JP2003055777A - Chromate-free treated hot-dip zinc-aluminum alloy coated steel sheet with excellent weldability and corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hot-dip zinc-aluminum alloy-plated steel sheet which has been subjected to a post-treatment that does not contain chromate and has excellent weldability and corrosion resistance. SOLUTION: On the surface of a steel sheet, Mg: 1 to 10% by mass, Al: 2
-19% by mass, Si: 0.01-2% by mass, and Mg and Al
Satisfies the following formula: Mg (% by mass) + Al (% by mass) ≦ 20% by mass, the balance forms a Zn alloy plating layer composed of Zn and unavoidable impurities, and further has a zirconium compound of 10 to A coating containing 30% by mass and 5 to 20% by mass of a vanadyl compound as vanadium is formed on at least one surface in an amount of 200 to 1200 mg / m ² .

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a chromate-free hot-dip zinc-aluminum alloy plated steel sheet having excellent weldability and corrosion resistance.

[0002]

2. Description of the Related Art Hot-dip zinc-aluminum plated steel sheets are superior in corrosion resistance as compared with hot-dip galvanized steel sheets, and therefore, their application to a wide range of applications such as building materials, automobiles, home electric appliances, etc. is being studied. Among them, Zn-Al-Mg-Si alloy plating containing Mg and Si has excellent corrosion resistance and is expected to be applied to various applications as a next-generation plated steel sheet. However, while having excellent corrosion resistance, the inclusion of Al has the drawback of poor weldability. This is because the melting point of normal zinc is about 419 ° C, but the melting point drops to 400 ° C or less due to the inclusion of Al, the plating layer melts easily during welding, the contact area with the electrode increases, and the welding current increases. This is because the density is reduced, the nugget formed is reduced, and Cu-Zn alloy is easily generated on the electrode surface, resulting in severe wear of the electrode.

As a method of improving the weldability in such galvannealing, a technique of forming an oxide film containing ZnO as a main component on the plating surface (Japanese Patent Laid-Open No. 2-004983),
Technique for improving weldability by promoting Fe alloying by adding Ti to Zn-5% Al plating (JP-A-5-263210), zinc-
Techniques such as forming a silica film on the surface of an aluminum-based hot-dip coating to improve weldability (Japanese Patent Laid-Open No. 6-336664) have been proposed. However, in practical use, there are restrictions on equipment, cost, performance balance, etc. I have a problem.

Further, although the hot-dip zinc-aluminum alloy plating is excellent in corrosion resistance, white rust is generated on the plating surface layer in the same manner as normal hot-dip galvanizing in an environment containing salt such as seawater or in a high temperature and high humidity environment, and appearance. There is a problem that surface properties such as surface and surface conductivity are significantly impaired.

As a means for preventing the occurrence of white rust, a chemical conversion treatment called chromate treatment has been conventionally used. Examples of the chromate treatment include electrolytic chromate, coating chromate, and reactive chromate.

Among the chromate films obtained by these treatments, the chromate film formed by electrolytic treatment or the like is mainly composed of trivalent chromium, and although the elution of hexavalent chromium is small, it cannot be said that the anticorrosion property is sufficient, If the film is damaged by a large amount of time, its corrosion resistance decreases. On the other hand, the coating containing a large amount of hexavalent chromium formed by coating type chromate treatment etc. has a high corrosion resistance and is particularly excellent in the corrosion resistance of the processed part, but it has the problem that the elution of hexavalent chromium from the chromate coating is large. ing. For this reason, the chromate treatment containing hexavalent chromium is not only problematic regarding waste liquid treatment in the treatment process and safety for workers, but also the environmental impact due to elution of hexavalent chromium is a problem.

[0007]

In view of such circumstances, the present invention improves the weldability of the conventional zinc-aluminum alloy plating and has a chromate-free treatment hot-dip zinc-aluminum alloy plating having excellent corrosion resistance. It provides a steel plate.

