What physical principle does brazing primarily rely on?

Brazing primarily relies on capillary action to draw liquid filler metal into the joint. This process involves the use of a filler metal with a melting point above 450 degrees Celsius, which is melted and then flows into the space between the closely fitted surfaces of the workpieces being joined.

Capillary action is critical in this process because it allows the molten filler metal to flow into narrow gaps where the two workpieces meet. As the filler metal is heated and liquefied, it is drawn into the joint by the cohesive forces acting within it and the adhesive forces acting between the filler and the base metals. This results in a strong bond once the filler metal cools and solidifies.

The other options do not capture the main principle of brazing: pressure application is not typically used to force the filler, instead, it flows naturally into the joint due to capillary action. Thermal fusion refers to the melting of base metals, which is not a characteristic of brazing as it uses a filler metal instead of fusing the base metals directly. Gravity may aid in the flow of the filler, but it is not the primary mechanism; rather, the ability of the filler to be drawn into the joint by capillary action is what distinguishes braz