KR20040059122A - Zinc-Cobalt-Tungsten Alloy Electroplating Steel Sheet Having Superior Whiteness and Corrosion Resistance and Preparing Method Thereof - Google Patents

Abstract

PURPOSE: A Zn-Co-W alloy electroplated steel sheet the surface of which has superior whiteness and corrosion resistance, and on which double plating layers are formed is provided, and a preparation method of the Zn-Co-W alloy electroplated steel sheet having superior whiteness and corrosion resistance by controlling tungsten content of the plating layers is provided. CONSTITUTION: The Zn-Co-W alloy electroplated steel sheet comprises a lower plating layer comprising 0.1 to 3 wt.% of cobalt as metal cobalt plated on steel sheet, 0.1 to 2 wt.% of tungsten as metal tungsten plated on the steel sheet and a balance of zinc and having the minimum plating adhesion amount of 5 g/m¬2; and an upper plating layer comprising 0.1 to 3 wt.% of cobalt as metal cobalt plated on the lower plating layer, less than 0.08 wt.% of tungsten as metal tungsten plated on the lower plating layer and a balance of zinc and having a plating adhesion amount of 0.5 to 2 g/m¬2. The preparation method of the Zn-Co-W alloy plated steel sheet comprises a step of forming a lower plating layer on a base steel sheet by plating a plating solution on the steel sheet at the minimum plating current density of 20 A/dm¬2 so that 5 g/m¬2 of the minimum plating adhesion amount is maintained, wherein the plating solution has pH of 3 to 6 and comprises 0.1 to 4 g/L of tungsten selected from the group consisting of 60 to 200 g/L of zinc chloride, 0.1 to 6 g/L of cobalt chloride, sodium tungstate, ammonium tungstate and potassium tungstate, 0.5 to 10 g/L of citric acid selected from the group consisting of sodium citrate, ammonium citrate and potassium citrate, 30 to 400 g/L of at least one or more of electroplating additives selected from the group consisting of potassium chloride, ammonium chloride and sodium chloride and 0.1 to 2 ml/L of polyethylene glycol based additive having a molecular weight ranging from 100 to 2000; and a step of forming an upper plating layer by plating the plating solution on the lower plating layer at a plating current density of 15 A/dm¬2 or less so that 0.5 to 2 g/m¬2 of a plating adhesion amount is maintained.

Description

Zinc-Cobalt-Tungsten Alloy Electroplating Steel Sheet Having Superior Whiteness and Corrosion Resistance and Preparing Method Thereof}

The present invention relates to a zinc-cobalt-tungsten alloy electroplated steel sheet having excellent whiteness and corrosion resistance, and to a method of manufacturing the same. More specifically, zinc-cobalt having excellent whiteness and corrosion resistance on a surface of a steel plate plated with a double layer by controlling the content of tungsten The present invention relates to a cobalt-tungsten alloy electroplated steel sheet and a method of manufacturing the same.

Galvanized steel sheet of the surface treatment steel sheet for rust prevention has excellent corrosion resistance compared to the steel sheet is widely used as a material for automobiles, home appliances and building materials. Particularly, in the case of galvanized steel sheet, the surface color of the steel sheet is bright and widely used for the base plate of the steel plate. Anti-fingerprint steel sheet is a steel plate coated with a colorless resin on a galvanized steel sheet, which is used for inner case of home appliances without coating because it is anti-fingerprint. Since the door steel plate is used without painting, the color of the steel plate determines the color of the home appliance, so the home appliance manufacturer prefers a bright color.

Plating deposition amount of the electro-galvanized steel sheet used for the base steel plate is generally used to about 20g / m ² , and even this coating deposition amount is given sufficient corrosion resistance to home appliances used indoors. However, in recent years, according to the trend of advanced home appliances, corrosion resistance is required to be improved. In particular, in the case of a washing machine for boiling, the corrosion is much faster due to the temperature increase of the product.

In order to improve the corrosion resistance of the steel door, there is a method of increasing the plating deposition amount or increasing the resin coating amount. However, if the plating deposition amount is increased, the unit of zinc increases as well as the plating speed becomes slow during the plating operation, which greatly reduces the productivity. In the case of increasing the amount of resin coating, there is a problem that spot welding is difficult in the assembly process of home appliances due to low electrical conductivity. Therefore, in order to solve this problem, a new plated steel sheet capable of obtaining high corrosion resistance by thin plating is required.

