JPH11209893A - Method of forming anodized film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coating film having excellent corrosion resistance almost without changing the brightness and the color tone of a bare surface by dipping magnesium or a magnesium alloy in an electrolyte containing a phosphate and an aluminate and treating the surface with anodic oxidation. SOLUTION: The concentration of the phosphate is preferably 0.05-0.2 M and the concentration of the aluminate is preferably 0.2-1 M. The electrolyte prepared by adding an organic compound bath stabilizer having a hydroxyl group in addition to the phosphate and the aluminate is suitable and as the bath stabilizer, glycerine, ethylene glycol or the like is used and the concentration is controlled to 1-20 g/l and 10-50 wt.% stabilizer based on the weight of the aluminate is suitably used. After the anodic oxidation, the coating film is sealing treated by dipping it in hot water. The hot water is a pure water of >=85 deg.C and the treating time is preferably 3-15 min. The anodic oxidation coating film is controlled to have a thickness, in which the brightness and the color tone of the metallic base is not changed, and preferably to <=0.1 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an anodic oxide film on the surface of magnesium or a magnesium alloy. More specifically, the present invention relates to a method for forming a metal substrate by anodizing using an electrolyte having a novel composition. The present invention relates to a method for obtaining a magnesium product or a magnesium alloy product which retains surface gloss and color tone and is corrosion-resistant.

[0002]

2. Description of the Related Art Magnesium and magnesium alloys (in the following description, both are referred to as magnesium materials) are the lightest and have the highest specific strength among practical metals. , Interior and exterior parts such as motorcycles, parts for home appliances, storage containers such as bags and suitcases, sports equipment, parts for optical equipment, canes, and applications to new fields in the electronics industry such as computers and sound. Has been put into practical use. However, since the magnesium material is the most active metal material among practical metals, it has been difficult to use the magnesium material as it is in terms of corrosion resistance.

Conventionally, as a surface treatment method for improving the corrosion resistance of a magnesium material, a chemical conversion treatment or an anodic oxidation treatment has been carried out. In particular, when a film is formed by anodic oxidation treatment and then sealing treatment is performed, a relatively uniform film is formed, so that it is used as a rust preventive treatment or a base treatment for coating.

[0004]

When a product made of a magnesium material is given a decorative property utilizing its metallic luster and color, its surface cannot be painted. However, since the surface of the magnesium material is easily oxidized, some surface treatment is required to maintain the initial metallic luster and color tone.

[0005] A film obtained by a conventional chemical conversion treatment or anodization treatment using chromic acid or dichromate is colored white to brown to black or green. In addition, corrosion resistance can be obtained even with a film obtained by anodizing treatment using neither chromate nor dichromate, but in that case, the film thickness becomes several μm or more, and the surface after anodizing becomes cloudy. It is unavoidable that coloration occurs or coloring occurs.

[0006] For example, Japanese Patent Application Laid-Open No. 9-176894 discloses an electrolytic solution prepared by adding a film-forming stabilizer to an aqueous solution containing at least one hydroxide, carbonate or bicarbonate of an alkali metal or alkaline earth metal. A surface treatment method of forming an anodic oxide film using a liquid is described.In this surface treatment method, it is described that the color tone of the anodic oxide film may be a base color, Even in the described forming method, the film is colored when the film thickness has the necessary corrosion resistance. Further, as a surface treatment method for maintaining the gloss and the color tone of the surface of the magnesium material, a method of applying an organic clear paint is generally used. However, slight changes in gloss and color tone due to the formation of the organic coating film are inevitable.

An object of the present invention is to provide a method for forming an anodized film which has solved the drawbacks of the conventional anodized film, that is, does not change the luster and color tone of the surface of a magnesium material and is corrosion resistant. And Further, the present invention provides a method for producing a magnesium material product that maintains the gloss and color tone of the base surface of the magnesium material and is corrosion-resistant by forming an anodic oxide film on the surface of the magnesium material product. It is an issue.

[0008]

Means for Solving the Problems The present inventors formed an electrolytic solution by using a phosphate, which had been added as a film-forming stabilizer when anodizing a metal, together with an aluminate to form a magnesium material. It has been found that by anodizing, an anodized film having high corrosion resistance, but thin and unprecedented colorless and transparent is obtained, and the present invention has been completed.

That is, the method for forming an anodic oxide film of the present invention is characterized in that magnesium or magnesium is contained in an electrolyte containing a phosphate and an aluminate, and optionally further containing a bath stabilizer comprising an organic compound having a hydroxyl group. It is characterized in that a magnesium alloy (that is, a magnesium material) is immersed, the surface thereof is anodized, and then, if necessary, is immersed in hot water to perform a sealing treatment.

