JPH08260199A - Production of highly corrosion resistant electroplating steel sheet - Google Patents

Abstract

PURPOSE: To produce the highly corrosion resistant Zn-Ni-SiO2 electroplating steel sheet excellent in plating adhesion by executing electroplating using a plating bath contg. a specified content of Zn and a specific chain silica by a specified amt. at specific pH. CONSTITUTION: Electroplating is executed by using a plating soln. contg. Zn, Ni and a chain silica, and a Zn-Ni-SiO2 plating layer is formed on the surface of a steel sheet. The plating soln. used therefor contains Zn by 0.5 to 1.5mol/l, in which the molar concn. ratio of Ni/(Zn+Ni) is regulated to 0.2 to 0.5 and contains the chain silica with 60 to 300nm average length, in which silica particles having 10 to 40nm average primary particle size are bonded in a chain shape, by 5 to 50g/l. Thus, adhesion and high corrosion resistance required for automobile steel sheets can be satisfied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention relates to a method of manufacturing a highly corrosion-resistant electroplated steel sheet, more particularly to a method of manufacturing a highly corrosion-resistant Zn-Ni-SiO ₂ electroplated steel sheet excellent in coating adhesion.

[0002]

2. Description of the Related Art Steel sheets for automobiles are required to have good pressability, that is, excellent workability, good adhesion to steel sheet and paint, and high corrosion resistance. ing. At present, Zn-based plated steel sheets such as Zn-plated, Zn-Ni alloy-plated, and Zn-Fe alloy-plated sheets are used as automobile steel sheets that satisfy these required performances. However, even the conventional Zn-based plated steel sheet may not be able to sufficiently satisfy the required corrosion resistance performance.

Therefore, a surface-treated steel sheet having higher corrosion resistance has been developed, and a Zn-plated steel sheet containing an alloying element different from the conventional one such as Zn-Mn plating and Zn-Cr plating has been studied. Also, Zn plating or Zn
Composite plating in which oxide particles are dispersed and co-deposited on alloy plating is also under study, and high corrosion resistance is expected. For example, in Japanese Patent Publication No. 56-49999, a dispersion-plated steel sheet containing ₂ to 15% of SiO ₂ in a Zn plating layer is a pure Z steel.
It is described that the corrosion resistance is about 1.5 to 3 times that of the n-plated steel sheet. Japanese Examined Patent Publication No. 62-6760 discloses that Fe ²⁺ , C is added to oxide particles having a particle size of 1 to 100 nm.
A method of adsorbing o ²⁺ and Ni ²⁺ to perform dispersion plating has been proposed, and a plating layer having a composition of Zn-10% Ni-10% SiO ₂ is a plating layer having a composition of Zn-13% Ni. Two
It is described that it shows about double the corrosion resistance. Further, Japanese Patent Kokoku 5-5911, and 100nm or less of the silica particles to produce a Zn-SiO ₂ plating NO ₃ ^-
A method using a plating bath to which ions are added has been proposed, and a plating layer containing approximately 5% or more of SiO ₂ is Z
It is described that it shows about three times as much corrosion resistance as a plated layer having a composition of n-13% Ni.

[0004]

