JPH1068063A - Zinc-magnesium series plated steel sheet excellent in blackening treatability and production of black zinc-magnesium series plated steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a Zn-Mg series plated steel sheet showing a black surface high in a blackening degree and free from deterioration in appearance. SOLUTION: This Zn-Mg series plated steel sheet has Zn-Mg series plating layers with a two layer structure in which a Zn-Mg layer contg. <=0.5% Mg and a Zn-Mg layer contg. 2 to 18% Mg are successively formed on the surface of a base steel respectively as a primary layer and a secondary layer or with a three layer structure in which <=0.5% Mg as a primary layer, 2 to 6% Mg as a secondary layer and a Zn-Mg layer contg. 9 to 18% Mg as a third layer are successively formed on the surface of a base steel. In the case a Zn-Fe alloy layer or a Zn-Fe-Mg alloy layer having <=0.5μm thickness is formed on the boundary between the base steel and the primary layer, the plating layer excellent in adhesion can be obtd. By subjecting it to contacting treatment in an Ni ion-contg. zinc phosphate treating soln. after vapor deposition plating, blackening treated coating film can be formed on the surface of the plating layer. Since it has self-restoring operation, even if there are flaws, the black surface excellent in designing properties can be maintained over a long period.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Zn-Mg-based plated steel sheet suitable for providing a black surface having excellent design properties and a method for treating black.

[0002]

2. Description of the Related Art In order to finish a black surface excellent in design in the fields of home electric appliances, OA equipment, construction, etc., a steel sheet is processed into a product shape and then painted to give a black color tone. Often. Further, in order to reduce costs by omitting the coating process, a steel plate subjected to black coating or black processing may be processed. As the black-treated steel sheet, Zn
A steel sheet obtained by immersing a Ni-plated steel sheet, a Zn-Co-plated steel sheet, or the like in an aqueous solution containing nitrate ions, sulfate ions, phosphate ions, and the like, and an electrolytically treated steel sheet are known (Japanese Patent Application Laid-Open No. 61-143594, JP-A-62-290880
Reference).

On the other hand, as a coated steel sheet exhibiting an excellent anticorrosion action, a Zn—Mg-based coated steel sheet manufactured by a vapor deposition method has been developed. For example, Japanese Patent Application Laid-Open No. 64-17853 discloses a Zn-M containing 0.5 to 40% by weight of Mg.
The formation of a g alloy plating layer is introduced. Further, between the Zn—Mg alloy plating layer and the base steel, Zn, N
Japanese Patent Application Laid-Open No. 2-141588 discloses that the presence of an intermediate layer of i, Cu, Mg, Al, Fe, Co, Ti, etc. improves the adhesion and workability of a plating layer. The present inventors have conducted various investigations and studies on the Zn—Mg-based plated steel sheet. In the process, a high Mg concentration layer is formed at the center of the plating layer, and a low Mg concentration layer is formed above and below the high Mg concentration layer.
It has been found that when a concentration layer is formed, powdering resistance, corrosion resistance, spot weldability, adhesion, discoloration resistance and the like are improved, and this is introduced in Japanese Patent Application Laid-Open No. 8-81761.

[0004]

SUMMARY OF THE INVENTION Black-treated Zn-
Ni-plated steel sheets are sufficient in terms of blackness, but the plating layers are hard and brittle. Therefore, during press forming, bending, or the like, the plating layer may be cracked or may be crushed like powdering and peeled off together with the black processing film. The portion where the powdering occurs has a metal-colored surface without a black-treated film, and deteriorates the appearance as a black-treated surface. In the case of a Zn—Ni plated steel sheet, the potential of the exposed portion of the base steel sheet caused by cracking of the plating layer, powdering, and the like shifts to a higher value than the steel sheet when corrosion starts, and the sacrificial corrosion prevention action is lost. As a result, red rust occurs even in a weakly corrosive environment, and the appearance which is regarded as the most important is extremely deteriorated. Similarly, the cut end face also has little sacrificial anticorrosive action, so that red rust is easily generated and the appearance is deteriorated.

