JP2024006186A - MANUFACTURING METHOD FOR ELECTRICAL Zn-Ni ALLOY PLATING STEEL PLATE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To develop a manufacturing technology to increase the metallic sheen of an electrical Zn-ni alloy plating steel plate to make an appearance of the electrical Zn-ni alloy plating steel plate based on dull original plate (assuming an arithmetic mean roughness Ra of 0.5 μm to 2.5 μm) that is commonly used for forming and processing closer to that of cold-rolled steel plate.

SOLUTION: In a plating bath containing not less than 0.25 mol/L and not more than 0.5 mol/L of Zn²⁺ and not more than 0.5 mol/L and not more than 1.0 mol/L of Ni²⁺, with a Ni²⁺/Zn²⁺ ratio (molar ratio) of not less than 1.5 and not more than 2.5, and a pH of not less than 1.0 and not more than 2.0, a steel plate having an arithmetic mean roughness of Ra not less that 0.5 μm and not more than 2.5 μm is used as a cathode, and the steel plate s electrolytically treated with plating solution at a relative flow velocity of 4 m/sec or more and with a current density of 10 A/dm² or more and 30 A/dm² or less and a bath temperature of 40°C or more and 70°C or less, and a Zn-Ni the Ni alloy plating layer the Ni content of which is 10 mass% or more and less than 16 mass%, the specular gloss (60°) of which is 60 or more, and the coating weight of which is 15 g/m² or more per one side is formed on the surface of the steel plate.

SELECTED DRAWING: None

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a method for producing an electrolytic Zn--Ni alloy plated steel sheet in which a Zn--Ni alloy plating layer is formed on the surface of the steel sheet by electrolytically treating the steel sheet in an acidic plating bath with the steel sheet serving as a cathode.

Typical electrogalvanized steel sheets are electrogalvanized steel sheets and electrolytic Zn-Ni alloy plated steel sheets, which are widely used mainly in home appliances, furniture and construction materials, and automobiles.

Electrogalvanized steel sheets are manufactured by electroplating and are characterized by a uniform and beautiful appearance, but there is always a demand for improvement in their appearance.

Electrolytic Zn-plated steel sheets are often used after being subjected to a thin film chemical conversion treatment, and the original white appearance of the electrolytic Zn-plated steel sheets is the mainstream appearance of the final product. Therefore, many studies have been made to improve the whiteness of the plating appearance.

Patent Document 1 discloses that electrogalvanizing is performed by adding one or more metal ions of Sn, Mo, and Cr, which are electrochemically nobler than zinc and nobler than iron, to an electrogalvanizing bath. A technique for increasing the whiteness of plating has been disclosed.

Electrolytic Zn--Ni alloy plated steel sheets have superior corrosion resistance compared to electrogalvanized steel sheets, and are widely used mainly in automobiles and home appliances. Electrolytic Zn--Ni alloy plated steel sheets have considerably lower whiteness than electrogalvanized steel sheets, and there is no requirement for an appearance similar to that of electrogalvanized steel sheets, so there is no requirement to improve whiteness.

On the other hand, electrolytic Zn--Ni alloy plated steel sheets have higher metallic gloss than electrogalvanized steel sheets, and have an appearance more similar to cold-rolled steel sheets. In automobiles and home appliances, electrolytic Zn--Ni alloy plated steel sheets and cold-rolled steel sheets are often used in combination, and most of them are used after being painted. When painting, the appearance after painting is strongly influenced by the surface gloss level before painting. Therefore, from the viewpoint of appearance uniformity in the final product, there is a potential need to further improve the metallic luster in order to make the appearance of the electrolytic Zn--Ni alloy coated steel sheet more similar to the appearance of a cold-rolled steel sheet.

However, no prior art has been found that attempts to improve the appearance, particularly the metallic gloss, of electrolytic Zn--Ni alloy plated steel sheets.