[0010] A method for producing a magnesium product or a magnesium alloy product of the present invention is characterized in that an anodized film is formed on the surface of a magnesium product or a magnesium alloy product by the above-described method for forming an anodized film. This is a method for producing a magnesium product or a magnesium alloy product which retains its surface gloss and color tone and is corrosion resistant.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION According to the method for forming an anodized film of the present invention, an anodized film can be formed on the surface of any magnesium material. Such materials include, for example, Mg-Al alloy, Mg-Al-Zn alloy, M
g-Al-Mn alloy, Mg-Zn-Zr alloy, Mg
-Magnesium alloys such as rare earth element alloys, Mg-Zn-rare earth element alloys, and magnesium metals. Further, an anodic oxide film can be formed on a magnesium material having any surface state. For example, the surface may be a die-cast surface or a surface which has been mirror-finished by polishing.

In the method of forming an anodized film according to the present invention, the pretreated magnesium material is anodized.
This pretreatment can be performed on the surface of the die-cast as it is by various known treatment methods conventionally performed prior to the anodic oxidation treatment of the magnesium material, for example, pyrophosphate treatment, caustic alkali treatment. It can be implemented in processing. In addition, when a glossy surface is formed, it is necessary to form a mirror-finished surface by polishing, and then perform a pretreatment that does not dissolve the polished surface (do not lose gloss). As such a pretreatment, it is preferable to carry out a cleaning by a surfactant treatment, an alkali treatment, or a combination thereof.

Examples of the phosphate used in the method of forming an anodic oxide film of the present invention include alkali metal salts, alkaline earth metal salts and ammonium salts of phosphoric acid.
These phosphates may be added to the electrolyte as phosphates, or phosphoric acid and an alkali metal hydroxide, an alkaline earth metal salt, ammonium hydroxide, or the like may be added to the electrolyte to form an electrolyte. Phosphates may be formed in the solution.

Regarding the concentration of phosphate in the electrolytic solution, if the phosphate concentration is too low, electrolysis tends to be unstable or the resulting anodic oxide film tends to be clouded, that is, the anodic oxidation The formation of the film tends to be unstable, and if the phosphate concentration is too high, it tends to be difficult to obtain an anodic oxide film having desired characteristics. Therefore, in the present invention, the concentration of the phosphate in the electrolyte is preferably 0.05%.
０．２0.2M.

The aluminate used in the method for forming an anodic oxide film of the present invention includes alkali metal salts, alkaline earth metal salts, ammonium salts and the like. Regarding the concentration of aluminate in the electrolyte, if the aluminate concentration is too low, electrolysis becomes unstable or the corrosion resistance of the resulting anodic oxide film tends to be insufficient,
On the other hand, if the aluminate concentration is too high, hydrolysis tends to occur and precipitation tends to occur. Therefore, in the present invention, the concentration of aluminate in the electrolyte is preferably 0.2
１1M.

The bath stabilizer optionally used in the method for forming an anodic oxide film of the present invention is an organic compound having a hydroxyl group which is known to inhibit the hydrolysis of aluminate, and includes glycerin, diethylene glycol and the like. Polyhydric alcohols are preferably used. When a bath stabilizer is used, the concentration of the bath stabilizer in the electrolytic solution is 1 to 20 g / l.
And 10 to 50% by weight based on the weight of the aluminate. When the concentration of the bath stabilizer is less than 1 g / l or less than 10% by weight based on the weight of the aluminate, the effect of adding the bath stabilizer tends to be insufficient, and The concentration of the bath stabilizer is 20 g / l
If it exceeds or exceeds 50% by weight based on the weight of the aluminate, the resulting anodic oxide film tends to have a bad influence on the corrosion resistance.

If the pH of the electrolytic solution used in the method of forming an anodic oxide film of the present invention is less than 12, stable electrolysis tends to be difficult, so the pH of the electrolytic solution is preferably 12 or more. . Since the pH changes depending on the concentrations of the phosphate and the aluminate, it is preferable to add an alkali substance to the electrolyte as needed to adjust the pH of the electrolyte to 12 or more. On the other hand, if the temperature of the electrolytic solution is too high, the electrolysis tends to be unstable or the resulting anodic oxide film tends to be fogged. Therefore, the temperature of the electrolytic solution is preferably from room temperature to 50 ° C.

