FAA AMT (Aviation Maintenance Technician) Airframe Practice Exam

How is flux removed from an aluminum tank after welded repairs?

1. Using a soap and water solution

2. With a 5 percent solution of nitric or sulfuric acid

3. Scrubbing with a brush

4. Using an alcohol-based cleaner

The correct answer is: With a 5 percent solution of nitric or sulfuric acid

After welded repairs, all flux residue must be removed from an aluminum tank to prevent contamination and corrosion. This is because flux, which is used during welding to prevent oxidation, can have harmful effects if left in the tank. Option A, using a soap and water solution, is incorrect because it is not strong enough to fully remove flux residue. Option C, scrubbing with a brush, is incorrect because it may not be thorough enough to fully remove all flux residue. Option D, using an alcohol-based cleaner, is incorrect because it may not be strong enough to fully remove all flux residue and can also leave behind a residue itself. Option B, with a 5 percent solution of nitric or sulfuric acid, is the most effective and commonly used method for removing flux residue from an aluminum tank. However, it is important to use proper safety precautions and neutralize the acid solution after use to prevent further damage to the tank.