JPH02270998A - Composite electroplated steel sheet having high corrosion resistance - Google Patents

Abstract

PURPOSE:To produce a composite electroplated steel sheet having high corrosion resistance by forming a plating layer consisting of specified percentages of Cr, oxide particles, a cationic polymer and Zn on the surface of a steel sheet by composite electroplating. CONSTITUTION:A plating layer consisting of 1-30wt.% Cr, 0.1-10wt.% fine oxide particles, 0.001-5wt.% cationic polymer and the balance Zn is formed on the surface of a steel sheet by composite electroplating by about 10-50g/m<2>. Particles of oxides of one or more among Si, Al, Zr, Ti, Cr, Mo and W are preferably used as the fine oxide particles and the average particle size is regulated to about <=1mum. A quat. amine polymer is preferably used as the cationic polymer and the mol. wt. is regulated to about 10<3>-10<6>. Though the plating layer may be used as a single layer, a Zn or Zn alloy plating layer is preferably formed as an upper layer by about 1-5g/m<2>. A rustproofing composite electroplated steel sheet having superior corrosion resistance and workability is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial 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 corrosion resistance can be improved by increasing the amount of zinc plating (adhesion amount). Many have been proposed.

Many of these contain iron group elements such as Fe, Ni, and Co as alloying components, and have superior corrosion resistance after unpainted or painted compared to galvanized steel sheets, making them difficult to produce industrially 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 in Zn or Zn-based alloy plating, for example, Japanese Patent Publication No. 59-383
13 and 59-40234.

JP-A-61-130498.61-270398゜62
-54099 etc. are disclosed.

All of these have a trace amount of Cr content, and the effect of Cr on corrosion resistance can only be incidental.

(Problem M to be solved by the invention) However, conventionally there has been no Zn-Cr electroplating technology capable of increasing the Cr content. 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 electroplated steel sheets with high Cr content cannot be manufactured industrially. It was extremely difficult to obtain.

In view of the above problems, the present invention provides a highly practical Zn-Cr composite electroplated steel sheet with an unprecedented high Cr content, excellent corrosion resistance and workability.

(Means for Solving the Problems) The present invention introduces a water-soluble cationic polymer into a plating bath containing Zn2'', Cr3+ ions and oxide fine particles, and this action promotes Cr precipitation, thereby improving the conventional method. It was possible to obtain a Zn-Cr-based composite electroplating with a high Cr content, and also to ensure workability by eutectoiding a small amount of cationic polymer.Also,
The effect of Cr on corrosion resistance is further improved by containing oxide fine particles.

The gist of the present invention is that 1 to 30% by weight of Cr is added to the surface of the steel plate.
Oxide fine particles 0.1-10% by weight, cationic polymer 0
．． A highly corrosion-resistant composite electroplated steel sheet characterized by forming a composite electroplated layer containing 001 to 5% Zn and the balance Zn; Composite electroplated steel sheet, oxide fine particles are Si, Al, Zr, Ti, Cr.

The above-mentioned highly corrosion-resistant composite electroplated steel sheet is made of one or more types of oxides of Mo and W. The above-mentioned highly corrosion-resistant composite electroplated steel sheet is such that the cationic polymer is a quaternary amine polymer.

(Function) The present inventors have discovered that Zn-Cr has a higher Cr content than ever before.
Developed a method for manufacturing 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. In other words, Cr does not become passivated in the coexistence with Zn, and Zn
In addition, 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 actual usage conditions, the drying time is long, so the corrosion caused by corrosion products of Cr is difficult to maintain. Cracks are likely to occur in the soluble protective film. For this reason,
After a certain period of time, corrosion progresses rapidly.

The inventors have found that eutectoiding oxide fine particles into the plating layer is effective as a method to compensate for this drawback. Oxide fine particles penetrate into Zn and Cr corrosion products and bond strongly with them, and because they have hygroscopic properties, even in dry conditions, they do not easily strain the protective film of the corrosion products. As a result, it is thought that the occurrence of cracks in the protective film is suppressed.In this way, by containing oxide fine particles, it is possible to further stabilize the corrosion products of the protective film of Zn-Cr composite plating. can.

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 Cr.
This is the effect of 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 generation of red rust is suppressed in, for example, a salt 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.

