PRODUCTION OF STEEL PLATE PLATED WITH ZN-NI-TI ALLOY WITH EXCELLENT ADHESION OF PLATING LAYER

摘要

PURPOSE:To obtain a steel plate which is electroplated thereon with a Zn-Ni-Ti alloy and is improved in th adhesion between the plating layer and the steel base by plating preliminarily a Zn-Ni alloy on a steel plate. CONSTITUTION:A Zn-Ni alloy contg. Ni in an amt. higher than in a Zn-Ni-Ti alloy of a top layer is preliminarily plated at a relatively low current density on a steel plate by using a plating bath contg. Zn2+ and Ni2+. The adhesion between the plating layer and the steel base is improved by such preliminary plating, and the corrosion between the steel base and the plating layer of the Zn-Ni- Ti alloy which is a substrate plating is suppressed. More specifically, the electroplating of the Zn-Ni-Ti alloy on the steel plate is accomplished after the steel plate is beforehand subjected to electroplating in an acidic preplating kath contg. Zn2+ and Ni2+ and consisting of Ni2+/(Zn2++Ni2+)=0.70-0.85 in ion concn. ratio. The current density in this stage is 2-20A/dm2 and the bath temp. is 55-80 deg.C. The Zn-Ni alloy having higher Ni content than the above-described Zn-Ni-Ti alloy and contg. 12-87% Ni is used in the preliminary electroplating.