Technology  >  Heat Treatment   >  Brazing

BRAZING AND SOLDERING require the application of a number of scientific and engineering skills to produce joints of satisfactory quality and reliability. Brazing employs higher temperatures than soldering, but the fundamental concepts are similar, particularly with respect to metallurgy and surface chemistry. However, joint design, materials to be joined, filler metal and flux selection, heating methods, and joint preparation can vary widely between the two processes. Economic considerations involving filler metal and process technology are also varied, particularly in relation to automated techniques and inspection and testing. Brazing and soldering are performed in many industries, from exotic applications in the electronics and aerospace field to everyday plumbing applications.
Brazing has many distinct advantages, including the following:
    •   Economical fabrication of complex and multi-component assemblies
    •   Simple method to obtain extensive joint area or joint length
    •   Joint temperature capability approaching that of base metal
    •   Excellent stress distribution and heat-transfer properties
    •   Ability to preserve protective metal coating or cladding
    •   Ability to join cast materials to wrought metals
    •   Ability to join nonmetals to metals
    •   Ability to join metal thicknesses that vary widely in size
    •   Ability to join dissimilar metals
    •   Ability to join porous metal components
    •   Ability to fabricate large assemblies in a stress-free condition
    •   Ability to preserve special metallurgical characteristics of metals
    •   Ability to join fiber- and dispersion-strengthened composites
    •   Capability for precision production tolerance
    •   Reproducible and reliable quality control techniques

Strong, uniform, leakproof joints can be made rapidly, inexpensively, and even simultaneously. Joints that are inaccessible and parts that may not be joinable at all by other methods often can be joined by brazing. Complicated assemblies comprising thick and thin sections, odd shapes, and differing wrought and cast alloys can be turned into integral components by a single trip through a brazing furnace or a dip pot. Metal as thin as 0.01 mm (0.0004 in.) and as thick as 150 mm (6 in.) can be brazed.

Brazed joint strength is high. The nature of the interatomic (metallic) bond is such that even a simple joint, when properly designed and made, will have strength equal to or greater than that of the as-brazed parent metal. The natural shapes of brazing fillets are excellent. The meniscus surface formed by the fillet metal as it curves across corners and adjoining sections is ideally shaped to resist fatigue.

Complex shapes with greatly varied sections can be brazed with little distortion, and precise joining is comparatively simple. Unlike welding, in which the application of intense heat to small areas acts to move the parts out of alignment and introduces residual stresses, brazing involves fairly even heating and thus part alignment is easier.