KR940011254B1 - Zn-ni alloy solution for electroplating and method for producing an electroplating steel sheet of zn-ni alloy using the same - Google Patents

Abstract

The Zn-Ni alloy electroplating solution is prepared by adding at least one ammonium salt selected from the group consisting of ammonium carbonate, ammonium sulfate, ammonium chloride and ammonium acetate to chloride salt consisting of zinc chloride, nickel chloride and potassium chloride. The solution has 1.0-2.2 mol/l of Zn2+ + Ni2+ mol. concentration ratio, 0.10-0.18 mol/l of Ni2+/Zn2+ + Ni2+ mol. concentration ratio, 0.2-1.2 mol/l of NH4+/Zn2+ + Ni2+ mol concentration ratio, 0.05-0.5 mol/l of NH4+/K+ mol concentration ratio and 2.0-4.5 pH. The steel sheet is electro-plated under the condition of 50-70 deg.C, 0.5-2.5 m/sec relative flow velocity and 30-180 A/dm2 current desntity.

Description

Zinc-Nickel Alloy Electroplating Solution and Manufacturing Method of Zinc-Nickel Alloy Electroplating Steel Sheet Using the Same

1 is an X-ray diffraction analysis result of sludge formed on zinc anode in zinc chloride-nickel chloride-potassium chloride plating solution.

2 is a graph showing a change in plating voltage according to the plating time for the present invention and comparative examples.

The present invention relates to a zinc-nickel alloy electroplating solution and a method for producing a zinc-nickel alloy electroplating steel sheet using the plating liquid, and more particularly, to significantly improve the reactivity of a zinc anode in a chloride bath using a soluble zinc anode. The present invention relates to a zinc-nickel alloy electroplating solution capable of securing excellent plating quality at high current density and to a method of manufacturing a zinc-nickel alloy electroplating steel sheet using the plating solution.

Conventionally, zinc-based alloy plating, including zinc plating, has been performed to improve corrosion resistance of steel sheets, and its use range is wide ranging from automobiles, buildings, and home appliances. Zinc-nickel alloy electroplated steel sheet with a nickel content of 10-18wt% of zinc-based galvanized steel sheet has excellent characteristics such as workability, corrosion resistance, weldability and paintability, and its demand is increasing mainly on automotive steel plates. In particular, in order to cope with the trend of high anti-rusting of steel sheets for automobiles, the importance of such as being used as the base steel sheet of the organic coated steel sheet.

Zinc-nickel alloy electroplating steel sheet is usually produced by continuously passing a cold rolled steel strip through a plurality of plating baths, a chloride bath or a sulfate bath is used as a plating solution. The chloride bath has higher electrical conductivity than sulfate bath, which is advantageous for high current density plating, and mainly maintains the metal ion concentration of the plating liquid by using zinc and nickel as soluble anodes. The use rate of zinc anode is 80-90%, and it is mainly used. The reactivity of zinc anode has a great influence on plating workability, plating solution concentration management, and plating quality.

As the chloride bath, zinc chloride-nickel chloride-potassium chloride-based plating solution (hereinafter referred to as "formerly plating solution system") is preferred in terms of good electrical conductivity and low cost, and it is possible to refine plating crystals and improve surface quality as necessary. Small amounts of additives may be used for this purpose. However, in the conventional plating solution system, nickel is electrolessly substituted on the zinc anode due to the potential difference between zinc and nickel, resulting in a non-uniform chemical reaction, thereby producing zinc hydroxide sludge. FIG. 1 is a result of X-ray diffraction analysis of the sludge produced in the zinc anode in the conventional plating solution system. As shown in FIG. 1, ZnCl ₂ · 4Zn (OH) ₂ and K ₂ ZnCl ₄ are composed of compounds. It can be seen. The sludge produced in the zinc anode not only lowers the plating solution concentration by preventing the normal dissolution reaction of zinc, but also grows thicker as the plating time elapses, thereby increasing the plating voltage. In addition, the gap between the zinc anode and the steel plate (steel strip) to be plated becomes uneven and narrow, resulting in quality defects such as edge burning and peeling of the plating layer. It causes serious problems that require you to stop working.

