Flux is essential in brazing to ensure clean, strong, and reliable joints. Its primary roles include:

• Preventing Oxidation: When metal is heated, it readily forms oxides. Flux acts as a protective shield, preventing oxygen from reaching the metal surfaces during the heating process.
• Cleaning the Surface: Flux chemically dissolves existing oxides and impurities, preparing the metal for optimal bonding.
• Promoting Filler Metal Flow: A clean, oxide-free surface enables smooth, uniform flow of molten filler metal into the joint by capillary action.
• Serving as a Temperature Indicator: Some fluxes become transparent or change color when the proper brazing temperature is reached, helping the operator identify the ideal moment to proceed.

Without flux, oxide buildup would inhibit adhesion, leading to poor wetting and weak or failed joints.