JP2002146506A - Aluminum based plated steel sheet for fuel tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum based plated steel sheet for a fuel tank having exceedingly improved corrosion resistance by allowing fluorides to coexist in a chemical conversion coating deposited on the surface of an Al-Si alloy plated layer as well as oxides or metallic hydroxides. SOLUTION: An Al-Si alloy plated steel sheet in which, preferably, the content of Si as the whole in the plated layer is controlled to 5 to 13 mass%, and the content of Si in the surface layer is controlled to 7 to 80 mass% is used as a base material. A chemical conversion coating in which the oxides or hydroxides and fluorides of valve metals such as Ti, Zr, Hf, V, Nb, Ta, Mo and W; wherein, the oxides exhibit high insulation resistance coexist is deposited on the surface of the base material. In the oxides or hydroxides and fluorides contained in the chemical conversion coating, the ratio of the atomic numbers, i.e., F/O is preferably controlled to 1/100 or higher. The chemical conversion coating may contain soluble or hardly soluble metallic phosphates or complex phosphates.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum-plated steel sheet suitable for a fuel tank for an automobile, which requires internal corrosion resistance, external corrosion resistance and workability.

[0002]

2. Description of the Related Art Aluminum-plated steel sheets are often used as a steel material having good corrosion resistance. And the appearance deteriorates. Although the generation of white rust can be prevented by subjecting the aluminum-based plated steel sheet to chromate treatment, a large burden is imposed on the treatment of the effluent containing Cr ions. Accordingly, Cr-free chemical conversion treatment methods using chemicals such as titanium-based, zirconium-based, molybdenum-based, and phosphate-based chemicals are being studied. For aluminum materials, many proposals have been made mainly for application to DI cans and the like. is there. For example, in the titanium series,
Japanese Patent Application Laid-Open No. 9-20984 discloses a method of forming a chemical conversion coating by bringing an aqueous solution containing a titanium compound, a phosphate ion, a fluoride and an accelerator into contact with an aluminum-containing metal material, washing with water and drying. On the other hand, in fuel tanks for automobiles, the use of aluminum-based plated steel sheets has been promoted in order to guarantee long-term corrosion resistance. However, when manufacturing an automotive fuel tank by press-forming a Cr-free aluminum-plated aluminum-plated steel sheet, defects such as galling and cracks are likely to occur in the chemical conversion coating and the plating layer. Specifically, in the manufacture of a fuel tank for an automobile, a press-formed upper half 1u and a lower half 1d are seam-welded to form a fuel tank body 1, an inlet pipe 2, a fuel pipe 3, a fuel return pipe 4, a sub-tank 5, Various members such as the drain plug 6 are attached (FIG. 1). The press working for forming the aluminum-based plated steel sheet into the shape of the upper half 1u and the lower half 1d is processing involving complex plastic deformation in which elongation, compression, and the like are combined. For this reason, the conventional Cr-free chemical conversion coating film lacks lubricity, and even when press oil is applied, the aluminum-based plating layer or the chemical conversion coating film cannot follow the plastic deformation during processing, resulting in galling,
Defects such as cracks are likely to occur.

[0003]

At the point where a defect occurs, the original advantages of the aluminum-based plating layer and the chemical conversion coating are not exhibited, and when the fuel tank is exposed to a corrosive environment, it becomes a starting point of corrosion and leads to perforation. Corrosion may occur. In addition, in a fuel tank that uses alcohol fuel, the sacrificial corrosion protection of the aluminum plating layer cannot be expected, and the corrosion of the steel base exposed at the location of the defect that occurred during press forming progresses, and the durability increases. descend.

[0004] By forming an organic resin film containing a polymer resin powder on the chromate film to improve the lubricity of the surface of the aluminum-plated steel sheet, the occurrence of defects such as galling and cracks can be suppressed (Japanese Unexamined Patent Publication No. Hei 8- No. 4,1651, JP-A-8-319550). Although the organic resin film is effective in suppressing the generation of defects, it thermally decomposes in a seam welding or spot welding process during fuel tank production to generate fumes and odors, thereby deteriorating the working environment. In addition, the adhesion of the organic resin film to the aluminum-based plating layer is reduced due to corrosion of the underlying plating layer. As a result, if the detached organic resin film pieces are mixed with the fuel, troubles such as filter clogging may occur. In this regard, it has been proposed to employ a film-removal type organic resin film and remove the organic resin film after press molding, but there is a problem in workability and manufacturability since a film-removal step is required.