However, in the method of eutectoidizing the oxide in the plating layer as described in Japanese Patent Publication No. 56-49999, in order to improve the corrosion resistance of the obtained plated steel sheet, a plating bath is used. 50 to ₂ of SiO ₂
It is necessary to add a high concentration of 200 g / l.
The reason why it is necessary to add a large amount of oxide to the plating bath in this way is that the surface of the oxide is negatively charged, so a small amount causes less eutectoid oxide and a smaller effect of improving corrosion resistance. is there. However, in a plating bath containing a high concentration of oxide, the viscosity of the plating solution increases and the flow rate of the plating solution decreases, causing insufficient diffusion of ions at the plating interface and causing plating burns, and continuous plating production. Since the oxide is aggregated or precipitated to lack the stability of the bath, the precipitation form and the distribution state become non-uniform, which causes not only manufacturing problems but also the problem that the expected corrosion resistance cannot be obtained. Therefore,
Japanese Examined Patent Publication No. 62-6760 discloses that Fe is formed on the surface of an oxide.
A method has been proposed in which ²⁺ , Co ²⁺ , and Ni ²⁺ are adsorbed to facilitate the co-deposition of oxides. Indeed, this special public Sho 62
According to the method described in JP-6760, SiO ₂ is 1
The effect of improving the corrosion resistance appears from a low concentration of 0 g / l, but when the concentration of SiO ₂ in the bath is low, the improving effect is small, about 1.1 times that of Zn-13% Ni. In order to secure twice the corrosion resistance of Zn-13% Ni, the SiO ₂ concentration must be as high as 150 g / l, and the bath stability is the same as in the method of Japanese Patent Publication No. 56-49999. There was a problem that the precipitation morphology and distribution were non-uniform. Further, Japanese Patent Publication No. 5-5911 describes a method of adding NO ₃ ⁻ as a co-deposition agent for SiO ₂ , and in this method, the amount of SiO ₂ added to the plating bath is as high as 5 g / l. Effective from low concentration, 10g /
It is described that when 1 is added, the content of SiO ₂ is 1.6% and the corrosion resistance is 20 times that of pure Zn plating. As described above, No ₃ ⁻ plays a major role in eutectoid SiO ₂ , but at the same time, there is a problem in plating performance other than corrosion resistance that the plating adhesion deteriorates. Furthermore, Japanese Patent Fairness 5-59
As can be seen from the example described in Japanese Patent Publication No. 11, the applied current density is 50 A / dm ² or less, and there is a problem that plating burn occurs at a current density of 100 A / dm ² or more used in electroplating operation. there were.

Therefore, an object of the present invention is to solve various problems in the manufacturing process in these conventional dispersion plating techniques,
It is an object of the present invention to provide a method for obtaining a Zn—Ni—SiO ₂ plated steel sheet that satisfies plating adhesion and high corrosion resistance required for automobile steel sheets.

[0006]

[Means for Solving the Problems] Zn-SiO ₂ system, which has high corrosion resistance as a performance of the plating to be produced, has good plating adhesion, and has no problems such as aggregation, precipitation or gelation of the dispersant in the plating production. In the development of electroplated steel sheet, the optimum form of colloidal silica to be added was investigated. Furthermore, various colloidal silicas were examined in combination with the conditions of the base plating solution, especially the Ni molar ratio in the plating solution.

As a result, in order to solve the above problems, the present invention contains Zn in an amount of 0.5 to 1.5 mol / l and Ni /
The molar concentration ratio of (Zn + Ni) is 0.2 to 0.5,
And, using a plating solution containing 5 to 50 g / l of chain-like silica having an average primary particle diameter of 10 to 40 nm bonded in a chain form and having an average length of 60 to 300 nm as silica, pH 1 Provided is a method for producing a highly corrosion-resistant electroplated steel sheet, which has a step of performing electroplating at 0.0 to 4.0.

The method for producing the highly corrosion-resistant electroplated steel sheet of the present invention (hereinafter referred to as the "method of the present invention") will be described in detail below.

The method of the present invention is a method of performing electroplating using a plating solution containing Zn, Ni and chain silica to form a Zn-Ni-SiO ₂ plating layer on the surface of a steel sheet. The steel sheet to which the present invention is applied to form a Zn—Ni—SiO ₂ plating layer is not particularly limited, and is applicable to all cold rolled steel sheets (SPCC, SPCD, SPCE, etc.), and deep drawing steel sheets. (SPCE), low carbon steel or ultra low carbon steel may be used.

The content of Zn in the plating solution used in the method of the present invention is 0.5 to 1.5 mol / l,
It is preferably 0.7 to 1.0 mol / l. When the content of Zn is less than 0.5 mol / l, the electrodeposition efficiency of plating is reduced, and when compared with plating performed with the same amount of electricity, the amount of deposited plating is small, the corrosion resistance is poor, and 1.5 mol / l When it exceeds 1, the concentration of the plating solution becomes high, and silica tends to gel, which is not preferable.

The content of Ni in the plating solution is Ni
The molar ratio [Ni ²⁺ / (Zn ²⁺ + Ni ²⁺ )] is in the range of 0 to 0.5, preferably 0.2 to 0.5, and particularly preferably 0.3 to 0.45. It will be adjusted to the range.
When the Ni molar ratio exceeds 0.5, it is difficult for silica to co-deposit on the plating layer, and the corrosion resistance of the plating layer itself cannot be improved.

