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Galvanized Treatment Production of galvannealed sheet steel begins with hot dip galvanization of sheet steel. After passing through the galvanizing zinc bath the sheet steel passes through air knives to remove excess zinc, and is then heated in an annealing furnace for several seconds causing iron and zinc layers to diffuse into one another causing the formation of zinc-iron alloy layers at the surface. The annealing step is performed with the strip still hot after the galvanizing step, with the zinc still liquid. The galvanising bath contains slightly over 0.1% aluminium, added to form a layer bonding between the iron and coated zinc. Annealing temperatures are around 500 to 565 °C.
The resulting coating has a matte appearance, and is hard and brittle - under further working such as pressing or bending powder is produced from degradation of the coating, together with cracks on the surface.In comparison to a zinc (galvanized) coating galvannealed has better spot weldability, and is paintable,Due to iron present in the surface alloy phase galvanneal develops a reddish patina in moist environments - it is generally used painted. Zinc phosphate coating is a common pre-painting Surface Treatment.
Galvannealed sheet can also be produced from electroplated zinc steel sheet.