[0005] Above all, titanium-based coatings, like conventional chromium-based coatings, tend to become polymerized oxides composed of oxides and hydroxides, and as a continuous coating having excellent barrier properties, the corrosion resistance of plated steel sheets is reduced. It is thought to improve, but unlike chromium-based polymerized oxides, it is hardly soluble in water and does not have a self-healing function. As a result, it is not possible to obtain an effective inhibitory effect on the progress of corrosion originating from a film defect portion generated during a chemical conversion treatment, a forming process, or the like. Other Cr-free coatings, like the titanium-based coatings, also have a weak self-healing effect, and their corrosion inhibitory effect is insufficient.

In addition, when a Cr-free chemical conversion treatment solution is applied to an aluminum-based plated steel sheet by a general-purpose roll coating method, a spray ringer method, or the like, the occurrence of Al exposed portions is inevitable with a small amount of application. The exposed portion of Al serves as a starting point of corrosion and a starting point of galling during press working, which causes damage to the chemical conversion film and the plating layer. Conversely, if the coating amount is increased to form a thick chemical conversion coating, defects such as cracks are likely to be generated in the chemical conversion coating during press molding, and the corrosion resistance is reduced due to insufficient self-healing action.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been devised to solve such a problem. It is based on an Al--Si alloy plated steel sheet, and comprises an oxide or hydroxide of a valve metal and Al-Si conversion coating with fluoride
It is an object of the present invention to provide an aluminum-plated steel sheet having excellent inner surface corrosion resistance even when formed into an automotive fuel tank by being formed on an alloy plating layer. In order to achieve the object, the aluminum-plated steel sheet for a fuel tank according to the present invention has an Al-Si alloy having an Si content of 5 to 13% by mass in the entire plating layer and a Si content of 7 to 80% by mass in the surface layer. Al-Si with plating layer formed
The present invention is characterized in that an alloy-plated steel sheet is used as a base material, and a chemical conversion treatment film in which an oxide or hydroxide of a valve metal exhibiting a high insulation resistance and a fluoride coexist is formed on the base material surface.

[0008] As the valve metal, Ti, Zr, H
f, V, Nb, Ta, Mo, W and the like. The concentration ratio F / O of O and F contained in the chemical conversion coating is 1/1 by atomic ratio.
When fluoride is contained so as to be not less than 00, the self-healing action caused by the fluoride becomes remarkable. An organic or inorganic lubricant may be added to the chemical conversion coating. The chemical conversion coating may further include a soluble or poorly soluble metal phosphate or composite phosphate. Examples of the soluble metal phosphate or composite phosphate include salts of alkali metals, alkaline earth metals, Mn, and the like. Examples of the poorly soluble metal phosphate or composite phosphate include Al, Ti, Zr, Hf,
There are salts such as Zn. An organic or inorganic lubricant may be further added to the chemical conversion coating.

[0009]

The aluminum-plated steel sheet for a fuel tank according to the present invention contains an oxide or hydroxide of a valve metal and a fluoride. The valve metal refers to a metal in which an oxide exhibits high insulation resistance, and includes Ti, Zr, Hf, V, Nb,
One or more of Ta, Mo, and W are used. The coating made of the oxide or hydroxide of the valve metal acts as a resistor against the transfer of electrons, and suppresses the reduction reaction (oxidation reaction with the underlying steel) due to dissolved oxygen contained in the moisture in the atmosphere. As a result, elution (corrosion) of the metal component from the base steel is prevented. Above all, Ti, Zr, H
A tetravalent compound of group IV A element such as f is a stable compound and is a suitable film component because it forms an excellent film.

When the oxide or hydroxide of the valve metal is formed as a continuous film on the surface of the steel sheet, it effectively acts as a resistor against electron transfer. Unavoidable film defects in Since the underlying steel is exposed at the film defect, the expected corrosion inhibiting action cannot be expected. Therefore, in the present invention, a self-repairing action is imparted to the chemical conversion treatment film by allowing the soluble fluoride of the valve metal to coexist. The fluoride of the valve metal dissolves in the moisture in the atmosphere and then re-precipitates as a hardly soluble oxide or hydroxide on the surface of the base steel exposed from the defective film portion, thereby filling the defective film portion. Exhibits self-healing action.

