JPH0814038B2 - Method for producing Zn-Ni alloy plated steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a method for producing a Zn-Ni alloy plated steel sheet, and particularly to a molar concentration ratio of Ni ²⁺ / (Zn ²⁺ + Ni ²⁺ ) ( Below, N
(i molar concentration ratio) is as low as 0.4 or more and less than 0.6, and relates to a method for economically producing a Zn—Ni alloy plated steel sheet.

<Prior art> In recent years, in order to improve the anticorrosive power of automobiles, surface-treated steel sheets have been used. One of them is Zn-Ni.
Plated steel sheets are often used.

Since Zn-Ni plating is an abnormal precipitation type, the target Ni content in the plating layer must be increased unless the Ni ²⁺ ion concentration, which should be noble and easy to deposit in potential, is significantly higher than the Zn ²⁺ ion concentration. Can't get

That is, according to Japanese Examined Patent Publication No. 58-39236, the molar concentration ratio of Ni ²⁺ / Zn ²⁺ is 1.5 to 4.0 [Ni ²⁺ / (Zn ²⁺ + Ni ²⁺ ).
0.6-0.8] is required and expensive Ni ²⁺ ions must be used in large amounts. Further, the loss of Ni ²⁺ ions due to the dragout of the plating solution is large, which is economically disadvantageous.

<Problems to be Solved by the Invention> As a manufacturing method using a low Ni concentration bath, Japanese Patent Laid-Open No. 136590/1987 is used.
According to the No. No., the Ni molar concentration ratio is 0.4 or more, the current density is 100 A / dm ² or more, and the plating solution flow rate is 1.5 m / sec or more. When the capacity of the rectifier and liquid flow pump is insufficient, the target Ni content in the plating layer cannot be obtained with the low Ni concentration bath.
In addition, there is a problem in that a large amount of capital investment is required to increase the capacity, which leads to an increase in cost.

The present inventors have conducted various experiments and researches on a method capable of forming a plating layer having a target Ni content even if the Ni ²⁺ ion concentration in the plating bath is low.
The inventors have found that by adding the above Tl ³⁺ ions, a Zn-Ni alloy plated layer having a Ni content of 7 to 18 wt% in the plated layer can be obtained at a low Ni concentration, and the present invention has been accomplished.

The present invention has been made in view of the above circumstances, and has a low
A Zn-Ni alloy plating layer with a Ni content of 7 to 18 wt% can be obtained using a Ni molar concentration bath, a current density of less than 100 A / dm ² and a plating solution flow rate of less than 1.5 m / sec. It is an object of the present invention to provide a method for manufacturing a Ni-based alloy plated steel sheet.

<Means for Solving the Problems> In order to achieve the above object, according to the present invention, in performing Zn-Ni-based alloy plating on the surface of the steel sheet, Ni ²⁺ ion concentration
25 g / min, Zn ²⁺ ion concentration 25 g / min, Ni ²⁺ / (Zn ²⁺
Provided is a method for producing a Zn-Ni alloy-plated steel sheet, which comprises plating with a bath having a molar concentration ratio of + Ni ²⁺ ) of 0.4 or more and less than 0.6 and Tl ³⁺ ions of 1 mg / or more. .

 The present invention will be described in more detail above.

In the present invention, a plating bath composition for obtaining a Ni content in the Zn-Ni alloy plating layer of 7 to 18 wt%, preferably 10 to 18 wt% when the surface of the steel sheet is plated with Zn-Ni alloy is as follows.

The Zn ²⁺ Ni ²⁺ ion concentration in the Zn-Ni alloy plating bath must be 25 g / min or more. If the concentration is less than this range, not only the appearance defect (plating burn, etc.) but also the current efficiency is lowered, which is not practical.

Figure 1 shows Tl ³⁺ in the plating bath at various Ni molar concentrations.
The relationship between the ion concentration and the Ni content in the plating layer is shown. Plating solution concentration is zinc sulfate + nickel sulfate = 380g / and Na ₂ SO
_{0 to} 5000mg / of Tl ₂ (SO ₄ ) ₃ as Tl ³⁺ ions in the baths of which the concentration of Zn ²⁺ and Ni ²⁺ was changed to 40 g / constant.
And add it, and use a counter flow to achieve a liquid flow rate of 1 m / se.
c, Zn-Ni alloy plating was performed at a line speed of 40 mpm. In addition, plating bath pH 1.8, bath temperature 55 ℃, current density 5
The amount was 0 A / dm ² and the coating weight was 30 g / m ² .

In any case, the Ni molar concentration ratio is 0.4 or more and less than 0.6,
In addition, the target Ni content of 7 to 18 wt% is obtained in the range of Tl ³⁺ ion of 1 mg / or more.

