JP2002249882A - Aluminum alloy material having excellent filiform corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Al-Mg-Si alloy in which phosphate treatability treated together with steel is improved, and filiform corrosion resistance is improved to the equal one of a surface treated steel sheet. SOLUTION: The content of Cu in the Al-Mg-Si based aluminum alloy material is controlled to <=0.2%. Further, in the analysis of an oxide film on the surface by ESCA(electron spectroscopy for chemical analysis), the thickness of the oxide film is <35Å, also, the content of Mg in the oxide film is 0%, and the covering ratio of phosphate crystals after phosphate treatment is >=90%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy for automotive panels which is suitable as an external material for automobile panels, has excellent thread rust resistance, and is coated after being subjected to a phosphate treatment as a coating base treatment.
-Mg-Si-based aluminum alloy material.

[0002]

2. Description of the Related Art In recent years, with respect to environmental problems such as global warming caused by carbon dioxide, reduction of the amount of carbon dioxide emitted by reducing the weight of automobiles has become a major issue. As a part of the reduction in the weight of automobiles, automobile members such as panels are being replaced with aluminum alloy materials (rolled sheets, extruded materials, forged materials, etc.). The aluminum alloy material has a specific gravity of about 1/3 lighter than a steel plate and has a large weight saving effect.

[0003] Taking the manufacturing process of an automobile panel as an example of an automobile member, a steel plate or an aluminum alloy plate is formed into a predetermined shape by press forming, and then assembled together with other parts into an automobile body. Finished as an automobile body by coating base treatment by phosphate treatment and painting. Of these, the panel skin located outside the car body has mechanical properties such as strength, as well as sharpness that affects the appearance of the car, thread rust resistance to surface scratches, coating film adhesion, etc. Required.

[0004] However, when compared with conventional steel sheets, particularly, surface-treated steel sheets frequently used for panel outer panels, the aluminum alloy sheets have poor thread rust resistance. This is because in the current situation where aluminum alloy plates are used only for a part of the vehicle body, phosphating conditions are suitable for steel materials that occupy most of the vehicle body.

[0005] When the aluminum alloy material is subjected to phosphating with steel, that is, when the phosphating is performed under conditions suitable for the steel, or when phosphating is performed on the same line as the steel, The phosphatability of the aluminum alloy material is poor, and the phosphate film does not cover the entire surface of the aluminum alloy material. Therefore, when an aluminum alloy plate is used as the panel outer plate, corrosion resistance such as thread rust resistance and sharpness are inferior to steel plates.

On the other hand, in order to improve the phosphatability of an aluminum alloy material, processing conditions suitable for the aluminum alloy material may be applied.

This typical technique is a method of adding an appropriate amount of free fluorine ions into a phosphating bath, which is disclosed in Japanese Patent Application Laid-Open No. 6-173026.

Various improvements from the material side of the aluminum alloy material have been proposed in the past. For example, Japanese Unexamined Patent Publication
No. 240467, Japanese Patent Application Laid-Open No. 5-33165, and the like, by depositing metals such as Fe, Ni, Cu, Cr, and Mn, which are noble with respect to aluminum, these deposited metals are used as cathodes in a phosphate reaction. Discloses a method of accelerating the dissolution of aluminum from an anode and accelerating the precipitation of phosphate on an aluminum alloy plate.

[0009]

However, even with these techniques, aluminum alloy materials do not provide sufficient thread rust resistance. This tendency is particularly remarkable in Al-Mg-Si-based aluminum alloy materials (AA-6000-based aluminum alloy materials specified in JIS standards).

First, the method of adding an appropriate amount of free fluorine ions to the phosphating bath depends on the amount of the aluminum alloy material to be treated, but the amount of sludge discharged in the phosphating step is significantly increased. There's a problem.

In practice, in order to change the phosphating treatment conditions for steel to the treatment conditions for aluminum alloy materials, due to the problem of sludge, a device for removing sludge to the treatment line and a facility for treating sludge discharged. Significant remodeling of the equipment such as installation is required. For this reason, an example in which the processing conditions suitable for the aluminum alloy material are applied is only a dedicated surface treatment line for an all-aluminum vehicle in which the aluminum alloy material is used for most of the vehicle body.