For example, a titanium-based film formed on the surface of a plated steel sheet is formed of an oxide [TiO ₂ ] or a hydroxide [Ti (O
H) ₄ ] is a composite film. Microscopically, the base steel is exposed at portions where the film thickness is extremely insufficient or at film defects such as pinholes, and is likely to be a starting point of corrosion. In this regard, in the conventional chromium-based coating, self-healing action is exhibited by soluble hexavalent Cr precipitated as a poorly soluble trivalent Cr compound in the coating defect portion, but the self-healing action cannot be expected in the titanium-based coating. Increasing the film thickness can reduce the number of film defects, but the hard and poorly ductile titanium film cannot follow the elongation of the steel sheet when forming a chemically treated steel sheet, and defects such as cracks and galling can occur. It is likely to occur in chemical conversion coatings.

On the other hand, X _n TiF ₆ (X: alkali metal, alkaline earth metal or NH ₄ , n = 1 or 2), T
Coexistence fluorides iF ₄ etc., fluorides are eluted from the chemical conversion ^{_{coating, TiF 6 2- + 4H 2 O}} → Ti (OH) 4
Due to the reaction of + 6F ^- or the like, it becomes a hardly soluble oxide or hydroxide and is reprecipitated at a film defect portion to exhibit a self-healing action. The fluoride may be the same or different from the metal to be an oxide or hydroxide. In addition, when Mo or W is selected as a valve metal, some of these hexavalent oxyacid salts have a solubility, and some exhibit a self-healing action. Therefore, restrictions on the fluoride contained in the chemical conversion coating are reduced.

Further, when regulating the Si content of the Al—Si alloy plating layer, even when the amount of the chemical conversion coating is small, A
1 can be prevented. Si of Al-Si alloy plating layer
The effect of the content on the Al exposure is presumed as follows. A in which Si is concentrated to some extent on the surface of the plating layer
When a chemical conversion treatment is performed using an l-Si alloy plated steel sheet as a base material,
Al on the surface of the plating layer is selectively removed by etching to form a surface having a convex portion mainly composed of metal Si and a concave portion rich in Al. Since the chemical conversion treatment liquid easily accumulates in the recesses, the composite coating composed of titanium oxide or hydroxide and fluoride has a
The rich recess is preferentially covered.

By forming the chemical conversion coating by this method, the surface layer of the plating layer is hardened by being covered with the composite compound film of metal Si and titanium, and the contact area with the mold is reduced by forming the irregularities. Therefore, the sliding resistance during press molding is reduced, and workability is improved. Further, since the Al-rich portion is not exposed on the surface layer of the plating layer, the pickup of Al to the electrode during resistance welding is reduced, and the life of the electrode is prolonged. The irregularities formed on the surface layer of the plating layer exhibit an anchor effect, and are also effective in improving the adhesion of a coating film formed in a later step.

As described above, A with the specified Si content is
By using a plated steel sheet having an l-Si alloy plating layer as a base material and providing a composite coating composed of an oxide or hydroxide of titanium and fluoride on the plating layer, an Al-rich portion can be obtained even if the coating amount is small. A good flat part is obtained because the exposure of the chemical conversion coating does not follow the plastic deformation of the steel sheet during press forming. Excellent internal corrosion resistance is obtained.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Low-carbon steel, medium-carbon steel,
High carbon steel, alloy steel, etc. are used. In particular, in applications where good press formability is required, low carbon Ti-added steel,
A deep drawing steel plate such as a low carbon Nb added steel is preferable. The base steel is hot-dip aluminum plated according to the usual method.
It is preferable to adjust the Si content of the l-Si alloy plating layer in the range of 5 to 13% by mass. 5% by mass Si content
By doing so, Si is easily concentrated in the surface layer of the plating layer, and the growth of an alloy layer which occurs at the interface between the base steel and the plating layer and is harmful to the workability is suppressed. However, when an excessive amount of Si exceeding 13% by mass is contained, primary crystal Si is crystallized in the plating layer in a cooling process after hot-dip plating, and workability is significantly deteriorated.

