ArcelorMittal S.A.
Metal sheet treatment method for reducing blackening or tarnishing during the storage thereof and metal sheet treated with this method

Abstract:

The present invention provides a metal sheet including a steel substrate coated on at least one face with a coating including from 0.1 to 20% by weight of magnesium, optionally from 0.1 to 20% by weight of aluminum, the balance being zinc, potential impurities linked to the method and optionally one or more additional elements selected from among Si, Sb, Pb, Ti, Ca, Mn, Sn, La, Ce, Cr, Ni, Zr and Bi, the content by weight of each additional element being less than 0.3%. The coating itself is covered by a layer, based on zinc hydroxychloride, having a chlorine coating weight of at least 1 mg/m.sup.2. The layer does not include hydrozincite or mixed hydroxycarbonates of zinc and aluminum or water-soluble compounds of sodium or potassium. The present invention also provides a method to obtain the metal sheet.