As a conventional technique for the chloride bath for zinc-nickel alloy plating, JP-A-58-55585, JP-A-59-211589 and JP-A-61-6290 are mentioned.

Japanese Patent Application Laid-Open No. 58-55585 is for improving the surface quality of a plated layer, which is composed of aluminum chloride, ammonium chloride, potassium chloride, calcium chloride, barium chloride, sodium chloride, etc. in a chloride bath composed mainly of zinc chloride and nickel chloride. It is characterized by adding one or two kinds of chloride salts, but due to the high molarity ratio of Ni ²⁺ / Zn ²⁺ + Ni ²⁺ , the potential difference between zinc anode and plating solution is increased, which causes the sludge generation of zinc anode. There is a problem that promotes the electroless substitution reaction of nickel.

In addition, Japanese Patent Application Laid-Open No. 59-211589 relates to a crystalline form which precipitates in the plating layer, characterized in that an ammonium salt is added to a mixture bath containing zinc chloride, nickel chloride as a main component, or a chloride bath. However, according to the experimental results of the present inventors, when the ammonium salt is used alone or the ammonium salt is excessive, a new type of brown sludge layer mainly containing nickel is formed on the zinc anode, and the zinc anode is dissolved due to gas generation during the electrolytic reaction. There is a problem that the efficiency is lowered.

In addition, Japanese Patent Application Laid-Open No. 61-6290 relates to a method for producing a plating layer having excellent corrosion resistance, and is characterized by limiting a current density range or adding an organic acid ion of a carboxyl group. In the potassium chloride bath, the above-described problems of the zinc positive electrode occur.

As described above, the above-mentioned prior arts are mainly related to the surface appearance and corrosion resistance of the plating layer, and there are no problems regarding the reactivity of the zinc anode, and there are no solutions to solve them.

The present inventors conducted research and experiments to solve the above-mentioned problems of the prior art, confirming that the addition of ammonium ions is effective to suppress the sludge generation of zinc anodes, and suggesting the present invention based thereon, The present invention is based on zinc chloride-nickel chloride-potassium chloride-ammonium salt, with a molar concentration of Zn ²⁺ + Ni ^{2+, a} molar concentration of Ni ²⁺ / Zn ²⁺ + Ni ²⁺ , NH ₄ ⁺ / Zn ²⁺ + Ni Zinc-nickel alloy electroplating solution which can improve process quality and quality by optimizing the reactivity of zinc anode by limiting molar concentration ratio of ²⁺ , molar concentration ratio of NH ₄ ⁺ / K ⁺ , and pH of plating solution to a certain range, respectively. By using this plating solution, zinc-nickel alloy electroplating of steel plate under certain plating condition prevents zinc anode from sludge, so that zinc anode melts normally, and the quality of edge burning, peeling, etc. Significantly to reduce the zinc-nickel-in to provide a method of manufacturing the alloy electroplated steel sheet, it is an object.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention provides a molar concentration of Zn ²⁺ + Ni ²⁺ by adding one or two or more ammonium salts to a chloride bath composed of zinc chloride, nickel chloride and potassium chloride: 1.0-2.2 mol / l, Ni ²⁺ / Zn Molarity ratio of ² ++ Ni ²⁺ : 0.10-0.18, molarity ratio of NH ₄ ⁺ / Zn ²⁺ + Ni ²⁺ : 0.2-1.2, molarity ratio of NH ₄ ⁺ / K ⁺ : 0.05-0.5, and pH: The present invention relates to a zinc-nickel alloy electroplating solution configured to be 2.0-4.5.

In addition, the present invention adds one or two or more kinds of ammonium salts to a chloride bath composed of zinc chloride, nickel chloride and potassium chloride, so that the molar concentration of Zn ²⁺ + Ni ²⁺ is 1.0-2.2 mol / l, Ni ²⁺ Molar concentration ratio of / Zn ²⁺ + Ni ²⁺ : 0.10-0.18, molar concentration ratio of NH ₄ ⁺ / Zn ²⁺ + Ni ²⁺ : 0.2-1.2, molar concentration ratio of NH ₄ ⁺ / K ⁺ : 0.05-0.5, and pH: Zinc-nickel alloy by electroplating the steel plate using 50 ~ 70 ℃ of temperature, relative flow rate of 0.5-2.5m / sec and current density of 30-180A / dm ² It relates to a method for producing an electroplated steel sheet.

