What does flux aid in regarding molten filler metal?

Flux plays a crucial role in the brazing process by promoting the flow of molten filler metal. When heat is applied, flux helps to remove any surface oxides and contaminants that can impede bonding. By creating a clean surface, flux facilitates better wetting of the base metals, allowing the molten filler metal to flow more readily into the joint. This enhanced flow is essential for ensuring a strong, uniform bond and achieving optimal joint integrity.

In the context of brazing, proper flow of the filler metal is necessary to fill gaps and ensure complete penetration of the joint. This is why flux is considered indispensable in aiding the flow of the molten filler metal during the brazing process. Other options, such as cooling, solidification, or evaporation, do not directly relate to the primary function of flux in improving the movement and adherence of the filler material.