Galvanization

Galvanization is the process of applying a protective zinc coating to steel or iron to prevent corrosion. The zinc coating provides sacrificial protection, corroding preferentially to zinc instead of the underlying metal, and also acts as a barrier to moisture. The term derives from galvanism, and the practice became widespread in the 19th and 20th centuries.

Common methods include hot-dip galvanizing, electrogalvanizing, and galvannealed coatings. In hot-dip galvanizing, parts are degreased, fluxed, and immersed in molten zinc at about 450°C, forming a metallurgical bond with one or more zinc-iron alloy layers and an outer zinc layer; typical coating thickness ranges from 40 to 85 micrometers. Electrogalvanizing uses an electrical current to deposit zinc from a zinc sulfate or zinc chloride bath, producing thinner, smoother coatings typically 5 to 25 micrometers. Galvannealed refers to galvanized steel that has been annealed to form a zinc-iron alloy layer, improving paint adhesion. Mechanical galvanizing coats steel with zinc powder through tumbling or abrasion.

Coatings extend the life of outdoor steelwork, including bridges, guard rails, pipes, fencing, and electrical enclosures, as well as automotive and appliance components. In many environments, galvanized steel requires little or no coating maintenance for decades. Zinc coatings can be damaged by abrasion or bending, exposing steel and sacrificing nearby coating; repairs typically involve re-galvanizing or touch-up.

Standards such as ISO 1461 and ASTM A123/A123M specify coating thickness, adhesion, and quality requirements for hot-dip galvanized products. Environmental considerations include zinc recovery, energy use, and zinc oxide emissions from galvanizing plants. The process remains widely used because of its durability, cost-effectiveness, and recyclability.