KR100786971B1 - Electroplated steel sheets with excellent corrosion resistance and electrolyte thereof - Google Patents

Abstract

The present invention relates to an electroplated steel sheet of zinc alloy-based and a plating solution for the production thereof. The steel plate is composed of 0.1 to 3.0 wt% and 0.05 to 5.0 wt% of cobalt and manganese on one or both surfaces of the surface, and one or more elements of chromium or molybdenum, if necessary, in an alloy layer composed of zinc. It is characterized by further containing at 5.0 wt% or less. In addition, a liquid containing 30 to 90, 1 to 30 and 3 to 150 g / l of Zn ²⁺ , Co ²⁺ and Mn ²⁺ ions in the plating solution, respectively, or one of Cr ³⁺ and Mo ⁶⁺ ions It is added to the 15 g / l or less to provide a plating solution composition to be electroplated at pH 0.5 ~ 2.5, temperature 40 ~ 70 ^° C conditions.

Electroplating, Zinc, Cobalt, Chrome, Manganese, Alloy Plating, Corrosion Resistance

Description

Plating solution composition for coating electroplated steel sheet with excellent corrosion resistance and electroplated steel sheet coated with the same {Electroplated steel sheets with excellent corrosion resistance and electrolyte

The present invention relates to a plating solution composition for coating zinc-based electroplated steel sheet. The present invention also relates to a zinc-based alloyed electroplated steel sheet coated with the plating solution composition on its surface. Here, the plating solution composition or the surface coating layer of the steel sheet coated with the coating solution composition is based on an alloy layer containing cobalt and manganese of Co: 0.1-3.0 wt% and Mn: 0.05-5.0 wt%, respectively, the remainder being made of zinc, If necessary, it is further characterized by containing at least one element of chromium (Cr) or molybdenum (Mo) in less than 5.0 wt%.

In the present invention, the content of Zn ²⁺ , Co ²⁺ and Mn ²⁺ ions is added in the plating solution having the amount and the amount of 30 to 90, 1 to 30 and 3 to 150 g / l, respectively, or Cr ^The invention relates to a plating solution composition in which at least one ion of ³⁺ and Mo ⁶⁺ ions is added to 15 g / l or less and is electroplated at a pH of 0.5 to 2.5 and a temperature of 40 to 70 ^° C.

Zinc electroplated steel sheet is widely used for home appliances, building materials and automobiles. In the continuous electro zinc plating process, post-treatment such as chromic acid treatment, phosphate treatment and anti-fingerprint treatment is mainly performed after zinc plating. However, as environmental regulations have recently been intensified, the chromic acid treatment process using hexavalent chromium is omitted, so that the corrosion resistance of galvanized steel sheet is reduced, and thus, development of a new plating layer having better corrosion resistance is required. One of those manufactured in response to this demand is zinc-iron (Zn-Fe), zinc-nickel (Zn-Ni) or zinc-cobalt-tungsten (Zn-Co-W) alloy plating and zinc-cobalt-molybdenum. (Zn-Co-Mo) composite plated steel sheets and the like.

However, these coated steel sheets have the following problems. When the zinc-iron alloy plated steel sheet contains iron (Fe) in the plating layer, when the surface of the steel sheet is exposed to the corrosion atmosphere, the zinc plating layer is dissolved and iron in the plating layer is oxidized to make red corrosion products. There are many. In addition, when manufacturing a zinc-iron alloy plated steel sheet, the plating workability is poor because Fe ²⁺ ions in the plating solution are oxidized to Fe ³⁺ ions to form sludge.

Zinc-nickel alloy plated steel sheet is widely used as a material for automobiles due to its excellent corrosion resistance, but is prohibited in Europe due to allergic reaction of nickel, and its use is spreading worldwide.