In addition, a small amount of additives may be added to the plating solution of the present invention for the purpose of miniaturizing the plating crystal, improving the appearance of the plating, and the like.

Hereinafter, the numerical limitation reason and the like will be described in detail.

The ammonium salt added to the chloride bath is preferably selected from the group consisting of ammonium carbonate, ammonium sulfate, ammonium chloride and ammonium acetate salt. However, in this invention, it is not necessarily limited only to these ammonium.

In the above plating solution, it is preferable to limit the molar concentration of Zn ²⁺ + Ni ^{2+ to be in} the range of 1.0-2.2 mol / l, since the reason is that the proper current density range becomes narrow when it is less than 1.0 mol / l, and 2.2 mol / This is because the plating appearance deteriorates due to discoloration or the like above l.

In addition, limiting the molar concentration ratio of Ni ²⁺ / Zn ²⁺ + Ni ²⁺ to 0.10-0.18 is for adjusting the nickel content of the plating layer, and when it is less than 0.10, the nickel content of the plating layer is low and corrosion resistance is lowered. If the nickel content of the plating layer is increased to 0.18 or more, the workability is deteriorated, and if the nickel concentration of the plating liquid is high, the electroless substitution reaction of nickel, which is the cause of sludge generation of the zinc anode, is accelerated and difficult to suppress.

In addition, the molar concentration ratio of NH ₄ ⁺ / Zn ²⁺ + Ni ²⁺ is a factor influencing the reactivity of the zinc anode. When the molar concentration ratio is less than 0.2, the zinc anode has insufficient effect of suppressing sludge formation, and the ratio is 1.2 or more. Since the new type of layered sludge is formed in the zinc anode, the molar concentration ratio is preferably limited to 0.2-1.2.

In addition, when the molar concentration ratio of NH ₄ ⁺ / K ⁺ is less than 0.05, the effect of adding ammonium salts is not obtained. If the molar concentration ratio is 0.5 or more, the nickel content of the plating layer tends to be lowered. It is preferable to limit.

When the pH of the plating liquid is less than 2.0, the plating efficiency is lowered due to hydrogen generation at the cathode, and when the pH of the plating liquid is higher than 4.5, the plating liquid is unstable due to the generation of hydroxide, etc., so the pH is preferably limited to 2.0-4.5. .

In addition, when the temperature of the plating solution is less than 50 ℃, the solubility of various salts including potassium chloride is lowered, the nickel content of the plating layer is also lowered, and above 70 ℃ the evaporation of the plating solution is severe, worsening the working environment and the corrosion of equipment It is preferable to limit the temperature of the plating liquid to 50-70 ° C. Under the plating conditions, when the relative flow velocity of the plating liquid to the zinc-nickel alloy steel sheet to be plated is less than 0.5 m / sec, plating properties such as coarsening of plating crystals and burning of the plating layer are deteriorated in a high current density region. , 2.5m / sec or more, since it corresponds to the flow rate range difficult to secure in practical terms, it is preferable to limit the relative flow rate of the plating solution to 0.5-2.5m / sec.

Further, when the above-mentioned current density of 30A / dm ² is less than denotes the tendency of increasing the nickel content decreased gloss of the coating layer even, the higher the current density of the plating rate is faster advantageous in terms of productivity, however, 180A / dm ² or more In this case, in addition to the burning phenomenon of the plating layer, a problem occurs in contact between the steel sheet and the current collector, and therefore, the current density is preferably limited to 30-180 A / dm ² .

In the present invention, a small amount of additives may be used in the plating solution of the present invention for the purpose of refining the plating crystals, improving the appearance of plating such as glossiness, and the like. It is possible to obtain an effect of improving the surface quality of the plating, and preferred additives include amine-based organic compound additives.

