JPH0673591A - Zinc-nickel-chromium alloy electroplated steel sheet with excellent corrosion resistance, plating adhesion, chemical conversion treatment and coating adhesion - Google Patents

Abstract

(57) [Summary] [Composition] 0.1 / to 5.0 on at least one surface thereof.
wt.% nickel, 2-30 wt.% chromium, 0.1-5.0
A zinc-nickel-chromium alloy electroplated steel sheet on which a zinc-nickel-chromium alloy electroplated coating consisting of wt.% iron or cobalt and the remaining zinc and unavoidable impurities is formed. [Effect] A zinc-nickel-chromium alloy electroplated steel sheet having excellent bare corrosion resistance, corrosion resistance after coating, plating adhesion, chemical conversion treatment and coating adhesion can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zinc-nickel-chromium alloy electroplated steel sheet which is suitable as a steel sheet for automobiles and which is excellent in bare corrosion resistance, corrosion resistance after painting, plating adhesion, chemical conversion treatment and coating adhesion. It is about.

[0002]

2. Description of the Prior Art Zinc-on at least one surface thereof
A zinc-nickel alloy electroplated steel sheet having a nickel alloy electroplated coating formed thereon is widely used as a steel sheet for automobiles because it has excellent corrosion resistance. Recently,
In the automobile industry, weight reduction of automobile bodies is actively promoted as a measure for energy saving. Therefore, a zinc-nickel having excellent corrosion resistance with a thinner plate and a smaller plating amount is obtained from an automobile manufacturer. The development of system alloy electroplated steel sheets is required.

Examples of zinc-nickel alloy electroplated steel sheets having more excellent corrosion resistance include, for example, JP-A-55-50484, JP-A-58-6796 and JP-B-59-38313 (hereinafter referred to as prior art 1). ) On at least one surface thereof,
A zinc-nickel-chromium alloy electroplated steel sheet having a zinc-nickel-chromium alloy electroplated coating formed thereon is disclosed. According to the zinc-nickel-chromium alloy electroplated steel sheet of Prior Art 1, although the corrosion resistance is improved as compared with the conventional zinc-nickel alloy electroplated steel sheet, the chromium content in the plating film is 0.005 to 1.0 wt. It is about.%, Which is an extremely small amount. Therefore, the main effect of improving the corrosion resistance still depends on the nickel content in the plating film. For example, in JP-B-59-38313 in Prior Art 1, the nickel content in the plating film is 11 to 20 wt. .%.

[0004]

However, as in Prior Art 1, when the nickel content of the plating film is high, the surface properties and structure of the plating film become non-uniform,
In addition, the adhesion of the plating film is poor, and therefore the adhesion of the coating film formed on the plating film is also poor. Therefore,
Such a zinc-nickel-chromium alloy electroplated steel sheet is unsuitable as a steel sheet for automobiles.

On the other hand, Japanese Patent Laid-Open No. 1-55397 (hereinafter referred to as Prior Art 2) discloses that at least one of the surfaces should have 5 to 5
Disclosed is a zinc-chromium alloy electroplated steel sheet on which a zinc-chromium alloy electroplated coating consisting of 40 wt.% Chromium and the balance zinc is formed. According to the prior art 2, an electroplated steel sheet having a zinc-chromium alloy electroplated film having a uniform surface property can be obtained.

However, in the zinc-chromium alloy electroplated steel sheet of Prior Art 2, when the phosphate coating by the chemical conversion treatment, which is an important pretreatment for coating, is formed on the plating coating, crystals of the phosphate coating are present. There is the problem of coarsening and incomplete formation of the phosphate coating. As described above, the zinc-chromium alloy electroplated steel sheet of Prior Art 2 is fatal with respect to the chemical conversion treatment property when performing the chemical conversion treatment necessary for enhancing the adhesion of the coating film and improving the corrosion resistance after coating. There is a defect.

Therefore, an object of the present invention is to solve the above-mentioned problems and to provide a zinc-nickel-chromium alloy electroplated steel sheet which is excellent in bare corrosion resistance, corrosion resistance after coating, plating adhesion, chemical conversion treatment and coating adhesion. To provide.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to solve the above-mentioned problems. As a result, the following findings were obtained. In the zinc-nickel alloy electroplated steel sheet, if the nickel content in the zinc-nickel alloy electroplated film is about 11 wt.% Or more, Cl present in the corrosive environment
^-, And the corrosion product formed by Zn in the plating film is deposited in the crystal of the γ phase, which is the Zn-Ni alloy phase, and as a result, imparts excellent corrosion resistance to the zinc-nickel alloy electroplating film. It has been known.

