Brazing

By definition, brazing is a metal-joining technique that uses a molten filler metal alloy having a melting temperature greater than about 425°C (800°F). In brazing, a filler metal is melted and drawn into a capillary formed by the assembly of two or more work pieces. The filler metal has a lower melting point than the adjoining metal. Brazing differs from welding in that it does not involve melting the work pieces and from soldering in using higher temperatures for a similar process, while also requiring much more closely fitted parts than when soldering. The filler metal flows between the closely fitting joint surfaces by means of capillary action.

Advantages and Disadvantages of Brazing

Advantages:

  • 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.
  • A major advantage of brazing is the ability to join the same or different metals with considerable strength.

Disadvantages:

  • One of the main disadvantages is the lack of joint strength as compared to a welded joint due to the softer filler metals used.
  • The strength of the brazed joint is likely to be less than that of the base metal(s) but greater than the filler metal.
  • Another disadvantage is that brazed joints can be damaged under high service temperatures.

Brazing Filler Material

A variety of alloys are used as filler metals for brazing depending on the intended use or application method. For manual brazing, wire and rod forms are generally used as they are the easiest to apply while heating. Some of the more common types of filler metals used are:

  • Aluminum-silicon
  • Copper
  • Copper-silver
  • Copper-zinc (brass)
  • Copper-tin (bronze)
  • Gold-silver
  • Nickel alloy
References:
Materials Science:

U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 2 and 2. January 1993.
William D. Callister, David G. Rethwisch. Materials Science and Engineering: An Introduction 9th Edition, Wiley; 9 edition (December 4, 2013), ISBN-13: 978-1118324578.
Eberhart, Mark (2003). Why Things Break: Understanding the World by the Way It Comes Apart. Harmony. ISBN 978-1-4000-4760-4.
Gaskell, David R. (1995). Introduction to the Thermodynamics of Materials (4th ed.). Taylor and Francis Publishing. ISBN 978-1-56032-992-3.
González-Viñas, W. & Mancini, H.L. (2004). An Introduction to Materials Science. Princeton University Press. ISBN 978-0-691-07097-1.
Ashby, Michael; Hugh Shercliff; David Cebon (2007). Materials: engineering, science, processing and design (1st ed.). Butterworth-Heinemann. ISBN 978-0-7506-8391-3.
J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.

See above:
Metal Joining