PRODUCTION OF ZN-NI ALLOY PLATED STEEL SHEET HAVING EXCELLENT CHIPPING RESISTANCE AND CORROSION RESISTANCE OF WELD ZONE

摘要

PURPOSE:To impart excellent chipping resistance and the corrosion resistance of a weld zone to the steel sheet by depositing Zn-Ni plating of a high Ni concn. under specific conditions on the steel sheet and dissolving this deposit, then subjecting the steel sheet to Zn-Ni alloy plating under specific conditions while the dissolved liquid is held stuck thereto. CONSTITUTION:The deposit of Zn-Ni corresponding to the Ni deposition of an 8-800mg/m2 range is first formed on the steel sheet at about 50-95 deg.C bath temp. by using the high-concn. plating bath adjusted to =5 molar concn. ratio of Ni ions and Zn ions and =25g/l total concn. thereof and to 1.0-4.5pH. The above-mentioned deposit is then redissolved in contact with the high-concn. plating bath or in the high concn. plating bath in accordance with an anodic dissolution method. The steel sheet which is held stuck with the redissolved liquid is introduced into the Zn-Ni alloy plating bath held at =10g/l Ni ions, =15g/l Zn ions, 0.5-1.5 molar concn. ratio of the Ni ions and the Zn ions, 0.8-3.8pH and 50-90 deg.C bath temp. and is continuously subjected to the Zn-Ni alloy plating.