Furthermore, the plating solution used in the method of the present invention contains chain silica formed by silica particles bonded in a chain. This chain-like silica has a mean length of 60 to 300 nm, which is formed by connecting silica particles having an average primary particle size of 10 to 40 nm in a chain, and has stability in a plating solution and sedimentation resistance. From the standpoint of obtaining a plating layer having excellent and excellent plating performance, silica particles having an average primary particle diameter of 10 to 20 nm are preferably linked in a chain form and have an average length of 60 to 200 nm. If the average particle size of the silica particles constituting the chain silica is less than 10 nm, the chain silica tends to aggregate and there is a problem in stability, and if the average particle size exceeds 40 nm, the silica tends to settle, resulting in plating. There is a problem with dispersibility in liquid. Further, if the average length of the chain-like silica is less than 60 nm, the adhesion between the silica and the plating in the plating outermost layer is not at a good level. Furthermore, if the average length exceeds 300 nm, gelation or the like may occur, and there is a problem in the stability of the plating solution.

Examples of the chain silica include chain type (ST-OUP) among those marketed by Nissan Kagaku Co. under the trade name: Snowtex.

The content of chain silica in the plating solution is 5 to 50 g / l, preferably 10 to 30 g / l as silica.
Is. If the content of chain silica in the plating solution is less than 5 g / l, the effect of improving the corrosion resistance due to the addition of silica is small, and if it exceeds 50 g / l, the viscosity of the plating solution increases and the appearance of plating burns etc. The unevenness occurs.

In the method of the present invention, the pH of the plating solution
Is preferably 1.0 to 4.0, and more preferably 1.5 to 3.0. When the pH of the plating solution is less than 1.0, silica is less likely to be co-deposited on the plating layer and the plating deposition efficiency is reduced, which is not suitable for operation. If the pH exceeds 4.0, silica may gel during continuous plating production, which is not preferable in operation. Furthermore, when the pH is 1.5 to 3.0, the plating deposition efficiency is high, and even at a high current density of 100 A / dm ² or more, there is no problem in plating appearance such as plating burn.

In the method of the present invention, the current density when electroplating using the plating solution is not particularly limited, but a plating layer having good plating performance can be obtained,
From the viewpoint of operation, it is usually 30 A / dm ² or more.

The plating bath temperature is preferably 40 to 65 ° C.
If the temperature is lower than 40 ° C, the plating may be discolored and the corrosion resistance is not stable. On the other hand, if the temperature exceeds 70 ° C., the plating solution evaporates violently and the amount of water to be evaporated increases, which is not preferable.

[0018]

As a result of the investigation, the co-deposition of silica in the method of the present invention is not a mechanism which has been conventionally known (Zn ²⁺ is not adsorbed on silica and Ni ²⁺ is adsorbed and electrodeposited), but a chain. It was found that the mechanism is such that Zn ²⁺ and Ni ²⁺ are adsorbed to the silica in the same degree. This means that when spherical silica (Silica G in Table 1 below) was used, the amount of eutectoid SiO ₂ increased as the Ni molar ratio increased, whereas when chained silica was used. Indicates that co-deposition of silica is observed even when Ni is not added to the plating bath, and that the amount of SiO ₂ co-deposition does not increase even if the Ni molar ratio in the plating bath increases, and conversely the Ni molar ratio is 0. When it is 0.55 or more, S
It is also inferred that the amount of iO ₂ co-deposition is reduced.

In the method of the present invention, the reason why a plated layer having excellent corrosion resistance and plating adhesion can be obtained by using chain silica is not clear, but it is presumed as follows. That is, the chain silica is entangled at the interface between the steel plate and the plating solution during electrodeposition. Zn ²⁺ ions and Ni ²⁺ ions diffuse through the entangled gaps and are electrodeposited on the surface of the steel sheet. At this time, the chain silica is partially Zn
Since it is embedded in the deposit of Ni or Ni, it is considered that silica is co-deposited in the deposit. Especially, the chain silica is partially embedded even in the outermost layer of the plating,
It is considered that silica on the outermost surface layer of the plating has excellent adhesion to the plating. On the other hand, in the case of spherical silica, it is present at the interface between the steel plate and the plating solution during electrodeposition, and when the amount of silica present at this interface is small, the gap is filled with Zn ²⁺ ions or N 2
The i ²⁺ ions diffuse and are electrodeposited on the surface of the steel sheet, but when the amount of silica present gradually increases, the gap disappears, and silica is deposited on the steel sheet at once. This is the same for spherical silica is adsorbed Ni ^2+, but is merely to facilitate the electrophoresis of the silica to the steel sheet surface by adsorption of Ni ^2+. That is, when spherical silica is used, a silica film is present on the outermost surface layer of the plating, although it is somewhat present. This silica film has no adhesion to the plating layer and is peeled off by a simple process, which causes stars in the press process. Regarding the corrosion resistance, it is considered that the silica rich portion in the outermost surface layer of the plating produced when chain silica is used and when spherical silica is used acts as a barrier against corrosion factors. However, the chain silica has good adhesion to the plating and acts as a barrier on the entire surface of the plating. However, when spherical silica is used, the adhesion to the plating is poor, and therefore, partial peeling or It is considered that the corrosion resistance is inferior because it is not sufficiently effective as a barrier due to the penetration of corrosion factors.

