Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2000-03-09
2003-08-19
La Villa, Michael (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S626000, C428S658000, C428S666000, C428S687000, C205S109000, C205S305000
Reexamination Certificate
active
06607844
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a Zn—Mg electroplated metal sheet and a fabrication process therefor and particularly, a Zn—Mg electroplated metal sheet showing excellent corrosion resistance suitable for use industrial fields such as of construction materials, household electric appliances, automobiles and others, and a fabrication process therefor. Metal substrate materials on which electroplating is performed in the present invention include Fe and Fe based alloys, and in addition nonferrous metals such as Cu, Al and Ti, and alloys thereof, wherein there is no specific limitation on shapes thereof, but any of a flat sheet and a corrugated sheet, which are primarily named, and a pipe, a rod and so on can be employed. Below, the present invention will be described of a case of a steel sheet as a metal substrate material, which is a typical substrate material.
2. Description of Related Art
In industrial fields such as of construction materials, household electric appliances, automobiles and others, Zn plated steel sheets have generally been employed as corrosion resistance means for a steel sheet or the like sheet and as fabrication processes for the Zn plated steel sheets, hot dip plating, electroplating and vapor deposition plating have widely been adopted. Various kinds of Zn plated steel sheets have been developed according to combinations of Zn alloy compositions and plating methods, and among them, a Zn—Mg alloy vapor deposition plated steel sheet (for example, JP-A-89-17852, JP-A-96-134632, JP-A-96-3728 and JP-A-97-195871) has been known as being excellent in corrosion resistance.
In recent years, a demand for improving corrosion resistance of steel sheets and so on has increasingly been on the upward move. While it is conceived to simply increase a coating weight on a steel sheet in order to improve corrosion resistance thereof, cost is always raised in company with such an improvement since a plating time is longer, or more of energy is consumed to realize more of vaporization of a plating metal, thus affecting the cost of fabrication upward. Since the vapor deposition plating method inherently requires a giant vacuum facility and others, a fabrication cost thereof is very high compared with any of other processes, making the further cost rise a fatal problem for the method. Further, since Mg is a metal of sublimation and vapor thereof is generated directly from the solid surface with no liquid phase interposed prior to the vaporization, a vaporization speed inevitably changes over elapsed time, which in turn makes stable control of a coating weight and a composition very hard. Besides, there has been available no established supply method suitable for its continuous operation, which is another problem in an aspect of the actual operation.
On the other hand, in a hot dip plating method, since a coating weight of the method is inherently large, if the coating weight is larger than in the current state, it causes troubles such as galling or flaking in press molding of a plated steel sheet. Furthermore, in more cases of the hot dipping method, a temperature of a plating bath has to be higher than a melting point of pure Zn and a fragile alloy layer including Fe is generated on the boundary surface of a substrate steel sheet, leading to a further problem since the plated layer is peeled off with ease in a forming process.
Furthermore, in a case of Zn—Mg alloy plating, if an electroplating method (using a normal aqueous solution) was adopted, Mg itself could not be deposited since a normal electrode potential of Mg is greatly low. However, if the Zn—Mg alloy plating can be performed with the electroplating process, a composition of components of the alloy and a coating weight thereof can be controlled with ease by properly controlling amounts of metal ions included in a plating solution, ratios of the metal ions, an over-potential (cathodic current density), a current amount and so on. Further, since no step of high temperature is included in the electroplating process, there is no risk that a fragile intermetallic compound and so on are formed at the interface between the plated layer and the substrate surface and in turn an interlayer adhesive force is reduced as well. Still further, consumed metal ions are supplemented from the cathode, which is soluble, or can be replenished as a solution including the metal ions from outside of the system when a non-soluble cathode is employed, which makes the electroplating method suitable for use in the continuous fabrication on an industrial scale.
If the Zn—Mg electroplated layer can be formed in such a way, it is conceived that steel sheets excellent in corrosion resistance can be fabricated with good productivity and no loss of formability. Hence, there has been built up a desire of development of a fabrication process for a Zn—Mg electroplated layer by means of an electroplating method.
SUMMARY OF THE INVENTION
The present invention has been made in light of the above described circumstances and it is accordingly an object of the present invention to provide a Zn—Mg electroplated metal sheet excellent in corrosion resistance, formability and productivity, and a fabrication process therefor.
A Zn—Mg alloy plated metal sheet of the present invention, which achieves the object, has a Zn—Mg electroplated layer including Mg and Zn, the Zn being a main component, formed on at least one surface of a metal substrate material. Further, a carbon component (as an organic compound) is preferably included in the Zn—Mg electroplated layer since corrosion resistance is greatly improved due to inclusion of the C (carbon) component.
A Mg content in the Zn—Mg electroplated layer is preferably in the range of from 0.08 to 40% (% means wt %, which applies hereinafter) and a C component content in the Zn—Mg electroplated layer is preferably in the range of from 0.01 to 10% on the basis of the carbon element.
While the Zn—Mg alloy plated metal sheet according to the present invention exerts an excellent corrosion resistance (red rust resistance), it is recommended in order to be of excellent white rust resistance that a crystallographic orientation index of the (002) plane of an electroplated layer is equal to or lower than 1.0 and a crystallographic orientation index of the (100) plane of an electroplated layer is equal to or higher than 0.6.
Further, the Zn—Mg alloy plated metal sheet according to the present invention has an improvement of the effects of corrosion resistance after painting on the Zn—Mg electroplated layer, particularly the effects in defective portions of a coat such as a physical flaw portion of the paint or a cutting edge thereof (hereinafter simply referred to as edge as well) after painting as compared with a conventional painted galvanized metal sheet. In connection to the corrosion resistance in defective portions of a paint, the effects on corrosion resistance are further improved by controlling a deposition state of the electroplated layer or providing an intermediate layer between the electroplated layer and the paint.
A fabrication process for the Zn—Mg alloy plated metal sheet of the present invention, which achieves the object, performs electroplating using an acidic aqueous solution including metal salts of Zn and Mg, and in addition, a surface active agent, wherein a crystallographic orientation index of an electroplated layer is preferably controlled in order to increase chemical treatability thereof.
It should be appreciated that the surface active agent is desirably a nonionic or cationic surface active agent and a concentration thereof in the acidic aqueous solution is preferably in the range of from 0.01 to 30 g/L.
As the nonionic surface active agent or agents, there can be recommended in use one or more selected from the group consisting of polyethylene glycol, polyoxyethylene-alkylether and polyoxyethylene-polyoxypropylene-alkylether. As the cationic surface agent or agents, there is preferably used one or more selected from the group consisting of a pr
Araga Kuniyasu
Iwai Masatoshi
Kitou Yutaka
Shige Hiroo
Watase Takeshi
(Kobe Steel, Ltd.)
La Villa Michael
LandOfFree
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