Multilayer electroplated steel sheet

Details Multilayer electroplated steel sheet Multilayer electroplated steel sheet

1987-12-31

1990-03-13

McDowell, Robert

Stock material or miscellaneous articles

All metal or with adjacent metals

Composite; i.e., plural, adjacent, spatially distinct metal...

428681, 428935, B32B 1518

Patent

active

049082795

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to a multilayer electroplated steel sheet that can have good coating appearance, and also can exhibit good corrosion resistance even in a corrosive environment like a road on which antifreezing agents such as rock salt have been sprayed.


BACKGROUND ART

Zinc metal-plated steel sheets, provided with a coating having a good sacrificial corrosion resistant ability, have hitherto widely used for the purposes in which corrosion resistance is required as in the various fields of automobiles, household electrical equipments, building materials, etc. When this zinc metal-plated steel sheets are used in automobile bodies as in recent years, they may be placed in a severe corrosive environment because antifreezing agents such as rock salt are sprayed on a road in winter as in the cold countries such as North America, Canada and elsewhere. Accordingly, they are required to have excellent blistering resistance, corrosion resistance and pin holing resistance even under such an environment.
As the zinc metal-plated steel sheets for use in automobiles, there have been hitherto chiefly used hot dip zinc-coated steel sheets, zinc-electroplated steel sheets and so forth, but it is difficult for these coated or plated steel sheets to achieve a sufficient performance in such severe use as mentioned above. Accordingly, recently developed are electroplated steel sheets of Zn alloys of a Zn-Ni base, Zn-Fe base, etc.
However, since these coated steel sheets have a poor phosphating performance, they have been involved in the problems such that craterings may be generated on coating films at the time of electrodeposition coating to damage the coating appearance, or that only poor corrosion resistance and pin holing resistance can be achieved at the portions where no coating film is applied or only a thin coating film is applied for structural reasons of automobile bodies as in the portions where plates are joined or hollow structure is taken.
To solve such problems, this invention aims at providing a multilayer zinc metal-electroplated steel sheet having a good phosphating performance, having good corrosion resistance and pin holing resistance even at the portoions where no coating film is applied or only a thin coating film is applied, and moreover having a good coating appearance.


DISCLOSURE OF THE INVENTION

This invention provides the multilayer zinc metal-electroplated steel sheet which is comprised of a multilayer zinc metal electroplated steel sheet comprising (i) a lower layer electroplated coating provided on the surface of the steel sheet and comprising a Zn-Ni base alloy having Ni content of 10 to 16 wt.% or Zn-Fe base alloy having Fe content of 10 to 30 wt.%, containing 0.005 to 5 wt.% of at least one of silica, alumina, titanium oxide, magnesia, chromium oxide and zirconium oxide, and (ii) an upper layer electroplated coating provided on said lower layer electroplated coating and comprising an Fe-B base alloy having B (boron) content of 0.001 to 3 wt.% or an Fe-rich Fe-Zn base alloy having Fe content of 60 wt.% or more, thereby improving the phosphating performance (i.e., coating appearance), corrosion resistance and pin holing resistance.
This plated steel sheet was developed based on the finding that the corrosion resistance and pin holing resistance can be improved by co-depositing 0.005 to 5 wt.% of particles of oxides such as silica, alumina, titanium oxide, magnesia, chromium oxide and zirconium oxide in a conventional Zn-Ni base alloy or Zn-Fe base alloy coating of an electroplated steel sheet.
However, when the coating contains such chemically stable oxide particles, it was found that the performance of the phosphating carried out before electrodeposition coating may be lowered and a large number of craterings may be generated in a coating film at the time of the electrodeposition coating to damage the appearance. Thus, in the present invention, an Fe-B base alloy or Fe-rich Fe-Zn base alloy coating is further applied on the electroplated coating on which the oxide pa

REFERENCES:
patent: 4491623 (1985-01-01), Kokubo et al.
patent: 4510209 (1985-04-01), Hada et al.

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