Which option is NOT a function of flux in brazing?

• A. To increase the hardness of the joint.
• B. To color the joint.
• C. To remove oxides.
• D. To increase dirtiness of the joint.

Answer: (D)

Flux in brazing is used to clean the metal surfaces by removing oxide films and to prevent re-oxidation during heating, which allows the filler metal to flow and wet the joints properly. It also helps protect the joint from the atmosphere as it heats. Because of these roles, flux is meant to reduce contamination and promote a clean, well-bonded joint. Increasing the dirtiness of the joint would work against these goals, so that option is not a function of flux. The other ideas—removing oxides and aiding wetting—are actual functions flux provides; any coloring or effect on hardness isn’t the primary purpose of flux, and any incidental color is not a stated functional goal.