Hot-dip galvanization is one of the processes of coating iron and steel with a layer of zinc. In this process, the metal is immersed in a bath of molten zinc. On being exposed to the atmosphere, the zinc reacts with the oxygen and forms zinc oxide. The zinc oxide then reacts with the carbon dioxide and forms zinc carbonate. Zinc carbonate is a dull grey, fairly strong material and protects any further corrosion. Without the cost of stainless steel, galvanized steel provides corrosion resistance in applications where it is most required. Galvanized steel is easily recognizable by the crystallisation patterning, called a spangle, on the surface.
Due to the release of toxic zinc fumes, even though galvanized zinc can be welded, one needs to exercise extreme caution while welding it. Using galvanized steel at temperatures above392 Â°F (200 Â°C) can result in the zinc being peeled off at the inner metallic layer. Electro galvanized sheet steel is obtained from a completely different process, under which a rather lower coating thicknesses of zinc is achieved. This process is often used in automotive manufacturing in order to enhance the corrosion performance of exterior body panels.
Galvanizing, like other corrosion protection systems, acts as a barrier between steel and the atmosphere, protecting the steel from corrosion. But as zinc is a more electronegative metal than steel, even if the galvanized coating gets damaged and exposes the steel to the atmosphere, the zinc can continue to protect steel through galvanic corrosion.