS element AM.I.G.K14 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONWhat is the protective "Alclad" surface on an aluminum alloy sheet?

  1. AA thin coating of relatively pure aluminum over the base alloy
  2. BA layer of aluminum oxide grown electrolytically in a chromic acid bath
  3. CA sacrificial cadmium plating that protects the alloy beneath
Show the answer and explanation

Correct answer: A. A thin coating of relatively pure aluminum over the base alloy

  • A — correct Relatively pure aluminum has considerably more corrosion resistance than the stronger alloys, so a thin coating of pure aluminum is applied over the base alloy; this clad surface is commonly called Alclad.
  • B — incorrect That describes anodizing, in which the part is the positive pole in an electrolytic bath; Alclad is a metallic cladding, not an oxide film.
  • C — incorrect Cadmium is used as a sacrificial plating to protect steel, not as the cladding on aluminum sheet.

BACKGROUND

Aluminum alloys are the most widely used material for aircraft construction, and although aluminum corrodes easily, a tightly adhering oxide film gives it increased resistance. Relatively pure aluminum has considerably more corrosion resistance than the stronger aluminum alloys, so a thin coating of relatively pure aluminum is applied over the base alloy; this pure-aluminum clad surface is commonly called Alclad and can be maintained in a polished condition. When cleaning Alclad, avoid unnecessary mechanical removal of the cladding, which would expose the more susceptible alloy beneath. Alclad surfaces left unpainted need no anodic treatment, but if they are to be painted they are usually anodized to provide a bond for the paint.

STUDY TIP

Remember why Alclad works (pure aluminum resists corrosion better than the alloy) and the practical rule that follows: do not polish or abrade through the cladding.

KEY POINTS

  • Alclad = thin layer of relatively pure aluminum over the alloy
  • Pure aluminum resists corrosion better than high-strength alloys
  • Avoid mechanical removal of the cladding during cleaning

SOURCES

  • FAA-H-8083-30B ch08 "Treatment of Unpainted Aluminum Surfaces"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-30B Aviation Maintenance Technician Handbook – General, 14 CFR part 43 and part 65. Regulations and handbooks are revised; confirm details against the current edition.