What is the recommended surface preparation sequence for aluminum prior to brazing to promote wetting?

• A. Degrease, etch, apply flux.
• B. Buff and paint the surface.
• C. Polish only.
• D. Soak in water then dry.

Answer: (A)

Aluminum brazing relies on a clean, oxide-free surface so the molten filler can wet and flow into the joint. The best preparation sequence starts with degreasing to remove oils, fingerprints, and hydrocarbon residues that would repel the molten metal. Next, etching removes the native oxide layer and creates a slightly rough surface, which helps the filler metal start to wet the surface and adhere. Finally, applying flux provides chemical cleansing of any remaining oxides and protects the surface from re-oxidizing during heating, allowing the filler metal to spread and bond more effectively.

Without degreasing, oils can block wetting; without etching, the oxide film remains and resists bonding; without flux, even small amounts of oxide can form during heating and prevent proper wetting. The other options don’t address all these essential steps and would leave contaminants or oxides that hinder wetting.