SFA-5.8/ SFA-58m: Specification for Filler Metals of Brazing and Braze Welding

This is the only specification for brazing filler metals that is referenced in Section IX (QB-Brazing). Although this specification includes materials for braze welding, the main application for these materials is for brazing. Filler metals classified in this specification include all metal and alloy compositions for brazing, with or without flux and in protective atmospheres. Standard forms include wire, strip, sheet, foil, rod, powder, and paste.

The brazing filler metals covered by this specification are classified according to their chemical composition. Defining the filler metal starts with “B” for brazing, followed by a chemical symbol (such as Cu) to identify the major element. The remaining elemental symbols indicate the principal alloying elements; for example, BCuP contains the primary element of copper with phosphorous alloying. Filler metals identified by the prefix “RB” indicate that the filler metal is suitable for use as a brazing rod for braze welding and as a brazing filler metal. Typically, the RBCuZn classifications are used in braze welding. Filler metal classifications for vacuum service are similar to those for other filler metals, except that the letter “V” appears in the classifications (e.g., BVAg-8). Devices brazed by the use of these filler metals are intended to operate in vacuums regardless of the atmosphere used in brazing the base metals. Vacuum service filler metals are manufactured to reduce the high vapor pressure impurities. Grade 1 filler metals meet more stringent requirements for the high vapor pressure impurities than those of Grade 2. As defined by the AWS:

Brazing is a group of metal joining processes which produces coalescence of materials by heating them to a suitable temperature and by using a filler metal having liquids above 840°F (450°C) and below the solidus of the base materials. The filler metal is distributed between the closely fitted surfaces of the joint by capillary action.

In braze welding; the primary difference is that the filler is not distributed in the joint by capillary action. The following paragraphs briefly discuss the brazing filler metals.