JPH0774472B2 - Multi-layer alloy electric plated steel sheet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a double-layer alloy electric-plated steel sheet having excellent corrosion resistance, adhesion of a plating layer, and low-temperature impact peel resistance after coating.

2. Description of the Related Art Zn-Ni alloy electroplated steel sheets are widely used as rustproof steel sheets for automobiles because of their excellent corrosion resistance.
Zn-Ni alloy plating is a γ-phase Zn-Ni alloy with a Ni content of 10 to 15%.
It has the highest corrosion resistance when it is mainly composed of alloys. However, this γ phase is an intermetallic compound, and its hardness is higher than that of a single metal such as Zn or Ni, or even a base steel sheet,
Since it is brittle, it has various problems as described below.

First, in press working, when the base steel is plastically deformed, the Zn-Ni alloy plated phase cannot follow this,
A crack occurs in the plating layer, and further, as the deformation of the base steel proceeds, a phenomenon of so-called powdering occurs in which the plating layer is separated into powder. When such powdering becomes remarkable, the generated powder accumulates in the press mold, which not only increases the frequency of maintenance of the mold but also causes surface defects called pimples or press butts on the press product due to the accumulated powder. It tends to occur.

Secondly, if cracking or peeling of the plating layer occurs due to the above-described processing, the corrosion resistance of the plating steel plate deteriorates. Zn-Ni
The alloy-based alloy plating layer has a base potential to steel and has a sacrificial anticorrosion effect on the base steel, so cracking or peeling of the plating layer immediately leads to a significant decrease in corrosion resistance. However, it is unavoidable that the corrosion resistance of the Zn-Ni alloy electroplated steel sheet deteriorates due to processing.

Thirdly, assuming that Zn-Ni alloy electroplated steel sheet is coated with 3 coats for automobiles (coating thickness is about 100 μm), stone bounce (chipping) on the road during highway driving in winter is assumed. Then, when a stepping stone test is performed at −20 ° C., it is found that the coating film largely separates from the interface between the plating layer and the base steel sheet, starting from the place where the stone collides. The plating layer does not remain in the peeled portion of this coating film, and red rust is generated from this in a short period of time.

Therefore, in order to prevent the deterioration of the corrosion resistance due to the above-mentioned coating film peeling due to chipping of the Zn-Ni alloy electroplated coated steel sheet, the coating film peeling diameter is made small, and the resistance to impact (hereinafter, It is necessary to improve this property with respect to low temperature impact peelability).

Incidentally, even when bending or shearing a pre-coated steel sheet using a Zn-Ni diameter alloy electroplated steel sheet as a base sheet, there is a phenomenon that the coating film of the processed part peels from the interface between the galling layer and the base steel, It can be considered that this is the same phenomenon as the low temperature impact peeling.

Fourthly, the Zn-Ni alloy electroplated steel sheet is sometimes used without coating for shears and interior parts of electric products due to its excellent luster and beautiful appearance. In this case, it is particularly required that the plating layer has a uniform gloss and no unevenness. However, depending on impurities such as lead in the plating solution during plating, and the composition ratio of Zn ions and Ni inverter in the plating solution, the gloss is not stable, and the flow of the plating solution may be delayed. This may cause uneven glossiness and significantly reduce the product value.

Various methods have already been proposed to solve the problems of the Zn-Ni alloy electroplated steel sheet as described above.
For example, JP-A-56-166389 discloses that Ni, Co on a steel plate
Alternatively, a method has been proposed in which a single metal layer of Cu is coated to a film thickness of 0.03 to 0.50 μm and then Zn-Ni alloy electroplating is performed. However, in this way, according to the method of pre-plating a single metal layer on a steel sheet, as the pre-plating thickness increases, initially, the low temperature impact peelability after coating is improved,
When the pre-plating thickness exceeds a certain value, the pre-plating thickness does not improve beyond a certain value determined by the type of pre-plating metal. Therefore, in order to further improve the low temperature impact peelability,
There is no choice but to use a method other than pre-plating of a single metal. Furthermore, when Cu is pre-plated, a significant decrease in corrosion resistance is unavoidable.

