JP2000192211A - Galvanizing method and galvanized material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve corrosion resistance and the coating property of coating layer by making crystal grain in the coating layer fine and restraining the development of scaly partial peeling. SOLUTION: In a hot-dipping high purity zinc bath having >=99.7 wt.% purity, an iron or iron alloy material is dipped to execute the first-step galvanizing. Successively, this material is dipped into a hot-dipping zinc base alloy bath containing by wt.% 4.0-10.0% Al, 0.1-0.5% Cu, 0.1-1.0% Mg and 100-1000 ppm Si to execute the second-step galvanizing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot dip galvanizing method using a zinc bath containing aluminum and a galvanized material obtained by the method. The present invention relates to a technique for enhancing the corrosion resistance of a plating layer, preventing flake-like partial peeling of a plating surface, and ensuring good adhesion to a paint during coating.

[0002]

2. Description of the Related Art Aluminum has high corrosion resistance.
Conventionally, a zinc bath containing aluminum has been used for plating a steel material such as a building material. In Japanese Patent Publication No. Hei 4-19299 proposed by the present applicant, in order to solve the problem that plating is not performed well in a zinc bath containing aluminum, the first-stage hot-dip galvanizing is performed in a high-purity zinc bath. The second stage hot dip galvanizing
A hot-dip galvanizing method performed in a zinc bath containing ８8% is proposed.

Japanese Patent Application Laid-Open No. 7-207421 discloses a technique in which the second-stage hot-dip galvanizing is performed in a zinc bath containing aluminum and magnesium to suppress the growth of intermetallic compounds and obtain a uniform plating layer. Is disclosed. Further, in Japanese Patent Application Laid-Open No. 57-35672, the second-stage hot-dip galvanizing is performed with aluminum,
There is disclosed a technique for further improving corrosion resistance by performing the treatment in a zinc bath containing at least one of copper, titanium, magnesium, and zirconium.

In the hot-dip galvanizing method described above, a highly corrosion-resistant zinc-aluminum alloy layer is formed on the entire surface of the plating film layer and the plating layer including the alloy layer.
It is known that in a salt spray test (Salt Shower Test, hereinafter referred to as SST), the time until red rust generation is 5,000 hours or more, and that the steel exhibits excellent corrosion resistance that is incomparable with ordinary hot-dip galvanizing.

[0005]

However, in the hot-dip galvanizing method, red rust hardly occurs even in a special test such as SST, but corrosion loss occurs in which the plating layer partially exfoliates in a scale-like manner. There is. In this case, no red rust was generated. For this reason, when a coating is applied to the plated product, there is a problem that the peeled portion comes out or the coating is peeled off with it (see FIG. 1B). As a result of studying the reason why such a phenomenon occurs, as shown in FIG. 4 (E), the present inventors found that in the conventional hot-dip galvanizing method performed in a zinc bath to which aluminum was added, the crystal grain of the plating film layer was formed. Was coarsened, and it was found that the corrosion partially penetrated into the plating layer through a fine shrinkage crack generated along the crystal grain boundary during solidification. In addition, it was found that when the plated metal solidified, shrinkage cracks reaching 50% or more of the thickness of the plating layer occurred in the direction of the depth from the surface of the plating layer (see FIG. 2).

[0006] In the two-stage hot-dip galvanizing method as described above, the iron-zinc alloy formed in the first-stage plating falls off in the bath in the second-stage plating, and a residue called dross is generated. There was a problem. This dross contaminates the plating bath and causes it to adhere to the product and impair the appearance. Was.

Accordingly, the present invention has been made in order to solve the above-mentioned problems of the prior art, and by making the crystal grain structure of a plating film layer fine, it is possible to prevent holes and the like generated in the plating layer as described above. Hot-dip galvanizing method and zinc capable of suppressing the depth, extending the corrosion resistance of plated products, and thus extending the life of the coated products, and suppressing the production of dross in the second plating bath to reduce the production cost The purpose is to provide a plating material.

[0008]

In the hot dip galvanizing method of the present invention, iron or iron alloy material is immersed in a high-purity zinc bath having a purity of 99.7% by weight or more to perform first-stage hot-dip galvanizing. The material is Al: 4.0 to 10.0 in weight ratio.
%, Cu: 0.1 to 0.5%, Mg: 0.1 to 1.0
%, Si: immersed in a zinc-based alloy bath containing 100 to 1000 ppm to perform second-stage hot-dip galvanizing. Hereinafter, the basis of the above numerical limitation will be described together with the operation of the present invention. In the following description, “%” means “% by weight”.

