JP2001059198A - Zn-Co PLATED METALLIC SHEET EXCELLENT IN CORROSION RESISTANCE AND ITS PRODUCTION - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a Zn-Co electroplated metallic sheet excellent in corrosion resistance even with small plating coating weight and moreover excellent also as to forming workability and productivity. SOLUTION: In this Zn-Co plated metallic sheet in which a plating layer essentially consisting of a Zn-Co alloy is formed, the Zn-Co plating layer is made amorphous. Moreover, it can be said that it is amorphous in the case the X-ray diffraction pattern of the plating layer measured by using Cu-Kα rays does not substantially include the peaks caused by a η phase of Zn, and peaks substantially resulted from substrate metal excepting the fact that the peaks of >=1 deg. half-value width are shown in the vicinity of 2 θ: 41 to 45 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin-plated electric Zn-Co plated metal sheet having excellent corrosion resistance and used in a wide range of fields such as building materials, household appliances, automobiles, and the like, and a method for producing the same.

The metal substrate to be plated in the present invention includes non-ferrous metals such as Cu and Al and alloys thereof in addition to Fe and Fe-based alloys. The present invention will be described with reference to a steel plate, which is a typical metal base material, regardless of a plate material such as a pipe material, a pipe material, a bar material, and a wire material.

[0003]

2. Description of the Related Art In a wide range of fields such as building materials, household appliances and automobiles, Zn plating has been widely used as a means for preventing corrosion of steel plates and the like. There are hot-dip galvanizing method, electroplating method, and vapor-deposition plating method as the plating method for Zn-plated steel sheet. For building materials and automobiles that require severe corrosion environment and long-term corrosion resistance, hot-dip plating that is easy to thick plating Has been done. Further, although the corrosive environment is mild, electroplating with a thin and beautiful plating appearance is mainly used for home appliances and OA equipment requiring a beautiful surface appearance.

[0004] In recent years, the demand for improved corrosion resistance of steel sheets and the like has tended to further increase. In any of the plating methods, the corrosion resistance can be improved by increasing the amount of plating, but the increase in the amount of plating is due to the workability. And deterioration of weldability. Therefore, many methods such as alloy plating of Zn and a dissimilar metal have been proposed. Among them, in the electroplating method in which thinning is easy, Zn—Ni, Zn—Fe, Zn
Various types of alloy plating such as -Co are employed. In particular, Z
The n-Co alloy plating can be expected to have high corrosion resistance, and as a technique for obtaining higher corrosion resistance, for example, JP-A-60-21109
No. 6 proposes a multi-layer plated steel sheet. This is to form a Zn—Co alloy plating layer containing 6 to 30% by weight of Co as the first layer and 0.1 to 6% by weight of Co as the second layer. However, there is still room for improvement in the corrosion resistance of the above-mentioned multi-layer plated steel sheet, and if necessary, the amount of coating must be increased, which is not economical and the workability of the plating film is low. And the improvement of weldability was also limited.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and is an electric Zn--Co alloy which is excellent in corrosion resistance with a small amount of plating adhesion and excellent in moldability and productivity. An object of the present invention is to provide a plated metal plate and a method of manufacturing the same.

[0006]

The Zn-Co-plated metal sheet excellent in corrosion resistance according to the present invention, which can achieve the above object, is a Zn-Co plated metal plate having a plating layer mainly composed of a Zn-Co alloy. A Co-plated metal plate, wherein the Zn-Co plated layer is amorphous. Specifically, the X-ray diffraction pattern of the plating layer measured using Cu-Kα radiation does not substantially include a peak due to the η phase of Zn, and has a half-value width in the vicinity of 2θ: 41 to 45 °. Amorphous can be said to be amorphous when a peak substantially derived from the substrate metal is observed except that a peak of 1 ° or more is observed.