[0005] On the other hand, a black-treated Zn—Co plated steel sheet lacks blackness. Since corrosion resistance is also poor, white rust is likely to occur in a corrosive environment starting from pinholes or flaws in the black coating film. The generation of white rust causes the appearance to deteriorate. When the corrosive environment becomes severe, red rust is generated in a relatively short time. Even at the cut end surface, the corrosion reaction is promoted due to the poor corrosion resistance. A disadvantage of the black-treated Zn—Co plated steel sheet is that the appearance tends to deteriorate due to the generation of such white rust and red rust. Moreover,
In a conventional plated steel sheet, when a flaw is formed in a black-treated film, a flaw having a metallic luster is conspicuous in contrast to a black surface part, and the appearance is significantly deteriorated.

[0006] Further, in the conventional black treatment method in which zinc-plated treatment is applied to a plated steel sheet, it takes several seconds using a surface conditioner.
Processing for several tens of seconds is required. Therefore, an extra treatment tank is required, and the treatment takes a long time, which is inconvenient for treating a plated steel sheet that continuously runs at a high speed. The present invention has been devised to solve such a problem. By utilizing the properties of a Zn—Mg-based plating layer for black processing, black processing can be performed in a short time, and powdering and the like can be performed. It is an object of the present invention to provide a black-treated Zn—Mg-based steel sheet which is excellent in corrosion resistance without causing cracks and recovers blackness by a self-repairing action even if a flaw occurs in a plating layer.

[0007]

In order to achieve the object, a Zn-Mg plated steel sheet according to the present invention has a Zn-Mg layer containing 0.5% by weight or less of Mg and a Mg-containing layer having a Mg content of 2% or less.
18 wt% Zn-Mg layer as a first layer and a second layer formed on a base steel sequentially as a second layer, Zn-Mg layer having a Mg content of 0.5 wt% or less as a first layer A Zn-Mg layer having a Mg content of 2 to 6% by weight as a second layer,
As the third layer, Zn-Mg having a Mg content of 9 to 18% by weight
Zn-Mg with a three-layer structure in which layers are sequentially formed on a base steel
Has a system plating layer. At the interface between the base steel and the first layer, a Zn-Fe alloy layer or Zn-Fe-
When the Mg alloy layer is formed, a plating layer having excellent adhesion can be obtained.

[0008] The Zn-Mg-based plating layer having such a multilayer structure is formed by sequentially depositing Zn and Mg under the condition that the temperature of the steel sheet after the deposition is 240 to 370 ° C. After the vapor deposition plating, a black treatment film is formed on the plating layer surface by performing a contact treatment with a zinc phosphate treatment solution containing Ni ions. As the Ni-ion-containing zinc phosphate treatment liquid, the total oxygen content expressed by titration with a 1N NaOH aqueous solution required to neutralize 100 ml with phenolphthalein as an indicator at a Ni ion concentration of 3 to 12 g / l. Is preferably adjusted to 2 to 30 ml. Zinc phosphate treated plated steel sheet has N
A black treatment film having an i content of 3% by weight or more is formed. After forming the black treatment film, a chromate treatment or a clear coating can be further applied. The clear coating film may be either a transparent or black organic coating film or an inorganic coating film.

[0009]

According to the present invention, the two-layer structure shown in FIG. 1 or FIG. 3 is used to impart good black processing properties and prevent the brittleness of the plated layer after the processing and the generation of red rust and white rust in the exposed portions of the base steel. The Zn-Mg plating layer having the three-layer structure of (1) is formed on the surface of the steel sheet. Regardless of the plating layer, since the surface layer contains a large amount of highly reactive Mg, the blackening treatment time is reduced. Further, a soft and ductile Zn—Mg layer having a low Mg concentration is formed under the surface layer containing a large amount of Mg, so that powdering is suppressed during press forming, bending, and the like. The Zn—Mg layer has a lower potential than a steel plate, and the potential is maintained even when corrosion occurs. Therefore, generation of red rust is suppressed even in a portion where the base steel is exposed, such as a flawed portion, a cut end surface, and the like, and deterioration of the appearance due to red rust is prevented. Further, the Zn-Mg layer is excellent in corrosion resistance and hardly generates white rust, so that appearance deterioration due to white rust is also prevented.