When the Cr content exceeds 30% by weight, corrosion resistance is good, but even with the effect of the eutectoid of the cationic polymer described below, deterioration of so-called powdering property, in which the plating layer peels off during processing such as press working, cannot be prevented. However, it is difficult to apply in practice.

From the viewpoint of corrosion resistance and workability, the Cr content is 5 to 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 corrosion products described above will be small and it will not be effective. If it exceeds 10% by weight, the workability will be significantly deteriorated. From the viewpoint of workability, from 0.1 to There are many types of oxide fine particles, which are more preferably 5% by weight, such as metalloid and metal oxides, but S
i, AQ.

Oxides of Zr, Ti, Cr, Mo, and W are particularly preferred;
These may be used alone or in a mixture of two or more.The size of the oxide fine particles is preferably 1μ or less as an average particle diameter, and if it exceeds 1μ, it is difficult to eutectoid in the plating layer. .

The cationic polymer is a precipitation accelerator for Cr and
By eutectoiding with r in a small amount within the plating layer, powdering resistance during processing is improved.

This eutectoid effect of cationic polymers is due to the fact that Cr ions inhibit the uniform deposition growth of Zn and iron group metals, resulting in uniformity and
It is presumed that the purpose is to prevent a plating structure lacking in smoothness. That is, it is thought that a dense plating layer in which Zn or iron group metals and Cr are uniformly mixed or alloyed is formed through the eutectoid cationic polymer. The content of cationic polymer is 0
．． 001 to 5% by weight. If the O,OQ content is less than 1% by weight, the effect on powdering resistance during processing is poor, and if the content exceeds 5% by weight, it is not only difficult to obtain even if the cationic polymer concentration in the plating bath is increased, but also a large amount If eutectoid is used, it will cause 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 effectively a quaternary amine polymer, and the molecular weight is preferably 10' to 10'' in this case. Among the following amine polymers, polyamine sulfone (PAS) ) and polyamine (PA) are the most effective as Cr precipitation promoters.It is thought that the adsorption effect of the amine group and the bond between the sulfone group and the metal ion or metal contribute6.
Basically, it is composed of the following quaternary amine salts (ammonium salts) or copolymers.

Some specific compounds are listed below.

Examples include polymers obtained from diallylamine. R1
, R2 represents an alkyl group, N...X/\1R2CH.

N...X X is CQ-, H3O4-, H, PO4-, R-8O3-
(R is a C-C4 alkyl group), No, and an anion of -.

Another example is a polymer synthesized from vinylbenzyl. R□, R,, R, represents a hydrocarbon, and 1,000 CH2-
CH+1 CI+□ X is Cα-, HSO4-, H2PO,-, R-8O,-
.

No, indicates an anion of -.

Alternatively, allylamine polymer can be mentioned.

Thousand C1+, -CH-9 N...X Abbreviated as 4PAR.

R= , Rz -R,- represents a hydrocarbon, X is CQ-
.

HS O4-, I(SP O4-, R-S O,-, N
Indicates an anion of o and -. In addition, polymers of primary, secondary, and tertiary amines are also effective as Cr precipitation promoters (not as good as the above-mentioned quaternary amine polymers).

A coating weight of 10 to 50 g/rd can ensure sufficient corrosion resistance. Also, Zn, Cr, oxide fine particles.

In addition to cationic polymers, Pb, Sn, A4. I
n.

Even if Bi, Cu, Sb, Am, 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-Ni as an upper layer.

7. A small amount of Zn-based alloy plating such as n-Fe may be applied. When Zn or Zn-based alloy plating is applied to the upper layer, 1 to 5 g/rd is desirable. By doing so, chemical conversion treatment and It makes the cationic electrodeposition more reliable and further improves the corrosion resistance after painting.

Next, the method for manufacturing a composite electroplated steel sheet of the present invention,
Zn"+ ion, Cr'+ ion, 5in2゜AQ
z03. Water-soluble polymers such as oxide fine particles such as TiO2 and polymers of quaternary amines such as PAS? −
containing 0.01 to 20 g IQ, p) 10.5 to 3, using an acidic plating bath with a bath temperature of 40 to 70°C, 2OA/dr+
Electroplating may be performed at f or higher.

Furthermore, addition of salts such as Na", K", NH4+ ions, etc. is effective in increasing the conductivity of the bath.