The Co content in the Zn—Co plating layer is desirably 1 to 35% by weight.
Using an acidic plating solution containing a metal salt of
By performing electroplating at a current density of 00 A / dm ² , an electroplated Zn—Co plated metal plate having an amorphous plating layer can be manufactured.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted intensive studies for the purpose of developing a technique for further improving the corrosion resistance of a Zn—Co plating layer having better corrosion resistance than a pure Zn plating layer. As a result, they found out that the Zn—Co plating layer was made to be an amorphous plating layer, thereby exhibiting significantly superior corrosion resistance as compared with the conventional Zn—Co plating layer, and reached the present invention.

The term "corrosion resistance" as used in the present invention means red rust resistance or pitting corrosion resistance as-plated (no coating), and after coating, the coating film has no scratches. It means the corrosion resistance and the swelling resistance of the coating film on the bent portion and the end face of the coated steel sheet.

[0010] Also, amorphous is that each of the constituent atoms is
State that has no crystal structure and is in a random positional relationship
U. For example, an alloy plating of Zn and Co is produced by an ordinary method.
Then, according to the Co content, the Zn phase, the gold of Zn and Co
Intergeneric compound phase (for example, CoZn ₁₃, Co_FiveZn_{twenty one}),
Multiple Co phases are observed. Pure with crystal structure
X-ray diffraction of metal, alloy or intermetallic compound plating layer
The pure Zn plating of FIG. 1 and the crystal of FIG.
Each surface of the crystal, like Zn-Co alloy plating with a structure
A sharp diffraction line (peak) corresponding to the interval is observed,
In the case of an amorphous plating layer, the present invention shown in FIG.
Sharp diffraction line like the measurement result of Zn-Co plating
Is not recognized and a broad diffraction pattern is obtained.

The Zn—Co plating layer has a crystalline Z
The reason for having extremely excellent corrosion resistance compared to an n-Co plating layer (hereinafter sometimes referred to as a crystalline plating layer with respect to an amorphous plating layer) is not completely understood at this time, but the following is described. It is thought like. Zn-
In the case of a Co crystalline plating layer, the plating layer usually has a plurality of “phases” described above, and the corrosion potential differs for each of these phases. Therefore, a micro corrosion cell is formed in the plating layer, and the dissolution of a phase having a low corrosion potential is promoted, and as a result, the corrosion resistance of the entire plating layer is lowered. On the other hand, in the case of the amorphous plating layer, since each atom is randomly arranged, there is no "phase" due to the crystal structure in the plating layer, and the plating layer is uniform. That is, since the corrosion potential of the plating layer is uniform, a corrosion battery is not formed and excellent corrosion resistance is exhibited. Also, crystal grain boundaries that are always present in the crystalline material are considered to be the starting points of corrosion, but since this crystal grain boundary does not exist in the amorphous plating layer, it can be inferred that this point is also very advantageous. .

The Zn-Co plating layer of the present invention must have a broad diffraction pattern measured by using the X-ray diffraction method. Specifically, in the case of X-ray diffraction using CuKα radiation as a radiation source, the half-value width is 1 ° in the vicinity of 2θ: 41 to 45 ° without substantially showing the diffraction pattern of the η phase of Zn.
In addition to the above peaks, it is necessary that a peak substantially derived from the substrate metal is recognized.
When the intermetallic compounds of CoZn ₁₃ , Co ₅ Zn ₂₁ , and CoZn are formed, a sharp diffraction pattern is observed at around 2θ: 41 to 45 °. Also, 2θ: 41 to 45
In the vicinity of °, even if it has only one sharp peak with a half-value width of less than 1 °, one of the intermetallic compounds has been generated, and it can no longer be said to be amorphous plating, and excellent corrosion resistance is expected. Can not.

A known method may be used for X-ray diffraction, and a CoKα ray or the like may be used as a radiation source in addition to CuKα rays. When a radiation source other than CuKα radiation is used, the peak diffraction angle (2θ) in the present invention changes according to the wavelength of the radiation source. Regarding the intensity of the radiation source, for example, in the case of a tube system, a generally used voltage 4
A current of about 0 kV and a current of about 20 mA may be employed. It is desirable that the range of the measurement angle is about 30 to 80 ° (when using CuKα radiation) in 2θ.