[0008]

[Means for solving the problems] The deterioration of the weldability is caused by the expansion of the current-carrying area and the Cu-Zn on the electrode due to the melting point drop of the plating alloy
Due to wear of electrodes due to alloy formation. Therefore, the aim was to solve the problem by providing a chromate-free coating on the plating surface layer, which is capable of suppressing these defective factors and has excellent corrosion resistance. As a result of extensive studies on various coatings, it was confirmed that the desired weldability and corrosion resistance could be obtained by applying a coating containing a zirconium compound or a vanadyl compound.

Although the mechanism of manifestation of weldability and corrosion resistance is not clear, a treatment solution containing zirconium carbonate complex ions and vanadyl ions is applied to a plated steel sheet containing Al and dried to obtain a zirconium compound and a vanadyl compound. To form a dense three-dimensional film.
For this weldability, this dense coating increases the electrical resistance of the steel sheet surface to increase the amount of heat generation and promotes the formation of weld nuggets, and the presence of the dense coating prevents direct contact between the electrode and the plated metal. It is considered that the formation of Cu-Zn alloy is suppressed and the wear of the electrode is suppressed.

Regarding the corrosion resistance, it is considered that the dense structure of the film exerts an excellent barrier property and the corrosion factor is shielded from the plating metal, whereby the excellent corrosion resistance can be obtained. Incidentally, the vanadyl compound in the film, in a wet environment, can be expected to have a so-called self-repairing action of reacting with the plating metal of the layer defect portion to form a protective layer, which also contributes to the development of excellent corrosion resistance. Conceivable.

That is, the gist of the present invention is as follows. (1) The surface of the steel sheet contains Mg: 1 to 10% by mass, Al: 2 to 19% by mass, Si: 0.01 to 2% by mass, and Mg and Al are represented by the following formula Mg (mass%) + Al ( %) ≤ 20% by mass and the balance has a Zn alloy plating layer consisting of Zn and unavoidable impurities. Further, the surface layer thereof has a zirconium compound content of 10 to 30 mass% and a vanadyl compound content of 5 to 5 vanadium. A chromate-free hot-dip zinc-aluminum alloy-plated steel sheet having excellent weldability and corrosion resistance, which has a coating containing 20 mass% of 200 to 1200 mg / m ^{2 on} at least one side as an adhesion amount. (2) The chromate-free hot-dip zinc-aluminum alloy plated steel sheet according to (1) above, wherein the coating film contains an organic acid in a solid content of 20 to 50 mass%. (3) The chromate-free treated hot dip zinc-aluminum alloy plated steel sheet according to any one of the above (1) to (2), wherein the coating film contains a phosphoric acid compound as PO _{4 in} an amount of 10 to 30 mass%. (4) The chromate-free treated hot dip zinc-aluminum alloy plated steel sheet according to any one of (1) to (3) above, wherein the coating contains a silica compound as SiO _{2 in} an amount of 10 to 30 mass%. (5) The chromate-free hot-dip zinc-aluminum alloy plated steel sheet according to any one of (1) to (4), wherein the coating contains a fluorine compound as F in an amount of 5 to 20% by mass. (6) The chromate-free hot-dip zinc-aluminum alloy plated steel sheet according to any one of (1) to (5) above, wherein the coating film contains 0.1 to 15 mass% of a lubricating component.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
First, the plating components will be described. Al in the plating layer is added to improve the corrosion resistance. If it is less than 2% by mass, sufficient improvement in corrosion resistance cannot be obtained, and if it exceeds 19% by mass, the effect of improving corrosion resistance is saturated and weldability is significantly reduced.
The Al content was 2 to 19 mass%. The purpose of adding Mg is also to improve the corrosion resistance. If it is less than 1% by mass, the effect of improving the corrosion resistance is insufficient, and if it exceeds 10% by mass, the plating layer becomes brittle and the adhesion is deteriorated. Therefore, the Mg content is 1 to 10% by mass.
And

The purpose of adding Si is to improve the corrosion resistance and to improve the plating adhesion by suppressing the reaction between Al and Fe in the plating layer. If it is less than 0.01% by mass, the effect of its addition is insufficient,
This is because if it exceeds 2% by mass, the effect of improving plating adhesion cannot be recognized.

