As a result, the European brazing industry has essentially abandoned the use of any BFMs that contain cadmium (Cd), as shown in Fig. However, the use of cadmium has been decreasing significantly amongst European Union (EU) member nations, where the “Restriction of Hazardous Substances” (RoHS) Directive, which originally took effect in July 2006, has severely restricted the use of a number of substances, including cadmium. Besides its use in brazing, Cd has been widely used in many industrial applications, such as in Nickel-Cadmium (Ni-Cd) batteries, and in solar-panels. In some cases, the Zn and Cd account for more than 50% of the total chemistry of that particular BFM, such as in BAg-5.Ĭd use in brazing and other industries today.Ĭd is primarily obtained as a byproduct when mining zinc ores. Notice in Table 1 how much Zinc (Zn) and Cadmium (Cd) are contained in those brazing filler metals (BFMs). Table 1 - A partial listing of the chemistries of a few of the BAg alloys listed in the AWS A5.8 Brazing Filler Metal Specification (Courtesy of the American Welding Society, Doral, Florida, 2013). A few examples of such BFMs (classified as BAg-1 through BAg-8a, are shown in Table 1. The American Welding Society (AWS) has published a brazing filler metal (BFM) specification, AWS A5.8, that lists many of the BFMs commonly being used today, and which also includes a lot of information about the composition of those BFMs along with numerous guidelines for their proper use. 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. However, both Zn and Cd are highly volatile, and can easily outgas from BFMs when heated. 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. 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.
Zn and Cd are added to some brazing filler metals (BFMs) to help lower the melting point of those particular BFMs. 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.
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