In brazing, the brazing assembly is heated to a temperature at which the filler rod or solder becomes liquid before flowing and spreading by the wetting action through the space "gap" between the closely adjacent surfaces of the parts to be joined. The interaction by capillarity between the liquid filler metal and the surface of the parent material makes a metallurgical continuity between the parts during the solidification phase of the liquid filler metal.

Unlike welding, the base metal remains in the solid state. In generally, brazing is related to melting points higher than 450°C (900°F) and lower than 450°C for soldering. Therefore, the base metals are less affected by heat and to a lesser degree by oxidation and warping.

Brazing is used in many industries such as plumbing, electronics, automotive, aerospace, food processing, pharmaceutical, jewelry and goldsmith, refrigeration and air conditioning industry, etc. The advantages of brazing consist mainly in the ability to mechanize or to automate the process for high speed production. This assembly process is well suited to intricate joints for almost all metals and ceramics, either for similar or dissimilar joints.

The heating of the material can be achieved by several means: torch, electric resistance furnace (controlled atmosphere or vacuum), magnetic induction, salt bath. The filler rod is available in several forms: rod or wire, strip, powder or paste. Regarding the flux, it is often available in the form of powder or liquid (gel or cream), as it may be integrated in the formulation of the filler metal itself (flux cored rod/wire). The role of the flux consists of dissolving the oxide on the surface and promoting wetting while protecting the liquid filler metal and the heated base metal against atmospheric contamination during brazing.

There is a wide variety in the filler metals series. The most common ones are: silver-based alloys, copper alloys, nickel alloys, gold-based alloys, aluminum and magnesium alloys, etc. The choice of the filler metal type depends on several factors including the base metals to be joined, design of the joint, service conditions (temperature, corrosion, etc.), soldering method (ex., Vacuum furnace, the torch), aesthetic and color matching, health and safety considerations etc.

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Brazing rods
Brazing rods