A with the Si content adjusted to 5 to 13% by mass
Pull up l-Si alloy plated steel sheet from hot-dip bath,
After concentrating Si in the surface layer of the plating layer in advance by adjusting the cooling rate and the like, a convex portion mainly composed of metal Si and an Al-rich concave portion are formed in the surface layer of the plating layer by performing pickling, alkali cleaning, and the like. Is done. When a convex portion mainly composed of metal Si and a concave portion rich in Al are formed by pickling, alkali cleaning, or the like, a water washing and drying step is required. On the other hand, in the case of using a chemical conversion treatment solution having an etching effect on Al, the surface Al is selectively removed by etching in the process of forming a chemical conversion treatment film in which the chemical conversion treatment solution is applied to the plating layer and dried.
An Al-rich recess is formed.

The situation in which the convex portion mainly composed of metallic Si and the Al-rich concave portion are dispersed in the surface layer of the plating layer is obtained by scanning and analyzing an area of 1000 μm square using the AES analysis method, and similarly, from the surface layer by Ar sputtering. It can be confirmed by repeatedly analyzing to a depth of 100 nm. From the experimental results by the present inventors, it has been found that when the Si concentration at a depth from the surface of the plating layer to 100 nm is 7% by mass or more, the desired flat portion corrosion resistance and inner surface corrosion resistance can be obtained. However, if Al is removed by etching until the Si concentration of the surface layer exceeds 80% by mass, the surface layer of the plating layer becomes brittle, and if the steel sheet is deformed at the time of press working or the like, the chemical conversion treatment film tends to fall off.

The chemical conversion treatment may be either a coating type or a reaction type. In the reaction type conversion treatment, the pH is adjusted to be slightly lower in order to maintain the stability of the processing solution. In the following description,
Although Ti is taken as an example of the valve metal, the same applies when a valve metal other than Ti is used.

The chemical conversion treatment solution contains a soluble halide or oxyacid salt as a Ti source. Ti fluoride is Ti
Although it is effective as a source and an F source, (NH ₄ ) F
In some cases, such a soluble fluoride as F source is separately added to the chemical conversion treatment solution. As a specific Ti source, X
_n TiF ₆ (X: alkali metal or alkaline earth metal,
n: 1 or 2), K ₂ [TiO (COO) ₂ ], (NH ₄ ) ₂ Ti
F ₆ , TiCl ₄ , TiOSO ₄ , Ti (SO ₄ ) ₂ , Ti (O
H) _Fourth magnitude. The mixing ratio of each component of the Ti source is selected so that a chemical conversion coating composed of an oxide or hydroxide and a fluoride having a predetermined composition is formed when the titanium source is dried and baked after applying the chemical conversion treatment liquid. You.

In order to stably maintain the Ti source as ions in the chemical conversion treatment solution, it is preferable to add an organic acid having a chelating action. When an organic acid is added, the molar ratio of organic acid / metal ion is determined to be 0.02 or more, since the chemical conversion treatment solution is stabilized by chelating metal ions. Examples of the organic acid include tartaric acid, tannic acid, citric acid, oxalic acid, malonic acid, lactic acid, and acetic acid. Among them, oxycarboxylic acids such as tartaric acid and polyhydric phenols such as tannic acid stabilize the processing solution and also exhibit the function of complementing the self-healing action of fluoride, which is also effective in improving coating film adhesion. It is. Orthophosphates or polyphosphates of various metals may be added in order to include soluble or hardly soluble metal phosphates or composite phosphates in the chemical conversion coating.

In order to exhibit the self-healing effect of the fluoride contained in the chemical conversion coating, it is preferable to adjust the atomic ratio F / O between O and F in the chemical conversion coating to 1/100 or more. . F and O in the chemical conversion coating are fluorescent X-rays,
It can be analyzed using ESCA or the like. The atomic ratio F / O is 1 /
If it is less than 100, the self-healing effect due to the hydrolysis of the fluoride is insufficient, and corrosion starting from a defective portion of the chemical conversion coating or a flaw at the time of molding may progress.

