Abstract: A plated composite steel strip having a high corrosion resistance comprises a steel strip substrate, a base electroplating layer comprising a Zn or Zn alloy matrix, substantially water-insoluble chromate particles, and additional fine or colloidal particles of SiO.sub.2, TiO.sub.2, Cr.sub.2 O.sub.3, Al.sub.2 O.sub.3, ZrO.sub.2,SnO.sub.2 and/or Sb.sub.2 O.sub.5, and optionally, an additional electroplating layer formed on the base layer and consisting of Zn, Fe, Co, Ni, Mn and/or Cr and/or a surface coating layer containing at least an organic resinous surface layer and formed on the base, or an additional electroplating layer.

Abstract: A chromate treatment of metal coated steel sheets comprising subjecting the sheets to a cathodic electrolytic treatment to form a chromate film thereon and subjecting the sheet to an anodic electrolytic treatment to form an anodic electrolytic film on the chromate film and to convert the chromate film. The treatment is applicable to various metal coated steel sheets, such as those coated with zinc, zinc alloy, aluminum, aluminum alloy, lead and lead alloy, and is effective to improve the corrosion resistance of the sheets, the quality of paint coating applied on the sheets and the adaptability of the sheets to a cation electro-deposition paint coating.