The power source for the anodic oxidation treatment in the method for forming an anodized film of the present invention includes a DC power source, an AC power source,
Although any power supply such as a PR power supply and a pulse power supply can be used, a DC power supply or an AC power supply is generally used. When the power supply voltage is less than 30 V, it is difficult to form an anodic oxide film.
When the voltage exceeds V and when the voltage exceeds 70 V with an AC power supply, the electrolysis tends to be unstable, which is not preferable. The voltage is preferably 90 V or less for a DC power supply, and 65 V or less for an AC power supply.

The coating obtained by the anodic oxidation treatment has a large number of pores. In order to further enhance the corrosion resistance of the anodic oxidation coating, it is preferable to seal these pores. In the method for forming an anodic oxide film of the present invention, after anodizing, if desired, it can be immersed in hot water and sealed according to a known treatment method. This hot water is 85 ° C
The above pure water is preferable, and the treatment time is 3
It is preferably about 15 minutes.

The anodic oxide film obtained by the prior art needs to have a thickness of 1 μm to several tens μm in order to obtain a desired corrosion resistance, so that the anodic oxide film is a film colored white to brown to black or green. Met. On the other hand, since the anodic oxide film obtained by the above-described forming method of the present invention is dense, it has good corrosion resistance even if it is extremely thin, for example, a thickness which does not change the luster and color tone of the metal substrate. However, even if the thickness is preferably 0.1 μm or less, sufficient corrosion resistance is exhibited. That is, a surface having excellent corrosion resistance can be obtained without substantially changing the gloss and color tone of the surface of the magnesium material.

Although the method of forming the anodic oxide film has been described above, from another viewpoint, the present invention is characterized in that the anodic oxide film is formed on the surface of a magnesium product or a magnesium alloy product by the above method. It can be regarded as a method for producing a magnesium product or a magnesium alloy product that retains the gloss and color tone of the surface of the metal base and is corrosion-resistant. Specific examples of such a magnesium product or a magnesium alloy product include a case of an MD recording / reproducing apparatus known as an MD Walkman (registered trademark) or a digital video camera, a bag, a suitcase, an automobile, and a motorcycle. There are welfare-related tools such as exterior parts, wheelchairs and canes.

The anodic oxide film obtained by the forming method of the present invention is a film excellent in corrosion resistance without substantially changing the gloss and color tone of the surface of the magnesium material substrate, as described above. In order to further increase the corrosion resistance even if the color tone is slightly sacrificed, it is also possible to use the method of forming an anodic oxide film of the present invention as a base treatment and apply a clear coating on the anodic oxide film. For example, when applying a clear acrylic lacquer coating, coating on the anodic oxide film obtained by the forming method of the present invention improves the adhesion of the coating film, rather than directly coating on the surface of the magnesium material, Corrosion resistance is also improved.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. Example 1 AZ91D die-cast plate (50 mm × 50 mm × 3 m
m) was mirror-finished by mechanical polishing, and the mirror-finished surface was washed with a surfactant. On the other hand, trisodium phosphate concentration 60 g / l, sodium aluminate concentration 60 g / l, glycerin concentration 10 g / l, pH13.
The electrolyte solution of No. 0 was prepared, and while maintaining the temperature of the electrolyte solution at 30 ° C., the washed die-cast plate was immersed, and DC electrolysis was performed at an electrolysis voltage of 80 V for 30 seconds. After washing with water, further immerse in pure water at 90 ° C. for 5 minutes to perform sealing treatment,
Then it was dried.

The die cast plate subjected to the anodic oxidation treatment and sealed as described above was compared with the die cast plate subjected to mirror finishing and washing only with respect to the gloss and color tone of their surfaces. Little difference was observed. The thickness of the anodic oxide film on the die-cast plate subjected to the anodic oxidation treatment and the sealing treatment as described above was measured by ellipsometry and found to be 60 nm.
The corrosion resistance of the die-cast plate having the above-described anodic oxide film was tested by repeating the salt spraying for 8 hours to 16 hours for 2 cycles, and evaluated by the rating number method. The result is R.E. N. 9.0.

Example 2 Example 1 except that the anodic oxidation treatment was carried out at 90 V DC.
The comparison, measurement, and evaluation were performed in the same manner as in Example 1. Almost no difference was observed in the gloss and color tone of the surfaces of the die-cast plate subjected to the anodizing treatment and subjected to the sealing treatment, and the surface of the die-cast plate subjected to only mirror finishing and washing. The thickness of the anodized film on the die-cast plate subjected to the anodizing treatment and the sealing treatment was 80 nm. The corrosion resistance of a die-cast plate having an anodized film is described in R.D. N. 9.0.