A well-known electroplating method can be applied to the Zn or Zn-based alloy plating on the upper layer. In that case, it is preferable to sufficiently remove drag-out 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 applied to both sides of a steel plate, but can be applied to only one side depending on the application, and the other side can be used as a steel plate or as a plating layer coated with another plating layer or an organic film. Good too.

The base steel sheet to which the present invention is applied is usually a mild steel sheet that has been subjected to dull finish rolling, but it may also be a mild steel sheet that has been brightly finished rolled, or a high-strength steel sheet that contains a large amount of Mn, S, P, etc. as a steel component.
It is also applicable to highly corrosion-resistant steel plates containing a large amount of , Cu, Ni+P, etc. and having a low corrosion rate.

(Example) A cold-rolled steel plate with a thickness of 0.8 mm was degreased with alkali, pickled with 5% sulfuric acid, washed with water, and electroplated under the following conditions. Liquid flow rate 9Qm/l1li by pump stirring
n, interelectrode distance 1-Onye, bath temperature 60℃, pH
No. 2 sulfuric acid acid bath was used. The plating bath composition was 70 g/Q of Zn"+ ions, 1 to 30 g of Cr" ions.
/ Q v oxide fine particles ('S j, 0., A Q
z○,.

ZrO2, TiO2 have an average particle size of 0.02 to 0.05μ
.

CrzOi)WO3 has an average particle size of 0.1-0.5p)
0 to l OOg/Q, cationic polymer (polyamine polymer (PA) with a molecular weight of 10,000, or molecular weight 1
20,000 polyamine sulfone polymer (PAS)) 0.0
1-20 g/Q, Na+ ion 16. As for IQ.

The content of each component in the plating layer is controlled by the amount added and current density, and the amount of plating deposited is 20g.
'/rrf. Further, for one part, the upper layer was plated with 3 g/bo 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 manufactured in this manner. In addition, Z in the plating layer
The n + CI7 + oxide fine particles 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 processability evaluation method is as follows.
Spraying salt water (abbreviated as "exposure") was evaluated based on the area where red rust occurred after one year.

1% or less: 0 More than 1% to less than 10%: 0 More than 10% to less than 30%: Δ More than 30%: Intermediate coating, wet sanding, and top coating to achieve a total film thickness of 10
A test piece with a 0 μ field and a cross cut reaching the base metal was subjected to a salt spray test (according to JIS Z 2371, abbreviated as SST) for 1000 hours and the above exposure test for 1 time.
The test was carried out for a year, and each test was evaluated based on the bulge width of the cross-cut part.

11[o below 20 More than 111n to less than 3m: 0 More than 3m to less than 5rrfa: Δ Over 51m: × (3) Spot weldability The welding conditions are as follows.

Current: 8 kA Number of cycles: 10 cycles Pressure crab 200 glare Welding tip shape: As shown in Figure 1. (A is 12 mφ, B is 6 omφ, and 0 is 30".) The nugget diameter after 3000 consecutive points was measured.

4 m or more: ◎ 3 m or more to less than 41 m: 0 Less than 3 wn:

2 ■ or less: ◎ Over 211g ~ 5■ or less: 0 More than 5III to less than 8■: Δ Over 8:X The present invention example has better corrosion resistance and weldability than the comparative example.

Both workability is clearly good.

(Effect of the invention) As described above, the composite electroplated steel sheet of the present invention has Z
By incorporating oxide fine particles into the n-Cr composite plating, the protective film-like corrosion products peculiar to Cr-containing plating are further stabilized, thereby improving corrosion resistance, especially in exposed environments. Because of its excellent weldability and workability, it is suitable as a rust-proof steel sheet for automobiles, home appliances, and building materials, which require a high degree of rust-proofing performance.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a welding tip shape used to evaluate spot weldability in Examples. -IJ- Figure 1

Claims (4)

[Claims] (1) On the surface of the steel plate, 1 to 30% by weight of Cr, 0.1 to 10% by weight of oxide fine particles, and 0.001 to 0.001% of cationic polymer.
A highly corrosion-resistant composite electroplated steel sheet characterized by forming a composite electroplating layer containing 5% by weight 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 are Si, Al, Zr, Ti, Cr
The highly corrosion-resistant composite electroplated steel sheet according to claims 1 and 2, comprising one or more of oxides of , Mo, and W. (4) The highly corrosion-resistant composite electroplated steel sheet according to claims 1 and 2, wherein the cationic polymer is a quaternary amine polymer.