Therefore, in the normal case where the aluminum alloy material is phosphated together with the steel material, the amount of free fluorine ions added to the phosphating bath is limited by the problem of sludge. However, the effect of improving the phosphatability cannot be said to be satisfactory when the amount of free fluorine ions is limited, and the rust resistance is not at a sufficient level.

More specifically, as a specific method for suppressing the generation of sludge, the amount of free fluorine ions in the phosphating bath is suppressed to about 100 to 200 ppm, or the amount of free fluorine ions is reduced to about 150 ppm or less. There is a method using a bath which is suppressed and to which an iron chelate compound is added. In these treatment baths, the amount of sludge can be suppressed, but it is difficult to coat a phosphate film over a wide range of the material surface, and as a result, the rust resistance is poor.

Further, the technique of depositing a metal on the aluminum alloy material has the effect of promoting the precipitation of phosphate and improving the phosphatability. However, in order to achieve this effect, a certain amount of metal deposition is required. For this reason, there is a problem that the deposited metal remains on the surface of the aluminum alloy plate even after the phosphate treatment, deteriorating the rust resistance and coating film adhesion. On the other hand, when the metal deposition amount is suppressed, the effect of improving the phosphatability is reduced, and it is difficult to coat the phosphate film over a wide range of the material surface, and as a result, the rust resistance is poor. .

Therefore, the amount of free fluorine ions is
When treating with a phosphating bath that is kept low to about 100 to 200 ppm, in other words, a phosphating bath that treats the current aluminum alloy material with steel and a phosphating bath that is suitable for current steel, To increase the coverage of the phosphate film of the aluminum alloy material and to improve the rust resistance of the aluminum alloy material to the same level as the surface-treated steel sheet, that is, to improve the phosphate treatment property of the aluminum alloy material. But,
This was one of the major issues in using aluminum alloy materials for automobiles.

SUMMARY OF THE INVENTION In view of these problems of the prior art, an object of the present invention is to improve the phosphatability of an aluminum alloy material to be phosphated together with a steel material, and to improve the rust resistance to a level equivalent to that of a surface-treated steel sheet. An object of the present invention is to provide an Al-Mg-Si-based aluminum alloy material which has been improved.

[0017]

In order to achieve this object, the gist of claim 1 of the present invention is to provide an aluminum alloy material having excellent rust resistance, which is coated after being treated with phosphate together with steel. An Al-Mg-Si-based aluminum alloy material for automotive panels.The Cu content is regulated to 0.2% or less, and when the oxide film on the aluminum alloy surface is analyzed by ESCA, the oxide film thickness is less than 35 mm. And the Mg content in the oxide film is 0%, and the coverage of phosphate crystals after the phosphate treatment is 90% or more.

The inventors of the present invention have substantially no Cu content.
Regulated Cu (hereinafter simply referred to as containing no Cu)
As a result of examining the filiform rust resistance of Mg-Si-based aluminum alloy materials (6000-based aluminum alloy materials specified in AA to JIS standards), the surface of the aluminum alloy material before phosphate treatment, When the oxide film was analyzed by ESCA, it was found that the oxide film thickness and the Mg content in the oxide film greatly affected the phosphatability and the rust resistance.

The oxide film thickness is less than 35 mm,
And, when the Mg content in the oxide film is 0%, compared to the case of the oxide film thickness and the Mg content in the oxide film exceeding these, the Cu-free Al-Mg-Si aluminum alloy material of,
It has also been found that when treated with steel, the phosphatability and the rust resistance are significantly improved.

Since the present invention has the effect of improving the phosphatability and the rust resistance, it is preferred that the amount of free fluorine in the phosphating bath is 200 ppm or less. Alternatively, a steel material containing an iron chelate compound and having a free fluorine content of 150 ppm or less (A
It is suitable for application to a phosphating bath under conditions that are disadvantageous for l-Mg-Si-based aluminum alloy materials.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Method of Analyzing Oxide Film) First, a method of analyzing or measuring a structure of an oxide film on the surface of an aluminum alloy material by ESCA according to the present invention will be described below. ESCA is an analytical method widely used for solid surface analysis. ESCA is an Electron Spectroscopy for Chemical Ana
Abbreviation for lysis, X-ray photoelectron spectroscopy (XPS: X-ray Pho
toelectron Spectroscopy). In the present invention, the measurement of the oxide film on the surface of the aluminum alloy material by ESCA is performed using ESCALAB-210D manufactured by VGScientific, and Al Kα radiation is used as the X-ray source. The detection angle is set at 0 ° with respect to the normal line of the sample.

