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Galvanization (also spelled galvanisation) [1] is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot-dip galvanizing , in which the parts are coated by submerging them in a bath of hot, molten zinc.
The British, European and International standard for hot-dip galvanizing is BS EN ISO 1461, which specifies a minimum coating thickness to be applied to steel in relation to the steels section thickness e.g. a steel fabrication with a section size thicker than 6 mm shall have a minimum galvanized coating thickness of 85 μm.
The coil coating process may be used for other substrates such as aluminium, or aluminium, stainless steel or alloy coated steel other than "pure" zinc coated steel. However, only "pure" zinc coated steel is typically referred to as PPGI. For example, PPGL may be used for pre-painted 55%Al/Zn alloy-coated steel (pre-painted GALVALUME(r) steel*)
Steel is preserved from corrosion by cathodic protection. Conversion coatings (hexavalent chromium (CrVI) or trivalent chromium (CrIII) depending upon OEM requirements) are applied to drastically enhance the corrosion protection by building an additional inhibiting layer of Chromium and Zinc hydroxides.
Galvannealed or galvanneal (galvannealed steel) is the result from the processes of galvanizing followed by annealing of sheet steel. Galvannealed steel is a matte uniform grey color, which can be easily painted. In comparison to galvanized steel the coating is harder, and more brittle.
A common example of galvanic corrosion occurs in galvanized iron, a sheet of iron or steel covered with a zinc coating. Even when the protective zinc coating is broken, the underlying steel is not attacked. Instead, the zinc is corroded because it is less "noble". Only after it has been consumed can rusting of the base metal occur.
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