Therefore, at least one of the steel sheets is coated with a zinc-nickel-chromium alloy electroplating film containing about 1 wt.% Chromium in addition to about 11 wt.% Or more nickel.
When formed on two surfaces, the corrosion resistance is further improved, for example
Red rust does not occur even when subjected to a salt spray test for 1000 hours. It is considered that the reason why the corrosion resistance is improved by the addition of chromium in this manner is that the chromium in the plating film forms an extremely stable protective film containing chromium in the surface layer of the plating film.

In the above-mentioned plated steel sheet having a zinc-nickel-chromium alloy electroplated coating containing nickel in an amount of about 11 wt.% Or more, the corrosion resistance is further improved if the content of chromium in the plated coating is increased. However, when a zinc-nickel-chromium alloy electroplating film having a high chromium content is formed on at least one surface of a steel sheet under normal electrolysis conditions, so-called plating burn occurs and a plating film having an appropriate surface texture is obtained. It is not obtained, and the adhesion of the plating film is deteriorated.

On the other hand, in a zinc-chromium alloy electroplated steel sheet having a nickel-free zinc-chromium alloy electroplated coating, if the chromium content in the plating coating exceeds 5 wt.%, It is important as a pretreatment for coating the coated steel sheet. In the chemical conversion treatment, the phosphate coating becomes coarse and the phosphate coating becomes unhealthy. So, in addition to such chromium, 0.1 wt.
When a zinc-nickel-chromium alloy electroplating film containing at least nickel is formed on at least one surface of the steel sheet, the phosphate film formed by the chemical conversion treatment becomes fine and a healthy phosphate film is formed. It Furthermore, when an appropriate amount of iron or cobalt is contained in the plating film in addition to chromium and nickel, the adhesion of the coating film formed on the phosphate film, especially the hot water adhesion, is improved.

From the above-mentioned viewpoint, in a zinc-nickel-chromium alloy electroplated steel sheet having a zinc-nickel-chromium alloy electroplated coating formed on at least one surface thereof, the nickel content in the plating coating To
0.1 to 5.0 wt.%, And chromium content to 2 to 30 wt.%, And 0.1 to 5.0 wt.% Iron or cobalt in the plating film. As a result, it was found that a zinc-nickel-chromium alloy electroplating film having excellent bare corrosion resistance, corrosion resistance after coating, plating adhesion, chemical conversion treatment property, and coating adhesion was obtained.

The present invention has been made based on the above-mentioned findings, and the present invention provides a zinc-nickel alloy having a zinc-nickel-chromium alloy electroplating film formed on at least one surface thereof. In the chromium-based alloy electroplated steel sheet, the zinc-nickel-chromium-based alloy electroplated coating has nickel: 0.1 to 5.0 wt.%, Chromium: 2 to 30 wt.%, Iron or cobalt: 0.1 to 5.0 wt.%. , And the rest: characterized by being composed of zinc and inevitable impurities.

[0014]

Next, the reason why the component composition of the plating film is limited as described above in the present invention will be described. (1) Nickel The content of nickel in the zinc-nickel-chromium alloy electroplating film should be limited to the range of 0.1 to 5.0 wt.%. If the nickel content in the plating film is less than 0.1 wt.%, The effect of improving chemical conversion treatability cannot be obtained. On the other hand, when the nickel content exceeds 5.0 wt.%, The surface properties of the plating film deteriorate and the adhesion of the plating film deteriorates.

(2) Chromium The content of chromium in the zinc-nickel-chromium alloy electroplating film should be limited to the range of 2 to 30 wt.%. When the chromium content in the plating film is less than 2 wt.%,
There is no effect of improving corrosion resistance. On the other hand, chromium content is 30 wt.%
When it exceeds, the phosphate film formed on the plating film by the chemical conversion treatment becomes coarse and the phosphate film becomes unhealthy.

FIG. 2 shows a conventional zinc-zinc-chromium alloy electroplated film containing 11 wt.% Chromium.
1 is an electron micrograph (magnification: 750 times) of a phosphate coating when a phosphate coating is formed by chemical conversion treatment on a chromium alloy electroplated steel sheet. It can be seen from FIG. 2 that the crystals of the phosphate coating are coarser than in the case of the zinc-nickel-chromium alloy electroplating coating of FIG. 1 described later.