If the detection angles are different, the oxide film and the metal Al
As a result of the change in the distance of the X-ray passing through the
The area value of each peak of _Al-O , I _Al-Al, etc. changes, and the thickness of the oxide film and the Mg content tend to have measurement variations.

Oxide film thickness d (d: Angstroms)
Is the Al bound to oxygen in the peak determined by ESCA
Area of the peak I due to is bonded to _Al-O and metallic Al
The area I _Al-Al of the peak caused by _Al is determined by waveform separation, and the ratio I _Al-O / I _{Al-Al is} converted into Å (angstrom) by the following known conversion formula. More specifically, the thickness of the oxide film was measured at the outermost layer portion of the aluminum oxide film, and the related peak was measured, and d = 20 × cos θIn (1.15 ×
I _Al-O / I _Al-Al +1) (where θ is the photoelectron detection angle).

Similarly, the Mg content is determined by the ICA determined by ESCA.
_Determine the area of the _Mg-O peak by converting it to mass%. The Mg content is detected at the outermost layer of the aluminum oxide film.
It is determined by converting the area of the Mg-related peak into an atomic weight.

The above _- mentioned I _Al-O / I _Al-Al and I _Mg-O
Is determined from the peak of Al _{2P and} the peak of Mg _2P in the narrow spectrum of ESCA, respectively. In addition, in consideration of material variations, the material measurement locations of peaks by ESCA are multiple locations (for example, 5 locations) separated by, for example, 20 cm or more.
It is preferable to take the average of the measured values.

When there are rust-preventive oils, lubricating oils, Al powder, or other contaminants on the surface of the aluminum alloy material to be analyzed by ESCA, the ESCA determines whether these oils or Al-derived substances are present. Other peaks, such as carbon and Al, which disturb the peak to be measured are generated, and a measurement error is likely to occur. For this reason, it is preferable that the surface of the aluminum alloy material to be analyzed is previously cleaned or cleaned in accordance with the deposit, such as ultrasonic cleaning with an organic solvent such as acetone.

It should be noted that JP-A-5-70970 and JP-A-8-92970
AES (Auger), a typical example of this type of measurement method disclosed in Japanese Patent Publication No. 773, has a resolution in the depth direction of several nm.
To several tens of nanometers, which is insufficient for analyzing the region of the oxide film on the surface of the thin aluminum alloy material. Also,
Accurate measurement of the Mg content of the thin oxide film of the present invention is also impossible by Kant analysis (emission spectroscopy) used for component analysis of ordinary materials. In contrast, the ES used in the present invention
The CA has a resolution of 1 nm to several nm, and can sufficiently evaluate the thickness and Mg content of the oxide film in the depth direction (region) of the thin oxide film of the present invention.

(Thickness of Oxide Film) The thickness of the oxide film on the surface of the aluminum alloy material before the phosphate treatment determined under these conditions is defined as a thin film of less than 35 ° (angstrom) in the present invention. By setting the thickness of the oxide film to less than 35 mm (I _Al-O / I _Al-Al before conversion becomes 4.0 or less), the phosphate crystal coating after phosphate treatment of the aluminum alloy material is performed. The phosphatability and the rust resistance are improved so that the rate becomes 90% or more. On the other hand, when the thickness of the oxide film is 35 mm or more, the coverage of the aluminum alloy material with the phosphate crystals is less than 90%, and the effect of improving the rust resistance cannot be obtained.

Incidentally, as shown in Table 2 in the working examples,
_Al-O/ I_Al-AlIn the conversion from_Al-O/
I_Al-AlIs 3.5, the thickness of oxide film is 32mm, I_Al-O/ I
_{Al-A l}Is 3.8, the thickness of the oxide film is 34mm, I_Al-O/ I
_Al-AlIs 4.2, the thickness of the oxide film is 35mm, I_Al-O/ I
_Al-AlIs 4.5, the thickness of the oxide film is 36mm, I_Al-O/ I
_{Al-A l}However, at 4.7, the thickness of the oxide film is 37 mm.

