| 摘要 |
PURPOSE:To provide corrosion resistance to a Zn or Zn alloy plated steel material by coating the steel material with an aq. soln. contg. specified amounts of chromic anhydride, phosphoric acid and hydrosilicofluoric acid and having a specified rate of reduction of Cr and by washing and drying the steel material. CONSTITUTION:A Zn or Zn alloy plated steel material is coated with an aq. soln. contg. 5-300g/l chromic anhydride, 7-18g/l phosphoric acid and 3-10g/l hydrosilicofluoric acid and having 50-70% rate or reduction of Cr by roll coating or other method. At this time, the amount of chromate stuck is preferably regulated to about 10-20mg/m<2> (expressed in terms of total Cr). The steel material is then washed and dried at about 45-150 deg.C. A chromate film having superior performance is formed on the steel material. |
