JPH0534436B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Field of Application) The present invention relates to a composite electroplated steel sheet for rust prevention that has excellent corrosion resistance and workability and is used in automobiles, home appliances, building materials, etc. (Prior Art) It is well known that electrogalvanized steel sheets are widely used as highly corrosion-resistant steel sheets that can be mass-produced without impairing the workability or strength of cold-rolled steel sheets. In recent years, attempts have been made to use galvanized steel sheets as anti-corrosive steel sheets for automobiles in response to salt sprayed to prevent roads from freezing during the winter in cold regions, and there is an increasing trend in the demand for corrosion resistance in harsh corrosive environments. In response to these demands for improving the corrosion resistance of galvanized steel sheets, it is known that the corrosion resistance can be improved by increasing the amount of zinc plating (adhesion amount). Many alloy plating methods have been proposed. Many of these are
It contains iron group elements such as Fe, Ni, and Co as alloy components, and has superior corrosion resistance after coating or painting compared to galvanized steel sheets, and has not been industrially produced and put into practical use. However, it is strongly desired to further improve corrosion resistance. On the other hand, as an electroplated steel sheet containing Cr during ZnN or Zn-based alloy plating, for example,
-38313 and 59-40234 public relations, JP-A-61-
130498, 61-270398, 62-54099 public relations etc. are disclosed. In all of these, the Cr content is very small, and the effect of Cr on corrosion resistance can only be incidental. (Problem to be solved by the invention) However, conventionally, Zn-
There was no Cr electroplating technology. In other words, even if the concentration of trivalent Cr ions in the plating bath is simply increased, normal plating with good workability cannot be obtained, and there are problems such as a sudden decrease in current efficiency, so that electrical metals with high Cr content cannot be used industrially. It was extremely difficult to obtain a steel plate. In view of the above problems, the present invention provides an unprecedented high
The present invention provides a highly practical Zn-Cr composite electroplated steel sheet with excellent corrosion resistance and workability due to its Cr content. (Means for Solving the Problems) The present invention introduces a water-soluble cationic polymer into a plating bath containing Zn ^{2+ ions} , Cr ³⁺ ions, and oxide fine particles, and promotes Cr precipitation through this action. ,
It was possible to obtain Zn-Cr composite electroplating with an unprecedentedly high Cr content, and also succeeded in ensuring processability through the eutectoiding of a small amount of cationic polymer. In addition, due to the inclusion of oxide fine particles,
This further improves the effect of Cr on corrosion resistance. The gist of the present invention is that 1 to 30% by weight of Cr is added to the surface of the steel plate.
Above, 0.1 to 10% by weight of oxide fine particles and 0.001 to 5% by weight of a cationic polymer obtained by electrically depositing a water-soluble cationic polymer made of a quaternary amine polymer with a molecular weight of 10 ³ to 10 ⁶ added to the plating solution. A highly corrosion-resistant composite electroplated steel sheet characterized by forming a composite electroplated layer with Zn as the balance. A highly corrosion-resistant composite electroplated steel sheet according to claim 1, characterized in that a Zn or Zn-based alloy plating layer is formed on the upper layer. Oxide fine particles include Si, Al, Zr, Ti, Cr, Mo, and W.
Claim 1 consisting of one or more oxides of
2. Highly corrosion-resistant composite electroplated steel sheet according to item 2. A patent claim characterized in that the water-soluble cathine polymer made of a quaternary amine polymer having a molecular weight of 10 ³ to 10 ⁶ is a homopolymer containing a quaternary amine group in the main chain represented by the following formula: The first term of the range,
The highly corrosion-resistant composite electroplated steel sheet according to Items 2 and 3. R ₁ , R ₂ , R ₃ and R ₄ are hydrocarbons (C _n H _o ) and X is an anion. (Function) The present inventors have discovered that Zn has a higher Cr content than ever before.