When a zinc phosphate treatment solution containing Ni ions is used for the blackening treatment of the Zn-Mg-based plated steel sheet, Ni enters the treated film as an oxide, and the blackness of the formed film increases. The black treated film also differs from the conventional black treated steel sheet in that it exhibits a self-healing action. In other words, even if the black coating film is scratched due to scratches or the like and the underlying plating layer is exposed, the surface Zn
-The Mg layer is oxidized by the moisture in the air, and the flaws gradually become black. As a result, the black appearance is restored. On the other hand, in the conventional black-processed steel sheet, the deteriorated appearance is maintained while the flaws have a metallic luster, and in some cases, the appearance is significantly impaired by corrosion.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first layer (FIG. 1) of a plating layer having a two-layer structure is a Zn-Mg layer having an action of preventing powdering and having a Mg concentration regulated to 0.5% by weight or less. The second layer serving as a surface layer is a Zn—Mg layer in which the Mg concentration is regulated in the range of 2 to 18% by weight in order to increase blackness and shorten the processing time in the processing using the phosphate-based processing solution. And If the Mg concentration is less than 2% by weight, the reactivity is low and the processing time is long. Conversely, Mg exceeding 18% by weight
When the concentration is high, the reaction becomes intense, and the formed zinc phosphate treated film becomes porous and poor in adhesion. Mg concentration 2
The Zn-Mg layer of 18% by weight is relatively hard, and a Zn-Mg layer having a Mg concentration of 0.5% by weight or less is formed under the Zn-Mg layer as a first layer. The first layer is soft and ductile,
It acts as an intermediate layer to absorb the difference in the amount of deformation between the steel sheet that deforms during forming and the second layer that hardly deforms. As a result, the occurrence of powdering during press forming, bending forming, and the like is suppressed.

When this Zn-Mg-based plated steel sheet having a two-layer structure is treated with a zinc phosphate treatment solution containing Ni ions, a zinc phosphate treatment film containing 3% by weight or more of Ni is formed as shown in FIG. A black Zn-Mg plated steel sheet is obtained. Ni is contained in the zinc phosphate-treated film in the form of an oxide. When the amount is 3% by weight or more, high blackness is obtained. In order to prevent powdering, flaking, and the like, a three-layer Zn-Mg-based plated steel sheet shown in FIG. 3 may be used. In this case, Z having a Mg concentration of 2 to 6% by weight is used.
The n-Mg layer is a second layer, and the Mg concentration is 9-18% by weight.
The Mg layer is the third layer. The second layer further reduces the rate of change of the amount of deformation that changes between the base steel and the third layer during molding, and improves powdering resistance. When a Zn-Mg-based plated steel sheet having a three-layer structure is treated with a zinc phosphate treatment solution containing Ni ions, black Zn having a zinc phosphate treatment film containing 3% by weight or more of Ni is formed as shown in FIG. -A Mg-plated steel sheet is obtained.

Further, a Zn—Fe alloy layer or a Zn—Mg layer having a thickness of 0.5 μm or less is formed at the interface between the base steel and the Zn—Mg plating layer.
When forming the -Fe-Mg alloy layer, the adhesion of the plating layer is enhanced, and the effect of suppressing the occurrence of powdering is further increased. However, the Zn—Fe alloy layer or the Zn—Fe—
If the thickness of the Mg alloy layer exceeds 0.5 μm, powdering is more likely to occur. In order to obtain a plating layer having the two-layer structure shown in FIG. 1 or the three-layer structure shown in FIG. 3, Zn and Mg are added so that the temperature of the steel sheet after the deposition is 240 to 370 ° C.
Are sequentially deposited. If the temperature of the steel sheet after the deposition does not reach 240 ° C., the diffusion is insufficient, and if it exceeds 370 ° C., it excessively diffuses. After the deposition, 1 ° C /
Rapid cooling at a cooling rate of at least 2 seconds. In this manner, the Zn-M of FIG. 1 or FIG.
A g-plated steel sheet is manufactured. Note that the two-layer structure in FIG. 1 or the three-layer structure in FIG. 3 can be separately formed depending on the temperature immediately after the end of vapor deposition.

