AWS Specifications and Classifications

Posted by Lucas-Milhaupt Brazing Experts on Dec 18, 2012

AWS Specifications and Classifications
The American Welding Society (AWS) is a nonprofit organization whose purpose is to support the growth of knowledge and technological advances in the field of brazing and other forms of metal joining.  They have put into place a list of standards and specifications for the different metal joining processes; these can increase your understanding of specific applications and alloys.  

A significant number of classifications and specifications pertain to brazing alloys and brazing applications.  The AWS classifies various brazing alloys and fluxes, holding them to specific chemical tolerances and reactivity characteristics.  They also have specifications for the joint designs and heating methods used in various brazing applications.  This acts as an instruction manual for those new to the field of brazing or its specific applications.

Specifications for Braze Alloys
The AWS A5.8 Specification classifies various braze alloys and their forms.  Each company that sells braze alloys has its own unique product name for each one of the braze alloys it supplies, but many companies supply alloy of the same chemistry, form, and brazing characteristics to meet customers' demands.  A significant number of these alloys have AWS Classification numbers that can be found in the AWS A5.8 booklet.  

For example, Lucas-Milhaupt Inc. has a Braze™ 505 alloy that is very successful in the brazing industry. This alloy has been tested to meet the AWS BAg-24 classification.  This means that the Braze 505 chemistry, solidus, and liquidus must all match those of BAg-24.  In BAg-24, B stands for braze and Ag stands for silver.  The number is assigned to distinguish it from the other alloys in the same category. Many prefixes are listed below:

  • BAg - silver braze alloy
  • BVAg - vacuum-grade silver braze alloy (the ‘V' stands for "vacuum")
  • BAlSi - aluminum braze alloy
  • BCu - copper braze alloy
  • RBCuZn -  copper-zinc braze alloy (the ‘R' stands for "rod")
  • BCuP -  copper-phosphorus braze alloy
  • BNi - nickel braze alloy
  • BTi - titanium braze alloy
  • BVAu - gold braze alloy
  • BVPd - palladium braze alloy

The AWS A5.8 Specification also requires melt cleanliness testing and spatter testing for vacuum alloys, sieve analysis for powders, and a binder content test for alloy tape.  If a specific alloy becomes mainstream in the brazing industry, it will likely be submitted for an AWS Classification number.

Specification for Fluxes
AWS A5.31 is the Specification for Fluxes for Brazing and Braze Welding.  This specification lists the various fluxes that have been classified by the American Welding Society and the testing requirements necessary to meet the classifications.  Fluxes can be tested on water content, particle tests, adhesion, fluidity, fluxing action, flow characteristics, and life duration.  The number of tests required to classify a flux is dependent on the form in which it comes.  Fluxes can be used as powders, pastes, liquids, or slurries.  The standard format of an AWS Flux Classification Title is FB#-A.  The FB is constant on every flux, but the number changes, depending on the base metal types that are to be joined:

     1 - aluminum brazing applications

     2 - magnesium brazing applications

     3 - dissimilar metal brazing applications (usually with a BAg alloy)

     4 - brazing base metals that contain 0.04% of aluminum or titanium.

The letter ‘A' will change from A-Z depending upon how many fluxes have been classified per application.

Specifications for Heating Methods
AWS C3.4, C3.5, C3.6, and C3.9 are specifications regarding the different heating methods: torch, induction, furnace, and resistance brazing.  These specifications are put into place to standardize the method and quality of braze joints formed in these various ways, so that those new to brazing can quickly develop the ability to braze adequately.  The definitions of brazing terms, classes of braze joints, brazing process requirements, and quality assurance provisions are described in detail.  Aluminum brazing requires different skills than other forms of brazing, so it has its own AWS specification, C3.7, for heating methods and quality procedures. 

These are only a few of the specifications the AWS has published, but they are some of the most important.  Leaders in the brazing industry from across America have come together to develop these documents for safe, high-quality brazing.

Are you new to brazing or some of its applications?  You may find our Fundamentals of Brazing webpage to be helpful.  Contact us if we can be of further service as you select brazing products or related services.

Topics: HVAC/R