The composition of the Zn—Co plating layer of the present invention is too small. If the amount of Co is too small, the effect of adding Co is not substantially exhibited, and an amorphous plating layer cannot be obtained. Therefore, no particular difference in the corrosion resistance from the Zn—Co crystalline plating layer is observed, so that it is desirable to contain 1% or more, more preferably 2% or more. On the other hand, if the amount of Co is too large, the corrosion potential of the plating layer itself becomes noble, and as a substrate, an Fe-based material such as a steel sheet or A
When an l-based material is used, the sacrificial anticorrosion effect peculiar to Zn-based plating is lost, or rather, the corrosion of the base material is promoted. Furthermore, the cost of C
Inclusion of a large amount of o is economically undesirable.
Therefore, it is preferably at most 35%, more preferably at most 30%. It is considered that the reason that the formability decreases when the content of Co increases is that the hardness of the plating layer increases with the increase of Co, cracks occur during the forming process, and the plating layer is easily peeled. Can be

In the present invention, the amount of Zn—Co plating is not particularly limited, but the amount of plating is 2 g.
/ M ² , the corrosion resistance in the as-plated state is insufficient. Conversely, if the amount of adhesion is too large, problems arise in the formability and spot weldability, and the economic efficiency is poor. Therefore, it is desirable to select from the range of ^{2 to} 60 g / m ² , and more preferably 5 to 40 g / m ² . The plating may be applied to the required surface of the metal plate as the base material, and may be applied to only one surface or both surfaces.

In the plated metal sheet according to the present invention, it is possible to use the plated metal sheet as it is without applying a finish coating. However, if necessary, characteristics such as corrosion resistance, scratch resistance, fingerprint resistance and workability are required. For the purpose of further improvement, various chemical conversion treatments (chromate film treatment, phosphate film treatment, clear film treatment, etc.) and painting may be applied. Among the chemical conversion treatments, typical chromate film treatments include reaction-type chromate film treatment, coating-type chromate treatment, and electrolytic chromate treatment. In order to improve characteristics such as corrosion resistance, scratch resistance, and blackening resistance, Various oxides such as silica and organic silane compounds,
Further, it is recommended to perform a chromate treatment in which various reaction accelerators such as phosphoric acid, nitric acid, fluoride, silicon fluoride and the like are contained in a treatment solution containing a Cr compound as a main component.

In the clear film treatment of the chemical conversion treatment, when the clear film is mainly composed of an organic resin,
Mainly composed of organic resin components such as epoxy resin, polyester resin, polyurethane resin, ethylene copolymer resin containing ethylenically unsaturated carboxylic acid as a polymerization component, polyvinyl resin, polyamide resin, and fluorine resin. Is used as a treatment liquid. Corrosion resistance, lubricity,
In order to improve the quality of scratch resistance, workability, weldability, electrodeposition coating properties, coating film adhesion, etc., various kinds of oxide particles such as silica, inorganic pigments such as various phosphates, wax particles, A treatment liquid containing an organic silane compound, a naphthenate or the like may be applied. Examples of the clear film mainly composed of an inorganic substance include those in which a treatment liquid mainly composed of a silicate such as sodium silicate, potassium silicate, lithium silicate, etc. is applied. Inorganic pigments such as colloidal silica, various kinds of phosphoric acid, etc., and wax for the purpose of improving the quality of lubrication, scratch resistance, workability, weldability, electrodeposition coating properties, coating film adhesion, etc. Particles and an organic silane compound may be contained in the treatment liquid.

These chemical conversion coatings may be applied alone or in various combinations. The preferred coating amount of the chemical conversion coating film may be selected from the range of 5 to 300 mg / m ² in consideration of economical efficiency while effectively exhibiting the effect of improving corrosion resistance and the like, and the preferable coating amount of the inorganic or organic film is , For the same reason, 0.05
The thickness may be up to 20 μm.