As described above, according to the present invention, by adding Tl ³⁺ ions in the Zn-Ni plating bath at 1.0 mg / or more, the Ni molar concentration ratio is 0.4 or more and less than 0.6, and the current density is low. It is possible to manufacture a Zn-Ni alloy-plated steel sheet having a corrosion resistance of 7 to 18 wt% and a Ni content of the plating layer of 7 to 18 wt% at a plating liquid flow rate of less than 100 A / dm ^{2 and} less than 1.5 m / sec.

When the Ni molar concentration ratio is 0.6 or more, a Zn-Ni plating layer having a Ni content of 7 wt% or more can be obtained, but as described above, the Ni ²⁺ ion concentration of the plating solution is increased, which is economically disadvantageous. It is not preferable because it involves.

The upper limit of the amount of Tl ³⁺ ions added to the plating bath is not limited, but is preferably less than 1000 mg / l. The reason for this is that the increase in the Ni content in the plating layer is rate-controlled by the Ni molar concentration ratio, and even if Tl ³⁺ ions are added at 1000 mg / mol or more,
This is because the effect of increasing the content decreases and it is economically disadvantageous to add expensive Tl more than necessary.

In Zn-Ni alloy plating, it is not clear why the target Ni content in the plating layer can be obtained by adding Tl ³⁺ ions to the plating bath in a Ni molar concentration ratio of 0.4 or more and less than 0.6. However, it is considered as follows. Addition of Tl ³⁺ ions to the plating bath suppresses the formation of a barrier layer of zinc hydroxide formed at the strip interface. Therefore, normal type precipitation is likely to occur. Therefore, it is considered that a Zn-Ni plating layer having a Ni content of 7 to 18 wt% can be obtained even at a low Ni molar concentration ratio.

Incidentally, the Zn-Ni alloy plating in the present invention means Zn-
For Ni plating, Ir, P, Co, Cr, Sn, Sb, V, Fe, Ti, Mn,
Any Zn such as Si, Bi, Pb, Al, Cu, Cd, etc. and their oxides, carbides, nitrides, etc. which are intentionally added or inevitably mixed with one or more kinds.
-It can be applied to the formation of a Ni-based alloy plating film.

<Examples> The present invention will be specifically described below based on Examples.

Pretreatment such as degreasing, pickling, and water washing was performed according to a conventional method.
Zn-Ni alloy plating was performed on 8 mm thick SPCC steel plate under the following conditions.

(1) Plating bath: ZnSO ₄ / 7H ₂ O + NiSO ₄ / 6H ₂ O 380g / l Na ₂ SO ₄ 40g / l Ni ²⁺ / (Zn ²⁺ + Ni ²⁺ ) molar concentration ratio 0.35 to 0.70 Tl ₂ (SO ₄ ) 0 to 1000mg / l as ₃ Tl ³⁺ ions (2) Plating conditions: pH 1.6 Bath temperature 60 ° C Current density 50A / dm ² Relative flow velocity of plating solution 1.0m / sec Line speed 40m / min (3) Coating weight 30g / m ^{2 The} Ni content in the plating layer of the obtained Zn-Ni alloy-plated steel sheet was measured by fluorescent X-ray analysis, and a corrosion resistance test was performed. The corrosion resistance test is carried out by a salt spray test, and the evaluation standard is visual judgment, and the judgment standard is as follows.

◯: Red rust occurrence rate after 300 hours is less than 5% △… Red rust occurrence rate after 300 hours is 5 to 10% ×… Red rust occurrence rate after 300 hours exceeds 10% The results are shown in Table 1.

As a comparative example, using the same SPCC steel sheet as the example, the same plating conditions as the example for those having a Ni molar concentration ratio of the plating bath outside the scope of the present invention and containing no Tl ³⁺ ion,
Plating was carried out according to the adhesion amount. The results are shown in Table 1.

<Effects of the Invention> Since the present invention is configured as described above,
Ni molar concentration ratio is as low as 0.4 or more and less than 0.6, and Tl ³⁺ ion is 1m
By using the plating bath containing g / or more, it is possible to economically obtain a Zn—Ni alloy plating layer having a Ni content of 7 to 18 wt%.

[Brief description of drawings]

Figure 1 shows Tl ³⁺ ion concentration in the plating bath and Ni in the plating layer.
It is a graph which shows the relationship with a content rate.

Front Page Continuation (72) Inventor Toshiro Ichida 1 Kawasaki-cho, Chiba-shi, Chiba Within the Technical Research Division, Kawasaki Steel Co., Ltd. (56) References JP-A-61-133394 (JP, A) JP-A-58-204195 (JP, A) JP-A-57-164999 (JP, A)

Claims (1)

[Claims] 1. A Upon applying Zn-Ni alloy plated steel sheet, Ni ²⁺ ion concentration 25 g / or more, Zn ²⁺ ion concentration 25 g /
Above, the molar concentration ratio of Ni ²⁺ / (Zn ²⁺ + Ni ²⁺ ) is 0.4 or more.
A method for producing a Zn-Ni alloy-plated steel sheet, which comprises plating in a bath having a composition of less than 6 and Tl ³⁺ ions of 1 mg / or more.