-Developed a manufacturing method for Cr-based composite electroplated steel sheets,
We have found a way to dramatically improve corrosion resistance. Further research and long-term exposure tests revealed that there was still room for improvement in improving corrosion resistance. That is, Cr does not become passivated in coexistence with Zn, but participates in the sacrificial anticorrosive action together with Zn, and the corrosion products of Cr deposit a poorly soluble protective film. It is thought that this suppresses corrosion and is the reason for its high corrosion resistance. However, under an exposure environment close to the conditions in which it is actually used, the drying time is long, so Cracks are likely to occur in the soluble protective coating. For this reason, corrosion progresses rapidly after a certain period of time. As a method to compensate for this drawback, it has been found that eutectoiding oxide fine particles into the plating layer is effective. Oxide fine particles are
It penetrates into the corrosion products of Zn and Cr and binds strongly with them, and because it has hygroscopic properties, it is difficult for the protective film of the corrosion products to be strained even in dry conditions, resulting in the damage of the protective film. It is thought that crack generation is suppressed. In this way, by containing the oxide fine particles, it is possible to further stabilize corrosion products that act as a protective film of Zn-Cr composite plating. The present invention will be explained in detail below. The corrosion resistance of the composite electroplated steel sheet of the present invention is mainly due to the effect of Cr. The Cr content is 1 to 30% by weight. If it is less than 1% by weight, it is not effective in improving corrosion resistance. When the amount is 5% by weight or more, the occurrence of red rust is suppressed in, for example, a salt water spray test, and an epoch-making effect appears. Such high corrosion resistance cannot be achieved by conventionally known Zn plating or alloy plating such as Zn-Fe or Zn-Ni. If the Cr content exceeds 30% by weight, corrosion resistance is good, but even with the eutectoid effect of the cationic polymer described below, the plating layer peels off during processing such as pressing, resulting in a so-called deterioration of powdering properties. cannot be prevented, making it difficult to apply in practice. From the viewpoint of corrosion resistance and workability, the Cr content is 5.
~20% by weight is more preferred. The content of oxide fine particles is 0.1 to 10% by weight. If it is less than 0.1% by weight, the effect on stabilizing the above-mentioned corrosion products will be small and will not be effective. Ten
If it exceeds % by weight, workability will be significantly deteriorated. From the viewpoint of processability, the content is more preferably 0.1 to 5% by weight. There are various types of oxide fine particles, such as metalloids and metal oxides, but they include Si, Al, Zr, Ti, Cr,
Oxides of Mo and W are particularly preferred;
A species or a mixture of two or more kinds may be used. The size of the oxide fine particles is preferably 1 μm or less as an average particle size, and if the size is more than 1 μm, it is difficult to eutectoid in the plating layer. Caotin polymer is a precipitation accelerator for Cr,
In addition, by eutectoiding a small amount of Cr in the plating layer, it improves powdering resistance during processing.
Such eutectoid effect of cationic polymers is due to Cr
It is presumed that the purpose is to prevent the ions from inhibiting the uniform electrophoretic growth of Zn and iron group metals, resulting in a glazed structure lacking uniformity and smoothness. That is, it is thought that a dense plating layer in which Zn, iron group metal, and Cr are uniformly mixed or alloyed is formed through the eutectoid cationic polymer. The content of cationic polymer is 0.001
~5% by weight. If the content is less than 0.001% by weight, it will have little effect on powdering resistance during processing, and if the content exceeds 5% by weight, it will not only be difficult to obtain even if the concentration of the cationic polymer in the plating bath is increased, but also a large amount will be required. Co-deposition causes a decrease in plating adhesion. From the viewpoint of processability, it is preferable to eutectoid the cationic polymer at a content of 1/1000 or more of the Cr content. The water-soluble cationic polymer used in the present invention is 4