Next, a method for manufacturing a Zn—Co plated metal sheet according to the present invention will be described in detail. The production method of the present invention
It is necessary to use an acidic plating solution containing a metal salt of n and Co, and perform electroplating at a current density of 300 A / dm ² or more, which is much higher than the conventional electroplating method. The reason why amorphous plating can be obtained by performing plating at a high current density is considered to be as follows. That is, the metal atoms reduced on the surface of the base material are usually taken in the kinks or steps of the plating atomic layer through a migration process of the metal atoms on the surface of the base material called migration, and grow as crystals. This migration process is a relatively slow elementary process. If the current density is increased and the amount of reduction (that is, the amount of precipitation) of metal atoms is increased, crystallization due to migration cannot be completed in time, and the deposited metal atoms form a crystal lattice. It is presumed that a plating layer is to be formed without forming a plating layer.

As described above, in order to obtain an amorphous plating layer, a current density of 300 A / dm ² or more is necessary, and preferably 500 A / dm ² or more. On the other hand, when it exceeds 2000A / dm ^2, the supply of metal ions to the substrate surface no longer keep up, the plating burnt phenomenon coating appearance may change color blackish occur, because the commercial value is seriously impaired, and 2000A / dm ² or less And 1800 A / dm ² is more preferable.

As the plating solution, an acidic bath (eg, a sulfate bath or a chloride bath) can be used. Zn and C
As for o, an amount of a metal salt such as a sulfate, a chloride, an acetate, a carbonate, or the like, which gives a desired plating film composition, may be added to the plating solution. For example, the amount of Zn ions in the plating solution is 10 to 110 g / L, and the amount of Co ions is 5 to 110 g / L.
At about g / L, amorphous plating could be obtained.
The pH of the plating solution is preferably in the range of 0.1 to 2.0 in view of the relationship between the current efficiency and the plating burn phenomenon. The plating solution contains Na ₂ SO ₄ , (NH ₄ ) ₂ S in order to increase conductivity and reduce power consumption.
A conductive auxiliary such as O ₄ , KCL, and NaCl may be added.

The other plating conditions such as the plating solution temperature and the relative flow rate may be set within a range that does not cause defects such as plating burns, and the former is 30 to 70 ° C., and the latter is 0.3 to 5 m / m. The effect of the present invention was confirmed for s. Note that the relative flow velocity is a difference between the liquid flow velocity and the passing speed in consideration of the flow direction of the liquid and the passing direction of the steel plate as the plating original plate.

The plating method is not particularly limited, and the plating base material may be subjected to a pretreatment such as degreasing or pickling according to a conventional method, and then subjected to electroplating in a vertical or horizontal plating cell. As the electroplating method, a known direct current (constant current) plating method or pulse plating method can be adopted.

Incidentally, regarding Zn-Co amorphous plating, 1-ethyl-3-methylimidazolium chloride is used.
A molten salt electrodeposition method using (EMIC) as an electrolyte is known [Summary of the 95th Annual Meeting of the Surface Technology Association of Japan (p.29)]. However, no knowledge is disclosed about the relationship between Zn—Co amorphous plating and corrosion resistance. Moreover, according to the molten salt electrodeposition method, an amorphous plating layer cannot be obtained unless a large amount of 40 to 70% of Co is contained. However, when such a large amount of Co is contained, excellent corrosion resistance is obtained as described above. I can't get it.

As the base material used for the surface-treated sheet of the present invention, various cold-rolled steel sheets used as materials for automobiles, home appliances, building materials and the like are mainly used. However, it is also possible to select a metal plate other than a steel plate such as a hot-rolled steel plate, an aluminum alloy plate, a copper plate, and the like, a tube material, a bar material, and a wire material according to the application.

Hereinafter, the structure, operation, and effects of the present invention will be described in detail with reference to examples. However, these do not limit the present invention in any way, and may be appropriately changed and implemented without departing from the spirit of the present invention. This is all included in the technical category of the present invention.

