JPH025833B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a zinc-nickel alloy plated steel sheet that does not contain oxides and has an excellent surface appearance.

In order to improve the corrosion resistance of galvanized steel sheets, various studies have been conducted on alloy plating and composite plating. Among them, Zn--Ni alloy plated steel sheets in particular have excellent surface properties such as corrosion resistance, weldability, and paintability.
Their usefulness has been reported in No. 152194, among others, and it has been announced that an alloy containing 10 to 20% Ni consisting of a single γ phase provides the best corrosion resistance. However, for alloy plating, plating bath composition, PH, current density,
The deposited alloy composition tends to fluctuate due to variations in plating conditions such as bath temperature and liquid stirring conditions, making it difficult to stably obtain a predetermined alloy composition industrially at high speed.

An improvement measure for stabilizing the deposited alloy composition in Zn--Ni alloy plating is disclosed in JP-A-55-110791, which states that in a sulfate bath using zinc sulfate and nickel sulfate, Ni ²⁺ and
The molar concentration ratio of Zn ²⁺ was varied from 1.5 to 4 (i.e., Ni ²⁺ /
(Molar concentration percentage of Ni ²⁺ + Zn ²⁺ ) is adjusted to 60 to 80%), and the relative movement speed between the plating solution and the steel plate in the plating bath is set to 10 m/min or more. . In other words, during the plating bath
By optimizing the two conditions of the molar ratio of Ni ²⁺ concentration and Zn ²⁺ concentration and the relative movement speed between the plating solution and the steel plate, Zn-Ni alloy plating with a Ni content of 9 to 20% was achieved. It's something you get.

Furthermore, according to the disclosure of JP-A No. 55-152194, in an acidic bath where the molar concentration ratio of Ni ²⁺ and Zn ²⁺ is not particularly limited, the flow rate of the plating solution is set to 20 m/min or more, and the current density is It is stated that if conditions of 20 A/dm ² or more are selected, Zn-Ni deposits can be obtained.
An example using chloride is Ni molar concentration percentage 36
%, and a precipitate with a Ni content of approximately 12-19% has been obtained.

The present inventors further investigated in detail the relationship between the plating bath composition and plating conditions in Zn-Ni alloy plating and the deposited alloy composition. A plating solution that significantly improves the appearance gloss of the yellow-brown to blue-purple precipitates that precipitate, and produces Zn-Ni alloy coated steel sheets with high current density, high speed, high efficiency, and a stable surface with no oxides. I found out.

That is, the Zn--Ni alloy plating solution used in the method of the present invention uses (1) a chloride bath containing zinc chloride and nickel chloride as main components, (2) aluminum chloride,
One or more chloride salts selected from the group such as aluminum ammonium chloride, ammonium chloride, potassium chloride, calcium chloride, barium chloride, sodium chloride, magnesium chloride, etc. are added in a total amount of 0.2 mol or more up to the solubility limit. (3)
Ni ²⁺ / (Ni ²⁺ + Zn ²⁺ ) molar concentration percentage in the bath
20 to 60%, and (4) adjusting the pH of the plating solution to 1.8 to 4.5. By optimizing the above four conditions and further increasing the current density to 20 A/dm ² or higher, the Ni content can be reduced to 10 to 10% without any oxides on the surface.
We succeeded in stably obtaining a 20% by weight Zn-Ni alloy plated steel plate with excellent appearance gloss.

Ni content 10 to 20% by weight precipitated from a chloride bath composed of conventional zinc chloride and nickel chloride
In the case of Zn--Ni alloy plating, only yellow-brown to bluish-purple oxide-containing precipitates were obtained at high current densities of 10 A/dm ² or higher, and improvements were needed. In other words, precipitates containing yellowish-brown to bluish-purple oxides not only have poor surface gloss and significantly reduce commercial value, but also because Zn-Ni alloy plated steel sheets are mainly used after being painted. The phosphate or chromate treatment used as the base treatment is not uniformly formed due to the presence of oxides, which causes a decrease in paint adhesion and corrosion resistance, which is disadvantageous.