When this Zn-Mg-based plated steel sheet is immersed in a zinc phosphate treatment liquid containing Ni ions or sprayed with a zinc phosphate treatment liquid containing Ni ions, a black zinc phosphate treatment film is formed on the surface of the plating layer. Is done. Prior to the zinc phosphate treatment solution, if necessary, the film can be treated with a surface conditioning agent such as a weak alkaline system containing titanium hydroxide in order to reduce the crystal size of the treatment film. The zinc phosphate treatment liquid adjusts the Ni ion concentration to 3 to 12 g / l. Further, the treatment liquid 100 was prepared using phenolphthalein as an indicator.
The total acidity, expressed as the titer of 1N aqueous NaOH required for neutralization of the ml, is adjusted to 2-30 ml. If the Ni ion concentration is less than 3 g / l, the degree of blackness is not sufficient, and if it exceeds 12 g / l, an excessive amount of nickel oxide is deposited in the treated film, and the resulting treated film becomes brittle. When the total acidity is less than 2 ml, the reaction is slow, and when the treatment is repeated many times, the blackness varies and the obtained color tone becomes unstable. vice versa,
At a total acidity of more than 30 ml, the reaction rate becomes too high and a mottled black film due to hydrogen bubbles is formed.

The zinc phosphate treatment liquid preferably contains 0.6 to 2 g / l of Zn ions and 5 to 30 g / l of phosphate ions as other ions. If the Zn ion concentration is less than 0.6 g / l, a uniform treated film is not formed, and a black color tone cannot be obtained. However, even if a large amount of Zn ion exceeding 2 g / l is added, there is no change in the treated film, which is not economical. If the phosphate ion concentration is less than 5 g / l, the crystal state of the treated film is not stable, and a uniform black color tone cannot be obtained. Further, even if phosphate ions are added at a concentration exceeding 30 g / l, the blackness does not change, and it is not economical.

In order to increase the formation rate of the black film, nitrite ion, fluorine ion, nitrate ion, chlorate ion and hydrogen peroxide can be added as an accelerator. The promoter is, for example, 0.005 to 5
0.1 g / l, 0.005 to 0.5 g for fluorine ions
/ L, nitrate ions in the range of 0.2 to 13 g / l, and hydrogen peroxide in the range of 1 to 10 g / l. Each of the accelerators has no effect if the amount is less than the specified amount, and if the amount exceeds the specified amount, the reaction becomes too vigorous, which causes the treated film to become non-uniform. In any case, the amount of the accelerator added is smaller than that of a normal zinc phosphate treatment solution because the reactivity of the surface Zn-Mg layer formed according to the present invention is high. The zinc phosphate treatment solution contains Fe ions, which are effective for improving the adhesion of the clear coating film,
Mn ions and the like can be further included.

The black treatment is performed at a treatment temperature of 40 to 80 ° C., and a dense film with stable blackness is formed. If the processing temperature does not reach 40 ° C., the reaction rate is low, and if it exceeds 80 ° C., the composition of the processing liquid is liable to fluctuate due to evaporation of water, and there are disadvantages in terms of energy and safety. By bringing the Zn-Mg-based plated steel sheet into contact with the black processing liquid by immersion or spraying for 3 seconds or more, a black color tone is imparted to the surface. Alternatively, even with anodic electrolysis using the same processing solution, a black surface is obtained.