The content of Mg and Al is calculated by the formula Mg (mass%) + Al
The reason for limiting to (mass%) ≤ 20 (mass%) is that when the Zn content in the plating layer becomes low, the sacrificial anticorrosion effect is lowered and the corrosion resistance is lowered.

Further, in addition to the above composition, F is contained in the plating layer.
Elements such as e, Ti, Ni, Sb, and Pb may be contained within 1 mass% individually or in combination. The coating weight is not particularly limited, but from the viewpoint of corrosion resistance, 10 g / m ² or more,
From the viewpoint of weldability and workability, it is preferably 350 g / m ² or less.

As a method for producing hot dip coating, there are a flux method, a Sendzimir method, a method of pre-plating Ni or the like to secure wettability, but any method may be used.
Also, for the purpose of changing the appearance after plating, spray water spray, steam spray, sodium phosphate solution or
Zn powder, further Zn phosphate powder, Mg hydrogen phosphate powder, or an aqueous solution thereof may be sprayed. After plating,
Before forming the film of the present invention, surface adjustment may be performed with a Co sulfate solution, a Ni sulfate solution, or the like in order to prevent discoloration of the plating.

As a method for forming a film, zirconium carbonate complex ion: [Zr (CO ₃ ) ₂ (OH) ₂ ] ²⁻ or [Zr (CO ₃ ) 2
₃ (OH)] ^3- and vanadyl ion: VO ²⁺ is applied to the surface of the steel sheet, the moisture is removed by heating, and the coating is dried to form a dense three-dimensional film with excellent barrier properties. To form.

Here, the zirconium carbonate complex ion is [Zr
(CO ₃ ) ₂ (OH) ₂ ] ^2- or [Zr (CO ₃ ) ₃ (OH)] ^3- ammonium salt, potassium salt, sodium salt and the like are supplied. Vanadyl ions (VO ²⁺ ) are used in hydrochloric acid, nitric acid, phosphoric acid,
The oxovanadium cation is supplied by a salt with an inorganic acid such as sulfuric acid, or an organic acid anion such as formic acid, acetic acid, propionic acid, butyric acid, and oxalic acid.

The zirconium compound contained in the film is preferably 10 to 30% by mass as zirconium, and the vanadyl compound is preferably 5 to 20% by mass as vanadium. Zirconium content is less than 10% by mass or vanadium content is 5
If less than mass%, the target corrosion resistance cannot be obtained, while if the content of zirconium exceeds 30 mass% or the content of vanadium exceeds 20 mass%, the corrosion resistance improving effect is Not economical because it saturates.

By adding an organic acid in the film, the corrosion resistance can be further improved. Examples of the organic acid include glycolic acid, malic acid, tartaric acid, citric acid, ascorbic acid, lactic acid, dehydroacetic acid, dehydrobenzoic acid, dehydroascorbic acid, gallic acid, tannic acid, and ammonium salts thereof. In the treatment liquid, these organic acids form a stable chelate complex with vanadyl ion.

As the vanadyl ion source, compounds such as vanadyl glycolate, vanadyl tartrate and vanadyl dehydroascorbate which have already been complexed with vanadyl ion using an organic acid as a ligand can be used. Does not require additional addition of organic acid.

The content of the organic acid contained in the film is preferably 20 to 50% by mass as the solid content. When the content of the organic acid is less than 20% by mass, the ability to form a chelate complex with vanadyl ions is weak and thus the effect of improving corrosion resistance is poor. On the other hand, when it exceeds 50% by mass, the ability to form a chelate with vanadyl ions is poor. It is not economical because it saturates.

Further, by adding a phosphoric acid compound, a silica compound or a fluorine compound into the film, it is possible to further improve the corrosion resistance. Examples of the phosphoric acid compound include ammonium phosphate, potassium phosphate, sodium phosphate and the like. Examples of the silica compound include vapor phase silica and silica sol. Examples of the fluorine compound include hydrofluoric acid salts and complex fluoride salts.

