Zinc & Zinc Alloys
, hot-dip galvanizing, and the metal fume fever hazard
AI generated Zinc is best known as corrosion protection — hot-dip galvanizing on steel. There's also zinc die casting for fittings and small parts. When galvanized parts, caution is needed: The vaporizing zinc fume causes metal fume fever and leaves porosity.
Zinc rarely shows up in your welding shop as a base material — but all the more often as a coating. protects steel from rust — the zinc sacrifices itself, corroding instead of the steel (cathodic protection). There's also zinc die casting (Zamak alloys) for door handles, trim strips, and small cast parts.
The real topic for you is galvanized steel. Zinc boils at 907 °C — far below welding temperature. When your hits the zinc layer, the zinc vaporizes instantly. That has two nasty consequences. First: The rising zinc vapor blows holes in the molten weld pool, leaving and spatter. Second, and far more important for your health: If you breathe in that white zinc oxide fume, you'll get metal fume fever — flu-like chills with fever, coughing, and nausea that hit hours later and last a day or two. It's rarely permanently dangerous, but it will reliably knock you flat.
That's why the golden rule when galvanized steel is: Remove the zinc layer at the joint beforehand. Grind it off or burn it off — but when burning off, definitely use fume extraction, because that's exactly when the toxic fume is produced. Alternatively, weld with a steady arc and strong extraction right at the torch.
Zinc die casting itself is rarely welded — it's usually instead. Zinc's low melting point (419 °C) makes soldering the first choice. Even when soldering, the same rules apply: use flux and fume extraction, because zinc fume is the same problem everywhere.
The modern alternative: MIG brazing
For galvanized sheet metal on car bodies, a more elegant method has become standard: MIG brazing with a copper-silicon wire (CuSi3). The burns cool enough that the zinc doesn't vaporize — the wire melts, the zinc stays as a protective layer, and you get a clean, corrosion-protected joint without the risk of metal fume fever. The catch: This is a brazed joint, not a weld bead — it takes less tensile load than a real weld. So for load-bearing joints, there's only one way: remove the zinc beforehand, extract the fume, weld, and then re-protect the bead with zinc spray.