JP2002256494A - Method for forming anodic oxide film on magnesium alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a corrosion resistance of a chemical conversion coated or anodized magnesium alloy, which has been conventionally unsatisfactory for a machine part or a car component, in which the corrosion resistance is thought important of. SOLUTION: This method comprises immersing an magnesium alloy into an electrolytic solution containing two or more of inorganic acid salts, inorganic bases, organic acid salts, and organic acids, and electrolyzing it with constant voltage by using a duty (periodically reversal waveform) power source and by gradually increasing the voltage in 3-100 V/min, or electrolyzing it with constant current and subsequently with constant voltage. The electrolytic solution preferably includes inorganic acid salts (phosphate and silicate) of two or more kinds of alkali metals. To be advantageous, holders made from titanium or aluminum can be used for the electrolytic treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for forming an anodic oxide film on a magnesium alloy.

[0002]

2. Description of the Related Art Magnesium alloys, which are lightweight and have high strength, have been subjected to a chemical conversion coating by chromate treatment or the like, and are used for housings of mobile phones, video cameras and the like. However, the chemical conversion film is easily peeled off and is unsatisfactory for use in mechanical parts and automotive parts in which corrosion resistance and functionality are important. Further, the anodic oxide film formed by the conventional method is also unsatisfactory in terms of corrosion resistance and undercoat performance of the coating film.

[0003]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for forming a film having excellent wear resistance and corrosion resistance on a magnesium alloy.

[0004]

Means for Solving the Problems In order to solve the above problems, the present inventors have made intensive studies and as a result, devised a devised electrolytic method and an electrolytic solution suitable for the method, and have completed the present invention. That is, the invention of claim 1 provides a magnesium alloy,
It is immersed in an electrolytic solution containing two or more of an inorganic acid salt, an inorganic base, an organic acid salt and an organic acid, and the voltage is gradually increased at a rate of 3 to 100 V / min using a Duty (PR waveform) power supply. This is a method for forming an anodic oxide film on a magnesium alloy, wherein voltage electrolysis or constant current electrolysis is performed followed by constant voltage electrolysis.

According to a second aspect of the present invention, there is provided a method for forming an anodic oxide film on a magnesium alloy according to the first aspect.
This is a forming method characterized by immersing in an electrolytic solution containing at least one inorganic salt of an alkali metal.

According to a third aspect of the present invention, in the method for forming an anodic oxide film on a magnesium alloy according to the first or second aspect, the inorganic acid is sulfuric acid, nitric acid, phosphoric acid or silicic acid, and the organic acid is dicarboxylic acid or tricarboxylic acid. This is a forming method characterized by being an acid.

According to a fourth aspect of the present invention, there is provided a method of forming an anodic oxide film on a magnesium alloy according to any one of the first to third aspects, wherein the duty ratio is 20 to 99%. is there.

According to a fifth aspect of the present invention, there is provided a method for forming an anodic oxide film on a magnesium alloy according to any one of the first to fourth aspects, wherein the magnesium alloy is placed in an electrolytic solution by using a jig made of titanium or aluminum. This is a forming method characterized by immersing and electrolyzing.

According to a sixth aspect of the present invention, there is provided a method for forming an anodic oxide film on a magnesium alloy according to the fifth aspect, wherein
After electrolytic treatment using an electrolytic solution containing an inorganic acid salt of at least one kind of alkali metal and an aluminum jig, the used jig is immersed in a solution containing an inorganic base to remove an oxide film formed on the surface, This is a forming method characterized by being reused in the next electrolytic treatment.

According to a seventh aspect of the present invention, there is provided a method for forming an anodic oxide film on a magnesium alloy according to the sixth aspect, wherein the method of removing the oxide film formed on the surface by immersing the film in a solution containing an inorganic base is carried out. This is a forming method characterized by using an oxidized magnesium alloy, removing an oxide film, performing an anodic oxidation treatment again, and reusing.