When an Al-Mg-Si-based aluminum alloy material is manufactured by a conventional method such as rolling or extrusion, the thickness of a normal oxide film of the aluminum alloy material after final cleaning accompanied by etching such as degreasing is 35 to 45 mm. Level. In contrast, in the present invention, the thickness of the oxide film is set to a very small level of less than 35 °.

The composition of the surface oxide film of the aluminum alloy material largely depends on the level of etching by the final cleaning in the manufacturing process of the aluminum alloy material. The present inventors performed various changes in the etching level by cleaning the surface of the aluminum alloy material from a weak level to a strong level in a wide range, changed the surface oxide film composition, and quantified the composition by the ESCA analysis. The relationship between phosphatability and yarn rust resistance was investigated in detail.

As a result, the oxide film on the surface of the aluminum alloy material changes into three stages depending on the etching strength of the cleaning involving etching. First, the oxide film at the cleaning level where the etching strength is weak is a thick oxide film with a thickness of 45 mm or more and contains a large amount of Mg. It is an oxide film. As described in JP-A-8-92773, the oxide film containing Mg significantly inhibits phosphatability, particularly under phosphating conditions for the steel material in which the amount of free fluorine ions is kept low. I do.

Next, the oxide film at the cleaning level with relatively high etching strength has a thickness of 35 ° to 45 ° (the thickness of the ordinary oxide film) and does not substantially contain Mg. However, when the thickness of the oxide film specified in the present invention is less than 35 mm, the oxide film is a relatively thick film made of aluminum oxide.
This oxide film also has poor phosphatability of the aluminum alloy material, particularly under the phosphating conditions for steel in which the amount of free fluorine ions is kept low, and after the aluminum alloy material has been phosphated, Does not exceed 90%.

Further, the oxide film at the cleaning level having a high etching strength is an oxide film having a thickness of less than 35 mm of the oxide film specified in the present invention and substantially not containing Mg. This oxide film has a high phosphatability with a phosphate crystal coverage of 90% or more even under the phosphating conditions for steel materials in which the amount of free fluorine ions is suppressed to about 200 ppm or less. Is obtained.

When the oxide film obtained by the above-mentioned cleaning with relatively high etching strength and having a thickness of 35 to 45 ° and containing substantially no Mg is used, the phosphoric acid treatment conditions for the steel material are phosphoric acid. The reason for poor salt treatment properties is due to the composition of the oxide film. That is, by etching, Mg
Even during the removal of the aluminum oxide, a relatively thick film of the aluminum oxide, which has a high passivation ability and is generated at a high temperature, remains in a manufacturing process of the aluminum alloy material such as hot rolling, extrusion, forging or heat treatment. The aluminum oxide film formed at this high temperature has particularly poor phosphatability under the phosphating conditions for steel.

Therefore, in order to obtain an oxide film substantially free of Mg and having a thickness of less than 35 mm as defined in the present invention and to improve the phosphatability under the phosphating conditions for the steel material, First, it is important to strongly wash (etch) the Al-Mg-Si-based aluminum alloy material to dissolve and remove the aluminum oxide film having a high passivation ability generated at a high temperature during the manufacturing process.

After this cleaning, an oxide film substantially free of Mg and having a thickness of less than 35 °, which is specified in the present invention, is newly formed in the air or a cleaning solution. However, at the stage where this new oxide film is generated or before the phosphate treatment, the Mg content in the oxide film is 0%
It is important that the oxide film has a thickness as small as less than 35 mm. Depending on the washing conditions, or the conditions before washing and phosphating,
Note that the oxide film may substantially contain Mg or the thickness may be 35 mm or more.

(Cleaning with Etching) Among the manufacturing conditions of the aluminum alloy material in the present invention, the washing step with etching is particularly important as described above for controlling the oxide film on the surface of the aluminum alloy material. .

In the cleaning process involving etching, Mg is dissolved and removed from the oxide film, and the aluminum oxide film having a high passivation generated during the manufacturing process of the aluminum alloy material is dissolved and removed. The conditions for reducing the thickness of the oxide film to 0% and the thickness of the oxide film to be less than 35 ° are selected in relation to the production history of the alloy and the component composition.