[0018]

【Example】

Example 1: As a plating base plate, C: 0.008% by weight,
Si: 0.05% by weight, Mn: 0.32% by weight, P:
0.009% by weight, S: 0.002% by weight, Ti: 0.
A 0.8 mm-thick steel sheet having a composition of 03 wt%, Al: 0.043 wt%, balance Fe and impurities was used. H
_After heating the plating base plate in a gas reduction chamber maintained in a 2-50 vol% N ₂ gas atmosphere to remove the oxide film and activate the surface, the plating base plate was introduced into the vacuum chamber via the N ₂ substitution chamber. . The vacuum chamber was evacuated with a vacuum pump so that the degree of vacuum was 5 × 10 ⁻² Torr because N ₂ gas leaked from the adjacent N ₂ substitution chamber. In this vacuum chamber, Zn-Mg-based plating was performed by a layer deposition method and a simultaneous deposition method.

The total deposition amount per one side of the layered vapor deposition method was set to 30 g / m ² , and Z
It was applied to the plating original plate in the order of n evaporation → Mg evaporation. The temperature of the steel sheet before vapor deposition was adjusted so that the temperature of the steel sheet immediately after the vapor deposition was 240 to 370 ° C., and the Zn vapor deposited layer and the Mg vapor deposited layer were mutually diffused by the retained heat of the steel sheet itself. After the deposition, the steel sheet
Gas cooling was performed in a N ₂ atmosphere. In the case of a Zn-Mg-based plated steel sheet having a two-layer structure, the first layer has an adhesion amount of 20 g / m ² ,
Zn deposition amount and M so that the adhesion amount of the layer becomes 10 g / m ^2.
g The deposition amount and the steel sheet temperature were adjusted. In addition, a three-layer Zn
-In the case of Mg-based plated steel sheet, the adhesion amount of the first layer is 15 g / m.
² , the adhesion amount of the second layer is 5 g / m ² , and the adhesion amount of the third layer is 1
The amount of Zn deposited, the amount of Mg deposited, and the temperature of the steel sheet were adjusted to be 0 g / m ² . As a result, the Mg concentration in the surface layer was 2 to 15%.
Two-layer structure (FIG. 1) having a Zn—Mg layer formed thereon and Mg
A Zn—Mg-based plated steel sheet having a three-layer structure (FIG. 3) having a concentration of 2 to 5% by weight in the second layer and 11 to 15% by weight in the third layer was obtained. In each of the multilayer structures, the Mg concentration of the first layer was about 0.1% by weight. Further, a Zn-Fe alloy layer or a Zn-Fe-M
A plated steel sheet on which a g alloy layer was formed was also prepared.

Simultaneous vapor deposition method First, Zn is vapor-deposited, and then Zn and Mg are simultaneously vapor-deposited, so that the deposition amount is 30 g / m 2 as in the two-layer structure of FIG.
² plated steel sheets were produced. The steel sheet temperature at this time was set to be 200 ° C. after the vapor deposition was completed in order to suppress the diffusion of Zn and Mg in the second simultaneous vapor deposition layer. The total adhesion amount, the first layer adhesion amount, and the second layer adhesion amount were each 30 g / g as in the case of the layered deposition method.
m ² , 20 g / m ² and 10 g / m ² . As a result of examining the layer configuration of the obtained Zn-Mg-based plated steel sheet,
The Mg concentration in the first layer was about 0.1% by weight, and the Mg concentration in the second layer was 1 to 25% by weight. However, it was difficult to form a plating layer having a two-layer structure, and the Mg concentration in the second layer was also unstable. Among the obtained Zn—Mg-based plated steel sheets, a sample on which a plated layer having a two-layer structure was formed was subjected to an evaluation test.

