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Choosing a cleaner for unpainted aluminum

Aviation Mechanic General (AMG) practice question 11 of 31 on Cleaning and Corrosion Control. ACS element AM.I.G.K11 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONA mechanic is selecting a cleaner to remove oil and surface dirt from an unpainted aluminum lap joint area before corrosion treatment. Which product characteristic should be chosen?

  1. AA strong alkaline formulation for faster cleaning
  2. BA mild acid to dissolve the oxide film
  3. CA neutral pH
Show the answer and explanation

Correct answer: C. A neutral pH

  • A — incorrect Alkaline cleaners trapped in lap joints of riveted or spot-welded sheet metal can cause corrosion; aluminum is exceedingly prone to attack by alkaline solutions.
  • B — incorrect The thin natural oxide film is protective and is not to be removed by the cleaner; the handbook calls for a neutral pH product.
  • C — correct The handbook cautions that many commercial consumer products are caustic enough to induce corrosion if trapped between aluminum lap joints, and directs choosing a neutral pH product.

BACKGROUND

The first step in treating unpainted aluminum is removing oil and surface dirt with a suitable mild cleaner. Care is needed because many commercial consumer products are caustic enough to induce corrosion if trapped between aluminum lap joints, so a neutral pH product is chosen. Aluminum and magnesium alloys are exceedingly prone to attack by alkaline solutions unless an inhibitor is present, and the handbook warns that cleaners which cannot be effectively rinsed and neutralized may cause corrosion within the lap joints of riveted or spot-welded sheet metal.

STUDY TIP

On aluminum, treat entrapment as the main risk: pick a neutral pH cleaner and make sure whatever you use can be fully rinsed out of joints.

KEY POINTS

  • Use a neutral pH cleaner on unpainted aluminum
  • Caustic consumer products can corrode aluminum trapped in lap joints
  • Aluminum and magnesium are highly susceptible to alkaline attack

SOURCES

  • FAA-H-8083-30B ch08 "Treatment of Unpainted Aluminum Surfaces"
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MORE ON CLEANING AND CORROSION CONTROL

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.