As high-purity zinc having a purity of 99.7% or more, distilled zinc, electric zinc or pure zinc can be used. Further, the first-stage zinc bath preferably contains 80 ppm or less of Al. By adding such a small amount of Al, zinc adheres uniformly to the surface of the material,
Diffusion of iron into the zinc-aluminum alloy generated by the second hot-dip galvanizing is suppressed.

Al: Al is an indispensable element for improving the corrosion resistance of the galvanized layer, and it is necessary that the zinc bath contains 4.0% or more in order to obtain the required corrosion resistance. On the other hand, if the Al content exceeds 10.0%, the melting temperature of the zinc bath is increased, and undesired results such as an increase in production cost and an increase in dross are produced. Therefore, A
The l content was 4.0 to 10.0%. However, the mere inclusion of Al cannot prevent the occurrence of deep shrinkage holes and the like that occur when the plating film layer solidifies. Therefore, in the present invention, refinement of crystal grains has been achieved by adding an appropriate amount of Si, Cu and Mg in addition to Al.

Si: The applicant of the present invention is Japanese Patent Publication No. 62-1861.
In the gazette of No. 8, 10 to 100 ppm of Si is contained in the zinc bath in order to make the Al concentration in the zinc bath uniform. The present inventors have paid attention to Si for the different purpose of refining the grain structure of the plating film layer. FIG. 3A shows a surface structure of a plating layer of a material plated by the hot-dip galvanizing method of the present invention. In the present invention, as a result of adding an appropriate amount of Si, a fine structure is uniformly distributed on the plating surface. Therefore, the occurrence of shrinkage cracks as shown in FIG. 3E can be prevented, and the corrosion resistance and paintability can be greatly improved. Here, FIG. 3 is a diagram showing a surface structure plated in a second-stage zinc bath containing the following components.
(A) is 5.8% Al, 0.57% Mg, 0.19% C
u, 0.04% Si, (B) is 6.2% Al, 0.47
% Mg, 0.21% Cu, (C) is 6.0% Al, 0.1%
43% Mg, 0.03% Si, (D) is 6.0% Al,
0.47% Mg, (E) is 7.0% Al.

The case where Si is not added to the plating bath (FIGS. 3B and 3D) and the case where Cu is not added (FIG. 3B)
In (C)), the material surface is finer, but the distribution is not uniform.
It is thought to be due to the synergistic effect of i and Cu. Further, as shown in FIG. 4, S
It can be seen that fine irregularities are uniformly generated only when both i and Cu are added. FIG. 4 is a chart when the surface of each material shown in FIG. 3 is measured by a surface roughness meter.
If the Si content is less than 100 ppm, the effect of refining the crystal grains cannot be obtained. The saturated solubility of Si in the bath is 1000 ppm or less. Therefore, the content of Si is set to 100 to 1000 ppm. In particular, the content of Si is preferably in the range of 430 to 680 ppm.

[0013] Cu: Cu can uniformly form a local battery even when α-Al or the like is generated, thereby contributing to the prevention of corrosion. In the present invention, however, Cu has a synergistic effect with Si on the plating surface. It works to distribute fine structures uniformly. If the Cu content is less than 0.1%, such effects cannot be obtained. Conversely, if the content exceeds 0.5%, no further effect of suppressing the formation of the local battery can be expected. Therefore, the content of Cu is set to 0.1 to 0.5%.

Mg: Mg is an element that prevents intergranular corrosion. In the present invention, Mg acts as a nucleus for the formation of equiaxed crystals together with Si and contributes to the refinement of crystal grains, and shrinkage caused by solidification during the cooling process. Suppress hole depth. Mg content is 0.
If it is less than 1%, such an effect cannot be obtained.
Conversely, if the content exceeds 1.0%, there is no change in the refinement of the microstructure and no further effect can be expected. In addition, oxides in the bath increase and waste of raw material costs increases. Become. Therefore, the content of Mg is set to 0.1 to 1.0%. In the plating according to the present method, even if the second-stage plating is performed immediately after the first-stage plating, dross does not occur much as compared with the case where only Al is added to the zinc bath. This is considered to prevent Si in the plating bath of the present method from concentrating near the plating interface and preventing Fe in the steel material from diffusing to the outside (see FIG. 5). Further, it is considered that the light metal such as Si or Mg is combined with the Fe-Al compound to form a compound having a lighter specific gravity and to easily float on the surface layer of the plating bath.

Elements other than zinc in the second hot-dip galvanizing can be contained by adding an Al casting alloy to high-purity zinc. As an aluminum casting alloy,
Cu: 2.0-4.0%, Mg: 0.5-1.
5%, Si: 8.5 to 10.5%, Ti: 1 to 20 pp
m, the balance: a composition composed of Al and unavoidable impurities can be used. In this case, Ti is 1 to 20
Since it contains ppm, it is more suitable for refining crystal grains.