The content of the phosphoric acid compound in the coating is preferably 10 to 30% by mass as PO ₄ . PO ₄
By setting the content of 10% by mass or more, a further effect of improving corrosion resistance can be obtained. On the other hand, if it exceeds 30% by mass, the effect of improving the corrosion resistance will be saturated, so that addition of more than this is not economical. In the case of a silica compound, SiO ₂ is preferably 10 to 30% by mass. By setting the content of SiO ₂ to 10 mass% or more,
A further effect of improving corrosion resistance can be obtained. On the other hand, if the amount exceeds 30% by mass, the effect of improving the corrosion resistance is saturated, so addition of more than this is not economical. In the case of a fluorine compound, F as 5 to
20 mass% is preferable. If the F content is less than 5% by mass, the effect of improving corrosion resistance is poor, and if it exceeds 20% by mass, the effect of improving corrosion resistance is saturated, which is not economical.

In the present invention, molybdenum disulfide, graphite, tungsten disulfide, boron nitride, graphite fluoride, cerium fluoride, melamine cyanurate, fluororesin wax, polyolefin wax, etc. are used as lubricating components in the coating. It is possible to improve workability, scratch resistance, etc. by adding The content of the lubricating component contained in the coating is preferably 0.1 to 15% by mass. If the content of the lubricating component is less than 0.1% by mass, processability,
The effect of improving scratch resistance is poor, and when it exceeds 15% by mass, the effect of improving workability and scratch resistance is saturated, which is not economical.

Further, an antifoaming agent or a leveling agent may be added to the film within a range that does not impair the original performance.

The amount of the film deposited is preferably 200 to 1,200 mg / m ² . If the adhesion amount is less than 200 mg / m ² , sufficient corrosion resistance cannot be obtained. Further, even if the adhesion amount exceeds 1,200 mg / m ² , further improvement in corrosion resistance cannot be expected, but rather, there is concern that corrosion resistance may deteriorate due to decreased adhesion, increased damage in the processed part, etc. Amount is 1,200 mg / m ²
The following is desirable.

The method of forming the film in the present invention is not particularly limited, and any method such as a spray method, a dipping method, a coater roll method, a Ringer roll method and an air-knife method can be used.

Although heating and drying are required after forming by the above method, the heating and drying method is not particularly specified, and any method such as hot air, direct flame, induction heating or the like can be used. In addition, the ultimate plate temperature during drying depends on the treatment equipment, treatment conditions, etc.
The temperature is set to an arbitrary temperature at which the film can be dried.

[0030]

EXAMPLES Next, the present invention will be specifically described with reference to examples, but the present invention is not limited to the following specific examples.

SPCC having a plate thickness of 0.8 mm was used as a plating original plate. For the plating, a Sendzimir type continuous hot dip galvanizing line was used, and heating, annealing and plating were performed. The annealing atmosphere was a 10% hydrogen, 90% remaining nitrogen gas atmosphere, and the dew point was -30 degrees. The annealing temperature is 730 ° C and the annealing time is 3 minutes. The plating composition is Al: 11 mass%, Mg: 3 mass%, Si: 0.
2% by mass and the balance Zn and unavoidable impurities, and plating was performed at a plating bath temperature of 460 ° C. After soaking in the plating bath, apply nitrogen gas wiping to apply the amount of plating per side
It was set to 90 g / m ² . After plating, temper rolling was performed at an elongation rate of 1%.

Confirmation of the amount of plating adhered and the% of plating layer component was carried out by measuring the zinc by a fluorescent X-ray device, dissolving and peeling the plating layer with an acid, and analyzing the solution by ICP, and quantifying Zn, Al, Mg and Si. I went.

Regarding the formation of the film after plating, a treatment liquid adjusted to the conditions shown in Table 1 in a laboratory was applied by a bar coater and dried at an ultimate plate temperature of 80 ° C. The adhesion amount was adjusted by adjusting the concentration of the treatment liquid (diluting with water) and counting the bar coater. Check the amount of adhesion in the film with a fluorescent X-ray device.
Zr was measured and used as the index.