FIG. 1 shows zinc-nickel-containing 0.9 wt.% Nickel and 11 wt.% Chromium on the surface of a steel sheet.
When a phosphate coating is formed by chemical conversion treatment on the zinc-nickel-chromium alloy electroplated steel sheet having the chromium alloy electroplated coating formed thereon under the same conditions as those of the conventional plated steel sheet of FIG. 2 described above. 2 is an electron micrograph (magnification: 750) of the phosphate coating. As is clear from FIG. 1, the crystals of the phosphate coating do not coarsen like the plated steel sheet on which the nickel-free zinc-chromium alloy electroplating coating of FIG. It has been miniaturized to the same level as system-plated steel sheets.

Iron or cobalt has the function of improving the adhesion of the coating film, especially the adhesion to hot water. The iron or cobalt content in the coating should be limited to within the range of 0.1 to 5.0 wt.%. When the content of iron or cobalt in the plating film is less than 0.1 wt.%, The effect of improving coating film adhesion, particularly hot water adhesion, cannot be obtained. On the other hand, when the content of iron or cobalt exceeds 5.0 wt.%, The properties of the plating film deteriorate and the adhesion of the plating film also deteriorates.

The formation of the phosphate coating on the surface of the plating coating is carried out by using a known phosphate treatment solution and performing a chemical conversion treatment by a known spray type or immersion type.

The preferable range of the thickness of the plating film, that is, the amount of coating is 10 to 100 g / m ² per side of the steel sheet. If the coating weight is less than 10 g / m ^{2 on} one side of the steel sheet, the corrosion resistance deteriorates. On the other hand, the amount of plating film deposited is 10
If it exceeds 0 g / m ² , weldability and workability deteriorate. The preferred coating weight is 20 to 50 g / m ² per side of the steel sheet.
Within the range of.

In addition to zinc, nickel, chromium, and iron or cobalt, a small amount of Mn, T is contained in the plating film.
i, F, B, N, C, P, etc. may be included.

Next, a method of manufacturing the zinc-nickel-chromium alloy electroplated steel sheet of the present invention will be described. As the plating solution, a predetermined amount of Zn ²⁺ , Ni ²⁺ , Cr ³⁺ , and
An acidic plating solution containing Fe ²⁺ or Co ²⁺ is used. In addition, in order to increase the conductivity of the plating solution,
Alkali metals such as Na ⁺ , K ⁺ and NH ₄ ⁺ may be added, and polymers that act as a chromium deposition accelerator may be added. As the anion, any one of SO ₄ ²⁻ , Cl ⁻ and BF ₄ ⁻ can be used.

The preferred pH value of the plating solution is 0.5 to 3.0. If the pH value of the plating solution is less than 0.5, the electrolysis efficiency will decrease. On the other hand, when the pH value of the plating solution exceeds 3.0, precipitates are easily generated in the plating solution. The preferred temperature of the plating solution is 30 to 70 ° C. If the temperature of the plating solution is less than 30 ° C, undissolved substances are likely to be generated in the plating solution, and
Electrodeposition efficiency decreases. On the other hand, if the temperature of the plating solution exceeds 70 ° C., problems will occur in terms of equipment such as a plating tank. The plating current density is not particularly limited because a plating film having a desired component composition can be formed by changing the plating current density, but the content of chromium increases as the current density increases, and The nickel content also tends to increase, though not to the same extent as chromium.

Instead of forming a phosphate coating on the plating coating by chemical conversion treatment, a chromate coating may be formed on the plating coating by chromate treatment. In the coating film of the plated steel sheet of the present invention, Cr ³⁺ , Cr ⁶⁺
The chromate film can be formed by any of the conventional reaction-type, coating-type, and electrolytic-type chromate treatment methods since it has a relatively high reactivity with the acidic treatment liquid. The preferable amount of the chromate film is 5 to 5 as chromium.
It is 100 mg / m ² . In addition, on the chromate film, 0.5
An organic resin coating in an amount of ~ 2.5 µm may be formed. For such an organic resin coating film, any conventionally used organic resin can be used. In particular, organic resins containing a rust preventive additive such as SiO ₂ are effective.