According to the method of the present invention, the plating process can be performed at high speed and with high efficiency over a wide range of plating conditions, and there is no oxide film on the surface.
A Zn-Ni alloy plated steel sheet is obtained. As mentioned above, conventional chloride baths yield only yellowish-brown to bluish-purple precipitates containing oxide or hydroxide impurities on the surface, but in the plating method of the present invention,
High current density, especially in the range of 20 to 200 A/dm ² , excellent Ni content with no oxides on the surface and a glossy appearance
A precipitate of 10-20% by weight is obtained. Furthermore, precipitation by the plating method of the present invention can be carried out without increasing the relative velocity between the plating solution and the steel plate, as has conventionally been generally done. The advantage is that Zn-Ni alloy plated steel sheets without oxides on the surface can be obtained at such high current densities.

The above-mentioned Japanese Patent Application Publication No. 110791 and Japanese Patent Application Publication No. 110791-
In conventional plating baths such as No. 152194, Ni10 to 20
wt% alloy composition at high current density (e.g. 10A/
dm ² or more) at high speed industrially, it is essential to set the relative movement speed between the plating solution and the steel plate to 10 m/min or more. Furthermore, as a result of detailed studies by the present inventors using conventional plating baths, we found that in order to conduct electrolysis at a high current density of 30 A/dm ² or more, it is necessary to forcefully circulate the plating bath or to use methods such as stirring. If the plating solution near the steel plate interface is not sufficiently stirred, a uniform γ phase (Ni content of 10 to 20%) cannot be obtained. Especially at high current densities of 70 A/dm2 or ^higher , stirring of these plating baths is difficult. In order to strengthen this process, it was found that new special stirring equipment was required, and that the existing plating equipment would require major changes and modifications.

In the plating method according to the present invention, when the relative speed between the plating liquid and the steel plate is relatively small (for example, 20 m/
Even at high current densities of 100 A/dm ² or higher, a desired alloy composition without oxides on the surface can be obtained even when Its contribution is extremely large when producing galvanized steel sheets industrially at high speed.

The advantage of the chloride bath in the present invention is that the conductivity is 2 to 3 times higher than that of the sulfuric acid bath, and the power consumption is reduced to 1/2 to 1/3, which is advantageous in terms of energy saving. Furthermore, it is easy to maintain a constant plating solution composition. In other words, in the chloride bath, the composition of the plating solution is always kept constant by arranging Zn and Ni anodes in a ratio corresponding to the amount of Zn and Ni deposited on the steel plate and ionizing in an amount commensurate with the amount of deposited. A stable Zn-Ni alloy plated steel sheet can be obtained. On the other hand, in a sulfuric acid bath, the Ni anode becomes passivated and is not ionized, so the Ni ²⁺ concentration decreases and it is difficult to continuously obtain alloy-plated steel sheets of stable quality. Therefore, there is a drawback that means for keeping the liquid composition constant is required.

In the plating solution used in the present invention, the Zn ²⁺ concentration in the plating solution is 30 g/or more, and the Ni ²⁺ concentration is 30 g/min.
g/ or more, the total amount of chloride salts as additives
0.2 mol/or more, and Ni ²⁺ / (Ni ²⁺ + Zn ²⁺ )
Adjust the molar percentage from 20 to 60% and the PH from 1.8 to 4.5
Adjust to. If the Zn ²⁺ and Ni ²⁺ concentration is less than 30g/20A/ ^dm2 or more, normal alloy plating cannot be obtained, and if the chloride salt as an additive is less than 0.2mol/20A/dm2 or ^more , high Yellowish brown at current density
Contains blue-purple oxide or hydroxide impurities
Only precipitates with Ni content of 10-20% are obtained. This oxide-containing precipitate is due to insufficient conductivity of the plating bath.

Also, the molar percentage of Ni ²⁺ /(Ni ²⁺ + Zn ²⁺ ) is
Below 20%, the Ni content in the precipitated alloy composition is 10%
If the corrosion resistance is less than that, sufficient corrosion resistance cannot be obtained. Conversely, when the molar percentage exceeds 60%, the Ni content becomes 20% or more and the sacrificial corrosion protection effect decreases. Note that the pH of the plating solution is preferably 1.8 to 4.5, and a pH of less than 1.8 is undesirable because chemical dissolution of the precipitated alloy occurs. Also, PH
If it exceeds 4.5, hydroxide will be generated and the plating solution will become unstable. The appropriate temperature of the plating bath is about 35 to 75°C.

