JP2003328188A - Surface treatment method of magnesium alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface treatment method by which the corrosion resistance and adhesion for a coating film in the surface of magnesium alloy can be improved. <P>SOLUTION: In the surface treatment method of a magnesium alloy, the surface of a magnesium alloy is subjected to anodic oxidation treatment in an electrolytic solution where the concentration of carbonate is 0.05 to 0.19 M, and the concentration of phosphate is 0.005 to 0.15 M at an electrolytic solution temperature of 50 to 95°C, at a current density of 1 to 50 A/dm<SP>2</SP>, under an electrolytic voltage of 40 to 150 V for 30 s to 20 min. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method for a magnesium alloy, and more specifically, a magnesium alloy surface is subjected to anodization treatment under a specific electrolysis condition using an electrolytic solution having a specific composition to obtain magnesium. The present invention relates to a surface treatment method for improving the corrosion resistance and coating adhesion of an alloy surface.

[0002]

2. Description of the Related Art Magnesium alloy is the lightest of practical metals and has the highest specific strength. Therefore, by utilizing its characteristics, structural materials such as aircraft, automobiles and motorcycles, interior and exterior parts, home appliance parts, bags, It is widely used for storage containers such as suitcases, and parts for electronic industrial products such as computers and acoustics.

However, since the magnesium alloy is the most active metal material in practical metals, it is difficult to use the magnesium alloy as it is in terms of corrosion resistance, and the magnesium alloy is oxidized immediately in the atmosphere and its surface is Since a thin film is formed on it, it has the drawbacks that it is difficult to apply it and the adhesion of the coating is significantly reduced.

As a surface treatment method for improving the corrosion resistance and coating film adhesion of magnesium alloys, chemical conversion treatment and anodizing treatment have been conventionally carried out. Conventional anodizing treatments include DOW17 method, HAE method and Japanese Patent Publication No. 56-11.
No. 392, Japanese Patent Publication No. 5-8278, and Japanese Patent Laid-Open No. 9-
There is a method disclosed in Japanese Patent No. 176894.

[0005]

[Problems to be Solved by the Invention] Japanese Patent Publication No. 56-1139
The method disclosed in Japanese Unexamined Patent Publication No. 2 is a method of performing anodization at a low electrolytic voltage of 30 V or less for the purpose of forming a color-developing film. At such a low electrolysis voltage, the thickness of the barrier-type coating becomes thin, resulting in insufficient corrosion resistance.

In the method disclosed in Japanese Patent Publication No. 5-8278, it is necessary to carry out anodizing treatment in a bath containing a carbonate in a concentration of 2 N or more.
In the method disclosed in Japanese Patent No. 6894, it is necessary to carry out anodizing treatment in a bath containing a carbonate at a concentration of 0.2 mol / liter or more. When anodizing treatment is performed at an electrolytic voltage of 40 to 150 V in a bath containing carbonate at such a concentration, spark discharge occurs and the resulting anodized film has insufficient corrosion resistance.

The present invention has been made in order to solve the problems of the conventional anodizing method, in which the surface of a magnesium alloy is anodized by using an electrolytic solution having a specific composition under specific electrolytic conditions. Accordingly, it is an object of the present invention to provide a surface treatment method for improving the corrosion resistance and the coating film adhesion of the surface of a magnesium alloy.

[0008]

Means for Solving the Problems As a result of intensive studies for achieving the above-mentioned object, the present inventors have found that spark discharge is not caused in an electrolytic solution containing a low concentration of phosphate and carbonate. By performing anodizing treatment at an electrolysis voltage of 40 to 150 V, it is possible to form an anodized film having high corrosion resistance and good coating adhesion even for a highly corrosive Mg-Li alloy or the like. Found and completed the present invention.

That is, according to the surface treatment method for a magnesium alloy of the present invention, the magnesium alloy surface is treated with a carbonate concentration of 0.0
5 to 0.19M, and the phosphate concentration is 0.005 to
Electrolyte temperature 50-95 in 0.15M electrolyte
It is characterized in that anodization treatment is carried out at a temperature of 0 ° C. and an electrolytic voltage of 40 to 150 V for 30 seconds to 20 minutes.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION According to the surface treatment method of a magnesium alloy of the present invention, an anodic oxide film can be formed on the surface of any magnesium alloy. Such magnesium alloys are, for example, Mg-Al alloys, Mg-Zn alloys, Mg-Mn alloys, and Mg-Zr alloys.
System alloy, Mg-Al-Zn system alloy, Mg-Al-Mn system alloy, Mg-Zn-Zr system alloy, Mg-rare earth element system alloy, Mg-Zn-rare earth element system alloy, Mg-Li system alloy, Mg There are magnesium alloys such as -Li-Y-based alloys and Mg-Ca-rare earth element-based alloys.
63, AZ91, AZ92, AM100, ZK51, E
Mold casting products made of Z33, ZE41, etc., sand casting products,
Die casting, AZ31, AZ61, AZ80, ZK6
There is a wrought material consisting of 0 grade. Further, an anodic oxide film can be formed on a magnesium alloy having any surface state, and for example, the surface may be a die-cast surface, a plastic-processed surface, or a mirror-finished surface by polishing.