[0011] The invention of claim 8 is a method for forming an anodized film on a magnesium alloy according to any one of claims 1 to 7, wherein the film is colored by dipping in an inorganic dye or an organic dye, and further sealed. This is a forming method characterized by improving the corrosion resistance of a film by performing a hole treatment.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for forming an anodic oxide film on a magnesium alloy will be described. The electrolyte is an inorganic acid salt,
It contains two or more of inorganic bases, organic acid salts and organic acids, and is colorless and transparent. Preferably, the inorganic acid of the inorganic acid salt is sulfuric acid, nitric acid, phosphoric acid, or silicic acid. Preferably, the inorganic base is a hydroxide of an alkali metal such as sodium hydroxide or potassium hydroxide. Preferably,
The organic acid of the organic acid salt is an organic acid having two or more carboxyl groups, for example, dicarboxylic acid and tricarboxylic acid. More preferably, it is a dicarboxylic acid having two or more carboxyl groups as an organic acid. The salts may be directly added to the electrolytic solution as a salt of an alkali metal, an alkaline earth metal, or the like, or an organic acid or an inorganic acid and a hydroxide may be added to the electrolytic solution. Preferably, it contains two or more kinds of inorganic acid salts of alkali metals, and more preferably contains phosphate and silicate. When a problem occurs in the anodic oxide film formed on the magnesium alloy, there is an advantage that the film can be removed by immersion in a solution containing an inorganic base.

Preferably, the pH is between 11 and 14. The temperature of the electrolyte is preferably from 0 to 40C, more preferably from 15 to 25C. During electrolysis (anodizing treatment), the temperature of the electrolytic solution rises due to the generation of sparks, so that the temperature of the electrolytic solution is kept in an appropriate range by the cooling means.

The electrolysis is performed according to a method shown in a time chart of two types of voltage and current shown in FIG. FIG. 1 (A)
5 is a time chart in the case of performing constant voltage electrolysis after performing constant current electrolysis. When the constant current electrolysis is started, a spark is generated and an insulating anodic oxide film (coarse film) starts to be formed, the resistance value increases, and the voltage increases linearly.
After the end of the spark, when switching to the constant voltage electrolysis, the coarse film matures during that time, and the current density decreases exponentially.
The switching from the constant current electrolysis to the constant voltage electrolysis may be performed when the voltage has risen to a specified voltage value, or may be performed when a specified time comes according to a time chart prepared in advance based on a preliminary experiment.

The current density value in the constant current electrolysis is preferably 0.1 to 3.0 A /% in order to form a dense film.
dm ² , more preferably 0.5 to 2.0 A / dm ² . In the constant current electrolysis, when the current density value is set, the voltage value increases with the formation of the film, and a spark occurs from 50 V or more. The voltage in the constant voltage electrolysis preferably ranges from the final voltage value in the constant current electrolysis to + 15V. By setting the voltage in this range, the current can be reduced from the set current value in the constant current electrolysis, and the film matures sufficiently.

FIG. 1B is a time chart in the case of performing constant voltage electrolysis in which the voltage is gradually increased (hereinafter, referred to as "soft start constant voltage electrolysis"). In the case of soft start constant voltage electrolysis, since the voltage is gradually increased to 3 to 100 V / min, generation of a film defect due to current concentration on a magnesium alloy defective portion is prevented. The voltage rising speed range is preferably 12 to 27 V / min.
When the constant voltage electrolysis is started, in the voltage rising region, the voltage gradually increases linearly, and the current density also increases linearly. Then, a spark is generated from about 70 V or more, and the formation of an anodic oxide film (coarse film) starts.

When a spark occurs, the current density increases, and when the voltage value increases to about 90 to 110 V, the current density increases to 7 to 10 A.
/ Dm ^{2 in} some cases. After the end of the spark, the current density decreases exponentially. When the current density decreases, the coarse film is aged. The constant voltage value in the constant voltage range is set based on a preliminary experiment (constant current electrolysis + constant voltage electrolysis). Since there is no step of constant current electrolysis in soft start constant voltage electrolysis, there is no electrolysis switching operation, and as a result, there is an advantage that the entire electrolysis operation is simplified.