Each of the galvanized steel sheets treated with zinc phosphate was immersed in a nickel ion-containing zinc phosphate treatment solution maintained at a temperature of 60 ° C. for 5 seconds, black-treated, washed with water, and dried with hot air. As the zinc phosphate treatment liquid, the total acidity was 15 ml, the Ni ion concentration was 8 g / l, and Zn
Ion concentration 1.2g / l, phosphate ion concentration 15g /
1, an aqueous solution having a nitrite ion concentration of 0.05 g / l and a nitrate ion concentration of 3.5 g / l was used.

Characteristics Investigation (Powdering Resistance) Black treated steel sheet was bent to 6 tons and peeled off tape test (6 sheets of dummy steel sheet were bent to 180 degrees, then returned to the original 0 degree state, and the tape was attached. A peeling test) was used to investigate the state of occurrence of powdering. The presence or absence of powdering was determined based on whether or not the plating layer or the black treatment film adhered to the peeled tape. (Red rust resistance) Each test piece treated with zinc phosphate was treated at a temperature of 50
It was left for 10 days in a humid environment at 98 ° C. and a relative humidity of 98%, and the occurrence of red rust on the cut end face was examined. (Blackness and blackness recovery ability) The surface of each test piece treated with zinc phosphate was measured with a color difference meter, and lightness L ^* was evaluated as blackness. Further, in order to investigate the tendency of the blackened film to recover when the blackened film is damaged, the blackened film was scratched with a marking needle, and then left in an atmosphere at a temperature of 50 ° C. and a relative humidity of 60% for 15 days. The change in the color tone of the flawed portion was measured. Tables 1 to 4 show the results of the investigations together with the production conditions.

[0023]

[0024]

[0025]

[0026]

As is clear from Tables 1 to 5, the Zn—Mg-based plated steel sheet according to the present invention is treated with a Ni-ion-containing zinc phosphate treating solution to form a large amount of Ni in the coating.
And a black treated steel sheet exhibiting sufficient blackness with a lightness L ^* of 20 or less. No generation of powdering was observed, and the blackness was not impaired by the processing. Further, it is also found that the end face has excellent red rust resistance, and the black appearance is not impaired at the end face. Furthermore, even if the treated film was flawed, the flawed portion was blackened again and the appearance was restored.

On the other hand, even in the case of a Zn—Mg-based plated steel sheet, as shown in Table 4 as a comparative example, the Mg concentration was 2% by weight.
If it is less than 30, sufficient blackness cannot be obtained after the treatment with the zinc phosphate treatment solution containing Ni ions. Conversely, at a Mg concentration exceeding 18% by weight, powdering occurred in the treated film itself. Further, characteristics of the Zn-plated product were similarly examined. In this case, as can be seen from the results of the investigation in Table 5, even when treated with the zinc phosphate treatment solution containing Ni ions, a surface having a gray color tone instead of black was formed. Red rust also occurred at the end face, and the appearance was impaired. Similarly, the test piece on which Zn-Ni plating was applied also suffered from powdering and impaired blackness. In addition, red rust occurred frequently at the end face, and the appearance was significantly deteriorated.

[0029]

As is clear from the comparison between Tables 1 to 3 and Tables 4 and 5, a Zn—Mg-based plated steel sheet satisfying the conditions specified in the present invention has blackness, powdering resistance, cut end face and the like. It was confirmed to be excellent in all aspects such as red rust resistance in the exposed portion of the base steel and black recovery in the scratched portion of the treated film.

Example 2: A two-layer structure comprising a first layer having an Mg concentration of 0.1% by weight and an adhesion amount of 15 g / m ^{2 and} a second layer having an Mg concentration of 13.0% by weight and an adhesion amount of 5 g / m ² ( Z in FIG. 1)
The plated steel sheet in which the n-Mg-based plating layer was sequentially formed on the base steel was subjected to a black treatment of dipping in a Ni-ion-containing zinc phosphate treatment solution having variously changed Ni-ion concentrations. In the zinc phosphate treatment liquid, as ions other than Ni ions, Z
It contained 1.0 g / l of n ions, 12 g / l of phosphate ions, 0.05 g / l of nitrite ions, and 3.5 g / l of nitrate ions. Table 6 shows the results of measuring the surface of the black-treated test piece with a color difference meter, together with the Ni ion concentration and the total acidity of the zinc phosphate-treated solution.