In the surface treatment method for a magnesium alloy of the present invention, generally, the pretreated magnesium alloy is anodized. This pretreatment is, for example, for the surface of the die-cast as it is, various known treatment methods that have been conventionally carried out prior to the anodizing treatment of the magnesium alloy, for example, acid cleaning, pyrophosphate treatment, caustic treatment. Can be implemented in. For example, 60% nitric acid solution 4
Immerse the solution in 1 L by diluting 0 mL at room temperature for 2 minutes, and then wash with water. Further, when forming a surface having gloss, it is necessary to perform a pretreatment that does not dissolve the polished surface (does not lose gloss) after forming a mirror-finished surface by polishing. As such pretreatment, washing with a surfactant treatment, an alkali treatment, or a combination thereof is preferably performed.

In the surface treatment method of the magnesium alloy of the present invention, the carbonate concentration is 0.05 to 0.19M,
An electrolytic solution having a phosphate concentration of 0.005 to 0.15M is used. As the carbonate, sodium carbonate, potassium carbonate and / or ammonium carbonate are preferably used. When the carbonate concentration exceeds 0.19M, the corrosion resistance of the obtained anodic oxide film tends to be insufficient, and when the carbonate concentration is less than 0.05M, electrolysis at high voltage is performed. Tends to be difficult. The carbonate concentration is preferably 0.07 to 0.15M.

Further, the phosphate is preferably sodium phosphate, potassium phosphate, ammonium phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, phosphoric acid. Potassium dihydrogen and / or ammonium dihydrogen phosphate are used, and more preferably disodium hydrogen phosphate, dipotassium hydrogen phosphate and / or diammonium hydrogen phosphate are used. If the phosphate concentration exceeds 0.15M,
The corrosion resistance of the obtained anodized film tends to be insufficient, and also when the phosphate concentration is less than 0.005 M, the corrosion resistance of the obtained anodized film tends to be insufficient. The phosphate concentration is preferably 0.02-0.1
It is 3M.

In the surface treatment method of the magnesium alloy of the present invention, the temperature of the electrolytic solution (bath temperature, electrolytic treatment temperature) is 50 to 50.
Maintain at 95 ° C, preferably 75-93 ° C. When the temperature of the electrolytic solution is lower than 50 ° C, the magnesium alloy tends to be dissolved, and when the temperature is higher than 95 ° C, the evaporation of the electrolytic solution becomes vigorous, which makes it difficult to control the bath.

In the surface treatment method of the magnesium alloy of the present invention, the anodizing treatment is carried out while maintaining the electrolysis voltage within the range of 40 to 150V.
Within the range of ˜50 A / dm ² , preferably 3-40 A / d
With a given initial current density in the range of m ² , usually 10-2
Constant current density electrolysis is performed for about 0 seconds, and the cell voltage is 40 to 1
Potential electrolysis is carried out after the voltage has risen to a predetermined voltage within the range of 50V, preferably within the range of 70-140V. The current density during the constant potential electrolysis is generally 0.1 A / dm ²
It is below the level. Constant current density Current density during electrolysis is 1A
If it is less than / dm ² , the electrolytic treatment for more than 20 minutes is required and the productivity is lowered, and the current density is 50A.
If it exceeds / dm ² , electrolysis at high voltage tends to be difficult. When the voltage during potentiostatic electrolysis is less than 40V, the corrosion resistance of the anodized film obtained tends to be insufficient, and when the voltage exceeds 150V, the corrosion resistance of the anodized film obtained is not sufficient. Tends to be enough.

In the surface treatment method for magnesium alloy of the present invention, the required electrolytic treatment time varies depending on the carbonate concentration and phosphate concentration in the electrolytic solution, the electrolytic solution temperature, the initial current density, and the electrolytic voltage. However, it is generally 30 seconds to 20 minutes, preferably 2 to 15 minutes. When the electrolytic treatment time is less than 30 seconds, the corrosion resistance of the anodized film obtained tends to be insufficient, and even when the electrolytic treatment time exceeds 20 minutes, the corrosion resistance of the anodized film obtained is more than that. Does not increase.