Regarding the appearance, it is possible to obtain an electrolytic Zn-Ni plated steel sheet with high gloss if the coating weight is less than about 5 g/ ^m2 per side, but as the coating weight increases, the gloss decreases. In the area where the plating deposition amount is 15 g/m ² or more that is actually used, it is difficult to achieve a high gloss level of 60 or more, which is a target value, as an example.

It is known that reducing the surface roughness of the plating base steel sheet is effective in improving the metallic luster. Electrolytic Zn-Ni alloy plating is almost always applied to cold-rolled steel sheets, but the base of cold-rolled steel sheets is often classified into two types: bright original sheets and dull original sheets. An electrolytic Zn--Ni alloy plated steel sheet manufactured by a normal manufacturing method using a bright original sheet with a small surface roughness exhibits a degree of metallic gloss equivalent to that of a cold-rolled steel sheet. However, when a bright original plate is used, the surface roughness is too small, so the friction coefficient of the steel plate becomes too small during press molding, etc., making it difficult to form, and it is not practical in applications where forming is performed.

Therefore, in applications where electrolytic Zn--Ni alloy plated steel sheets are used for forming, which is the main application, it is a prerequisite that dull original sheets are used in the case of cold-rolled steel sheets.

On the other hand, as a method of increasing the glossiness of the plating surface, a technique of adding a brightener mainly composed of an organic substance to the plating bath is widely used. However, the addition of a small amount of brighteners such as organic substances often greatly changes the glossiness, and in order to obtain a stable appearance, controlling the brightener concentration is extremely complicated. Furthermore, brighteners often increase the internal stress of the plating film and reduce plating adhesion during molding, making them unsuitable for producing electrolytic Zn--Ni alloy plated steel sheets.

Japanese Patent Application Publication No. 2006-316329

The appearance of an electrolytic Zn-Ni alloy plated steel sheet is the appearance of a cold-rolled steel sheet, which is based on a dull original plate (assumed to have a surface arithmetic mean roughness Ra of 0.5 to 2.5 μm) that is commonly used for forming processing. The purpose is to improve the metallic luster of electrolytic Zn--Ni alloy plated steel sheets in order to bring it closer to that of Zn--Ni alloy plated steel sheets. We will develop manufacturing technology for this purpose.

As a result of extensive research to solve the above problems, the present inventors have discovered a method for electroplating using a Zn-Ni alloy plating bath, in which a plating solution is brought into contact with a steel plate at a specific flow rate, and a specific We have found that by plating at current density, the metallic gloss of the surface of the plated steel sheet can be greatly improved even if a dull original sheet is used. As for the surface roughness of a normal dull original plate, the arithmetic mean roughness Ra is often in the range of 0.5 μm or more and 2.5 μm or less.

A commonly used Zn--Ni alloy plating bath can be used. It is believed that Zn-Ni alloy plating has the best corrosion resistance when the Ni content of the alloy is in the range of 10% by mass to 16% by mass, so in order to obtain an alloy with such a composition, The Zn ²⁺ concentration is 0.25 mol/L or more and 0.5 mol/L or less. The Ni ²⁺ concentration in the plating bath is 0.5 mol/L or more and 1.0 mol/L or less. At the same time, the Ni ²⁺ concentration in the plating bath/Zn ²⁺ concentration ratio (molar ratio) in the plating bath needs to be 1.5 or more and 2.5 or less.

The pH of the plating bath and the temperature of the plating bath are within a commonly used range, and conditions are selected such that the Ni content of the alloy is 10% by mass or more and 16% by mass or less. The plating bath pH is in the range of 1.0 or more and 2.0 or less. The plating bath temperature is in the range of 40°C or higher and 70°C or lower.

In addition to Zn ²⁺ and Ni ²⁺ , additives such as conductivity aids may be added to the plating bath.

As mentioned above, a normal plating bath can be used, but a Zn--Ni alloy plating with excellent gloss cannot be obtained under normal plating conditions.

