TABLE OF CONTENTS Soldering and brazing are useful, fairly simple joining processes in which metals are wetted and joined together by a dissimilar metal of lower melting temperature. When compared with mechanical joints and adhesives, the join is permanent unless remelted, has good electrical and thermal conductivity and is unaffected by organic solvents. It is also resistant to failures at temperatures under those of the original joining technique. There are many filler metals available for a variety of applications with melting temperatures from just above room temperature upwards, the majority of conventional solders being molten below 300 C. Brazing is basically similar to soldering but takes place at a higher temperature, above 450 C according to the definitions of BS 499 but, unlike welding, always below the melting temperature of the parent metals. Brazing is also distinguished from welding by the fact that the brazed joint is formed mainly by capillary action between adjacent surfaces whereas welding starts by local melting of the base metals and continues with the addition of larger fillets of welding filler metal.
The majority of soldering and brazing alloys are based on binary or ternary eutectic systems, sometimes with small amounts of other addition elements. The compositions are chosen to have good wetting and capillarity at the joining temperatures, good corrosion resistance and reasonable strength. Brazed joints are generally significantly stronger than soldered ones and are usually intended to be permanent. The higher the joining temperature, the greater will be the heat-affected zone in the parent...