[0017]

EXAMPLES The present invention will be specifically described below based on Examples and Comparative Examples. Examples 1 to 24 A large number of test pieces (45 mm x 40 mm x 0.5 mm) of Mg-9.5Li-1Y alloy produced by rolling were used in a room temperature 2.4% dilute nitric acid solution (60% nitric acid solution (Kanto Chemical Co., Inc. It was immersed for 2 minutes in a solution) (40 mL diluted to 1 L), and then washed with tap water at room temperature for 30 seconds and then with pure water at room temperature for 30 seconds.

Each test piece treated as described above was
In the electrolyte solution of carbonate concentration and phosphate concentration shown in Table 1,
At the electrolyte temperature shown in Table 1, constant current density electrolysis was started at the initial current density shown in Table 1, and when the cell voltage increased to the electrolysis voltage shown in Table 1, (constant current density electrolysis was started. Potential electrolysis was carried out after 10 to 20 seconds from the start, and the first
Electrolysis was performed for the treatment time shown in the table. Then tap water at room temperature for 30
It was washed for 2 seconds and then for 30 seconds with pure water at room temperature. Finally, it was dried at 80 ° C. for 20 minutes.

Corrosion resistance of each test piece dried by anodizing treatment as described above JIS Z 237
The salt spray test was carried out for 24 hours according to 1 and evaluated by the rating number method. The results are shown in Table 1. In addition, the anodizing treatment was performed as described above, and the epoxy-based baking coating was applied to the surface of each dried test piece by the dip coating method, and the mixture was allowed to stand for 15 minutes and then dried by heating at 150 ° C. for 20 minutes. Carried out. Then J
A coating film adhesion test was carried out by a cross-cut tape method (1 mm interval) based on ISK 5400, 8.5.2.
The results are as shown in Table 1.

[0020]

[Table 1]

Examples 25 to 34 A large number of test pieces (45 mm × 40 mm × 0.5 mm) of Mg-9.5Li-1Y alloy produced by rolling were tested at room temperature with 2.4% dilute nitric acid solution (60% nitric acid solution ( It was immersed for 2 minutes in a solution obtained by diluting 40 mL (made by Kanto Chemical Co., Inc.) to 1 L, and then washed with tap water at room temperature for 30 seconds and then with pure water at room temperature for 30 seconds.

Each test piece treated as described above was
In a electrolytic solution containing carbonates and phosphates of the types shown in Table 2 at concentrations shown in Table ² , constant current density electrolysis was started at an electrolytic solution temperature of 90 ° C. and an initial current density of 16 A / dm ² . At the time when the cell voltage increased to 110 V (10 to 20 seconds after starting the constant current density electrolysis), constant potential electrolysis was performed, and electrolysis was performed for 10 minutes in total. Then, it was washed with tap water at room temperature for 30 seconds and then with pure water at room temperature for 30 seconds. Finally, it was dried at 80 ° C. for 20 minutes.

The corrosion resistance of each of the dried test pieces which were anodized as described above was measured according to JIS Z237.
The salt spray test was carried out for 24 hours according to 1 and evaluated by the rating number method. The results are shown in Table 2. In addition, the anodizing treatment was performed as described above, and the epoxy-based baking coating was applied to the surface of each dried test piece by the dip coating method, and the mixture was allowed to stand for 15 minutes and then dried by heating at 150 ° C. for 20 minutes. Carried out. Then J
A coating film adhesion test was carried out by a cross-cut tape method (1 mm interval) based on ISK 5400, 8.5.2.
The results are shown in Table 2.

[0024]

[Table 2]

Examples 35 to 39 Specimens of magnesium alloy of the alloy species of Examples 35 to 36 shown in Table 3 produced by rolling (45 mm × 40 m)
m × 0.5 mm) and the third made by die casting
Test pieces (45 mm × 40 mm × 0.8 mm) of magnesium alloys of the alloy types of Examples 37 to 39 shown in the table were used at room temperature in a 2.4% dilute nitric acid solution (60% nitric acid solution (manufactured by Kanto Chemical Co., Inc.).
It was immersed in a solution of 40 mL diluted to 1 L) for 2 minutes, and then washed with room temperature tap water for 30 seconds and then with room temperature pure water for 30 seconds.

Each test piece treated as described above was
Na ₂ CO ₃ concentration 12.5 g / L, K ₂ HPO ₄ concentration 1
In a 5 g / L electrolytic solution, constant current density electrolysis was started at an electrolytic solution temperature of 90 ° C. and an initial current density of 16 A / dm ² , and when the cell voltage increased to 110 V (after starting constant current density electrolysis Potential electrolysis was carried out (after 10 to 20 seconds) for a total of 10 minutes. Then, it was washed with tap water at room temperature for 30 seconds and then with pure water at room temperature for 30 seconds. Finally 80
It was dried at 0 ° C for 20 minutes.