For cleaning with etching, generally,
Examples include electrolytic degreasing, an aqueous alkali solution such as sodium hydroxide and sodium carbonate, an aqueous acid solution such as sulfuric acid and nitric acid, a commercially available cleaning solution, or a cleaning step combining these. In the present invention, too, a condition that satisfies the above-mentioned oxide film conditions of the present invention is appropriately selected from these known cleaning conditions, instead of selecting specific cleaning methods and conditions.

However, even under the same cleaning conditions, when the manufacturing histories of the aluminum alloy material are significantly different and the film conditions of the thick aluminum oxide having a high passivation ability generated during the manufacturing process of the aluminum alloy material are different. In some cases, the oxide film conditions of the present invention may not be satisfied. Further, when the film conditions of the aluminum oxide produced during the manufacturing process of the aluminum alloy material are the same, and the cleaning chemical solution is the same, when the cleaning temperature and the processing time are greatly different, the oxide film conditions of the present invention are not changed. Care must be taken because it may not be satisfied.

Further, it is important to store the aluminum alloy material after the cleaning with etching until the phosphate treatment. If the oxidation of the oxide film after the cleaning is further advanced, the thickness of the oxide film formed after the cleaning, particularly the thickness of the oxide film, may fall outside the range of the present invention. For this reason, in order to prevent the oxide film of the aluminum alloy material from changing with time, some measures such as applying a rust-preventive oil or a rust-preventive agent and packaging may be required.

(Coverage rate of phosphate crystals and rust resistance) When a thin oxide film having substantially no Mg and having a thickness of less than 35 mm as defined in the present invention is used, the coverage rate of phosphate crystals Is 90% or more, and the maximum yarn rust length in the corrosion resistance test is sharply shortened.

[0044] Yarn rust occurs when an automobile outer panel is supposed to cause peeling of the coating film due to chipping or bruising, thereby exposing the aluminum base material at the peeled part, thereby causing chlorine content to corrode the aluminum base material. It has been known. The growth of thread rust starts from this corrosion, and the moisture in the air is supplied from the uncoated portion of the phosphate crystal to the aluminum substrate through the coating film, and the electrochemical lithography under the coating film occurs. It is considered that the reaction proceeds as thread-like rust.

For this reason, if the phosphate crystals do not cover the aluminum alloy material, it is presumed that water and oxygen are supplied from the coating film side and that rust easily grows.
Therefore, when the coverage of the phosphate film on the surface of the aluminum alloy material is large, the growth of thread rust is small. On the other hand, when the phosphate crystal coverage is small, the growth of thread rust under the coating film increases.

Further, the filiform rust is more likely to grow when the uncoated portions of the phosphate crystals are continuously connected. As described above, the growth of the thread rust progresses by the electrochemical reaction, and therefore, if the supply of moisture from the coating film to the tip of the thread rust is continuously performed in the traveling direction of the thread rust, the growth of the thread rust does not occur. Promoted.

On the other hand, in the present invention, the coverage of phosphate crystals is specified to be 90% or more so that water is not continuously supplied from the coating film to the tip of the thread rust. When the proportion of the phosphate coated portion exceeded 90% or more, the maximum thread rust length was suddenly shortened because the ratio of the phosphate coated portion was 90% as the critical value, and the uncoated portion was 90%. Sharply decreases,
It is presumed that the continuous uncoated portion decreased and became an island shape.

The coating condition of the phosphate crystals is generally defined by SE
Observed by M. However, many phosphate crystals are grown at an angle, and the uncoated portions are often hidden by the crystals. As a result, it is difficult to know details of the uncovered portion, such as whether the uncovered portion is continuously connected or has an island shape.

For this reason, in the present invention, it is assumed that the coverage of the phosphate crystals is determined by SEM observation, and the condition is determined by observing the area of 40 μm × 50 μm by 2000 times magnification in two visual fields. The value shall be determined by applying the following formula. Phosphate crystal coverage% = 100-(Area of exposed aluminum substrate / Area of observation field x 100)

The phosphating conditions serving as the criteria for determining the coverage of the phosphate crystals are such that the amount of free fluorine ions is suppressed to about 200 ppm or less and the phosphating bath composition is adjusted to a zinc ion concentration of 0.6 ppm. Use a compound having a general range of 2.0 g / l and a phosphate ion concentration of 5 to 30 g / l. Phosphate treatment time is 2 minutes, treatment temperature is 33-45 ° C
Do with.

