Earlier this year, I wrote an article on this website about the use of Zinc (Zn) in brazing, and strongly warned readers to never vacuum-braze any metals/alloys that contained any Zn in their chemistry or if they had Zn-plating on their surface. The same warnings apply to Cadmium (Cd).
Zn and Cd are added to some brazing filler metals (BFMs) to help lower the melting point of those particular BFMs. Both Zn and Cd are very effective “temperature-depressants”, i.e., they significantly lower the melting temp of any silver-based BFMs into which they are added, and they also help those BFMs to “wet” (i.e., to diffuse into and spread out over) the clean base-metal surfaces that are being brazed. Thus, both of these elements began being added to silver-based BFMs early in the last century in order to enable low-temp torch-brazing (flame-brazing) that was not only easy to perform but produced high-quality joints. This is still the case today. However, both Zn and Cd are highly volatile, and can easily outgas from BFMs when heated. This must be clearly understood when considering which brazing methods to use for such BFMs so that the resulting brazed joints will be properly made.