Polymers of grade amines are effective polymers, the molecular weight being preferably between 10 ³ and 10 ⁶ in this case. Among the following amine polymers, polyamine sulfone (abbreviated as PAS) and polyamine (PA) are the most effective as Cr precipitation promoters. It is thought that the adsorption effect by the amine group and the bond between the sulfone group and the metal ion or metal contribute. Basically, the following quaternary amine salts (ammonium salts)

It is composed of a homopolymer or copolymer containing [Formula] in the main chain. Some compounds will be specifically listed below. Examples include polymers obtained from diallylamine. R ₁ and R ₂ represent an alkyl group, →Abbreviated as PA →Abbreviated as PAS X is Cl ^- , HSO ₄ ^- , H ₂ PO ₄ ^- , R-SO ₃ ^- (R is
C ₁ -C ₄ alkyl group), NO ₃ ^- anion. Another example is a polymer synthesized from vinylbenzyl. R ₁ , R ₂ , R ₃ represent hydrocarbons, →Abbreviated as PB X is Cl ^- , HSO ₄ ^- , H ₂ PO ₄ ^- , R-SO ₃ ^- , NO ₃ ^-
indicates the anion of Alternatively, allylamine polymer is mentioned. →Abbreviated as PAR. R ₁ , R ₂ , R ₃ represent hydrocarbons, X is Cl ^- ,
It represents an anion of HSO ₄ ^- , H _s PO ₄ ^- , R-SO ₃ ^- , NO ₃ ^- . In addition, polymers of primary, secondary, and tertiary amines are also effective as Cr precipitation promoters, although they are not as effective as the above-mentioned quaternary amine polymers. The amount of plating deposited is 10 to 50 g/m ² to ensure sufficient corrosion resistance. In addition to Zn, Cr, oxide fine particles, and cationic polymers, we also offer Pb, Sn, Ag, In, Bi,
Even if a small amount of Cu, Sb, As, Na, P, S, etc. inevitably eutectoid, the effects of the present invention remain essentially the same. The composite electroplated steel sheet formed in this way may be left as a single layer, or may have Zn or Zn-
A small amount of Zn-based alloy plating such as Ni or Zn-Fe may be applied. When applying Zn or Zn-based alloy plating to the upper layer, it is desirable to have a plating rate of 1 to 5 g/ ^m2.This will ensure chemical conversion treatment and cationic electrodeposition, and will further improve corrosion resistance after painting. Improve. Next, regarding the method for manufacturing a composite electroplated steel sheet of the present invention, Zn ²⁺ ions, Cr ³⁺ ions, SiO ₂ ,
Contains 0.01 to 20 g of water-soluble cationic polymers such as oxide particles such as Al ₂ O ₃ and TiO ₂ and polymers of quaternary amines such as PAS, pH 0.5 to 3, bath temperature
Electroplating may be carried out at 20 A/dm ² or more using an acidic plating bath at 40 to 70°C. Furthermore, addition of salts such as Na ⁺ , K ⁺ , NH ₄ ⁺ ions is effective in increasing the conductivity of the bath. For plating the upper layer with Zn or Zn-based alloy, a well-known electroplating method can be applied. In that case, it is preferable to thoroughly remove dragout containing Cr ions and cationic polymers carried out from the plating bath of the lower layer by washing with water before plating the upper layer. The structure of the present invention does not necessarily have to be used for a steel plate screen, but can be applied to only one side depending on the application, and the other side can be left as a steel plate, or covered with another plating layer or an organic film. It may also be used as a layer. The base steel plate to which the present invention is applied is usually a mild steel plate that has been subjected to dull finish rolling, but it can also be a mild steel plate that has been brightly finished rolled, a high tensile steel plate that contains a large amount of Mn, S, P, etc. as steel components, Cr, Cu, Ni, etc. Highly corrosion resistant steel plates containing a large amount of P etc. and having a low corrosion rate can also be used. (Example) A cold-rolled steel plate with a thickness of 0.8 mm was degreased with alkali, and
After pickling with % sulfuric acid, washing with water, electroplating was performed under the following conditions. The liquid flow rate was 90 m/min by pump stirring, the distance between the poles was 10 mm, and the bath temperature was 60°C.