The soluble metal phosphate or composite phosphate elutes from the chemical conversion treatment film and elutes at the defect of the film, reacts with Al or the like of the base steel, and precipitates insoluble phosphate, thereby producing titanium phosphate. Complements the self-healing action of the compound.
Further, since the atmosphere is slightly acidified when the soluble phosphate dissociates, the hydrolysis of titanium fluoride and, consequently, the formation of poorly soluble titanium oxide or hydroxide are promoted. Metals that form soluble phosphates or complex phosphates include alkali metals, alkaline earth metals, Mn, and the like, and are formed from various metal phosphates or various metal salts and phosphoric acid, polyphosphoric acid, and phosphates. Is added to The poorly soluble metal phosphate or composite phosphate disperses in the chemical conversion treatment film to eliminate film defects and improve film strength. Al, Ti, Zr,
Hf, Zn, etc. are added to the chemical conversion treatment liquid as various metal phosphates or various metal salts and phosphoric acid, polyphosphoric acid, and phosphate.

In the chemical conversion treatment liquid, a wax effective for improving lubricity is contained in the chemical conversion treatment film, so that a fluorine-based, polyethylene-based or styrene-based organic wax or an inorganic lubricant such as silica, molybdenum disulfide, or talc is used. Agents and the like can also be added. It is considered that the organic wax having a low melting point bleeds on the surface when the film is dried, and exhibits lubricity. The high melting point organic wax and the inorganic lubricant are present in a dispersed state in the film, but it is considered that lubricity is exhibited by being exposed on the surface of the film in an island-like distribution on the outermost layer of the treated film.

The prepared chemical conversion solution is roll-coated,
A chemical conversion coating film having excellent corrosion resistance is formed on the surface of the Al-Si alloy plating layer by applying the composition to the Al-Si alloy plating steel sheet by spin coating, spraying, or the like, and drying the coating without washing with water. The application amount of the chemical conversion treatment liquid is preferably adjusted so that the titanium adhesion amount is 1 mg / m ² or more in order to secure sufficient corrosion resistance. The chemical conversion coating can be dried at room temperature, but in consideration of continuous operation, it is preferable to keep the temperature at 50 ° C. or higher to shorten the drying time. However, if the drying temperature exceeds 200 ° C., the organic components contained in the chemical conversion treatment film may be thermally decomposed and the properties imparted by the organic components may be impaired.

Depending on the use environment and the manufacturing process of the fuel tank, an organic film is provided after forming the chemical conversion film, if necessary, in order to improve press formability, corrosion resistance, resistance weldability, and the like. As this kind of film, for example, urethane resin,
A resin film such as epoxy resin, polyethylene, polypropylene, olefin resin such as ethylene-acrylic acid copolymer, styrene resin such as polystyrene, polyester, or a copolymer or modified product thereof, acrylic resin, etc. When provided on the chemical conversion treatment film at 1 to 5 μm,
High corrosion resistance surpassing chromate film is obtained.

It is also possible to add an organic or inorganic lubricant to the organic resin film to ensure lubricity during press molding, or to add an inorganic sol to improve resistance weldability.
The resin film may be either an alkali-soluble type or a non-soluble type that can be easily removed by alkali washing. The solubility in alkali can be adjusted by the amount of acrylic acid contained in the resin film. The higher the amount of acrylic acid, the more alkali-soluble, and the lower the amount, the more insoluble. This type of resin film can be formed by a roll coating method or electrostatic atomization.

[0028]

EXAMPLE A chemical conversion treatment solution having the composition shown in Table 1 was prepared by blending a Ti source and an F source, optionally adding various metal compounds, organic acids, and phosphates.

[0029]

A very low carbon Ti-added cold-rolled steel sheet having a thickness of 0.8 mm is passed through a continuous hot-dip galvanizing line, and an Al—Si alloy plating layer of Si: 6 to 11% by mass is coated with a coating weight of 35 g /
m ² (average layer thickness: 13 μm). This Al-S
An i-alloy-plated steel sheet was used as a base plate for chemical conversion treatment. A chemical conversion treatment solution having the composition shown in Table 1 was applied by a roll coating method, and then charged into an oven without washing with water, and dried at an ultimate plate temperature of 120 ° C. A treated film was formed. The formed chemical conversion film is analyzed by X-ray fluorescence, AES and ESCA,
The Si content in the surface layer from the surface of the plating layer to a depth of 100 nm and the concentration of each component of the chemical conversion coating were determined. Table 2 shows the survey results.

