How does capillary action assist in the brazing process?

Capillary action is a crucial phenomenon in the brazing process as it enables the molten filler metal to flow into the narrow spaces between the surfaces being joined. When the filler metal is heated to its melting point, it becomes liquid and, due to surface tension, is drawn into the joint gap through the capillary effect. This action is essential for achieving a strong bond because it ensures that the filler metal fully penetrates the interface between the parts, effectively filling any voids or gaps and creating a complete seal. The strength of the joint and its ability to withstand stress and environmental factors largely depend on how well the filler metal can access and fill these spaces.

The other options do not accurately describe the role of capillary action in brazing. Quick cooling or immediate solidification does not involve capillary movement, and while preventing oxidation is important, it is more related to the brazing atmosphere than to capillary action itself.