In the plating bath used in the present invention, the relative movement speed between the plating liquid and the strip is not particularly limited depending on the flow rate of the plating liquid or the line speed of the strip, but even at a low flow rate of 20 m/min or less, a surface free from oxides can be obtained. A single γ phase with excellent appearance is obtained. Therefore, the plating of the present invention does not require a special stirring device as described above even in electrolysis at high current density, and even in plating methods where the liquid flow rate is non-uniform (e.g. CAROSEL, vertical plating cell). The method can be advantageously applied.

Hereinafter, the plating method of the present invention will be specifically explained with reference to Examples.

Example 1 ZnCl ₂ 136g/and NiCl ₂・6H ₂ O238g/
NaCl ^0.2 to 4.0 mol/(11.6 to 232 g/
) with a current density of 75A/
dm ² , liquid flow rate 50m/min, Zn-Ni area weight 20g/
Electrolysis was carried out so that m ² was obtained.

FIG. 1 shows the relationship between the amount of NaCl added to the plating solution used in the method of the present invention and the electrical conductivity. As is clear from FIG. 1, as the amount of NaCl added increases, the electrical conductivity of the plating solution increases almost linearly. Figure 2 shows the amount of NaCl added to the plating solution of the present invention and the obtained
The relationship between the glossiness of the Zn-Ni alloy plating (γ single phase with Ni content of about 13 to 16% by weight) film is shown. As is clear from FIG. 2, the gloss of the plating film is significantly improved by adding 0.2 mol/or more of NaCl.

FIG. 3 shows the results of X-ray diffraction of the tamping film obtained by the method of the present invention and the tamping film obtained by the conventional method. As is clear from Fig. 3, in the example of the present invention, a single phase diffraction peak of NiZn ₃ (γ phase) is obtained, whereas in the conventional example, a diffraction peak (2θ≒49°) which is considered to be an oxide in addition to NiZn ₃ is obtained. exists,
It is thought that impurities other than NiZn ₃ are co-deposited, giving the precipitate a brown color.

Thus, by using the plating method of the present invention, a precipitate containing no impurities was obtained, completely different from conventional baths.

Example 2 ZnCl ₂ 164g/and NiCl ₂ 6H ₂ O 190g/
The pH was adjusted to 3.0 by adding 2 mol/each of KCl, NH ₄ Cl, AlCl ₃ , and CaCl ₂ to the tamping solution containing 40% Ni ²⁺ molar concentration. Similar to Example 1, current density 75A/
dm ² , liquid flow rate 50m/min, Zn-Ni area weight 20g/
Electrolysis was carried out so that m ² was obtained.

As a result, as in Example 1, the electrical conductivity of the plating bath was improved to 230 to 270 m/cm, and a precipitate with excellent gloss (γ single phase with Ni content of 12 to 17% by weight) was obtained.

[Brief explanation of drawings]

Figure 1 shows the plating solution used in the method of the present invention.
A graph showing the relationship between the amount of NaCl added and the electrical conductivity, Figure 2 is a graph showing the relationship between the amount of Na added and the gloss of the obtained Zn-Ni alloy plating film, and Figure 3 is a graph showing the relationship between the amount of NaCl added and the gloss of the obtained Zn-Ni alloy plating film. 1 is a graph showing the results of X-ray diffraction of a Zn--Ni alloy plating film obtained from a plating bath and a plating bath in a conventional method.

Claims (1)

[Claims] 1 Main ingredients are zinc chloride and nickel chloride,
Solubility limit of one or more chloride salts selected from the group consisting of aluminum chloride, ammonium aluminum chloride, ammonium chloride, potassium chloride, calcium chloride, barium chloride, sodium chloride and magnesium chloride in total of 0.2 mol/or more Ni ²⁺ / (Zn ²⁺ +
After adjusting the pH of this plating solution to 1.8 to 4.5 using a plating solution with a molar concentration percentage of Ni ²⁺ ) of 20 to 60%, the steel plate is plated at a current density of 20 A/dm ² or more. A method for producing a zinc-nickel alloy plated steel sheet.