JP2001329354A - Hot dip zinc-aluminum alloy plated steel sheet excellent in chemical conversion treatability and its production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a steel sheet where both of the corrosion resistance and the chemical conversion treatability of a hot dip zinc-aluminum alloy plated steel sheet are improved. SOLUTION: The hot zinc aluminum alloy plated steel sheet excellent in the corrosion resistance as well as the chemical conversion treatability can be obtained by plating with plating bath composed by mass % of 0.5-20% Al, >2% to 10% Mg and the balance Zn with inevitable impurities to attain >=50% of surface length ratio of Zn-Al-Mg eutectic + Zn single phase on the plated surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel sheet having improved corrosion resistance and chemical conversion property of a hot-dip zinc-aluminum alloy-coated steel sheet and a method for producing the same.

[0002]

2. Description of the Related Art Hot-dip Zn-coated steel sheets have been improved in corrosion resistance.
-55% Al steel sheet and the like. Hot-dip Zn-5% Al steel sheet has recently been used because of its high corrosion resistance, but the melting point of the alloy is high and the line is restricted. The end face corrosion resistance after coating is poor and the cost is high. There is a demand for improved corrosion resistance. This plated steel material is frequently used for building materials and home appliances, and is used bare or painted. In the case of applying a coating, the substrate may be subjected to phosphating, and excellent phosphating properties are required. However, Al is eluted in the phosphating solution and the treating solution is deteriorated, the phosphating property is deteriorated, the amount of the film is reduced, and formation failure such as generation of transparency may occur rarely,
Methods such as strengthening of degreasing and strengthening of surface adjustment have been adopted, but this is a cost constraint. In addition, there is a problem that black change is easily caused by the presence of the eutectic phase of the plating layer as compared with hot-dip plating.

To solve these problems, the following proposals have been made.

(1) Japanese Patent Application Laid-Open No. 9-228017 discloses molten Zn-containing Al at 2 wt% or more and 6 wt% or less.
There is disclosed a technique in which the surface treatment of an Al-based alloy-plated steel sheet has a β phase or a eutectic phase with the β phase, and a lower layer has a eutectic phase, thereby improving the phosphatability.

(2) Japanese Patent Application Laid-Open No. 60-110860 discloses that the weight percentage of Al in a Zn-Al layer is set to 7% or less, a Zn-rich phase exists on the plating surface, and a eutectic continuous inside the plating layer. A technique in which a layer is present to improve corrosion resistance and chemical conversion treatment is disclosed.

(3) JP-A-58-177449 discloses that Al is 0.1 to 25.0 wt% and Mg is 0.05
~ 2.0wt%, Sb is 0.005-1.5wt%, P
b is 0.01 wt% or less, and the balance consists of Zn and unavoidable impurities. By Zn-Al-based alloy plating, Sb is distributed as an Al-Sb compound throughout the plating phase surface layer to finely crystallize the phosphate-treated film. There is disclosed a technique for improving the coating property by improving the paintability.

(4) Japanese Patent Application Laid-Open No. 61-231178 discloses that the surface of a Zn—Al alloy-plated steel sheet is coated with a Co—P alloy by an electroless immersion treatment to thereby improve phosphatability and blackening. Techniques for improving are disclosed.

However, the above technique has the following problems.

In the techniques (1) and (2), bare corrosion resistance was inferior because the Al content was not high, and as a result of investigation, blackening was inferior.

The technique (3) has no description of blackening resistance, and according to the investigation by the present inventors, the blackening resistance was inferior.
As a result of the investigation, the technique (4) was inferior in phosphatability and blackening resistance.

[0011]

In view of these circumstances, it is an object of the present invention to obtain a plated steel sheet having good corrosion resistance and blackening and excellent chemical conversion treatment in an Al-Zn-containing steel sheet. An object of the invention is to provide the steel sheet and a manufacturing method.

[0012]

As a measure for improving the corrosion resistance and the chemical conversion treatment of a Zn-5% Al-plated steel sheet, it is not effective to change the structure of the outermost plating layer. Based on the recognition, Zn-Al
Attention was paid to adding Mg to the alloy. As a result, it was found that chemical conversion treatability is improved when the plating surface is Zn-Al-Mg ₃ ternary eutectic.

This is probably because the presence of Mg activated the surface. As a result of further investigation, it was found that the Zn—Al—Mg eutectic on the plating surface and the surface length ratio of the Zn phase =
When expressed as (surface length of Zn-Al-Mg eutectic and Zn phase) / surface length x 100 (%), it was found that when this is 50% or more, the chemical conversion treatment is excellent. .

