Vacuum brazing is a material joining technique that offers significant advantages: extremely clean, high quality, fluxless brazed joints with high integrity and strength. This process can be expensive because it must be carried out in a vacuum chamber vessel. When heated in a vacuum, temperature uniformity is maintained across the workpiece, greatly reducing residual stresses due to slow heating and cooling cycles. This, in turn, can significantly improve the thermal and mechanical properties of the material, providing a unique heat treatment capability. One such capability is to heat treat or age harden the workpiece while performing the metal joining process, all in a single furnace thermal cycle.
Products that are most commonly vacuum-brazed include aluminum cold plates, plate-fin heat exchangers, and flat tube heat exchangers.
Vacuum brazing is often conducted in a furnace; this means that several joints can be made at once because the whole workpiece reaches the brazing temperature. The heat is transferred using radiation, as many other methods cannot be used in a vacuum.
Dip brazing is particularly suitable for brazing aluminum because it excludes air and prevents the formation of oxides. The components to be joined are fixed and the brazing compound is typically applied to the mating surface in the form of a slurry. The assembly is then immersed in a molten salt bath (typically NaCl, KCl and other compounds) which acts as a heat transfer medium and flux. Many dip brazed components are used in heat transfer applications in the aerospace industry.