[0025]

EXAMPLES Next, the present invention will be described in more detail by way of examples and in comparison with comparative examples. As the plating solution, the following A ~
Six types of F plating solutions were used. Plating solution A ZnSO ₄ 7H ₂ 0: 100 to 500 g / l, NiSO ₄ 6H ₂₀ : 100 to 500 g / l, FeSO ₄ 7H ₂₀ : 100 to 500 g / l, Cr ₂ (SO ₄ ) ₃ : 100-500 g / l, Na ₂ SO ₄ : 60 g / l, pH value: 1.2

Plating solution B Zn (BF ₄ ) ₂ : 10 to 100 g / l, Ni (BF ₄ ) ₂ : 10 to 100 g / l, Fe (BF ₄ ) ₂ : 10 to 100 g / l, H ₃ BO ₃ : 60 g / l, Cr (BF ₄ ) ₃ : 10-100 g / l, pH value: 2.0

Plating solution C ZnCl ₂ : 10 to 300 g / l, NiCl ₂ 6H ₂ O: 10 to 300 g / l, FeCl ₂ 6H ₂ O: 10 to 300 g / l, CrCl ₃ : 20 g / l, pH value: 2.5

Plating solution D ZnSO ₄ 7H ₂ 0: 100 to 500 g / l, NiSO ₄ 6H ₂₀ : 100 to 500 g / l, CoSO ₄ 7H ₂ 0: 100 to 500 g / l, Cr ₂ (SO ₄ ) ₃ : 100-500 g / l, Na ₂ SO ₄ : 60 g / l, pH value: 1.2

Plating solution E Zn (BF ₄ ) ₂ : 10 to 100 g / l, Ni (BF ₄ ) ₂ : 10 to 100 g / l, Co (BF ₄ ) ₂ : 10 to 100 g / l, H ₃ BO ₃ : 60 g / l, Cr (BF ₄ ) ₃ : 10-100 g / l, pH value: 2.0

Plating solution F ZnCl ₂ : 10 to 300 g / l, NiCl ₂ 6H ₂ O: 10 to 300 g / l, CoCl ₂ 6H ₂ O: 10 to 300 g / l, CrCl ₃ : 20 g / l, pH value: 2.5 Using a plating solution having a temperature of 50 to 60 ° C., which has any of the above-mentioned component compositions and pH values of 30 to 150 A / dm
^The current density was changed within the range of ² to form a zinc-nickel-chromium alloy electroplating film in an amount of 20 g / m ² on one surface of a steel plate having a plate thickness of 0.7 mm and shown in Table 1. , A specimen having a zinc-nickel-chromium alloy electroplating coating within the scope of the present invention (hereinafter referred to as the present invention specimen) No. 1
~ 26 was prepared. For comparison, specimens having a zinc-nickel-chromium alloy electroplating coating outside the scope of the present invention (hereinafter referred to as comparative specimens) No. 1 to 1 shown in Table 2
22 was prepared.

[0031]

[Table 1]

[0032]

[Table 2]

For each specimen thus prepared,
The tests described below were conducted. (1) Adhesion test of plating film It is a test based on JIS H 8504, each sample is bent at a predetermined angle, then an adhesive tape is attached to the alloy plating film of the bent sample and then peeled off. The peeling amount of the plating film at that time was visually inspected, and based on the peeling amount, the following evaluation was made. ◯: Good, Δ: Slightly bad, X: Bad.

(2) Chemical conversion treatment test Each specimen was subjected to immersion type phosphate treatment with a phosphate treatment solution to form a phosphate coating on the surface of the specimen. The crystalline state of the obtained phosphate coating was observed by an electron microscope and evaluated as follows. ◯: Dense crystals, ×: Coarse or unhealthy crystals.

(3) Bare corrosion resistance test This is a test based on JIS-Z-2371. Each sample was subjected to a salt spray test, and the time until the occurrence of red rust was examined and evaluated.

(4) Corrosion resistance test after coating Each specimen is subjected to a dip-type phosphate treatment with a phosphate treatment solution to form a phosphate coating on the surface of the specimen, and then a cation-type electrolyte. After applying the coating process,
An undercoating film having a thickness of 20 μm was formed on the phosphate film. Then, an intermediate coating film having a thickness of 30 μm and an upper coating film having a thickness of 30 μm were formed on the surface of the undercoating film.
A cross-cut is applied to the coating film of the test piece having the three-layer coating film thus obtained, and the test piece with the cross-cut is subjected to salt spray, drying, wetting and drying for one cycle per day. After 120 cycles of the corrosion acceleration test, the blister width generated in the cross cut portion was examined and evaluated by the following. ⊚: Bulging width 0 to less than 1 mm, ◯: Bulging width 1 mm to less than 3 mm, Δ: Blistering width 3 mm to less than 5 mm, ×: Bulging width of 5 mm or more