The main plating conditions that affect the appearance of the plating, such as the glossiness of the plated steel sheet, include the flow condition of the plating solution on the surface of the steel sheet in the plating bath and the plating current density.

Typical Zn-Ni alloy plating conditions include that the flow of the plating solution on the surface of the steel plate in the plating bath is 0.5 to 2 m/sec, as evaluated by the relative flow velocity of the steel plate and the plating solution, and the plating current density is 0.5 to 2 m/sec. It is 50 to 100 A/ ^dm2 . Under these conditions, Zn--Ni alloy plating with high gloss cannot be obtained.

However, by setting the relative flow velocity between the steel sheet and the plating solution to 4 m/sec or more, which is not normally selected, and the plating current density to 10 A/dm ² or more and 30 A/dm ² or less, which is less than the normal lower limit, Zn- It has been found that Ni alloy plating can be obtained.

Note that the arithmetic mean roughness Ra (μm) of a steel plate can be measured in accordance with JIS B 0633:2001 (ISO 4288:1996).

Specular gloss can be measured using a commercially available gloss meter, for example, Nippon Denshoku Handy Gloss Meter PG-1M. Preferably, the measurements are carried out at a standard angle of 60° (Gs(60°)). The amount of Zn--Ni alloy plating deposited on one side is required to be 15 g/m ² or more from the viewpoint of corrosion resistance.

The present invention was made based on such knowledge and has the following gist.
[1] By electrolytically treating a steel plate with an arithmetic mean roughness Ra of 0.5 μm or more and 2.5 μm or less as a cathode in a plating bath, the steel plate surface has a Ni content of 10% by mass or more and 16% by mass or less, and a specular gloss. A method for producing an electrolytic Zn-Ni alloy plated steel sheet forming a Zn-Ni alloy plating layer with a degree (60°) of 60 or more and a coating weight of 15 g/m2 or ^more per side, the method comprising:
Contains Zn ²⁺ of 0.25 mol/L or more and 0.5 mol/L or less, contains Ni ²⁺ of 0.5 mol/L or more and 1.0 mol/L or less, and has a Ni ²⁺ concentration/Zn ²⁺ concentration ratio (molar ratio). Using a plating bath with a pH of 1.0 or more and 2.0 or less, which is 1.5 or more and 2.5 or less,
Electrolytic Zn-Ni alloy plated steel sheet characterized by electrolyzing at a relative flow rate of 4 m/sec or more between the steel sheet and the plating solution, a current density of 10 A/dm ² or more and 30 A/dm ² or less, and a bath temperature of 40° C. or more and 70° C. or less. manufacturing method.

According to the present invention, even if a dull original sheet is used as the steel sheet, it is possible to obtain an electrolytic Zn--Ni alloy plated steel sheet with a high gloss of 60 or more and a specular gloss (60°) close to the appearance of a cold-rolled steel sheet.

Embodiments of the present invention will be described below.

A steel plate with an arithmetic mean roughness Ra of 0.5 μm or more and 2.5 μm or less is subjected to pretreatment such as degreasing, pickling, and water washing as necessary, and then electrolyzed in an electrolytic Zn-Ni alloy plating bath with the steel plate serving as a cathode. to form an electrolytic Zn--Ni alloy plating layer, followed by washing with water and drying.

The electrolytic Zn-Ni alloy plating bath contains Zn ²⁺ in an amount of 0.25 mol/L or more and 0.5 mol/L or less, contains Ni ²⁺ in an amount of 0.5 mol/L or more and 1.0 mol/L or less, and has a Ni ²⁺ concentration. /Zn ²⁺ concentration ratio (molar ratio) is 1.5 or more and 2.5 or less, pH is 1.0 or more and 2.0 or less, the relative flow velocity of the steel sheet and the plating solution is 4 m/sec or more, and the current is Electrolysis is performed at a density of 10 A/dm ² or more and 30 A/dm ² or less.

