What is the role of flux in brazing?

The role of flux in brazing is crucial for achieving strong and reliable joints. Flux serves two primary functions: it aids in the flow of the filler metal and prevents oxidation of the base metals during the process. When heat is applied in brazing, it is essential that both the base metal and the filler metal remain clean and free of contaminants such as oxides, which can interfere with the bonding process.

Flux works by creating a barrier that protects the surfaces from oxidation, allowing the filler metal to flow smoothly into the joint. This flow is critical because proper capillary action is necessary for the filler metal to fill gaps effectively and create a strong joint. The right flux facilitates this action, ensuring a good connection between the components being joined.

In contrast to the other choices, reducing the melting point of the base metals, increasing the overall weld size, or strengthening the base metals are not functions of flux in brazing. Thus, option B accurately captures the essential role of flux in the brazing process.