Since it is possible to apply zinc to the surface of steel sheet in large quantities, hot-dipped zinc coated steel sheet is used for applications that require long period corrosion resistance, such as automotive bodies, prefab and metal buildings.
Zinc coated steel sheet can be roughly divided into zinc coated steel sheet (Galvanized steel sheet: GI) which is plated by immersing the steel sheet in a molten zinc bath and zinc–iron alloy coated steel sheet (Galvannealed steel sheet: GA) which diffuses the iron in the steel to coated zinc through the boundary of the zinc and steel by heating after plating treatment to make a zinc–iron alloy. GI capable of coating weight of 400 g/m² or more is widely used for applications requiring severe weather resistance, such as outdoor units of air conditioners, guardrails, construction materials, and so on. Since GA whose plating layer is zinc–iron alloy has the futures of that (1) it is easy to form into complex shapes because of harder plating than zinc alone and hardly adhering to the mold at the time of press molding, (2) it has excellent weldability because of its high melting point, (3) since the surface has dense irregularities, it is excellent in paint adhesion because of dense asperities on the surface, In addition to having anticorrosive property of GI, GA has been expanding its use mainly for automobile bodies with high demand for shape design.