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

A cold rolled steel sheet of 0.7 mm thickness was used as a base metal, and after using a 60 mm thick zinc anode, electroplating was performed continuously for 10 hours under the plating solution and plating conditions shown in Table 1 below, the reactivity of the zinc anode could be evaluated. The plating voltage, the sludge generation thickness of the zinc anode, and the amount of the zinc anode dissolved were measured, and the edge burn generation width, the peeling property, and the nickel content of the plating layer were measured as the evaluation items of the plating quality. Indicated.

Also, in Comparative Examples and Inventive Examples of Table 1, Comparative Examples (2-3) and Inventive Examples (2-3) are shown in FIG. 2 by comparing trends of changes in plating voltage over time.

TABLE 1

* Additives: Commercially available polishers for Zn-Ni alloy electroplating, amine-based organic compound additives.

TABLE 2

* Plating peeling: ○: Excellent (no plating peeling), ×: Poor (plating peeling during processing)

As shown in Table 2, the invention according to the present invention (1-5) has a lower plating voltage, significantly less sludge generation of the zinc anode, and the amount of dissolution of the zinc anode than the comparative example (1-4). It can be seen that the reactivity of the zinc anode is very stable in that it is normal and there is almost no edge burning and plating peeling even in the plating property.

When the current density of 80A / dm ² was plated for 10 hours, the electrochemical calculation of the zinc anode dissolution amount was 976 g / dm ² , and the comparative examples showed 150-190 g / dm ² lower than the calculated value. It can be seen that it affects.

In addition, as shown in FIG. 2, the inventive examples (2, 3) show a stable plating voltage with the passage of plating time, whereas in the comparative examples (2, 3), the plating voltage tends to increase gradually. The sludge on the zinc anode grows thicker.

As described above, the present invention can significantly improve processes such as continuous workability, power source unit reduction, and plating solution concentration stabilization by optimizing the reactivity of the zinc anode in the chloride plating solution. There is a practical effect to be able to manufacture a high quality zinc-nickel alloy electroplating steel sheet with little stability at high current density.

Claims (3)

The molarity of Zn ²⁺ + Ni ²⁺ by adding one or more selected from the group consisting of ammonium carbonate, ammonium sulfate, ammonium chloride and ammonium acetate to the chloride bath consisting of zinc chloride, nickel chloride and potassium chloride : 1.0-2.2 mol / l, molar concentration ratio of Ni ²⁺ / Zn ²⁺ + Ni ²⁺ : 0.10-0.18, molar concentration ratio of NH ₄ ⁺ / Zn ²⁺ + Ni ²⁺ : 0.2-1.2, NH ₄ ⁺ / A zinc-nickel alloy electroplating solution, characterized in that the molar concentration ratio of K ⁺ : 0.05-0.5, and pH: 2.0-4.5. The molarity of Zn ²⁺ + Ni ²⁺ by adding one or two or more selected from the group consisting of ammonium carbonate, ammonium sulfate, ammonium chloride and ammonium acetate to the chloride bath consisting of zinc chloride, nickel chloride and potassium chloride: Molar concentration ratio of 1.0-2.2 mol / l, Ni / Zn ²⁺ + Ni ²⁺ : 0.10-0.18, molar concentration ratio of NH ₄ ⁺ / Zn ²⁺ + Ni ²⁺ : 0.2-1.2, NH ₄ ⁺ / K ⁺ Using a plating liquid composed of a molar concentration ratio of 0.05-0.5 and a pH of 2.0-4.5, the temperature of the plating liquid: 50-70 ° C., the relative flow rate of the plating liquid: 0.5-2.5 m / sec and the current density: 30-180 A / dm ^A method for producing a zinc-nickel alloy electroplated steel sheet, characterized in that the steel plate is electroplated under the plating conditions of ² . The method for producing a zinc-nickel alloy electroplated steel sheet according to claim 2, wherein the steel sheet is electroplated by further adding a small amount of additives for the purpose of miniaturizing the plating crystals and improving the appearance of the plating.