According to the above-mentioned Japanese Patent Application Laid-Open No. 8-92773, if the ratio of the amount of etching by cleaning / the mass of the oxide film is in the range of 0.8 to 1.5, the phosphatability is good. However, in the above-mentioned JP-A-8-92773, the target has a Mg content of 4.
It is intended for aluminum alloy materials that are Al-Mg-based (5000-based) with as high as 5% and have better phosphatability than Al-Mg-Si-based aluminum alloy materials. In addition, the present invention does not intend to treat the phosphating bath which is the object of the present invention, particularly, the phosphating bath in which the amount of free fluorine ions is suppressed to about 200 ppm or less.

Further, the present invention is not directed to the method of depositing a metal on the surface of an aluminum alloy material disclosed in JP-A-6-240467 and JP-A-5-33165, but to an oxide film on the surface of the aluminum alloy material. Appropriate adjustment is made by cleaning with etching or the like. As a result, the deposited metal does not cause a problem such as a decrease in rust resistance.

(Aluminum Alloy Material) The Al-Mg-Si-based aluminum alloy materials to which the present invention is applied are all 6000-based aluminum alloy materials specified in AA to JIS standards. However, depending on the application, it is necessary to satisfy the basic characteristics, so the most suitable alloy material (rolled plate,
Aluminum alloy wrought materials such as extruded and forged materials).

However, among the 6000 series alloys, in particular, they are excellent in press formability and bending workability, which are required properties as a panel material, a frame material and a member material of the automobile body, or 150 MPa or more after baking. It is preferable to be excellent in artificial age hardening property, which is the proof stress.

A preferable chemical composition of the Al-Mg-Si-based aluminum alloy for satisfying this property is that it is essential to limit the Cu content to 0.2% or less from the viewpoint of improving the rust resistance. Basically Si: 0.6-1.3% (mass%, the same applies hereinafter),
Mg: 0.4 to 1.2%, with the balance being Al and unavoidable impurities. Satisfies the chemical composition and the above characteristics
6000 series Al alloy is JIS to AA standard, 6016, 6111,
Temper materials such as T4 and T6 such as 6022, 6061 and 6N01 are exemplified.

In the case of the 6000 series aluminum alloy panel material of the present invention, if the Cu content exceeds 0.2%, the corrosion resistance and the rust resistance after coating are significantly deteriorated. For this reason, there is a high possibility that the stricter requirements for string rust resistance in the case of the outer panel of an automobile panel structure cannot be satisfied. Therefore, in the present invention, the content of Cu is preferably as small as possible.

In addition, Mn, Cr, Zr, Ti, B, Fe, Zn, N
Other alloying elements such as i and V are basically impurity elements. However, from the viewpoint of recycling of 6000 series alloys, when using not only high-purity Al metal but also 6000 series alloys, other Al alloy scrap materials, low-purity Al metal, etc. Including. For this reason, these elements are allowed to be contained within the JIS to AA standards as long as the effects of improving various properties aimed at by the present invention are not impaired.

The aluminum alloy material itself in the present invention is usually subjected to processes such as melting, casting, homogenizing heat treatment, hot working (rolling, extrusion, forging), intermediate annealing and cold working (rolling, forging) and rolling if necessary. It can be manufactured by the method.

[0059]

Next, embodiments of the present invention will be described. An ingot having an Al-Mg-Si-based aluminum alloy composition shown in Table 1 was melted by DC casting, subjected to a homogenizing heat treatment at 470 ° C for 8 hours, and hot-rolled to a thickness of 2.5 mm. Next, the steel sheet was cold-rolled to a thickness of 1.0 mm, and then subjected to a T4 temper treatment in which a solution treatment was carried out at 560 ° C. and water quenching was immediately performed using a nitrite furnace to produce a rolled aluminum alloy sheet. Al in Table 1
-Mg-Si based rolled aluminum alloy is 125MP at 6016-T4
a, 6016-T4 had a proof stress of 150 MPa.