Here, the Zn phase and the Zn-Al-Mg eutectic represent a plating layer structure. The former is almost a single Zn phase, and the latter is close to an average plating composition. By subjecting the plated plate to light corrosion treatment, it becomes whitish petal-like and streak-like, respectively, and can be easily identified.

In order to further improve the chemical conversion,
An attempt was made to replace the surface with a transition metal after plating. Then, they found that the chemical conversion treatment was promoted by performing the substitution treatment.

The present invention has been completed based on such findings, and the gist thereof is as follows.

(1) Al: 0.5 to 20% by mass
%, Mg: more than 2% to 10%, the balance being Zn and unavoidable impurities.
A hot-dip zinc-aluminum alloy-plated steel sheet having excellent chemical conversion properties, characterized in that the surface length ratio of a Mg eutectic + Zn single phase is 50% or more.

(2) Al: 0.5 to 20% by mass
%, Mg: more than 2% to 10%, Si: 0.01 to 2.0
%, The balance being Zn and unavoidable impurities, and having a surface length ratio of Zn-Al-Mg eutectic + Zn single phase of the plating surface of 50% or more. Excellent hot-dip zinc-aluminum alloy plated steel sheet.

(3) The plating layer according to (1) or (2) further contains at least one of Pb, Ti, Mn, Sn, and Ni in an amount of 0.01 to 0.5%, A hot-dip zinc-aluminum alloy coated steel sheet excellent in chemical conversion treatment, characterized in that the surface length ratio of a Zn-Al-Mg eutectic + Zn single phase on a plating surface is 50% or more.

(4) It has a plating layer according to any one of the above (1) to (3), and has a Zn-Al-M
g eutectic + Zn single phase has a surface length ratio of 50% or more, and has a transition metal layer of 0.1 mg / m ^{2 to 1} g / m ^{2 as} an upper layer, and is excellent in chemical conversion treatment property. Molten zinc
Aluminum alloy plated steel sheet.

(5) Al: 0.5 to 20% by mass
%, Mg: more than 2% to 10%, and plating in a plating bath composed of a balance of Zn and unavoidable impurities, and Zn-
The surface length ratio of the Al-Mg eutectic + Zn single phase is set to 50% or more, and further a transition metal substitution treatment is performed so that a transition metal layer of 0.1 mg / m ^{2 to 1} g / m ² is formed thereon. A method for producing a hot-dip zinc-aluminum alloy-plated steel sheet having excellent chemical conversion properties.

(6) Al: 0.5 to 20% by mass
%, Mg: more than 2% to 10%, Si: 0.01 to 2.0
%, The balance being Zn and inevitable impurities, plating by plating, the surface length ratio of the Zn-Al-Mg eutectic + Zn single phase on the plating surface is 50% or more, and the transition metal substitution treatment is performed. 0.1 mg / m ^{2 to 1} g for upper layer
A method for producing a hot-dip zinc-aluminum alloy-plated steel sheet having excellent chemical conversion properties, characterized by having a transition metal phase of / m ² .

(7) The plating bath according to (5) or (6) further contains at least one of Pb, Ti, Mn, Sn and Ni in an amount of 0.01 to 0.5%. After plating in a plating bath, the surface length ratio of the Zn-Al-Mg eutectic + Zn single phase on the plating surface is set to 50% or more, and further, a transition metal replacement treatment is performed to add 0.1 mg to the upper layer.
A method for producing a hot-dip zinc-aluminum alloy-plated steel sheet having excellent chemical conversion properties, characterized in that the steel sheet has a transition metal phase of ¹ g / m ^{2 to 1} g / m ² .

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

Al in the plating layer is added for improving corrosion resistance. If less than 0.5%, the corrosion resistance is inferior, and 20%
Above, the corrosion resistance improving effect is saturated and the chemical conversion property deteriorates, so the content is set to 0.5 to 20%.

Mg is an important element for the present invention.
Mg is an active element compared to Al, and its corrosion products have the effect of increasing the corrosion resistance of the plated steel sheet. In addition, in the transition metal treatment of the chemical conversion treatment, Mg is easily replaced and the replacement speed increases. . When the content is 2.0% or less, the effect of improving corrosion resistance is reduced, the transition metal substitution treatment speed is reduced, and blackening is also deteriorated. On the other hand, if it exceeds 10%, dross is generated so much that there is a problem in operation, so that it exceeds 2.0%.
10%.

Si is an element added for improving corrosion resistance, and it is necessary to add 0.01% or more to obtain the effect. If the content exceeds 2.0%, the chemical conversion property deteriorates, so the content was set to 0.01 to 2.0%.

Pb, Ti, Mn, Sn, and Ni are one or more elements that may be added in some cases in order to improve the chemical conversion property by being unevenly distributed in the plating layer. Less harm to corrosion resistance and blackening resistance. In order to exert a sufficient effect, 0.01% or more must be added. 1.0%
Exceeds 0.01%, the effect is saturated. Preferably it is 0.01-0.5%.