On the other hand, JP-A-58-6995 discloses that a Zn-Ni alloy plated layer consisting of a mixed phase of η phase and γ phase having a Ni content of 2 to 9% is provided as a lower layer of the Zn-Ni alloy electroplated layer. Zn having a thickness of 0.05 to 2 μm and a γ phase single phase with a Ni content of 10 to 20%
A method of applying Ni alloy plating has been proposed. surely,
According to this method, the low temperature impact peelability after coating can be improved to some extent, but since the lower layer is composed of the mixed phase of the η layer and the γ layer as described above, the corrosion resistance is deteriorated. In addition, since the lower layer of Ni content of 2 to 9% has no luster, Ni content of 10 to 10% which has luster by itself
Even if 15% γ single phase Zn-Ni alloy plating is applied on it,
It is no longer possible to obtain a shiny and beautiful plated surface.

In addition, a Zn-Ni alloy with a higher Ni content than the upper layer is used for the lower layer.
JP-A-58-201496 proposes a method of applying a predetermined Zn-Ni alloy electroplating after applying a thickness of 05 to 0.8 μm. According to the experiments of the present inventors, according to this method, when the Ni content of the lower layer is less than 20%, it is effective in improving the low temperature impact peel resistance after coating. But Ni
When the content is 20% or more, Zn-Ni alloy electroplating has low current efficiency, and the composition of the plating layer changes greatly with respect to the composition change of the plating solution, making process control difficult. Is.

Furthermore, first, a Zn-Ni alloy plating is applied very thinly, and the plating layer is partially redissolved in a plating solution, and then a Zn-Ni alloy plating having a predetermined plating thickness is applied. JP-A-62-1213
No. 97 publication. This method is the first ultra-thin Zn
Appropriate selection of Ni plating thickness and subsequent remelting time is effective in improving low temperature impact peel resistance after coating and powdering resistance. However, if the remelting time required for this method is to be secured with the existing horizontal electrogalvanizing line, one or more plating cells must be placed in a non-energized state, which reduces productivity. I cannot escape. In addition, the surface gloss of the product obtained by this method has a defect that uneven gloss is more likely to occur as compared with the usual Zn-Ni alloy plating.

In addition to the above, methods for strengthening the plating pretreatment of steel sheets have been proposed. For example, a method of electrolytically pickling a steel sheet is described in JP-A-63-238297, and a method of polishing the surface of the steel sheet with an abrasive containing abrasive before plating is disclosed in JP-A-63-140098. It is described in Japanese Patent Publication No. However, these methods are merely auxiliary means for improving the powdering resistance and the low temperature impact peeling resistance after coating. Cannot reach the strict level required for automobile steel sheets.

Problems to be Solved by the Invention As described above, conventionally, although various methods have been proposed, these can simultaneously solve the above-mentioned problems in the Zn-Ni alloy electroplated steel sheet. Instead, new technology is strongly demanded.

The present invention has been made in order to meet such a demand, which is resistance to low-temperature impact peeling after coating, powdering resistance,
It is an object of the present invention to provide a double-layer alloy electroplated steel sheet having excellent corrosion resistance and surface gloss.

Means for Solving the Problems A double-layered alloy electroplated steel sheet according to the present invention has a
It has a Ni-Co alloy plating with a Co content of 5 to 20% as a layer at an adhesion amount of 0.05 to 1.0 g / m ^2, and a Ni content of 8 to 16% as a second layer on this first layer. The Zn-Ni alloy has a galvanic plating.

The multi-layered alloy electroplated steel sheet according to the present invention has a first coating on the steel sheet.
As a layer (lower layer), a Ni-Co based alloy plating layer having a Co content of 5 to 20% is attached at an adhesion amount of 0.05 to 1.0 g / m ² . Ni-Co alloy plating is superior to Ni or Co single metal layer in powdering resistance, low temperature impact peeling resistance after coating, and corrosion resistance when the Co content is in the range of 5 to 20%. I also get better. First
The figure shows the relationship between the Co content in the lower Ni-Co alloy plating and the powdering resistance of the plating layer. Also, the second
The figure shows the relationship between the Co content in the Ni-Co alloy plating of the lower layer and the low temperature impact peel resistance after coating.

As described above, when the Co content is in the range of 5 to 20%, the Ni-Co alloy plating has a powdering resistance, a low temperature impact peeling resistance after coating, and a corrosion resistance that are either Ni or Co. The reason why it is superior to the single metal layer is not clear, but it seems to be as follows.

For powdering and low-temperature impact peelability, the plating layer is Zn-
From where it separates at the interface between the Ni alloy layer and the base steel sheet,
It is considered that these problems occur in the adhesion between the Zn-Ni alloy layer and the joint steel sheet.