A test material was sampled from the Al-Mg-Si-based aluminum alloy plate, and was subjected to a cleaning process involving etching of the test material (selectively including electrolytic degreasing) under the conditions shown in Table 2.
Then, the Mg content and the thickness (Å) in the oxide film on the surface of the aluminum alloy plate after cleaning were determined under the above-described preferable ESCA measurement conditions. Table 3 shows these results. For reference, Table 3 also shows the values of I _Al-o / I _{Al-Al used} as the basis for thickness conversion.

Next, the test materials after these washing treatments were further converted into a colloidal dispersion containing 0.1% of titanium phosphate,
A treatment of immersion at room temperature for 20 seconds was performed, and the surface of the test material was coated with titanium phosphate by adsorption. Immediately after that, a zinc phosphate treatment of immersing for 2 minutes in a zinc phosphate bath containing 150 ppm of free fluorine suitable for a steel sheet was performed under the same conditions in each example.
Then, the coverage of zinc phosphate on the surface of each test material was determined by SEM observation under the above conditions. Table 3 also shows these results.

Further, the test material provided with the phosphate film is subjected to cationic electrodeposition coating and spray coating.
Two coats and two bake coatings were provided, and the test material provided with these coatings was subjected to a yarn rust resistance evaluation test. Table 3 also shows these results.

In the evaluation test for the rust resistance of the yarn, one piece was
After a 7 cm cross-cut, it was immersed in a 1.7% hydrochloric acid aqueous solution at 35 ° C for 2 minutes, and then at 40 ° C and 85% R.C. H. For 1008 hours in a constant temperature and humidity atmosphere, and the maximum length L of generated thread rust
(The distance in the vertical direction from the cross cut, mm) was measured.
For comparison, Table 3 also shows the zinc phosphate coverage and the maximum length of thread rust of SPCE steel sheets that were subjected to the same zinc phosphate treatment and coating, and a test for evaluating thread rust resistance.

As is clear from Table 3, when the oxide film on the surface of the aluminum alloy material after cleaning was analyzed by ESCA,
Invention Example No. 1 in which the oxide film thickness is less than 35 mm and the Mg content in the oxide film is 0%. 1 to 4 have an oxide film thickness of 35
ÅComparative Example No. containing Mg in the oxide film 5 to 9
Comparative Example No. The phosphate coverage increased to more than 90%, the same as that of 10 SPCE steel sheets. Furthermore, in Invention Example No. 14
In Comparative Example No. Compared with Nos. 5 to 9, the maximum yarn rust length was clearly shorter. It can be seen that the thread rust resistance is improved as much as 10 hot-dip galvanized steel sheets.

The results of these examples support the critical significance of the conditions of the present invention in the phosphatability and the rust resistance after painting of aluminum alloy materials. Also,
Further, it can be seen that the wrought aluminum alloy of the present invention is particularly suitably used as a material for transportation equipment such as automobiles.

[0066]

[Table 1]

[0067]

[Table 2]

[0068]

[Table 3]

[0069]

According to the present invention, when the aluminum alloy material is treated simultaneously with the steel material, or when the aluminum alloy material is treated with a phosphate bath suitable for the steel material, the coverage of the phosphate film is increased. As a result, it is possible to provide an aluminum alloy material in which the thread rust resistance of the aluminum alloy material is improved to the same level as a steel plate. Therefore, it is of great industrial value in that aluminum alloy materials can be expanded to applications such as automobiles.

Claims (2)

[Claims] An Al-Mg-Si-based aluminum alloy material for an automobile panel, which is coated after being phosphated together with a steel material, wherein the Cu content is regulated to 0.2% or less.
When the oxide film on the surface of the aluminum alloy material was analyzed by ESCA, the thickness of the oxide film was less than 35 mm, the Mg content in the oxide film was 0%, and the phosphate crystals after the phosphate treatment. An aluminum alloy material excellent in thread rust resistance, characterized in that the coating ratio of the aluminum alloy is 90% or more. 2. The aluminum alloy excellent in thread rust resistance according to claim 1, wherein the phosphate treatment bath contains 200 ppm or less of an iron chelate compound and / or 150 ppm or less of free fluorine ions. Wood.