Further, it is desirable to cool the material with hot water at 60 to 90 ° C. after the second step of galvanizing. By cooling the material in warm water after the second plating,
The temperature gradient of the plating layer becomes slow, the difference between the material temperature and the plating surface temperature becomes small, and shrinkage holes and irregularities formed during solidification, as well as grain boundary cracks, etc. can be suppressed. However, when the material is cooled with cold water, a temperature drop occurs between the material temperature and the plating surface layer, which causes a crack or the like to occur in the plating layer due to strain due to rapid shrinkage. The first stage bath temperature was 430
It is desirable that the immersion time is 0.5 to 2 minutes, and the material pulling speed is 5 to 8 m / min. Further, the bath temperature of the second stage is desirably 420 to 460 ° C, the immersion time is 0.5 to 1 minute, and the pulling speed of the material is desirably 0.5 to 3.5 m / min.

Next, the galvanized material of the present invention is a galvanized material in which an alloy plating layer mainly composed of zinc is coated on the surface of an iron or iron alloy material. Of alloy elements in the range of Al: 20 to 50%, Si: 1 to 5%, and Cu:
0.1 to 1.0%, and Mg: 0.1 to 1.0%. This galvanized material can be obtained by the hot-dip galvanizing method described above.

[0018]

Next, the present invention will be described in detail with reference to specific examples. 1. Preparation of Sample A. Example 1 An SS41 steel sample was immersed in an alkaline bath at a temperature of 80 ° C. for 30 minutes to perform degreasing, washed with hot water, and then immersed in a 10% hydrochloric acid solution (normal temperature) for 30 minutes to remove rust.
Next, the sample is immersed in a solution of ZnCl ₂ —NH ₄ Cl for 30 seconds to prevent oxidation of the base material by coating with chloride, and immersed in a pure zinc bath at 450 ° C. containing 60 ppm of Al for 1 minute. did. Next, the sample was pulled up, immersed in a 420 ° C. bath having an Al concentration of 5.7% by weight by adding an Al casting alloy to the purest zinc for 1 minute, and the pulled up sample was cooled with warm water at 80 ° C. In addition, due to the addition of the Al casting alloy, Cu: 0.19 to 0.20
%, Mg: 0.51% by weight, Si: 0.04% by weight, and Ti: 0.002% by weight.

B. Example 2 The components of the second-stage bath were as follows: Al: 7.2% by weight, Cu: 0.2
Hot-dip galvanizing was performed in the same manner as in Example 1 except that 6 wt%, Mg: 0.56 wt%, Si: 0.064 wt%, and Ti: 0.0025 wt%.

COMPARATIVE EXAMPLE For comparison, the same as in Example 1 above, except that the bath in the second stage was prepared by adding 5.7% by weight of Al to pure zinc, and was gradually cooled after plating. And hot-dip galvanized.

2. Evaluation In the hot-dip galvanizing described above, no dross was found in Examples 1 and 2, but was found in the comparative example. Further, the plating cross section of the sample of Example 1 was analyzed by an X-ray microanalyzer, and the element content at a plurality of locations from the background of the steel material to the plating layer side was quantitatively analyzed. Table 1 shows the results. Note that the measurement positions in Table 1 are points separated by 2 μm from the background to the plating layer side. According to Table 1, in the example, the Si concentration was 4.6 at a position 10 μm deep from the ground.
Wt%, and Si around the position
It can be seen that the concentration is high.

[0022]

[Table 1]

Next, the plating layers of the samples of Example 1 and Comparative Example were observed with a laser microscope, and the depth and the number of cracks from the plating layer surface were counted. The result is shown in FIG. As shown in FIG. 2, in Example 1, cracks having a depth of 20 μm or less were almost present, and the effect of crystal refinement by an alloy element such as Si was remarkably exhibited. On the other hand, in the comparative example, 4
Most of the cracks have a depth of 0 to 60 μm, and it can be assumed that corrosion easily proceeds to the inside.

3. Corrosion resistance test SS for pipe-shaped samples of Examples 1 and 2 and Comparative Example
When T was performed, Examples 1 and 2 and Comparative Example were 4600.
No red rust was observed at the time. However,
When the surface state of each sample was observed, in Examples 1 and 2, peeling of the surface portion of the plating layer did not occur as shown in FIG. On the other hand, in the comparative example, as shown in FIG. 1 (B), scale-like exfoliation occurred at the surface layer in some places.

