PRODUCTION OF PB-SN ALLOY PLATED STEEL SHEET HAVING HIGH CORROSION RESISTANCE, UNIFORM COVERING PROPERTY AND SUPERIOR ADHESION OF COATING LAYER

摘要

PURPOSE:To improve the uniform covering property and adhesion of a plating layer by successively subjecting a steel sheet contg. Cr to cathodic electrolysis under specified conditions, undercoating with Ni or Co by electroplating at a low pH and Pb-Sn alloy plating. CONSTITUTION:A steel sheet contg. =25% Cr is subjected to cathodic electrolysis at =7.5A/dm2 current density for 1-15sec in an aq. soln. having 1/50-1/5 weight ratio of (Ni2++Co2+)/SO42- and contg. 75-350g/l free sulfuric acid. The resulting activated surface is coated with an Ni, Co or Ni-Co alloy layer of 0.01-1mum thickness in an electroplating bath of =3.0pH contg. Ni2+ and/or Co2+ by =50wt.% of the total amt. of SO42- and Cl-. A Pb-Sn alloy plating layer contg. 3-30% Sn is then formed on the coating layer. A Pb-Sn alloy plated steel sheet having superior corrosion resistance, superior uniform covering property and adhesion of the plating layer is obtd.