Brazing filler choice

An interesting example of judicious choice of braze filler is to be found in the selection of silver alloys for the brazing of stainless steels to be subsequently used in a tap-water environment . Although the brazed joint may appear to be quite satisfactory, after a relatively short exposure period failure of the joint occurs by a mechanism which appears to be due to the break-down of the bond between the filler and the base metal. Dezincifica-tion is a prominent feature of the phenomenon and zinc-free braze alloys based on the Ag-Cu system with the addition of nickel and tin have been found to inhibit this form of attack. A similar result is obtained by electroplating 0-007 mm of nickel over the joint area prior to brazing with a more conventional Ag-Cu-Zn-Cd alloy. 

Braze welding (see Fig. 2.35) uses filler metals such as brass or bronze, which are not distributed in the joint by capillary action. The benefits of the flexible oxy-acetylene process make this a frequent choice here. Braze welding produces very strong joints in steel and copper. It is widely used to repair cast parts. 

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