The distribution of the Zn-Al-Mg eutectic and the Zn phase on the surface of the plating layer is also important. FIG. 1 shows a cross-sectional photograph of the plating obtained by the present invention after etching. In the figure, those that look like streaks are Zn-Al-Mg eutectic 1 and those that look like white petals are Zn single phase 2. The presence of these layers on the surface improves the chemical conversion treatment property. In addition, 3 in a figure is Zn-Al-Mg eutectic + Zn single phase, 4
Indicates a plating length, 5 indicates a plating layer, and 6 indicates a base iron. Here, the Zn-Al-Mg eutectic on the plating surface and Z
The surface length ratio of the n single phase is represented by (surface length of Zn-Al-Mg eutectic and Zn single phase) / surface length x 100 (%).

Next, the manufacturing conditions will be described.

The plating can be produced by a commonly used hot-dip plating line such as a Sendzimir type or a flux type. In some cases, pre-plating of Ni or the like before plating does not hinder.

After the plating, the surface replacement treatment with a transition metal such as Ni, Co, Fe or the like improves the chemical conversion treatment speed and makes the effect of the present invention more remarkable. This method can use any of immersion treatment, spray treatment, or dry treatment.
The adhesion amount is less than 0.1 mg / m ^2, no effect of improving the chemical conversion treatability, since the corrosion resistance is deteriorated more than 1 g / m ^2, was ^{0.1mg / m 2 ~1g / m 2} . After that, it is needless to say that the corrosion resistance can be further improved by performing a treatment such as chromate.

[0033]

EXAMPLES The original plate used was S described in JIS G3141.
PCC was used. This was reduced to a thickness of 0.8
A steel sheet having a thickness of 1 mm was hot-dipped using plating baths having different compositions such as Al, Mg, and Si to produce a steel sheet as shown in Table 1. The plating bath temperature was 390 ° C to 485 ° C. Wiping was performed using high-temperature nitrogen with the aim of 120 g / m ² . The temper rolling reduction was 1%. The metal replacement treatment after plating was performed by immersing for 1 second using a Co sulfate solution, a Ni sulfate, or an iron sulfate solution adjusted to a concentration of 50 to 150 g / m ² and a pH of ² to 5. The surface length ratio of the plating layer is as follows.
After performing an etching treatment with 1% hydrochloric acid for 2 minutes, observing the outermost layer of the plating at a magnification of 400 with an optical microscope, a stripe-like Zn-Al-Mg eutectic +
The length was calculated by determining the length of the Zn single phase portion.

The chemical conversion treatment is a zinc phosphate treatment using PALBOND 3308 manufactured by Nippon Parker Rising, and a bath temperature of 6%.
Chemical conversion treatment with n = 5 was performed under severer conditions than the standard conditions of 0 ° C. and spray treatment time of 1 to 5 seconds, and the adhesion amount was determined by a wet method. The evaluation was based on the amount of adhesion and the presence or absence of transparency.
The chemical conversion treatment rate is evaluated by the amount of adhesion when the spray time is 1 second, and it is sufficient if the conversion rate is about 0.4 g / m ² or more.
Desirably, it is at least m ² . The adhesion amount was evaluated by the adhesion amount when the spraying time was 5 seconds, and was 1 to 2 g / m2.
² was passed.

The blackening test was conducted at 50 ° C. and 80% humidity after packing.
Was visually observed after being left for 2 weeks in the above environment. X indicates rejection, は indicates good, ◎ indicates extremely good, and these are acceptable.

In the corrosion resistance test, a salt water spray test was performed using a bare flat plate portion, and the evaluation was made based on the time until the occurrence of red rust. × is 300
Failed in less than 0 hours. ○: Passed after 3000 hours or more, ◎
Is passed after 3500 hours or more, and ○ and ◎ are passed.

No. 1 to No. 26 is an example of the present invention,
Excellent chemical conversion treatment, blackening, and corrosion resistance. In particular, in the case of No. 3-No. 5, no.
8, no. 11-No. In No. 14, etc., the amount of adhesion is 0.7 g / m ² or more even with a short time of 1 second spray treatment, and the chemical conversion treatment speed is good.

No. 27-No. 31 is a comparative example,
No. 27, no. No. 28 is poor in chemical conversion treatment, blackening resistance, corrosion resistance, etc. because Mg is too small. No. 29 is M
Since the g is too small, the chemical conversion property and the blackening resistance are poor. N
o. In No. 30, the corrosion resistance is deteriorated because the metal substitution treatment layer is too thick. No. Sample No. 31 has an excessively high amount of Al and an excessively small amount of Mg, so that the chemical conversion property and the corrosion resistance are poor.