Pre-plating with Ni or Co improves the adhesion between the Zn-Ni alloy layer and the base steel sheet. The reason is Ni
Since Co and Co are not intermetallic compounds such as Zn-Ni alloys, they are rich in ductility, and as a result, become a kind of relaxation layer when the force is transmitted between the plating layer and the base material. Co acts in the direction of reducing the misfit of the atomic spacing between the base steel sheet and the Zn-Ni alloy, and the adhesion force between the base steel sheet and the pre-plating and the adhesion force between the pre-plating and the Zn-Ni alloy are both the base steel sheet. It is considered that this is because the adhesion strength between the Zn-Ni alloy and Zn-Ni alloy becomes larger.

According to the present invention, the pre-plating is Ni- with a Co content of 5-20%.
By using the Co alloy, the reason why the powdering resistance and the low temperature impact peeling resistance are further improved as compared with the case of Ni or Co alone metal is that the Ni-Co alloy in this range is solid-dissolved in Ni. In the state of solid solution, that it is not a brittle intermetallic compound, and as described above, the misfit of the atomic spacing can be optimized by the Ni-Co alloy in the above range, further,
It is considered that this is because the effects such as the fact that the electrodeposition stress of the pre-plating layer is minimized within the above range act comprehensively.

Next, as shown in FIG. 3 showing the relationship between the Co content of the lower Ni-Co alloy and the corrosion resistance, when the Co content is in the range of 5 to 20%, the corrosion resistance is improved. The reason is that since the Ni-Co alloy has good uniform coverage, even if cracks occur in the Zn-Ni plating layer due to corrosion, there are few defects in the Ni-Co pre-plating layer. It seems that there is little exposure of the base steel sheet.

Further, in the present invention, the amount of adhesion to the base steel sheet with the Ni-Co alloy plating of the lower layer needs to be in the range of 0.05 to 1.0 g / m ² . FIG. 4 shows the relationship between the adhesion amount of Ni-Co alloy plating of the lower layer and the low temperature impact peel resistance after coating. It has been shown that when the amount of adhesion of the lower layer is 0.02 g / m ² or more, the peeling diameter of the coating film decreases, and particularly when the coating amount is 0.2 g / m ² or more, the peeling diameter of the coating film becomes almost constant.

With respect to corrosion resistance, when the amount of adhesion of the lower layer is 0.05 g / m ^2, the extension of the time of occurrence of red rust was observed, it becomes constant at 0.1 g / m ² or more.

In the present invention, the Ni-Co pre-plating as described above,
In addition to electric plating method, electroless plating method, replacement plating method,
It may be plated on the steel sheet by any method such as a vapor deposition plating method.

In the multilayer alloy electroplated steel sheet according to the present invention, Zn-Ni having a Ni content of 8 to 16% is formed as the second layer on the lower layer.
With alloy electric plating.

In this Zn-Ni alloy electroplating, when the Ni content is less than 8%, the Zn-Ni alloy electroplated steel sheet has the best low-temperature impact peeling resistance, powdering resistance, and corrosion resistance after coating. Since it is superior to Zn-Ni alloy plating with a Ni content of 13%, it is not necessary to improve it by Ni-Co pre-plating, and corrosion resistance is improved even when Ni-Co pre-plating is applied. This is because the surface gloss does not improve even when Ni-Co pre-plating is applied. On the other hand, when the Ni content exceeds 16%, the corrosion resistance deteriorates fatally.

The amount of such Zn-Ni alloy electroplating is appropriately selected depending on the environment in which the steel sheet is used, but usually 10 to
It is in the range of 50 g / m ² .

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

A cold rolled steel sheet having a thickness of 0.8 mm was electrolytically degreased, pickled, and then Ni-Co pre-plated by an electric plating method. A sulfate bath was used as the plating bath, the amount of adhesion was adjusted by the amount of electricity applied per unit area, and the Co content was adjusted by the concentration of cobalt sulfate in the bath.

After this Ni-Co pre-plating, the steel sheet was further electroplated with Zn-Ni alloy, washed with water and dried. The amount of Zn-Ni alloy electroplating is adjusted according to the amount of electricity applied per unit area,
The Ni content was adjusted by the ratio of Ni ions and Zn ions in the bath.

Table 1 shows the composition of the multi-layer alloy electroplated steel sheet thus obtained.

Steel plate powdering resistance, low temperature impact peel resistance after painting,
The corrosion resistance and surface gloss were evaluated as follows.