An example of a zinc-cobalt-tungsten alloy electroplated steel sheet is disclosed in Korean Patent 10-0455083-0000 (October 21, 2004). According to the composition of the coating layer is cobalt 0.1 ~ 3.0 wt%, tungsten 0.1 ~ 2.0 wt%, the remainder is composed of zinc and excellent corrosion resistance and weldability. However, the plating aqueous solution is characterized in that it is managed in the range of pH 3 ~ 6, it is difficult to manufacture a zinc plating equipment of insoluble anodes working at pH 1 ~ 2 which is strongly acidic.

Zinc-cobalt-molybdenum composite plated steel sheet is disclosed in Japanese Patent Publication No. 49-19979 and US Patent US 3791801. According to the present invention, there is an electroplated steel sheet in which at least one oxide of molybdenum oxide or tungsten oxide is present in the galvanized layer by 0.05 to 2% by weight to improve corrosion resistance, and in claim 2 of the patent, one of molybdenum oxide or tungsten oxide in the galvanized layer. An electroplated steel sheet is disclosed in which the vacancy is 0.05 to 2% by weight and the metal or oxide of iron, nickel, cobalt, tin, lead, or the like is 0.5 to 15%.

The characteristic of the US 3791801 patent is that since molybdenum and tungsten are present as colloidal oxides in an acidic plating solution, these oxides are physically embedded or chemically adsorbed to the plating layer during the plating process, thereby providing MoO ₂ , Mo ₂ O ₃ and WO _2. And oxides or hydroxides such as W ₂ O ₃ . When molybdenum or tungsten oxides are present in the plating layer, these oxides inhibit the elution of zinc, which slows the progress of corrosion and improves the corrosion resistance. In addition, when an oxide is present in the plating layer, the oxide is excellent in adhesiveness with paint, and thus has excellent adhesiveness after coating.

Therefore, galvanized steel sheets containing oxides such as MoO ₂ , Mo ₂ O ₃ and WO ₂ , W ₂ O ₃ in the plating layer have excellent characteristics in the production of home appliances requiring corrosion resistance and paintability, but these oxides in the plating layer. Since it does not exist as an alloy phase with zinc, but exists as an oxide in a single phase, when spot welding is performed as in a vehicle body, oxides present in the surface layer of the coating layer interfere with the flow of electric current, thereby degrading weldability. There is a problem.
Zinc-cobalt alloy electroplating provides excellent corrosion resistance with cobalt content in the range of about 5-15 wt.%. However, due to the high price of cobalt, the price competitiveness is lower than that of conventional alloy plated steel sheets, so it is rarely actually produced as a product.

Therefore, in the present invention, the new alloy plated steel sheet and the plating solution composition which can be produced by the electroplating method with similar or better corrosion resistance than the existing zinc-nickel or zinc-iron alloy plating but low manufacturing cost and coating the same The purpose is to provide a coated steel sheet.

In order to achieve the above object, the present invention provides a plating solution composition for producing an electroplated steel sheet of zinc-based alloy excellent in corrosion resistance, but 0.1 to 3.0 wt% of cobalt and manganese to be coated on one or both surfaces of the steel sheet, respectively. And 0.05 to 5.0 wt%, and a plating solution composition composed of zinc, the remainder of which is prepared. If necessary, a plating solution composition further containing 5.0 wt% or less of chromium or molybdenum is additionally prepared. In addition, it is characterized by providing a plated steel sheet coated with the plating solution composition on a plated steel sheet, in particular a zinc-based alloy plated steel sheet excellent in corrosion resistance.

The reason for limiting the cobalt content of the plating layer to 0.1 to 3.0 wt% in the zinc-based alloy plated steel sheet of the present invention is that the cobalt content is less than 0.1 wt%, the effect of improving the corrosion resistance of the plating layer is less, and the cobalt content may exceed 3.0 wt%. In this case, the corrosion resistance is excellent, but it is easy to discolor due to easy oxide formation, which may increase the brittleness of the surface tissue, and above all, the manufacturing cost is excessively limited.