It is known that Zn--Ni alloy plating has the best corrosion resistance in a Ni content range of 10% by mass or more and 16% by mass or less, and needs to be manufactured with a Ni content of 10% by mass or more and 16% by mass or less.

By electrolyzing using the above plating bath at a relative flow rate of 4 m/s or more between the steel sheet and the plating solution and a current density of 10 A/dm2 or ^more and 30 A/dm2 or ^less , the amount of plating deposited per side can be 15 g/ ^m2 or more. Even in terms of coating amount, a high-gloss electrolytic Zn--Ni plated steel sheet with a gloss level of 60 or higher can be obtained. Although this mechanism is not certain, the following possibilities are considered. Here, the relative flow velocity between the steel plate and the plating solution is the flow velocity of the plating solution as seen from a certain point on the moving steel plate. The flow rate of the plating solution can be determined from calculations including the discharge flow rate of the jet nozzle that supplies the plating solution between the steel plate and the anode electrode, the arrangement of the jet nozzle with respect to the steel plate, and the like. Generally, in zinc-based electroplating, a jet nozzle is often installed that sprays the plating solution in the opposite direction to the direction in which the steel sheet travels. In that case, the relative flow velocity can be simply calculated by the sum of the jet nozzle exit injection velocity (plating solution discharge flow rate/nozzle exit cross-sectional area) and the steel plate velocity.

In electrolytic Zn--Ni alloy plating, it is known that Zn--Ni alloy is precipitated through a process in which the pH of the plating solution at the interface between the steel sheet and the plating solution increases. Because the relative flow rate is clearly higher than during normal electrolytic Zn-Ni alloy plating production, the convex portions of the uneven surface of the steel sheet are constantly exposed to new plating solution with a low pH, making it difficult for the pH of the plating solution to rise. It is thought that the pH of the plating solution tends to increase. Therefore, it is thought that the Zn--Ni alloy is preferentially deposited in the recesses, improving the surface smoothness and increasing the gloss.

Therefore, the relative flow velocity between the steel plate and the plating solution needs to be 4 m/sec or more. If it is less than 4 m/sec, high gloss cannot be obtained. The upper limit of the relative flow velocity between the steel plate and the plating solution is desirably 10 m/sec or less from the viewpoint of equipment costs such as a pump for supplying the plating solution.

The amount of Zn--Ni alloy plating deposited is required to be 15 g/m ² or more per side from the viewpoint of corrosion resistance, but it is preferably 80 g/m ² or less because an increase in the amount of deposit leads to an increase in manufacturing costs.

The solution must contain Zn ²⁺ in an amount of 0.25 mol/L or more and 0.5 mol/L or less, and Ni ²⁺ in a solution of 0.5 mol/L or more and 1.0 mol/L or less. If the concentration is below a predetermined concentration, Zn ² and Ni ²⁺ will be insufficiently supplied, making it impossible to form electrolytic Zn--Ni plating with a gloss level of 60 or higher. If the concentration exceeds a predetermined concentration, maintenance of the plating bath becomes costly. The Ni ²⁺ concentration/Zn ²⁺ concentration ratio (molar ratio) in the bath needs to be 1.5 or more and 2.5 or less. If it is lower than 1.5 or exceeds 2.5, plating with a Ni content of 10% by mass or more and 16% by mass or less cannot be obtained. The pH of the acidic solution is 1.0 or more and 2.0 or less. If the pH is less than 1.0, the amount of hydrogen gas generated will increase and the electrolysis efficiency will decrease. If the pH exceeds 2.0, the electrical conductivity of the bath will increase, leading to increased electricity costs.

The current density needs to be 10 A/dm ² or more and 30 A/dm ² or less. If the current density is less than 10 A/dm ² , Ni will precipitate preferentially, making it impossible to obtain a plating with a Ni content of 10% by mass or more and 16% by mass or less. If the current density exceeds 30 A/dm ² , the gloss level will decrease.