Powdering resistance Steel plate with galling is processed into JIS No. 5 tensile test piece, and after giving 30% elongation with a gauge length of 50 mm using a tensile tester, the processed part is taped with cellophane adhesive tape, This was peeled off, and the powdered sticking piece attached to the tape was dissolved in hydrochloric acid and quantified by atomic absorption spectrometry.

Resistance to low temperature impact peeling after coating Following the automotive coating process, a steel sheet with dipping method, phosphate treatment, cationic electrodeposition coating (20 μm), intermediate coating (40 μm)
m) and the top coat (40 μm), respectively, and then stored in a refrigerator at −20 ° C. for 24 hours, and immediately after taking out, the coating film was chipped with a gravure meter under the following conditions.

Stone type: Granite Stone diameter: 7.9 to 11.1 mm Stone amount: 100 g / time Air thickness: 4.0 kgf / cm ² After chipping, the steel sheet after taping was measured for the peeled coating film diameter. The measurement was carried out for the one having the largest peeling diameter, and the average value of the steel sheets with n = 5 was defined as the coating peeling diameter.

Corrosion resistance Both so-called bare corrosion resistance in the uncoated state and corrosion resistance after coating were evaluated.

The bare corrosion resistance was evaluated by performing a salt spray test specified in JIS Z 2371 on a plated steel plate and measuring the time until 1% of red rust was generated on one surface of the test piece.

Corrosion resistance after coating is performed by dipping the coated steel sheet in a dipping method and cation electrodeposition coating (20 μm), then cross-cutting the coating film, and conducting a salt spray test for 840 hours. The swelling width from the cross cut was evaluated.

Surface gloss The surface gloss of the plated steel sheet was visually evaluated in the following four stages.

Uniform gloss: ◎ Slightly uneven gloss: ○ Uneven gloss: △ Significant uneven gloss or no gloss: × The above results are shown in Table 1. Examples 1 to 4 and Comparative Example 1
As is clear by comparing with No. 4, Co with Ni-Co pre-plating
It is understood that in the content range of 5 to 20%, the double-layer electroplated steel sheet according to the present invention has excellent powdering resistance, low temperature impact peel resistance after coating, bare corrosion resistance, and corrosion resistance after coating. It Also, as is clear from comparison between Examples 5 to 8 and Comparative Examples 5 to 7, the amount of Ni-Co pre-plated adhesion was 0.05.
When it is g / m ² or more, the double-layered alloy plated steel sheet according to the present invention has excellent powdering resistance, low temperature impact peeling resistance after coating, bare corrosion resistance and corrosion resistance after coating, and surface gloss. Has been done.

Furthermore, as is clear from comparison between Examples 9 and 10 and Comparative Examples 8 and 9, both corrosion resistance and surface gloss Excellent Zn-Ni alloy electroplated Ni content is 8-16%
It is understood that the range is.

As described above, the double-layer alloy electric-plated steel sheet according to the present invention has improved powdering resistance and low-temperature impact peeling resistance after coating, which are problems in the conventional Zn-Ni alloy electric-plated steel sheet. In addition, the high corrosion resistance and surface gloss which are the characteristics of Zn-Ni alloy electroplated steel sheets are further improved.

[Brief description of drawings]

Figure 1 shows a cold-rolled steel sheet with Ni-Co alloy plating as the lower layer and Zn-Ni (13%) alloy electrical plating as the upper layer (deposition amount 30 g /
² ) is a graph showing the relationship between the Co content and the amount of powdering in the Ni-Co alloy plating (adhesion amount 0.3 g / m ² ) of the lower layer in the multi-layer plating steel sheet having m ² ). Lower layer
Fig. 3 is a graph showing the relationship between the Co content in Ni-Co alloy plating and the peeling diameter of the coating film. Fig. 3 shows the relationship between the Co content of the lower Ni-Co alloy and the 1% red rust generation time in the salt spray test. The graph shown in FIG. 4 is Ni-Co as a lower layer on a cold rolled steel sheet.
(10%) alloy plating and Zn-Ni (13%) alloy electric plating (30 g / m ² ) in the upper layer, in a multi-layer plating steel sheet, the adhesion amount of the lower Ni-Co alloy coating It is a graph which shows the relationship between a coating film peeling diameter.

Claims (1)

[Claims] 1. A steel sheet having a Co content of 5 to 20% as a first layer.
It has a Ni-Co alloy plated layer with a deposition amount of 0.05 to 1.0 g / m ^{2 and} has a Ni content of 8 to 16% as a second layer on the first layer.
A multi-layer alloy electroplated steel sheet having Zn-Ni alloy electroplating.