(5) Coating Film Adhesion Test Each specimen is subjected to a dip-type phosphate treatment with a phosphate treatment liquid to form a phosphate coating on the surface of the specimen, and then a cation-type After applying electrodeposition coating,
An undercoating film having a thickness of 20 μm was formed on the phosphate film. Then, an intermediate coating film having a thickness of 30 μm and an upper coating film having a thickness of 30 μm were formed on the surface of the undercoating film.
The thus-obtained specimen having the three-layer coating film is cut into 100 grid-shaped cuts at 2 mm intervals, and the cut specimens are put into warm water at a temperature of 40 ° C. After soaking in it for 10 days, an adhesive tape was applied onto the surface of the coating film having cuts and then peeled off. Then, the peeled state of the coating film was examined and evaluated by the following. ◯: No peeling, Δ: Less than 10% peeled, ×: 10%
The above was peeled off.

(6) Appearance The surface appearance of the test piece was visually evaluated.

Table 3 shows the test results of the above-described test sample of the present invention, and Table 4 shows the test results of the comparative sample.

[0040]

[Table 3]

[0041]

[Table 4]

As is clear from Tables 2 and 4, Comparative Specimens Nos. 1 and 12 in which the amount of chromium in the plating film exceeds the range of the present invention are chemical conversion treatability, bare corrosion resistance, and post-coating corrosion resistance. And the coating film adhesion was poor. Comparative specimens Nos. 2 to 5 and Nos. 13 to 16 in which the amount of nickel in the plating film exceeds the range of the present invention, the adhesion of the plating film is poor, and the corrosion resistance after coating and the adhesion of the coating film are also a little. It was poor and the surface appearance was poor.

Comparative samples No. 6, 7 and No. 17, 18 having a nickel content outside the range of the present invention were poor in chemical conversion treatment and post-coating corrosion resistance, as well as bare corrosion resistance and coating adhesion. It was a little bad. Comparative specimens Nos. 8 and 19 containing no iron or cobalt had poor coating film adhesion and slightly poor corrosion resistance after coating. Comparative sample Nos. 9 and 20 in which the amount of iron or cobalt was out of the range of the present invention was poor in coating film adhesion. Comparative specimens Nos. 10 and 21, which contained iron or cobalt in an amount exceeding the range of the present invention, had slightly poor chemical conversion treatability and coating adhesion, and also had poor surface appearance. Comparative specimens Nos. 11 and 22 having a chromium content outside the range of the present invention and having a low chromium content had poor bare corrosion resistance and slightly poor coating adhesion.

On the other hand, the sample Nos. 1 to 26 of the present invention are
It was excellent in terms of adhesion of the plating film, chemical conversion treatment, bare corrosion resistance, corrosion resistance after coating, coating adhesion and surface appearance.

[0045]

As described above, according to the present invention,
Suitable for steel sheet for automobiles, bare corrosion resistance, corrosion resistance after painting,
A zinc-nickel-chromium alloy electroplated steel sheet having excellent plating adhesion, chemical conversion treatment property, coating film adhesion and surface appearance can be obtained, which brings industrially useful effects.

[Brief description of drawings]

FIG. 1 is an electron micrograph (750 × magnification) of a phosphate coating formed on a zinc-nickel-chromium alloy electroplated steel sheet.

FIG. 2 is an electron micrograph (750 × magnification) of a phosphate coating formed on a coating of a conventional zinc-chromium alloy electroplated steel sheet.

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[Procedure amendment]

[Submission date] August 17, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

FIG. 1 shows a crystal structure of a phosphate coating formed on a zinc-nickel-chromium alloy electroplated steel sheet.
3 is an electron micrograph (magnification: 750).

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

FIG. 2 is an electron micrograph (magnification: 750 times) showing a crystal structure of a phosphate coating formed on a plating coating of a conventional zinc-chromium alloy electroplated steel sheet.

Claims (1)

[Claims] 1. Zinc-on at least one surface thereof
In a zinc-nickel-chromium alloy electroplated steel sheet having a nickel-chromium alloy electroplated coating formed thereon, the zinc-nickel-chromium alloy electroplated coating is nickel: 0.1 to 5.0 wt.%, Chromium: 2 ~ 30 wt.%, Iron or cobalt: 0.1-5.0 wt.%, And balance: zinc and unavoidable impurities, corrosion resistance, plating adhesion, chemical conversion treatment and coating adhesion Excellent zinc-nickel-chromium alloy electroplated steel sheet.