The plating bath temperature needs to be 40°C or higher and 70°C or lower. Although the mechanism is not clear, when the plating bath temperature is less than 40°C or more than 70°C, the specular gloss (60°) becomes less than 60.

A conductivity aid such as sodium sulfate or potassium sulfate may be added to the plating bath.
After plating, wash with water and dry. The washing and drying methods are not particularly limited, and general methods can be used. Note that, depending on the application, an inorganic or organic film may be formed on the plating layer.

The present invention will be explained below using examples. Note that the present invention is not limited to the following examples.

Using a cold-rolled steel plate with a thickness of 0.6 mm as a cathode, it was electrolytically treated in the plating bath shown in Table 1 under the plating conditions shown in Table 1. Next, after washing with water, it was dried.

The electrolytic Zn--Ni alloy plated steel sheet obtained above was evaluated as follows.
(1) Evaluation of the coating amount and Ni content of the coating film For the test piece (size: 50 mm x 50 mm) taken from the electrolytic Zn-Ni alloy plated steel sheet, the coating layer was dissolved in hydrochloric acid, and the Zn coating amount and Ni content were evaluated. The amount of adhesion was measured using an ICP emission spectrometer. The plating amount is the total value of the Zn adhesion amount and the Ni adhesion amount, and is shown as the adhesion amount per one side. The Ni content in the film was calculated by Ni adhesion amount/(Ni adhesion amount + Zn adhesion amount). Then, based on this Ni content, evaluation was performed according to the following criteria.
○: Ni content is 10% by mass or more and 16% by mass or less ×: Ni content is less than 10% by mass or more than 16% by mass (2) Evaluation of glossiness Test piece taken from an electrolytic Zn-Ni alloy plated steel sheet ( Size: 150 mm x 50 mm) was measured at an angle of 60° using a handy gloss meter PG-1M manufactured by Nippon Denshoku, and evaluated based on the following criteria.
○: 60 or more ×: less than 60 The obtained results are shown in Table 1.

As shown in Table 1, all the invention examples satisfying the requirements of the present invention had a Ni content of 10% by mass or more and 16% by mass or less, and a glossiness of 60 or more.

On the other hand, all of the comparative examples that do not meet the requirements of the present invention either have a Ni content of 10% by mass or more and 16% by mass or less, a gloss level of less than 60, or both, and the desired performance is achieved. did not show.

The electrolytic Zn-Ni alloy plated steel sheet of the present invention has a Ni content of 10% by mass or more and 16% by mass or less, which is excellent in corrosion resistance, and a coating weight of 15 g/m ² or more, yet has a metallic luster with a specular gloss of 60 or more. Therefore, it is a useful plated steel sheet for applications that require corrosion resistance and high gloss.

Claims (1)

By electrolytically treating a steel plate with an arithmetic mean roughness Ra of 0.5 μm or more and 2.5 μm or less as a cathode in a plating bath, the steel plate surface has a Ni content of 10 mass% or more and 16 mass% or less, and a specular gloss (60 A method for producing an electrolytic Zn-Ni alloy plated steel sheet forming a Zn-Ni alloy plating layer with a coating weight of 60 or more and a coating weight of 15 g/m2 ^{or more} per side, the method comprising:
Contains Zn ²⁺ of 0.25 mol/L or more and 0.5 mol/L or less, contains Ni ²⁺ of 0.5 mol/L or more and 1.0 mol/L or less, and has a Ni ²⁺ /Zn ²⁺ ratio (molar ratio) of 1 Using a plating bath with a pH of 1.0 or more and 2.0 or less, which is .5 or more and 2.5 or less,
Electrolytic Zn-Ni alloy plated steel sheet characterized by electrolyzing at a relative flow rate of 4 m/sec or more between the steel sheet and the plating solution, a current density of 10 A/dm ² or more and 30 A/dm ² or less, and a bath temperature of 40° C. or more and 70° C. or less. manufacturing method.