[0031]

A test piece was cut out from the chemical conversion-treated Al—Si alloy plated steel sheet and subjected to a flat portion corrosion test, an inner surface corrosion test, and a resistance weldability test. In the flat part corrosion test, the end face of the test piece was sealed, and a 5% NaCl aqueous solution at 35 ° C. was sprayed according to JIS Z2371. 2 salt sprays
After continuing for 4,72,120 hours, white rust generated on the surface of the test piece was observed. The area ratio of white rust occupying 5% or less of the surface of the test piece was evaluated as ◎, 5 to 10% as ○, 10 to 30% as Δ, 3
The corrosion resistance of the flat portion was evaluated by setting ▲ to 0 to 50% and × to 50% or more.

In the inner surface corrosion test, a test piece cut from an aluminum-plated steel sheet pressed into a shape of an automobile fuel tank was used, assuming that the inner surface of the fuel tank was exposed to a corrosive atmosphere composed of deteriorated gasoline. 50 ℃
The test pieces were immersed in the heated test liquids A and B, and the test liquids were changed every week and kept immersed. After 9 weeks, the test piece was pulled up from the test solution, and the corrosion state of the test piece was observed. Corrosion occurred and grew from the inside of the machined part that had undergone the largest machining. The maximum depth of corrosion generated in the test piece was measured, and the maximum corrosion depth was evaluated as ◎ when the maximum erosion depth was 100 μm or less, を when 100 to 200 μm, Δ when 200 to 300 μm, and × when 300 μm or more. Test solution A: water containing 400 ppm of formic acid + equivalent gasoline Test solution B: methanol 80% by mass + gasoline 20% by mass
In the + formic acid 400 ppm resistance welding test, two superposed test pieces were spot-welded using a Cr-Cu alloy electrode. As the welding conditions, a method was adopted in which an appropriate current and an appropriate load were obtained in advance for each test piece, and the welding current was increased at a fixed rate at each fixed point. And the number of welding points is 500-100
The resistance welding property was evaluated by setting 0 points as 打 and 500 points or less as ×.

As can be seen from the survey results in Table 3, the test numbers 1 to 6 in which the chemical conversion coating was formed according to the present invention were:
All exhibited good flat section corrosion resistance, inner surface corrosion resistance, and resistance weldability. On the other hand, in Test No. 7 (Comparative Example) in which a chemical conversion treatment film containing no soluble titanium fluoride was formed, the self-healing effect was insufficient, so that corrosion starting from a film defect portion was observed. In Test No. 8 (Comparative Example) in which a chemical conversion film containing no titanium compound was formed, the barrier effect was poor and both the flat portion corrosion resistance and the inner surface corrosion resistance were poor. Even when the same chemical conversion solution was used, an aluminum-plated steel sheet containing no Si was converted to the chemical conversion solution No. In Test No. 9 (Comparative Example) subjected to the chemical conversion treatment in No. 1, a part of the Al-rich portion was exposed, and the target quality performance was not obtained.

[0035]

[0036]

Example 2 A valve metal source other than Ti and an F source were blended, and in some cases, various metal compounds, organic acids,
Phosphoric acid was added, and a chemical conversion treatment solution having the composition shown in Table 4 was prepared. Each of the chemical conversion treatment solutions was applied to an Al—Si alloy plated steel plate by a roll coating method, then charged into an oven without washing with water, and dried at a reaching plate temperature of 160 ° C. to form a chemical conversion treatment film.

[0037]

For each Al-Si alloy plated steel sheet on which the chemical conversion coating was formed, the Si content and the concentration of each component in the surface layer from the plating layer surface to a depth of 100 nm were determined in the same manner as in Example 1. Was. Table 5 shows the survey results
Shown in

[0039]

Next, a test piece was cut out from each of the chemical conversion-treated Al—Si alloy plated steel sheets, and subjected to a flat portion corrosion test, an inner surface corrosion test, and a resistance weldability test in the same manner as in Example 1. As can be seen from the investigation results in Table 6, Test Nos. 1 to 6 in which the chemical conversion coating was formed according to the present invention were excellent in all of the flat portion corrosion resistance, the inner surface corrosion resistance, and the resistance weldability.