Manganese (Mn) vaccinated in the plating layer becomes an alloy phase with zinc (Zn) and cobalt (Co) to improve the corrosion resistance, but when the content is less than 0.05 wt%, the effect of improving the corrosion resistance is small, and when the content exceeds 5.0wt%, the powdering property of the plating layer This decreases. Therefore, Mn is limited to 0.05 to 5.0 wt%.

The alloy layer provides corrosion resistance similar to that of conventional zinc (Zn) -15% iron (Fe) alloys. In this composition, when chromium (Cr) or molybdenum (Mo) is added, there is an excellent corrosion resistance increase effect. However, excessive addition of expensive chromium or molybdenum may cause brittleness of the structure and increase the manufacturing cost. Therefore, the upper limit is limited to 5.0 wt%.

Cobalt added as a metal state during the corrosion of the plating layer forms a porous hydroxide film. Manganese, chromium and molybdenum, however, form a fine and dense passivation layer of complex hydroxides during corrosion. Therefore, in the zinc-based alloy layer of the present invention containing cobalt, a porous and dense passivation film is formed during corrosion, thereby suppressing excessive corrosion of zinc, but providing excellent corrosion resistance because iron provides sacrificial corrosion resistance to iron.

The plating solution composition for preparing the zinc-based alloy plating layer is basically a liquid in which Zn ²⁺ , Co ²⁺ and Mn ²⁺ ions are added in amounts of 30 to 90, 1 to 30, and 3 to 150 g / l, respectively. If necessary, at least one of Cr ³⁺ and Mo ⁶⁺ ions is added at 15 g / l or less, and electroplated at a pH of 0.5 to 2.5 and a temperature of 40 to 70 ^° C. The scope of the scope and the method of realization are described.

The concentration of zinc ions (Zn ²⁺ ) in the plating solution is limited to 30-90 g / l. When the zinc concentration is less than 30 g / l, the high-speed plating cannot be performed because the limit current density is low, and the manufacturing cost increases rapidly. When the concentration exceeds 90 g / l, the alloy ratio of cobalt (Co) and manganese (Mn) is lowered. Because it is difficult. In this plating solution, zinc ions may be supplied by dissolving zinc sulfate or by reaction of metal zinc with sulfuric acid.

The concentration of cobalt ions (Co ²⁺ ) in the plating solution is limited to 1 to 30 g / l. This is a range of concentrations suitable for the cobalt content of the alloy plating layer corresponds to 0.1 ~ 3.0 wt% management as it is. Cobalt ions can be supplied by dissolution of cobalt sulfate or cobalt hydroxide.

The concentration of manganese ions (Mn ²⁺ ) in the plating solution is limited to 3 ~ 150 g / l. This is a range of concentrations suitable for the range of manganese content of the alloy plating layer to correspond to 0.05 ~ 5.0 wt% management. Manganese ions may be supplied by dissolution of manganese sulfate salts or manganese hydroxides.

One or more ions of chromium ions (Cr ³⁺ ) and molybdenum ions (Mo ⁶⁺ ) ions are added to the plating solution, and the amount of addition is limited to 15 g / l or less per each ion, so the total is limited to 30 g / l or less. .

The concentration of chromium ion (Cr ³⁺ ) in the plating solution is limited to 15 g / l or less. This is a range of concentrations suitable for managing the chromium content of the alloy plating layer to 5.0 wt% or less. The chromium ion can be supplied because the trivalent chromium sulfate salt is dissolved or the powdered metal chromium is dissolved in sulfuric acid. In this case, in order to prevent olization of chromium, EDTA is added in a 1: 1 ratio with chromium ions to form a Cr-EDTA complex ion. In reality, it is difficult to accurately adjust the ratio of EDTA and Cr ³⁺ to 1: 1. However, if the coincidence is within the 5% margin, the chromium is fine.

