摘要:
A surface-treated steel sheet for fuel tanks comprising a Zn--X alloy plating layer + a chromate film, in which the Zn--X alloy plating layer has an X content for the plating metal as a whole of Ni: 9-18 wt %, Co: 0.02-3 wt %, Mn: 25-45 wt %, or Cr: 8-20 wt %, the amount of deposition of the plating layer is 5-40 g/m.sup.2 and the amount of the chromate film is 10-200 mg/m.sup.2 on a metallic Cr basis, the Zn--X alloy plating layer corresponding to at least the inner surface of a tank has: (1) cracks in the surface layer, with the density of the cracks being 1000-150000 in terms of the number of plated regions surrounded by cracks in a visual field of 1 mm.times.1 mm, and the maximum width of the cracks is not more than 0.5 .mu.m, or (2) an X/(X+Zn) atomic percentage (X.sub.2) determined by surface analysis based on ESCA with X.sub.1 .noteq.X.sub.2 (wherein X.sub.1 =average value of the X content of the plating metal as a whole), and with X.sub.2 being Ni: 5-25 at %, Co: 0.009-10 at %, Mn: 15-65 at % or Cr: 5-25 at %.
摘要:
A material which can be improved in its resistance to corrosion caused by alcohol-containing fuels after formation without detriment to weldability and without any substantial cost increase is developed.ConstitutionA chromate film is applied to a Zn--X alloy electroplating layer, in which X is one or more of Ni: 3-18 wt %, Co: 0.02-3 wt %, Mn: 25-45 wt %, or Cr: 8-20 wt %. The Zn--Ni alloy plating layer underlying the chromate film has cracks with a density of 1000-150000 in terms of the number of plated regions surrounded by cracks in a 1 mm.times.1 mm visual field, with cracks having a maximum width of 0.5 .mu.m or less comprising 90% or more of the total number of the cracks, and with cracks having a depth of 80% or more of the thickness of the plating layer comprising 80% or more of the total number of the cracks.