In Example 2, the Al concentration in the bath was 7.
Since it is relatively high at 2% by weight, it is considered that stable operation can be performed with respect to the reduction due to the removal of Al from the plating bath. Therefore, even if the replenishment of the Al alloy casting is delayed during the plating operation, it is considered that the influence on the quality is small.

[0026]

As described above, in the present invention,
Since an appropriate amount of Si, Cu and Mg is contained in the second-stage zinc bath, crystal grains can be refined to prevent the occurrence of scale-like partial exfoliation in the surface layer portion, and the surface can be finely divided. Since the structure is uniformly dispersed, the corrosion resistance and the paintability can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a view showing a state of a sample subjected to a salt spray test, wherein (A) shows an example and (B) shows a comparative example.

FIG. 2 is a diagram showing the relationship between the depth of a crack from the plating layer surface and the number of cracks.

FIG. 3 is a view showing the surface texture of various plating layers.

FIG. 4 is a diagram showing the surface roughness of various plating layers.

FIG. 5 is a diagram showing the effect of preventing the elution of Fe by the addition of Si.

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[Procedure amendment]

[Submission date] October 28, 1999 (1999.10.
28)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 2

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[Procedure amendment 2]

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[Correction target item name] Claim 3

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[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] Claim 4

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[Procedure amendment 4]

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[Correction target item name] Claim 5

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[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

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[0015] A zinc base used for the second stage hot-dip galvanizing.
In an aluminum alloy bath, an aluminum casting alloy is added to high-purity zinc.
In addition, the alloy bath contains elements other than zinc.
Can be done. As an Al casting alloy, Cu: 2.0 to 4.0%, Mg: 0.5 to 1.5%, S
i: 8.5 to 10.5%, Ti: 1 to 20 ppm, balance: Al and an unavoidable impurity can be used. In this case, 1-20 ppm of Ti
Since it is contained, it is more suitable for refining crystal grains.

[Procedure amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction contents]

Next, the galvanized material of the present invention is a galvanized material in which an alloy plating layer mainly composed of zinc is coated on the surface of an iron or iron alloy material .
The concentration of alloying elements in the range of 20 μm from the surface of the iron or iron alloy material to be processed is : Al: 20 to 50% by weight, Si:
1 to 5%, Cu: 0.1 to 1.0%, Mg: 0.1 to
1.0% , balance: Zn and inevitable impurities . This galvanized material can be obtained by the hot-dip galvanizing method described above.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Toshio Narita 1-9-9-8 Shinkotoni, Kita-ku, Sapporo, Hokkaido (72) Inventor Junichi Tanaka 9-2, 4-5-1 Shinoji, Shino, Kita-ku, Sapporo, Hokkaido ( 72) Inventor Yusaku Masuda 1-1-2, Shiroganecho, Hitachi City, Ibaraki Prefecture Nippon Mining & Metals Co., Ltd.Hitachi Plant Technology Development Center (72) Inventor Koji Vice 1-2-1, Shiroganecho, Hitachi City, Ibaraki Prefecture Nikko Metals Stock F-term (reference) in Hitachi Technology Development Center, Hitachi, Ltd. 4K027 AA06 AA22 AB05 AB07 AB09 AB26 AB42 AB44 AC47 AC72 AE03 AE18 AE21

Claims (5)

[Claims] An iron or iron alloy material is immersed in a high-purity zinc bath having a purity of 99.7% by weight or more to perform first-stage hot-dip galvanizing.
10.0%, Cu: 0.1 to 0.5%, Mg: 0.1 to
A hot-dip galvanizing method characterized by immersing in a zinc-based alloy bath containing 1.0% and Si: 100 to 1000 ppm to perform second-stage hot-dip galvanizing. 2. The element other than zinc contains A in high purity zinc.
The hot dip galvanizing method according to claim 1, wherein the zinc bath is contained in the zinc bath by adding a casting alloy. 3. The Al casting alloy has a weight ratio of Cu:
2.0-4.0%, Mg: 0.5-1.5%, Si:
8.5 to 10.5%, Ti: 1 to 20 ppm, balance: A
The hot-dip galvanizing method according to claim 1, wherein the hot-dip galvanizing method comprises l and unavoidable impurities. 4. The hot-dip galvanized steel according to claim 1, wherein the material is cooled with hot water at 60 to 90 ° C. within one minute after the second hot-dip galvanizing. Plating method. 5. A galvanized material in which a surface of an iron or iron alloy material is coated with an alloy plating layer mainly composed of zinc, wherein 0 to 20 μm from the surface of the material to the alloy plating layer side.
Of the alloy element in the range of Al: 20 to 50 by weight ratio.
%, Si: 1 to 5%, Cu: 0.1 to 1.0%, Mg:
A galvanized material having a content of 0.1 to 1.0%.