The concentration of molybdenum ions (Mo ⁶⁺ ) in the plating solution is limited to 15 g / l or less. This is a range of concentrations suitable for managing the molybdenum content of the alloy plating layer to 5.0 wt% or less. Molybdenum ions are supplied as MoO ₄ ^- ions. This is produced when MoO ₃ is heated in aqueous solution with sodium or potassium hydroxide in a 1: 2 ratio.

The concentration of hydrogen ions in the plating solution affects the current efficiency of the cathode and the composition of the alloy. In the present invention, the pH is limited to the range of 0.5 to 2.5. If the pH is less than 0.5, the current efficiency of the cathode is too low to reduce the economic efficiency. If the pH is more than 2.5, metal hydroxide is vaccinated in the plating layer, thereby reducing the adhesion and weldability of the plating layer. The concentration of hydrogen ions can be adjusted by adding sulfuric acid, sodium hydroxide or potassium hydroxide.

The temperature of the plating liquid is limited to the range 40 to 70 ^o C. If the temperature is below 40 ^o C, the limit current density is reduced, making high-speed plating difficult. On the other hand, when it is higher than 70 ^° C., the electrodeposition ratio of cobalt, manganese and chromium decreases, making it difficult to manufacture a plating layer of an alloy having a composition in a prescribed range.

As described above, the electroplating by the plating solution formed in the limited range of the present invention is carried out the plating on the steel sheet in the range of 50 ~ 150A / dm ² cathode current density through the process of continuous electroplating alloy having excellent corrosion resistance of the present invention Plated steel sheet can be produced. Sodium sulfate or potassium sulfate may be complementarily added within the solubility range to increase the electrical conductivity to the plating solution described above.

The present invention will be described in more detail with reference to the following Examples.

(Example)

Table 1 After preparing zinc-based alloy electroplating solution to have the same composition as the left column, degreasing and pickling a common cold rolled steel plate having a thickness of 0.8 mm, plating, and then analyzing the chemical composition of the plating layer 1 column at the same time. Cr ³⁺ ions in the plating solution were complexed at the same molecular ratio as EDTA, Mo ⁶⁺ ions were added to MoO _3, and other metal ions were added as sulfates of the metals, respectively. PH of the plating solution was 1.5. At this time, the temperature of the plating solution was 60 ℃, the current density was 100A / dm ² , the plating deposition was 20g / m ² . Corrosion resistance was indicated by the red blue color development time (unit: hours (hr.)) By 5% brine spray test at 35 ℃ temperature as described below the table below.

TABLE 1

Table 1 is shown in Comparative Examples 1 to 5 and Inventive Examples 6 to 14 that do not correspond to the present invention. Comparative Examples 1 and 2 contained 0.6 wt% and 5.2 wt% of the cobalt of the metal in the alloy plating layer plated in the plating solution in which 12 g / l and 30 g / l of cobalt ions were added in the zinc plating solution, respectively. Corrosion resistance can be seen that the corrosion resistance increases as the content of cobalt increases. Comparative Examples 3 to 5 show chromium, which is added to the alloy plating layer when 12 g / l of cobalt ions are added and 15 g / l, 15 g / l, and 3 g / l of chromium, molybdenum and manganese ions, respectively, are added to the zinc-based plating solution. Molybdenum and manganese precipitated 0.1 wt%, 0.8 wt% and 0.01 wt%, respectively. In the alloy plating layers of these comparative examples, it was found that the red blue generation time was 152 hours, 205 hours, and 154 hours, respectively, and did not provide very high corrosion resistance.

Inventive Examples 6 to 7 show that 0.7 wt% of cobalt is added to the alloy plating layer when 12 g / l of cobalt ions are added and 30 g / l, 75 g / l, and 150 g / l of manganese ions, respectively, in the zinc plating solution. , 1.1 wt% and 1.4 wt% were precipitated and manganese was precipitated at 0.1 wt%, 2.3 wt% and 4.6 wt%, respectively. It can be seen that the red blue color development time in these alloy plating layers is 250 hours, 298 hours and 303 hours, respectively, to provide very high corrosion resistance. It can be seen that as the manganese increases, manganese in the plating layer plays a role of increasing the vacancy ratio of cobalt.