[0027]

EXAMPLE An Al-killed cold-rolled steel sheet produced by a conventional method was used as a plating base material. This was degreased and pickled, and then electroplated using a sulfate bath under the following conditions.

[0028] <Electroplating Conditions> plating solution _{composition: ZnSO 4 · 7H 2 O 50~400g} / L CoSO 4 · 7H 2 O 50~400g / L Na 2 SO 4 20~100g / L H 2 SO 4 10~ 70 g / L ・ Current density: 100-2500 A / dm ²・ Plating bath temperature: 60 ± 5 ° C. ・ Plating solution flow rate: 0.5-5 m / sec ・ Electrode (anode): IrO _x electrode ・ Plating weight: 20 g / for m ² obtained plated steel sheet, the corrosion resistance of unpainted (as plating) was evaluated by JIS Z2371 salt spray test. The red rust generation area rate after 960 hours (40 days) of the salt spray test was determined according to the following criteria. In addition, as a determination of the formability, a 180 ° close contact bending was performed with the plating surface outside, and a Nichiban cellophane tape was attached to the bent portion and peeled off. The plating strips adhered to the tape were visually observed and plated according to the following criteria. The adhesion was determined. Table 1 shows the obtained results.
Are shown together.

<Corrosion resistance>: 0%: Less than 10% △: 10 or more and less than 50% ×: 50% or more Big

[0030]

[Table 1]

As is clear from Table 1, Example No. 1 of the present invention in which the plating layer structure was amorphous. In the cases of Nos. 1 to 23, all have both excellent corrosion resistance and plating adhesion. On the other hand, in the case of Comparative Example No. 1 in which the η phase of Zn is contained in the plating layer, and the half width of the peak near 2θ: 41 to 45 ° is less than 1 °. In the case of Nos. 24 to 29, the corrosion resistance was clearly inferior, and some test materials (Comparative Example Nos.
As for 27), it can be seen that the plating adhesion is also inferior.

[0032]

As described above, the present invention is constructed as described above, so that it is possible to provide a Zn-Co plated metal sheet which is excellent in corrosion resistance, and is excellent in molding workability and productivity, and a method for producing the same. . In particular, the amorphous-plated metal sheet of the present invention has thinning and high corrosion resistance not found in conventional surface-treated metal materials, is excellent in continuous operability on an industrial scale, and can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is an example showing an X-ray diffraction pattern of a pure Zn plating layer.

FIG. 2 shows a X of a Zn—Co alloy plating layer having a crystal structure.
It is an example which shows a line diffraction pattern.

FIG. 3 is an example showing an X-ray diffraction pattern of a Zn—Co plating layer of the present invention.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Masatoshi Iwai 1 Kanazawacho, Kakogawa-shi, Hyogo Prefecture Kobe Steel Works Kakogawa Works F-term (reference) 4K023 AB29 BA06 BA08 BA21 BA29 DA02 DA06 DA07

Claims (4)

[Claims] 1. A Zn—Co plated metal plate on which a plated layer mainly composed of a Zn—Co alloy is formed.
A Zn-Co plated metal plate having excellent corrosion resistance, characterized in that the o-plated layer is amorphous. 2. The X-ray diffraction pattern of the plating layer measured using Cu-Kα radiation does not substantially include a peak attributed to the η phase of Zn and has a half-value width near 2θ: 41 to 45 °. 2. The Zn according to claim 1, wherein a peak substantially derived from the substrate metal is observed except for a peak of 1 ° or more.
-Co-plated metal plate. 3. The Zn according to claim 1, wherein the Co content in the Zn—Co plating layer is 1 to 35% by weight.
-Co-plated metal plate. 4. An electric Zn—Co electrode, wherein an electroplating is performed at a current density of 300 to 2000 A / dm ² using an acidic plating solution containing a metal salt of Zn and Co.
Manufacturing method of plated metal sheet.