[0020]

EXAMPLES Examples and comparative examples of the present invention will be shown below.
The present invention will be described more specifically.

(Examples 1 to 20 and Comparative Examples 1 to 14) In each example, the plating baths shown in Table 2 were used, in which silica AG shown in Table 1 was added to SPCE steel plate having a thickness of 0.8 mm. , Electroplating was performed under the plating conditions shown in Table 2, and Zn-
To produce a Ni-SiO ₂ plated steel sheet. In addition, 0-100 g / l of sodium sulfate was added to the plating bath as a conduction aid.
Was added in the range.

In order to evaluate the plating performance of the obtained Zn-Ni-SiO ₂ plated steel sheet, the adhesion and corrosion resistance of the plating were evaluated according to the following methods. The results are shown in Table 2. Further, FIG. 1 shows the relationship between the corrosion resistance and the Ni molar ratio [Ni / (Zn + Ni)] in the plating bath, and FIG. 2 shows the relationship between the red rust generation area ratio and the salt spray test days. Further, in the corrosion resistance investigation, Zn with different adhesion amount was used as a comparative material.
-Ni alloy electroplating (Ni content rate: 12 to 13 wt
%).

Adhesion of Plating A so-called zero-T bending adhesion test was conducted in which the plated steel sheet was bent 180 degrees and the processed portion (curved portion) was peeled off with a tape. The evaluation of adhesion was performed according to the following criteria. ○ ・ ・ ・ ・ Good (no peeling) △ ・ ・ ・ ・ ・ ・ Slightly peeling × ・ ・ ・ ・ ・ ・ Peeling

Corrosion Resistance of Plating The coated steel sheet was subjected to the following combined cycle corrosion acceleration test in the unpainted state, and the number of test days until the area ratio of red rust on the plated surface became 5% was measured.

(Cycle of Combined Cycle Test) Salt Spray → Dry → Wet 35 ° C. 60 ° C. 50 ° C. 7 hours 3 hours 14 hours Salt spray was performed according to JIS Z2371. The corrosion resistance was evaluated according to the following criteria. ◎ ・ ・ ・ Very good (more than twice the Zn-Ni plating with the same amount of adhesion in this combined cycle test) ○ ・ ・ ・ Good (better than Zn-Ni plating with the same amount of adhesion) △ ・ ・ ・ The same adhesion Amount of Zn-Ni plating is about the same as that of Zn-Ni plating.

[0026]

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

[0030]

According to the method of the present invention, it is possible to produce a highly corrosion-resistant Zn-Ni-SiO ₂ electroplated steel sheet excellent in coating adhesion.

[Brief description of drawings]

FIG. 1 shows the relationship between the corrosion resistance measured in Examples and Comparative Examples and the Ni molar ratio [Ni / (Zn + Ni)] in the plating bath.

FIG. 2 shows the relationship between the red rust generation area ratio measured in Examples and Comparative Examples and the number of days of a salt spray test.

Claims (1)

[Claims] 1. Containing 0.5 to 1.5 mol / l of Zn, N
Silica particles having a molar concentration ratio of i / (Zn + Ni) of 0.2 to 0.5 and an average primary particle diameter of 10 to 40 nm are linked in a chain form, and have an average length of 60 to 300 n.
A method for producing a highly corrosion-resistant electroplated steel sheet, comprising the step of performing electroplating at a pH of 1.0 to 4.0 using a plating solution containing 5 to 50 g / l of chained silica as m as silica.