Why is lead added to the galvanizing bath?
Lead is not purposely added to galvanizing baths, rather it is an impurity in zinc. Different types of zinc have different levels of lead. The specified lead maximums for the various types of zinc can be found in ASTM B6.
Lead does have the beneficial effect of decreasing the surface tension of zinc, which allows it to flow off the steel easier as it is being removed from the kettle. This creates thinner galvanized coatings that have less runs and drips. Bismuth is sometimes added to galvanizing baths to achieve the same effect as lead has when types of zinc are used that have very low levels of lead.
Occasionally, the AGA receives questions about "lead free" zinc. All zinc grades contain at least a small amount of lead, because lead is found in most natural deposits of zinc. Some galvanizers utilize high grade and special high grade zinc ingots which have very low lead content (<0.03% and <0.003%, respectively) and are acceptable for most low-lead applications.
© 2024 American Galvanizers Association. The material provided herein has been developed to provide accurate and authoritative information about after-fabrication hot-dip galvanized steel. This material provides general information only and is not intended as a substitute for competent professional examination and verification as to suitability and applicability. The information provided herein is not intended as a representation or warranty on the part of the AGA. Anyone making use of this information assumes all liability arising from such use.