Zinc-cobalt-tungsten alloy plated steel sheet is used as the steel plate developed in order to meet this demand. The zinc-cobalt-tungsten alloy plated steel sheet is an alloy plated steel sheet containing 0.1 to 3 wt% of cobalt and 0.1 to 2 wt% of tungsten in the galvanized layer.Tungsten forms an oxide on the surface of the steel sheet in a corrosive environment, thereby preventing corrosion. Because of its excellent characteristics, it is advantageous to ensure sufficient corrosion resistance even with thin plating. In addition, it is possible to secure sufficient corrosion resistance even with thin plating, so that the cost of plating solution is low and the plating speed is fast, so the productivity is high and the production cost of plating steel sheet is low, so it can be useful for automobile body and home appliances requiring high corrosion resistance. have.

However, the zinc-cobalt-tungsten alloy plated steel sheet has no problem when it is used for painting because the color of the steel sheet is dark, but the color of the steel plate is used when the base plate is coated with a transparent resin coated on the plated steel sheet. There is a problem with this darkening.

As a method for increasing the surface whiteness while maintaining the corrosion resistance of the zinc-cobalt-tungsten alloy plated steel sheet, pure zinc is deposited on the zinc-cobalt-tungsten alloy plated steel sheet in a manner similar to that of Japanese Patent Laid-Open Publication No. 59-25992. When plated, it is possible to produce a steel sheet having a surface color similar to that of a pure galvanized steel sheet. However, since the two-layer plating method has to be carried out in two stages of plating, the plating solution has to be managed twice, and the plating equipment has to be separated in two stages.

On the other hand, the color of the pure galvanized steel sheet is light grayish white, but the zinc-cobalt-tungsten alloy plated steel sheet is black gray. The color of the zinc-cobalt-tungsten alloy plated steel sheet is almost independent of the cobalt content in the cobalt of 3wt% or less, and when tungsten is added more than 0.08wt%, the color becomes black gray and the whiteness gradually decreases as the amount of tungsten is increased. Therefore, when vacancy is less than 0.08 wt% of tungsten in the plating layer, a steel sheet having excellent whiteness may be manufactured, but in this case, a problem of inferior corrosion resistance occurs.

Accordingly, an object of the present invention is to provide a zinc-cobalt-tungsten alloy plated steel sheet excellent in whiteness and corrosion resistance of a steel plate surface having a double plating layer.

Another object of the present invention is to provide a method for producing a zinc-cobalt-tungsten alloy plated steel sheet having excellent whiteness and corrosion resistance of the surface of the steel sheet by plating by adjusting the tungsten content of the lower layer and the upper plating layer.

According to one aspect of the invention,

A lower plated layer having a cobalt content of 0.1 to 3 wt% with a metal cobalt plated on a steel plate, a tungsten content of 0.1 to 2 wt% with a metal tungsten, and a balance zinc, and a plating deposition amount of at least 5 g / m ² ; And

An upper plating layer having a cobalt content of 0.1 to 3wt%, a metal tungsten content of less than 0.08wt% and a balance zinc plated on the lower plating layer, and a plating deposition amount of 0.5 to 2g / m ² ;

A zinc-cobalt-tungsten alloy plated steel sheet is provided.

According to another aspect of the present invention,

Zinc chloride 60-200 g / l, cobalt chloride 0.1-6 g / l, tungsten 0.1-4 g / l selected from the group consisting of sodium tungstate, ammonium tungstate or potassium tungstate, sodium citrate, ammonium citrate and potassium citrate At least one conduction aid selected from the group consisting of 0.5-10 g / l citric acid, potassium chloride, ammonium chloride and sodium chloride, selected from the group consisting of: and polyethylene glycol-based additives 0.1-2 ml / l, having a molecular weight ranging from 100-2000. If it is made, including, the plating solution having a pH range of 3 ~ 6 at a plating current density of at least 20A / dm ² plated on the steel sheet to form a lower plating layer on the steel sheet so that the plating adhesion amount to at least 5g / m ² ; And

Plating the plating solution on the lower plating layer at a plating current density of 15 A / dm ² or less to form an upper plating layer with a plating deposition amount of 0.5 to 2 g / m ² ;

Provided is a method for producing a zinc-cobalt-tungsten alloy plated steel sheet comprising a.