Example 3 AZ91D die-cast plate (50 mm × 50 mm × 3 m
m) was mirror-finished by mechanical polishing, and the mirror-finished surface was washed with a surfactant. On the other hand, an electrolytic solution having a concentration of trisodium phosphate of 40 g / l and a concentration of sodium aluminate of 20 g / l and a pH of 13.0 was prepared, and the washed die-cast plate was immersed while maintaining the temperature of the electrolytic solution at 30 ° C. Then, DC electrolysis was performed at an electrolysis voltage of 80 V for 30 seconds. After washing with water, it was further immersed in pure water at 90 ° C. for 5 minutes to perform a sealing treatment, and then dried.

The die cast plate subjected to the anodic oxidation treatment and sealing treatment as described above and the die cast plate subjected to only mirror finishing and cleaning were compared visually with respect to the gloss and color tone of their surfaces. Little difference was observed. The thickness of the anodic oxide film on the die-cast plate subjected to the anodic oxidation treatment and the sealing treatment as described above was measured by ellipsometry and found to be 60 nm.
The corrosion resistance of the die-cast plate having the above-described anodic oxide film was tested by repeating the salt spraying for 8 hours to 16 hours for 2 cycles, and evaluated by the rating number method. The result is R.E. N. 9.0.

[0028]

The anodic oxide film obtained by the method for forming an anodic oxide film of the present invention is dense, so that it has good corrosion resistance even if it is extremely thin, and has a thickness that does not change the luster and color tone of the metal substrate. However, even if the thickness is preferably 0.1 μm or less, sufficient corrosion resistance is exhibited. That is, a surface having excellent corrosion resistance can be obtained without substantially changing the gloss and color tone of the surface of the magnesium material.

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[Procedure amendment]

[Submission date] February 26, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0023

[Correction method] Change

[Correction contents]

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. Example 1 AZ91D die-cast plate (50 mm × 50 mm × 3 m
m) was mirror-finished by mechanical polishing, and the mirror-finished surface was washed with a surfactant. On the other hand, trisodium phosphate dodecahydrate concentration 60 g / l, sodium aluminate concentration 60 g / l, glycerin concentration 10 g / l,
An electrolyte having a pH of 13.0 was prepared, and the temperature of the electrolyte was adjusted to 3
While maintaining the temperature at 0 ° C., the washed die-cast plate was immersed, and DC electrolysis was performed at an electrolysis voltage of 80 V for 30 seconds.
After washing with water, it was further immersed in pure water at 90 ° C. for 5 minutes to perform a sealing treatment, and then dried.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction contents]

Example 3 AZ91D die-cast plate (50 mm × 50 mm × 3 m
m) was mirror-finished by mechanical polishing, and the mirror-finished surface was washed with a surfactant. On the other hand, an electrolytic solution having a concentration of trisodium phosphate dodecahydrate of 40 g / l and a concentration of sodium aluminate of 20 g / l and a pH of 13.0 was prepared, and the above-mentioned washing was carried out while maintaining the temperature of the electrolytic solution at 30 ° C. Immerse the die-casting plate,
DC electrolysis was performed for seconds. After washing with water, it was further immersed in pure water at 90 ° C. for 5 minutes to perform a sealing treatment, and then dried.

Claims (8)

[Claims] 1. A method for forming an anodized film, comprising immersing magnesium or a magnesium alloy in an electrolytic solution containing a phosphate and an aluminate and subjecting the surface to anodizing treatment. 2. The concentration of the phosphate is 0.05 to 0.2M, and the concentration of the aluminate is 0.2 to 1M.
The method for forming an anodic oxide film according to the above. 3. immersing magnesium or a magnesium alloy in an electrolyte containing a bath stabilizer comprising a phosphate, an aluminate, and an organic compound having a hydroxyl group;
A method for forming an anodic oxide film, wherein the surface is anodized. 4. The concentration of the phosphate is 0.05 to 0.2 M, the concentration of the aluminate is 0.2 to 1 M, the concentration of the bath stabilizer is 1 to 20 g / l, and the concentration of the aluminate is The method for forming an anodized film according to claim 3, wherein the amount is 10 to 50% by weight based on the weight of the salt. 5. The method for forming an anodized film according to claim 1, wherein the sealing process is performed by immersing the film in hot water after the anodizing treatment. 6. The method for forming an anodized film according to claim 1, wherein the thickness of the anodized film does not change the gloss and the color tone of the metal substrate. 7. The method according to claim 6, wherein the thickness of the anodic oxide film is 0.1 μm or less. 8. A method for forming an anodized film on a surface of a magnesium product or a magnesium alloy product according to any one of claims 1 to 7, while maintaining the luster and color tone of the surface of the metal substrate. A method for producing a magnesium product or a magnesium alloy product which is corrosion-resistant.