As is clear from Table 6, when the Ni ion concentration and the total acidity satisfy the conditions specified in the present invention, the lightness L ^* is less than 20 and the color tone is excellent in blackness. Met. On the other hand, in Test Nos. 16 and 17 in which the Ni ion concentration was insufficient, the lightness L ^* showed a value exceeding 20, and the surface had a dull color tone. Test No. 18 with low total acidity was poor in blackness and too high in Test No. 1
In No. 9, peeling occurred in the treated film.

[0033]

[0034]

As described above, as described above, the Zn-
The Mg-based plated steel sheet is formed with a Zn-Mg-based plating layer having a two-layer structure having a second layer having a Mg concentration of 2 to 18% by weight or a three-layer structure having a third layer having a Mg concentration of 9 to 18% by weight. Therefore, the blackness treatment using the Ni-ion-containing zinc phosphate treatment liquid provides a surface having a lightness L ^* of less than 20 and excellent blackness. Since the formed black treated film exhibits a self-healing action even if a part of the treated film is peeled off due to scratches, etc.,
Maintain high design quality over a long period of time. Moreover, Mg
Since the first layer has a concentration of 0.5% by weight or less, the adhesion of the plating layer itself is excellent, and the occurrence of peeling or cracking in the plating layer even during press molding or bending is suppressed.

[Brief description of the drawings]

FIG. 1 shows a Zn-Mg based plating layer having a two-layer structure.

FIG. 2 is a black-treated two-layer Zn—Mg-based plating layer

FIG. 3 shows a Zn-Mg-based plating layer having a three-layer structure.

FIG. 4 is a Zn-Mg-based plating layer having a three-layer structure treated with black.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Koichi Watanabe, Inventor Koichi Watanabe, 5-5 Ishizu Nishimachi, Sakai City, Osaka Nisshin Steel Co., Ltd. Inside the Technical Research Institute

Claims (6)

[Claims] Claims 1. An Mg content of 0.5% by weight on a base steel
A Zn-Mg-based plated steel sheet having excellent black processing properties, in which the following Zn-Mg layer and Zn-Mg layer having a Mg content of 2 to 18% by weight are sequentially formed as a first layer and a second layer, respectively. 2. The first layer having a Mg content of 0.5% by weight.
The following Zn—Mg layer, the second layer having a Mg content of 2 to 6
Weight% Zn-Mg layer, Mg content of 9-
A Zn-Mg-based plated steel sheet excellent in blackness processing properties in which an 18% by weight Zn-Mg layer is sequentially formed on a base steel. 3. A thickness of 0.5 μm at an interface between the base steel and the first layer.
The Zn-Mg-based plated steel sheet excellent in blackness treatment according to claim 1 or 2, wherein a Zn-Fe alloy layer or a Zn-Fe-Mg alloy layer of m or less is formed. 4. The Zn—Mg-based plated steel sheet according to claim 1, wherein a zinc phosphate treated film having a Ni content of 3% by weight or more is formed on a surface layer. 5. The steel sheet temperature after vapor deposition is 240 to 370.
Under the condition that the temperature becomes 0 ° C., Zn and Mg are sequentially deposited and M
After forming a Zn-Mg layer having a g content of 2 to 18% by weight, a contact treatment is performed with a zinc phosphate treatment liquid containing Ni ions to form a black treated film on the plating layer surface.
Production method of base plated steel sheet. 6. A phosphorous containing 2 to 30 ml of Ni ion having a total acidity of 2 to 30 ml expressed by titration with a 1N aqueous solution of NaOH required to neutralize 100 ml with phenolphthalein as an indicator, with a Ni ion concentration of 3 to 12 g / l. The method for producing a black Zn-Mg-based plated steel sheet according to claim 5, wherein a zinc oxyacid treatment solution is used.