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

Usually, in the continuous electroplating equipment, the plating bath is composed of several, and the steel sheet is processed so as to be plated with the plating amount of the target deposition amount while continuously passing the several plating baths. At this time, the plating bath is plated according to the amount of electricity that is energized, and the final plating amount is determined by the amount of electricity that is supplied to the entire plating bath. Therefore, the amount of electricity supplied to each plating bath can be controlled differently for each plating bath. If the current is adjusted for each plating bath, the plating operation can be performed with different current density for each plating bath.

In the present invention, by appropriately adjusting the plating operation conditions by using the same plating solution to specifically control the tungsten content of the lower plating layer and the upper plating layer is provided a steel sheet which is excellent in corrosion resistance and at the same time ensures excellent whiteness.

That is, tungsten content in the plating layer is adjusted according to the current density applied when electroplating in the zinc-cobalt-tungsten alloy plating solution. In particular, the content of tungsten in the plating layer is very low at the current density of 15 A / dm ² or less.

According to the present invention, in plating an alloy plating layer of zinc, cobalt and tungsten on a resin steel plate, the lower layer of the plating layer is plated to have an alloy composition range excellent in corrosion resistance and weldability, and the upper portion has an alloy composition range having excellent whiteness on the surface. It is formed of two layers of plating layers. The intended physical properties of each of the double plating layers are achieved by controlling the content of tungsten vaccinated in each plating layer.

That is, the content of tungsten in the lower plating layer having a plating deposition amount of at least 5 g / m2 is 0.1-2 wt% with metal tungsten and the content of tungsten in the upper plating layer plated with the plating deposition amount of 0.5-2 g / m ² is 0.08 with metal tungsten. less than wt%.

The lower plating layer is formed with a plating deposition amount of at least 5 g / m ² , and a tungsten content of 0.1-2 wt% is ensured with tungsten metal in the lower plating layer to exhibit sufficient corrosion resistance. The upper plating layer has a plating deposition amount of 0.5-2 g / m ² and the tungsten content in the plating layer is less than 0.08 wt% to secure whiteness. In addition, if the adhesion amount of the upper plating layer having a tungsten content of less than 0.08wt% is less than 0.5g / m ^2, the color of the lower plating layer is transferred to the upper side, and thus the whiteness is not improved, and if it exceeds 2g / m ² , the corrosion resistance is lowered. It is preferable to limit the deposition amount to 0.5 to 2 g / m ² .

If the cobalt content in the lower plating layer and the upper plating layer is less than 0.1 wt% of metal cobalt, powdering property of the plating layer may be poor, and thus the plating layer may be dropped during processing, and the effect of improving corrosion resistance is weak. If the cobalt content exceeds 3wt% with metal cobalt, it is uneconomical because the cost is significantly increased compared to the increased corrosion resistance. Therefore, it is preferable to make the cobalt content in the lower plating layer and the upper plating layer to 0.1 to 3wt% with metal cobalt.

Hereinafter, the plating solution used in the production of the zinc-cobalt-tungsten alloy plated steel sheet will be described. The plating solution contains 60 to 200 g / l of zinc chloride. If zinc chloride is less than 60 g / l, high-speed plating is not possible by the continuous plating method, and if it exceeds 200 g / l, solubility of zinc is exceeded, and zinc is precipitated as a zinc salt.

The content of cobalt chloride in the plating solution is 0.1 to 6 g / l. Cobalt chloride must be at least 0.1g / l in the plating solution to ensure stable cobalt content of 0.1% or more in the plating layer, and the reason for limiting the upper limit of cobalt chloride to 6g / l is 0.1 ~ 3wt% of the cobalt content in the plating layer. This is because the concentration of cobalt ions to be obtained is 6 g / l or less.

The content of tungsten in the plating solution is preferably 0.1 ~ 4g / l. Tungsten content in the plating solution must be at least 0.1g / l to ensure stable tungsten content of 0.1% or more in the plating layer, and the reason for limiting the upper limit of tungsten to 5g / l is 0.1 ~ 2wt% This is because the concentration of tungsten to obtain 5g / l or less is sufficient. As tungsten, sodium tungstate, ammonium tungstate or potassium tungstate is added alone or in combination.

Citric acid in the plating solution prevents tungstate ions from colliding with tungsten oxide in the colloidal state. If the citric acid content is less than 0.5g / l, tungsten oxide in the colloidal state will precipitate over time. The upper limit of the citric acid content is limited to 10g / l, although there is no problem in plating even if the citric acid concentration exceeds 10g / l, but in the tungsten content of 0.1 ~ 4g / l in the plating solution, the colloid is less than 10g / l. It is because it is enough for the tungsten oxide precipitation prevention action of a state.