A sulfuric acid acid bath of pH 2 was used. The plating bath composition is
Zn ²⁺ ion 70g/, Cr ³⁺ ion 1~30g/,
Oxide fine particles (SiO ₂ , Al ₂ O ₃ , ZrO ₂ , TiO ₂ are
Average particle size 0.02~0.05μ, Cr ₂ O ₃ , WO ₃ is average particle meter
0.1-0.5μ) at 10-100g/, cationic polymer (polyamine polymer (PA) with a molecular weight of 10,000, or polyamine sulfone polymer (PAS) with a molecular weight of 120,000) at 0.01-20g/, Na ⁺ ion 16g/, and each component. The content in the plating layer was controlled by the amount added and current density, and the plating amount was 20 g/m ² . In addition, the upper layer of one part was plated with 3 g/m ² of Zn or Zn-based alloy under well-known conditions. Table 1 shows the plating composition and evaluation results of the composite electroplated steel sheet produced in this way. In addition,
The Zn, Cr, and oxide fine particles in the plating layer were analyzed by atomic absorption spectrometry, and the cationic polymer was analyzed by C analysis by the combustion method and converted into the amount of cationic polymer. The corrosion resistance and workability evaluation methods are as follows. (1) Corrosion resistance of finished coating Salt water spray exposure test (exposure in Chiba Prefecture area, spraying 5% salt water once a week, abbreviated as exposure) Evaluated by the area where red rust occurred after one year. 1% or less: ◎ More than 1% to 10% or less: ○ More than 10% to 30%: △ More than 30%: × (2) Corrosion resistance after painting Immersion phosphate treatment, cationic electrodeposition coating 20μ
A salt water spray test (according to JIS Z 2371, abbreviated as SST) was carried out on the test shoulder with a cross cut reaching the base steel. The above exposure tests were conducted for 1000 hours and for 1 year, and each was evaluated based on the bulge width of the cross cut portion. 1 mm or less: ◎ More than 1 mm to 3 mm or less: ○ More than 3 mm to 5 mm or less: △ More than 5 mm: × (3) Spot weldability The welding conditions are as follows. Current: 8kA Number of cycles: 10 cycles Pressure force: 200Kg Welding tip shape: Shown in Figure 1. (A is 12mm
φ.B is 6mm φ.θ is 30°. ) The nugget diameter was measured after 3000 consecutive points were made. 4mm or more: ◎ 3mm or more and less than 4mm: ○ Less than 3mm: × (4) Workability After performing cylindrical press forming of 50φ x 25H,
Tape peeling was performed on the processed surface, and the amount of weight loss was evaluated. 2 mg or less: ◎ More than 2 mg to 5 mg or less: ○ More than 5 mm to 8 mg or less: △ More than 8 mg: × The inventive example has better corrosion resistance, weldability,
Both workability is clearly good.

【table】

[Table] (Effects of the invention) As described above, the composite electroplated steel sheet of the present invention has a protective film characteristic unique to Cr-containing plating by incorporating oxide fine particles into the Zn-Cr composite plating. By further stabilizing corrosion products, it is designed to improve corrosion resistance, especially in exposed environments, and has excellent weldability and workability, making it ideal for automotive applications that require advanced rust prevention performance. It is suitable as a rust-proof steel plate for home appliances and building materials.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the shape of a welding tip used to evaluate spot weldability in Examples.

Claims (1)

[Claims] 1. A water-soluble material containing 1 to 30% by weight or more of Cr, 0.1 to 10% by weight of oxide fine particles, and a quaternary amine polymer with a molecular weight of 10 ³ to 10 ⁶ added to the plating solution on the surface of the steel plate. A highly corrosion-resistant composite electroplated steel sheet comprising a composite electroplated layer comprising 0.001 to 5% by weight of a cationic polymer obtained by electrically depositing a cationic polymer, and the balance being Zn. 2. A highly corrosion-resistant composite electroplated steel sheet according to claim 1, characterized in that a Zn or Zn-based alloy plating layer is formed on the upper layer. 3 Oxide fine particles include Si, Al, Zr, Ti, Cr, Mo,
A highly corrosion-resistant composite electroplated steel sheet according to claims 1 and 2, comprising one or more types of oxides of W. 4. A patent characterized in that the water-soluble cationic polymer consisting of a quaternary amine polymer having a molecular weight of 10 ³ to 10 ⁶ is a homopolymer containing a quaternary amine group in the main chain represented by the following formula: Claim 1
Highly corrosion resistant composite electroplated steel sheet as described in Items 1, 2 and 3. R ₁ , R ₂ , R ₃ and R ₄ are hydrocarbons (C _n H _o ) and X is an anion.