When in a molten state, where does the filler metal flow?

In a molten state, filler metal flows from a hot area to a cold area due to the natural process of heat transfer and the behavior of liquids. When metals are heated and become molten, they possess a lower viscosity compared to their solid state, allowing them to move more freely. The flow direction is driven by the temperature difference; the molten filler metal moves toward the cooler areas to fill gaps and create a bond between the parts being brazed. This movement is part of the principles of thermodynamics, where heat tends to move from regions of higher temperature (hot area) to regions of lower temperature (cold area) until thermal equilibrium is reached.

Understanding this principle is crucial in brazing applications as it ensures that the joint is properly filled, facilitating optimum adhesion and mechanical integrity in the finished assembly. This flow behavior is a fundamental characteristic of liquid metals during the brazing process.