[0039]

[Table 1]

[0040]

As described above, the plated steel sheet of the present invention has an unprecedented chemical conversion treatment having both blackening resistance and corrosion resistance, and is suitable for use in building materials, civil engineering, automobiles and the like. Useful.

[Brief description of the drawings]

FIG. 1 is a view showing a photograph of a cross section after etching of plating according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Zn-Al-Mg eutectic 2 Zn single phase 3 Zn-Al-Mg eutectic + Zn single phase 4 Plating length 5 Plating 6 Ground iron

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Gen Moto Onozawa 1 Kimitsu, Kimitsu City Inside Nippon Steel Corporation Kimitsu Works (72) Inventor Kazuhiko Honda 1 Kimitsu, Kimitsu City Nippon Steel Corporation Kimitsu Inside the steelworks (72) Inventor Akira Takahashi 1 Kimitsu, Kimitsu City Inside the Nippon Steel Corporation Kimitsu Works (72) Inventor Yasuhide Morimoto 20-1 Shintomi, Futtsu City Inside the Technology Development Division, Nippon Steel Corporation (72) Inventor Masao Kurosaki 20-1 Shintomi, Futtsu City Nippon Steel Corporation Technology Development Division (72) Inventor Kazumi Nishimura 1 Fujimachi, Hirohata-ku, Himeji City Nippon Steel Corporation Hirohata Inside the ironworks (72) Inventor Go Miyake 1 Kimitsu, Kimitsu City Nippon Steel Corporation Inside the Kimitsu Works

Claims (7)

[Claims] 1. Al in mass%: 0.5-20%, M
g: More than 2% to 10%, having a plating layer composed of Zn and unavoidable impurities, with Zn-Al-Mg on the plating surface
A hot-dip zinc-aluminum alloy-coated steel sheet having excellent chemical conversion properties, wherein the surface length ratio of a eutectic + Zn single phase is 50% or more. 2. In mass%, Al: 0.5 to 20%, M
g: more than 2% to 10%, Si: 0.01 to 2.0%, having a plating layer composed of Zn and unavoidable impurities, and a surface of a Zn-Al-Mg eutectic + Zn single phase on the plating surface A hot-dip zinc-aluminum alloy-plated steel sheet having excellent chemical conversion property, wherein the length ratio is 50% or more. 3. The plating surface according to claim 1, further comprising 0.01 to 0.5% of at least one of Pb, Ti, Mn, Sn and Ni. The surface length ratio of the Zn-Al-Mg eutectic + Zn single phase of
% Of a hot-dip zinc-aluminum alloy-plated steel sheet having excellent chemical conversion property. 4. The plating layer according to claim 1, wherein a surface length ratio of a Zn—Al—Mg eutectic + Zn single phase on a plating surface is 50% or more. A hot-dip zinc-aluminum alloy-plated steel sheet having excellent chemical conversion properties, comprising an upper layer having a transition metal layer of 0.1 mg / m ^{2 to 1} g / m ² . 5. Al: 0.5 to 20% by mass%, M
g: More than 2% to 10%, plated with a plating bath consisting of the balance of Zn and unavoidable impurities, and Zn-Al-
By making the surface length ratio of the Mg eutectic + Zn single phase 50% or more and further performing a transition metal substitution treatment,
Molten zinc excellent in chemical conversion treatment characterized by having a transition metal layer of 0.1 mg / m ^{2 to 1} g / m ^2-
Manufacturing method of aluminum alloy plated steel sheet. 6. Al: 0.5 to 20% by mass, M
g: more than 2% to 10%, Si: 0.01 to 2.0%, balance
Plating in a plating bath composed of Zn and unavoidable impurities
Table of Zn-Al-Mg eutectic + Zn single phase on plating surface
The surface length ratio is set to 50% or more, and a transition metal replacement treatment is performed.
0.1 mg / m in the upper layer ^Two~ 1g / m^Two
Characterized by having a transition metal phase of
Hot-dip zinc-aluminum alloy coated steel sheet with excellent processability
Manufacturing method. 7. A plating bath according to claim 5, further comprising at least one of Pb, Ti, Mn, Sn, and Ni in an amount of 0.01 to 0.5%. And Zn-Al-Mg eutectic + Zn on the plating surface
By making the surface length ratio of the single phase 50% or more, and further performing transition metal substitution treatment, 0.1 mg / m ²
A method for producing a hot-dip zinc-aluminum alloy-plated steel sheet excellent in chemical conversion treatment, characterized by having a transition metal phase of ¹ g / m ^{2 to 1} g / m ² .