METHOD FOR MAKING DOUBLE COATING STEEL OF THE ZN-CR/ZN ALLOY OR ZNIC SYSTEM ALLOY WITH EXCELLENT CORROSION RESISTANCE AFTER COATING

摘要

PURPOSE: A process for preparing the titled steel sheet having corrosion resistance by forming a Zn or Zn-alloy plated layer on a steel sheet and forming a Zn-Cr alloy plated layer thereon is provided. Whereby, the obtained steel sheet has excellent bare corrosion resistance and corrosion resistance after coating. CONSTITUTION: The double layer plated steel sheet is prepared by the process consisting of: forming a Zn or Zn-alloy plated layer on a steel sheet and forming a Zn-Cr alloy plated layer having a Cr precipitation amount of 5 to 12.7% by weight thereon, with a concentration rate of Cr and Zn1 and a current density of 60 to 100A/dm¬2 in 20 to 40g/l plating solution.