As citric acid, sodium citrate, ammonium citrate or potassium citrate is added alone or in combination.

If citric acid is not added to the plating solution, or less than 0.5g / l, tungsten in the plating solution is in the state of tungsten oxide, and is present in the oxide state by physical embedding or chemical adsorption in the zinc plating layer during the plating process. .

In addition, a conductive aid is added to improve the electrical conductivity of the plating solution. Conductivity aids may be used alone or in combination with potassium chloride, ammonium chloride or sodium chloride. In the continuous plating equipment for plating with high current density, it is possible to produce products stably only when the concentration of the conductive assistant is added at least 30g / l. When the concentration of the conductive assistant exceeds 400g / l, the temperature of the plating solution is low. Since there is a risk of precipitation, it is preferable to use a conductive aid 30 ~ 400g / l.

The polyethylene glycol additive in the plating solution is added at 0.1 to 2 ml / l for the purpose of improving the flatness of the plating layer. If the content is less than 0.1ml / l, the plating layer is rough, and if the plating layer is rough, there is a problem of deterioration after coating. Even if the content of polyethylene glycol exceeds 2ml / l, there is no problem in the quality of the plating operation and plated steel sheet, but it is preferable to limit the upper limit of polyethylene glycol in consideration of economical efficiency because sufficient smoothness is achieved even if only 2ml / l.

The plating solution is preferably in the pH range of 3-6. This is because when the pH plating solution is less than pH 3, the plating efficiency is low, and when the pH plating solution is higher than pH 6, zinc ions and cobalt ions may precipitate as hydroxides.

After the plating solution prepared as described above is prepared, an upper plating layer is formed on the lower plating layer and the lower plating layer on the steel sheet using the plating solution.

The lower plating layer is plated with a current density of 20 A / dm ² or more so that the plating deposition amount is at least 5 g / m ² and the upper plating layer is made with a current density of 15 A / dm ² or less so that the plating deposition amount is 0.5-2 g / m ² . The current density applied in the plating of the lower plating layer should be at least 20A / dm ² to ensure a plating deposition amount of at least 5 g / m ² in the lower plating layer.

Tungsten metal content of 0.1-2 wt% is secured by the tungsten metal in the lower plating layer, and exhibits sufficient corrosion resistance. The lower plating layer serves to impart corrosion resistance, and the upper limit of the plating deposition amount is not particularly limited, and is generally adjustable according to the requirements of the steel sheet. However, in consideration of corrosion resistance and economical efficiency, it may be plated so that the coating weight of up to about 60g / m ² . The current density is also appropriately adjusted according to the plating deposition amount, and increases as the plating deposition amount increases, but is plated at the plating deposition amount in the above range at 20-120 A / dm ² .

The current density for plating the upper plating layer should be plated at 15 A / dm ² or less, so that the content of tungsten in the plating layer is controlled to less than 0.08 wt%, thereby forming the upper plating layer at a current density of less than 15 A / dm ² . The current density is adjusted to control the plating deposition amount and tungsten content of the upper plating layer, and the lower limit is not particularly limited, but may be plated to be at least about 5 A / dm ² to the deposition amount. If the tungsten content is less than 0.08wt% the coating weight of the upper plated layer 0.5g / m ² or less when the color of the lower coating layer is transferred to the upper part there is no increase whiteness effect, exceeds 2g / m ² The coating weight of the upper plated layer with a degraded corrosion resistance It is preferable to limit to 0.5-2 g / m <^2> .

By plating as described above, a plating layer having excellent corrosion resistance and weldability, which is composed of 0.1 to 3 wt% of Co, 0.1 to 2 wt% of W and residual zinc, is formed as the lower plating layer, and the upper plating layer is 0.08 wt% of tungsten. It is composed of a zinc-cobalt-tungsten alloy electroplating steel sheet composed of less than a plating layer and excellent in corrosion resistance and surface whiteness.

In addition, the reason for limiting the tungsten content of the upper plating layer to less than 0.08wt% in the present invention is that when the tungsten content is more than 0.08wt%, the whiteness of the steel sheet is reduced.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples do not limit the present invention.