Inventive Examples 9 to 11 are alloys in the case where 12 g / l and 75 g / l of cobalt and manganese ions are added and 1.0 g / l, 7.5 g / l and 15 g / l, respectively, in a zinc plating solution. Cobalt precipitated 0.7 wt%, 1.2 wt% and 1.5 wt% in the plating layer, and 2.3 wt% of manganese and 0.1 wt%, 2.2 wt% and 4.3 wt% of chromium, respectively. It can be seen that the red blue color development time in these alloy plating layers is 259 hours, 307 hours, and 311 hours, respectively, to provide very high corrosion resistance. This is believed to be due to an increase in the content of cobalt, manganese and chromium in the plating layer as manganese is added. In addition, it can be seen that the increase in manganese ions in the plating solution increases the vacancy ratio of cobalt and chromium.

Inventive Examples 12 to 14 are alloys when 12 g / l and 75 g / l of cobalt and manganese ions are added and 1.0 g / l, 7.5 g / l and 15 g / l of molybdenum ions, respectively, in a zinc plating solution. Cobalt precipitated 0.8 wt%, 1.2 wt% and 1.7 wt% in the plating layer, and 2.3 wt% of manganese and 0.2 wt%, 2.5 wt% and 4.6 wt% of manganese, respectively. In addition, it was found that the red blue generation time in these alloy plating layers was very high corrosion resistance of 261 hours, 315 hours and 316 hours, respectively. This is believed to be due to an increase in the content of cobalt, manganese and molybdenum in the plating layer. In addition, it can be seen that the increase in manganese ions in the plating solution increases the vacancy ratio of cobalt and molybdenum.

It can be seen from the above results that the increase of manganese ions in the plating solution causes an increase in the vacancy ratio of cobalt, chromium and molybdenum. The reason for this is that when manganese ions coexist, zinc-based (water) oxides containing these ions and manganese are preferentially formed and reduced in the surface layer of the plating layer. In particular, it can be seen that the corrosion resistance of the plating layer is increased when the manganese is contained in the plating layer and at least one of cobalt, chromium, and molybdenum is contained.

As described above, the content of Zn ²⁺ , Co ²⁺ and Mn ²⁺ ions in the plating solution is 30 to 90 g / l, 1 to 30 g / l and 3 to 150 g / l, respectively. Here, a steel plate coated with a zinc-based alloy layer having excellent corrosion resistance may be manufactured by a plating solution in which one ion of Cr ³⁺ and Mo ⁶⁺ ions is added with 0 to 15 g / l.

Claims (4)

delete In the plating solution composition for zinc-based alloy electroplating steel sheet to be treated with electroplating while maintaining a pH of 0.5 ~ 2.5, temperature 40 ℃ ~ 70 ℃, Plating solution composition coated on the surface of the zinc-based alloy plated steel sheet Zn ²⁺ ion content 30 ~ 90 g / l Co ²⁺ ion content 1 ~ 30 g / l Mn ²⁺ ion content 3 ~ 150 g / l At least one of Cr ²⁺ and Mo ⁶⁺ ions is added at 15 g / l or less; Plating solution composition for zinc-based alloy electroplating steel sheet composed of zinc (Zn) plating solution delete The zinc-based alloy electroplated steel sheet coated with the plating solution composition for zinc-based alloy electroplated steel sheet described in claim 2 has a surface plating layer. Cobalt (Co): 0.1-30 wt.% Manganese (Mn): 0.05-5.0 wt.% Zinc-based alloy electroplating with excellent corrosion resistance, characterized in that it contains less than 5.0 wt.% Of at least one element of chromium (Cr) and molybdenum (Mo), and the rest is composed of an alloy layer composed of zinc (Zn). Grater