[0041]

[0042]

As described above, the aluminum-plated steel sheet for a fuel tank according to the present invention has an Al-Si alloy plating layer having a specified Si content.
Since the base material surface is covered with a chemical conversion coating in which metal oxides or hydroxides and fluorides coexist with a base material of an alloy plated steel sheet, the hardly soluble metal oxides or hydroxides function as an environmental barrier. To prevent corrosion of the underlying steel, and the soluble fluoride exhibits a self-healing action. Therefore, even after being formed into the shape of a fuel tank by severe processing, the film defects introduced by the forming process are self-repaired by re-precipitation of eluted fluoride, and the underlying steel is exposed through the film defect part. And excellent corrosion resistance is maintained.
Further, by including a phosphate or a composite phosphate, corrosion resistance is further improved, and excellent corrosion resistance comparable to a conventional chromate film is exhibited. In addition, since it is a chemical conversion treatment film that does not contain Cr, which may have an adverse effect on the environment,
As a material that replaces the conventional chromate-treated steel sheet, it is suitably used for automotive fuel tanks that require long-term corrosion resistance.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a fuel tank.

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[Procedure amendment]

[Submission Date] January 24, 2002 (2002.1.2
4)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 1

[Correction method] Change

[Correction contents]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction contents]

[0007]

SUMMARY OF THE INVENTION The present invention has been devised to solve such a problem. It is based on an Al--Si alloy plated steel sheet as a base material, and contains an oxide or hydroxide of a valve metal. An object of the present invention is to provide an aluminum-plated steel sheet having excellent inner surface corrosion resistance even when formed into a fuel tank for an automobile by forming a chemical conversion treatment film in which fluoride coexists on an Al-Si alloy plating layer. I do.
The aluminum-plated steel sheet for a fuel tank according to the present invention is based on an Al-Si alloy-plated steel sheet as a base material, and the oxide or hydroxide of a valve metal having a high insulation resistance and a fluoride to achieve the object. Is formed on the surface of the base material. Base material A
In the l-Si alloy plated steel sheet, an Al-Si alloy plated layer having a Si content of 5 to 13% by mass in the entire plating layer and a Si content of 7 to 80% by mass in the surface layer is formed.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) C23C 22/36 C23C 28/00 C 28/00 B60K 15/02 A (72) Inventor Shigeyasu Morikawa Osaka Sakai 5 Nisshin Steel Co., Ltd., Nisshin Steel Co., Ltd.Technical Research Laboratories (72) Inventor Shinya Furukawa 5th Nisshin Steel Co., Ltd. No. 5 F-term in Nisshin Steel Co., Ltd. Technical Research Laboratories (Reference) BA17 BA20 BB03 BC02 BC05 CA11 CA16 CA53 CA62

Claims (6)

[Claims] 1. An Al-Si alloy plated steel sheet as a base material,
An aluminum-plated steel sheet for a fuel tank, characterized in that a chemical conversion coating in which an oxide or hydroxide of a valve metal and a fluoride exhibiting high insulation resistance coexist is formed on the surface of the base material. 2. The Si content of the plating layer as a whole is 5 to 5.
13% by mass, Al whose surface Si content is 7 to 80% by mass
The aluminum-plated steel sheet for a fuel tank according to claim 1, wherein the base material is a plated steel sheet on which a -Si alloy plating layer is formed. 3. The valve metal is Ti, Zr, Hf, V,
The aluminum-plated steel sheet for a fuel tank according to claim 1, wherein the steel sheet is at least one selected from Nb, Ta, Mo, and W. 4. The aluminum-coated steel sheet for a fuel tank according to claim 1, wherein the concentration ratio F / O of O and F contained in the chemical conversion treatment film is 1/100 or more in atomic ratio. 5. An aluminum-plated steel sheet for a fuel tank, wherein the chemical conversion coating according to claim 1 further contains a phosphate or a composite phosphate of a soluble or insoluble metal. 6. An aluminum-coated steel sheet for a fuel tank, wherein the chemical conversion coating according to claim 1 further contains a lubricant.