The corrosion resistance of each of the dried test pieces which were anodized as described above was measured according to JIS Z237.
Each time, the salt spray test for each time shown in Table 3 was performed according to 1, and evaluated by the rating number method. The results are shown in Table 3. In addition, the anodizing treatment was performed as described above, and an epoxy baking paint was applied to the surface of each dried test piece by the dip coating method, and 1
After allowing to stand for 5 minutes, heat drying was carried out at 150 ° C. for 20 minutes. After that, a coating film adhesion test was carried out by a cross-cut tape method (1 mm interval) in accordance with JIS K 5400, 8.5.2. The results are shown in Table 3.

[0028]

[Table 3]

Comparative Examples 1 to 10 A large number of test pieces (45 mm × 40 mm × 0.5 mm) of Mg-9.5Li-1Y alloy produced by rolling were used in a room temperature 2.4% dilute nitric acid solution (60% nitric acid solution ( It was immersed for 2 minutes in a solution obtained by diluting 40 mL (made by Kanto Chemical Co., Inc.) to 1 L, and then washed with tap water at room temperature for 30 seconds and then with pure water at room temperature for 30 seconds.

Each test piece treated as described above was
In the electrolyte solution of carbonate concentration and phosphate concentration shown in Table 4,
At the temperature of the electrolyte shown in Table 4, constant current density electrolysis was started at the initial current density shown in Table 4, and when the tank voltage increased to the electrolysis voltage shown in Table 4, (constant current density electrolysis was started. Potential electrolysis was carried out after 10 to 20 seconds from the start, and a total of 4th
Electrolysis was performed for the treatment time shown in the table. Then tap water at room temperature for 30
It was washed for 2 seconds and then for 30 seconds with pure water at room temperature. Finally, it was dried at 80 ° C. for 20 minutes.

The corrosion resistance of each of the dried test pieces which were anodized as described above was measured according to JIS Z237.
The salt spray test was carried out for 24 hours according to 1 and evaluated by the rating number method. The results are shown in Table 4. In addition, the anodizing treatment was performed as described above, and the epoxy-based baking coating was applied to the surface of each dried test piece by the dip coating method, and the mixture was allowed to stand for 15 minutes and then dried by heating at 150 ° C. for 20 minutes. Carried out. Then J
A coating film adhesion test was carried out by a cross-cut tape method (1 mm interval) based on ISK 5400, 8.5.2.
The results are shown in Table 4.

[0032]

[Table 4]

As is clear from the comparison between the rating numbers shown in Tables 1 to 3 corresponding to the examples of the present invention and the rating numbers shown in Table 4 as a comparative example,
The magnesium alloy treated by the magnesium alloy surface treatment method of the present invention has excellent corrosion resistance.

[0034]

The anodized film obtained by the method for surface treatment of magnesium alloy of the present invention is excellent in corrosion resistance and coating adhesion.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masahiro Hyakutake             1333-2 Hara-shi, Ageo-shi, Saitama Mitsui Mining & Smelting             Research Institute, Inc. (72) Inventor Makoto Dobashi             1333-2 Hara-shi, Ageo-shi, Saitama Mitsui Mining & Smelting             Research Institute, Inc.

Claims (4)

[Claims] 1. A magnesium alloy surface having a carbonate concentration of 0.05 to 0.19 M and a phosphate concentration of 0.00.
In the electrolytic solution of 5 to 0.15 M, the electrolytic solution temperature is 50 to 9
A surface treatment method for a magnesium alloy, characterized by performing anodizing treatment at 5 ° C and an electrolysis voltage of 40 to 150 V for 30 seconds to 20 minutes. 2. The magnesium alloy surface has a carbonate concentration of 0.07 to 0.15 M and a phosphate concentration of 0.02.
In the electrolytic solution of 0.13M, the electrolytic solution temperature is 75 to 93.
The surface treatment method for a magnesium alloy according to claim 1, wherein anodization treatment is performed at a temperature of 70 ° C. and an electrolysis voltage of 70 to 140 V for 2 to 15 minutes. 3. The surface treatment method for a magnesium alloy according to claim 1, wherein the carbonate is sodium carbonate, potassium carbonate or ammonium carbonate. 4. The phosphate is sodium phosphate, potassium phosphate, ammonium phosphate, disodium hydrogen phosphate,
The surface treatment method for a magnesium alloy according to claim 1, 2 or 3, wherein the surface treatment is dipotassium hydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate or ammonium dihydrogen phosphate.