German to English Tech/Engineering Metallurgy / Casting automotive applications

This comes from a trainer's outline for an automotive repair workshop. One of the objectives of the workshop is to impart knowledge of how to work with lead-free *Schwemmzinn*, which appears to refer to a hard solder. One product safety analysis identifies a specific product referred to as *Schwemmzinn* as a tin-antimony-lead alloy, but other references indicate that the term is somewhat less specific than this. I haven't been able to find a German definition, unfortunately. How does the "Schwemm-" qualify the "Zinn"? Does it refer to how the tin is mined (as in "alluvial" tin); or does it refer to the tin's behavior when it reaches the melting point? Is there an equivalent for *Schwemmzinn* in English?