As a comparative material, a test material under the conditions shown in Table 2 was prepared by the following procedure and evaluated by the same procedure. The adhesion amount was confirmed by measuring Si, Zr, and Cr in each film by a fluorescent X-ray device and using them as indices.

Steel plate treatment conditions / levels 1 to 100: A treatment liquid adjusted to the conditions shown in Table 1 was applied by a bar coater and dried at an ultimate plate temperature of 80 ° C. The adhesion amount was adjusted by adjusting the concentration of the treatment liquid (water dilution) and the number of the bar coater (the conditions of the adhesion amount are shown in Tables 3 and 4). The polyethylene wax is Chemipearl W950.
(Mitsui Chemicals) was used.・ Level 102: Zircosol A as zirconium compound
C-7 (manufactured by Matsumoto Pharmaceutical Co., Ltd.) was applied with a bar coater so that the dry mass was 0.5 g / m ^2, and the plate was dried at an ultimate plate temperature of 80 ° C.
The adhesion amount was adjusted by adjusting the concentration of the treatment liquid (diluting with water) and counting the bar coater.・ Level 103: Snowtex-O as silica compound
(Nissan Chemical Co., Ltd.) with a bar coater dry mass 0.5g / m
^{It was} coated so as to be ^2, and dried at an ultimate plate temperature of 80 ° C. The adhesion amount was adjusted by adjusting the concentration of the treatment liquid (diluting with water) and counting the bar coater.・ Levels 104 and 105: Commercial acrylic resin emulsion (Mitsui Chemicals) with colloidal silica (Snowtex-O: Nissan Chemical) in dry mass resin: silica = 75:25
In addition to the above, the test material was applied using a bar coater and dried in a drying oven at 200 ° C. for 10 seconds. The adhesion amount was adjusted by adjusting the concentration of the treatment liquid (diluting with water) and counting the bar coater. Adhesion amount of test material is 104: 0.5g / m ² , level
105: 1.0 g / m ² .・ Levels 106 and 107: partially reduced chromic acid (chromium reduction rate 40
%) And colloidal silica (CrO ₃ : SiO ₂ = 1: 3) were diluted with water and applied to a test plate with a bar coater, and dried at a plate temperature of 60 ° C. Cr adhesion level 106: Cr: 20 mg / m ² , level 10
7: Cr: 40 mg / m ² .

In the weldability test, two sample steel sheets produced under the same conditions were overlapped and a spot welding continuous spotting property test was carried out. The test conditions are: electrode shape: dome shape, tip diameter: 12 mmφ, pressure force: 220 kgf, welding time: 12 cycles (AC 50 cycles), welding current: 12 KA, welded sample: shear pull test nugget diameter: 4.5 The number of times that it became less than or equal to mm was defined as the electrode life.

The evaluation of the continuous dot was carried out when this electrode life was 2,000.
The points and above were rated as ○, 1,000 to less than 2,000 as △, and less than 1,000 points as x. Welding stability was evaluated by a continuous dotability of ○ (2,00
(0 points or more) was evaluated by the variation of the nugget diameter from 2,000 to 2,010 points, and a difference of 0.5 mm or less between the maximum nugget diameter and the minimum nugget diameter was 0.5 mm or less and was evaluated as ◯.

For the corrosion resistance test, the steel plate to be tested is 150 mm
Cut out to 70 mm, apply Erichsen processing with a height of 8 mm, tape the end faces, and then perform a JIS Z 2371 salt water spray test to determine the occurrence of white rust on the flat plate and Erichsen processed parts for a test time of 72 hours. evaluated. The evaluation indexes of the flat plate part and the processed part are as follows. Flat plate ◎: White rust 0%, ○: White rust 0% over 5% or less, △: White rust 5%
Super 30% or less, ×: White rust 30% super processed part ◎: White rust 0%, ○: White rust 0% over 30%, △: White rust 3
Greater than 0% and less than 50%, ×: Greater than 50% white rust

