For capillary attraction to occur, what must be done to the base metals?

For capillary attraction to occur in the brazing process, it is essential that the base metals are cleaned and fluxed. This cleaning process removes contaminants such as oils, oxides, and other surface impurities that could prevent the molten filler metal from properly flowing into the joint. Flux acts as a chemical cleaning agent, ensuring that the surfaces of the metals are adequately prepared for the brazing process.

The role of flux is crucial because it also helps to reduce the surface tension of the filler metal, allowing it to better penetrate the narrow spaces between the closely fit parts. This is what facilitates the capillary action needed for an effective braze. Without proper cleaning and the application of flux, the filler metal may not adhere properly, leading to weak joints or complete failure to bond.