Example

After the zinc-cobalt-tungsten alloy electroplating solution was prepared to have a composition as shown in Table 1, the lower plating layer and the upper plating layer were plated on a cold rolled steel sheet having a thickness of 0.8 mm by using the same. Then, the cobalt and tungsten content in each plating layer was quantitatively analyzed and the results are shown in Table 2 below. Plating was carried out using a carousel continuous electroplating facility in which 11 plating baths were arranged in series, and the top plating was plated in the last 11 plating baths.

Zinc and cobalt in the plating solution were added in the form of chloride, tungsten in the form of sodium tungstate, and citric acid in the form of sodium citrate. 250 g / l potassium chloride and polyethylene glycol (PEG) were charged as a conduction aid, and the pH of the plating solution was set at 5. At this time, the temperature of the plating solution was 60 ° C., and the total plating deposition amount was 20 g / m ² .

The corrosion resistance of the plated layer was evaluated by the salt water test, and the time until the red blue color occurred on the surface of the steel sheet was measured, and the whiteness of the plated layer was measured using a color difference meter.

As shown in Tables 1 and 2, Inventive Examples 1 to 8 had a cobalt content of 0.11 to 2.97 wt% and a tungsten content of 0.14 to 1.98 wt% in the lower plating layer, and a cobalt content of 0.08 to 2.32 wt% in the upper plating layer. , Tungsten content is 0.01 ~ 0.07wt%, red blue red color development time is 154 hours or more, excellent corrosion resistance, and also the degree of whiteness of the plated steel sheet is 83 or more.

The zinc-plated steel plate plated with the plating solution of Comparative Example 1, in which only zinc chloride and potassium chloride were added, had excellent whiteness of 87, but was inferior in corrosion resistance with a red blue anti-rusting time of 25 hours.

In Comparative Example 2 plated with the same current density of the lower plating bath and the upper plating bath, a large amount of tungsten was vaccinated on the surface of the upper plating layer, so the corrosion resistance was excellent, but the whiteness was low.

In the case of Comparative Example 3 in which the plating current density applied when forming the upper plating layer was out of the range of the present invention, a large amount of tungsten was vaccinated in the upper plating to show poor whiteness.

In Comparative Example 4, where the adhesion amount of the upper plating layer was small, the color of the lower plating layer was transferred, so that the whiteness improvement effect was weak.

In Comparative Example 5 in which the plating current density applied at the time of forming the lower plating layer was lower than the limited range of the present invention, a small amount of tungsten was vaccinated in the plating layer, indicating poor corrosion resistance.

In the case of Comparative Example 6 in which the plating deposition amount of the upper plating layer exceeded the range defined in the present invention, poor corrosion resistance was shown.

The zinc-cobalt-tungsten alloy plated steel sheet of the present invention having a plating layer formed of a lower plating layer and an upper plating layer optimized to have a different metal content has excellent corrosion resistance and whiteness.

Claims (2)

A lower plated layer having a cobalt content of 0.1 to 3 wt% with a metal cobalt plated on a steel plate, a tungsten content of 0.1 to 2 wt% with a metal tungsten, and a balance zinc, and a plating deposition amount of at least 5 g / m ² ; And An upper plating layer having a cobalt content of 0.1 to 3 wt% and a tungsten content of less than 0.08 wt% and residual zinc plated on the lower plating layer, and a plating deposition amount of 0.5 to 2 g / m ² ; Zinc-cobalt-tungsten alloy plated steel sheet. Zinc chloride 60-200 g / l, cobalt chloride 0.1-6 g / l, tungsten 0.1-4 g / l selected from the group consisting of sodium tungstate, ammonium tungstate or potassium tungstate, sodium citrate, ammonium citrate and potassium citrate At least one conduction aid selected from the group consisting of 0.5-10 g / l citric acid selected from the group consisting of potassium chloride, ammonium chloride and sodium chloride, and 0.1-2 ml / l polyethylene glycol additive with a molecular weight ranging from 100-2000 If it is made, including, the plating solution having a pH range of 3 ~ 6 at a plating current density of at least 20A / dm ² plated on the steel sheet to form a lower plating layer on the steel sheet so that the plating adhesion amount to at least 5g / m ² ; And Plating the plating solution on the lower plating layer at a plating current density of 15 A / dm ² or less to form an upper plating layer with a plating deposition amount of 0.5 to 2 g / m ² ; Zinc-cobalt-tungsten alloy plated steel sheet production method comprising a.