In the workability test, the steel plate to be tested is 150 mm
Cut out to 70mm, Bowden test (load 500g, indenter 10m
mφSUJ-2, sliding distance 50 mm, sliding speed 50 mm / sec) were performed, and the friction coefficient at the 10th slide was evaluated. The processability evaluation index is as follows. Workability ○: Friction coefficient less than 0.2, △: Friction coefficient 0.2 to 0.
4, ×: Friction coefficient over 0.4

The evaluation results of each test are as shown in Tables 3-5. It can be seen that the plated steel sheet having the coating according to the present invention exhibits excellent weldability and corrosion resistance, and that the level to which a lubricating component is added is also excellent in workability.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

[Table 3]

[0044]

[Table 4]

[0045]

[Table 5]

[0046]

[Table 6]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C23C 28/00 C23C 28/00 B (72) Inventor Toshikazu Amemiya 1 Kimitsu, Chiba City, Chiba New Nippon Steel Stock company Kimitsu Steel Works (72) Inventor Akira Tanaka 1 Kimitsu, Kimitsu City, Chiba Prefecture Nippon Steel Co., Ltd. Kimitsu Works (72) Inventor Yoshihiro Suemune 1 Kimitsu, Kimitsu City, Chiba Prefecture Nippon Steel Co., Ltd. Kimitsu Works Ltd. (72) Inventor Akira Takahashi Kimitsu City, Chiba Pref. Steelworks (72) Inventor Ryosuke Sako 1-15-1 Nihonbashi, Chuo-ku, Tokyo Inside Parkerizing Co., Ltd. Japan (72) Inventor Ryu Hasegawa Chuo-ku, Tokyo 1-15-1 Motohashi, Japan Parkerizing Co., Ltd. (72) Inventor Keiichi Ueno 1-15-1, Nihonbashi, Chuo-ku, Tokyo F-Term (Reference) 4K026 AA02 AA07 AA13 AA22 BA12 BB08 BB10 CA16 CA18 in Japan Parkerizing Co., Ltd. CA23 CA27 CA28 CA30 CA38 DA02 DA03 DA06 4K027 AA05 AB05 AB13 AB44 AC82 AE03 4K044 AA02 AB02 BA01 BA10 BA11 BA14 BA17 BA19 BA21 BB03 BC02 BC08 CA11 CA16 CA53

Claims (6)

[Claims] 1. The surface of the steel sheet contains Mg: 1 to 10% by mass, Al: 2 to 19% by mass, Si: 0.01 to 2% by mass, and Mg and Al are represented by the following formula Mg (mass%) + It has a Zn alloy plating layer that satisfies Al (mass%) ≤ 20 mass%, and the balance Zn and unavoidable impurities, and further has 10 to 30 mass% of zirconium compound as zirconium and vanadyl compound as vanadium on its surface layer. A chromate-free hot-dip zinc-aluminum alloy-plated steel sheet having excellent weldability and corrosion resistance, which has a coating amount of 5 to 20% by mass of 200 to 1200 mg / m ^{2 on} at least one side. 2. The chromate-free treated hot dip zinc-aluminum alloy plated steel sheet according to claim 1, wherein the coating film contains an organic acid in a solid content of 20 to 50 mass%. 3. A film containing a phosphoric acid compound as PO _{4 in an amount} of 10 to 3
The chromate-free hot-dip zinc-aluminum alloy plated steel sheet according to any one of claims 1 to 2, wherein the content is 0 mass%. 4. A silica compound as SiO _{2 in the} coating is 10 to 10.
30 mass% is contained, The chromate-free process hot-dip zinc-aluminum alloy plating steel plate in any one of Claims 1-3 characterized by the above-mentioned. 5. The chromate-free hot-dip zinc-aluminum alloy plated steel sheet according to any one of claims 1 to 4, wherein the coating contains a fluorine compound as F in an amount of 5 to 20% by mass. 6. The chromate-free hot-dip zinc-aluminum alloy plated steel sheet according to any one of claims 1 to 5, wherein the coating contains 0.1 to 15 mass% of a lubricating component.