Regardless of the method of applying the constant voltage in either of the methods (A) and (B) of FIG. 1, even when the applied current is reduced to a prescribed value, the application of the constant voltage is performed in a preliminary experiment. The processing may be terminated when a specified time comes according to a time chart prepared in advance based on the time chart. Power supply is Duty (PR
Waveform) power supply. The duty ratio is preferably 20 to
It is 99%, more preferably 50 to 95.24%. The frequency is preferably 1 to 500 Hz, more preferably 1 to 80 Hz. The ratio of the positive voltage to the negative voltage is 1:
1-1: 0.1. After the completion of the electrolytic treatment, it is washed with water and dried sufficiently. In consideration of production efficiency, the total electrolysis time is preferably 5 to 60 minutes when the upper limit voltage is about 120 V, regardless of the method of FIGS. 1A and 1B. Preferably, it is set to 10 to 30 minutes.

According to the method of the present invention, advantageously, D
Even if a uty power source is used, an aluminum jig other than titanium can be used. Titanium jigs do not dissolve and can be reused. In addition, an oxide film is formed on the surface of an aluminum jig during electrolysis, and since the oxide film can be removed by immersion in a solution containing an inorganic base, it can be reused. Since aluminum jigs are less expensive than titanium jigs, using aluminum jigs has the advantage of lower running costs.

Preferably, the following steps are sequentially performed as pretreatment. (1) Degreasing treatment step This is a preliminary treatment for removing fats and oils adhering to the surface of a magnesium alloy to be treated. Using an organic solvent or alkaline degreasing agent such as sodium carbonate, 50 ~
It is immersed at 80 ° C, preferably 65 to 75 ° C for about 2 to 10 minutes, and then washed with water.

(2) Activation treatment step This is a treatment for activating the surface by removing an oxide film from the surface of the magnesium alloy by etching. Using alkalis such as sodium hydroxide, acids such as nitric acid, and metal salts such as ferric chloride, preferably at 45 to 75 ° C,
More preferably, it is immersed at 55 to 65 ° C., preferably for about 2 to 10 minutes, and then washed with water.

(3) Surface adjustment step This is a step for making the surface potential uniform and preventing potential corrosion due to chemicals in the next step. It is immersed in a commercially available surface conditioner at room temperature for about 1 to 5 minutes and then washed with water.

As a post-treatment, after forming the anodic oxide film,
By immersing in high-temperature pure water of about 90 ° C for about 5 minutes,
Sealing treatment may be performed. It is also possible to improve the corrosion resistance of the film by coloring the film by immersing it in an inorganic dye or an organic dye and then performing a sealing treatment. As the dye, those conventionally used for coloring the anodic oxide film of aluminum can be used. As a specific dye, TAC BLACK-SLH manufactured by Okuno Pharmaceutical Co., Ltd.
(Azo dye), Alumin manufactured by Clariant Japan KK
ium Bordeaux RL (azo dye), Sanodal Blue G (anthraquinone dye), Aluminum Green LWN (azo dye)
These include trivalent chromium compounds, 2
-Methyl-2,4-pentanediol, dextrin,
Contains sodium acetate and the like.

[0024]

EXAMPLE An AZ91D thixomolding material was used as a test material, and an oxide film was formed as follows. As pretreatment, degreasing treatment (drug: aqueous solution of sodium carbonate, pH: 11.0, liquid temperature: 60 ° C, immersion time: 5
Min), water washing, activation treatment (drug: aqueous solution of sodium hydroxide, pH: 11.0, liquid temperature: 50 ° C., immersion time: 5
Min), water washing, surface conditioning treatment (drug: manufactured by Kizai Co., Ltd., liquid temperature: room temperature, immersion time: 5 minutes), and water washing.

Next, electrolytic treatment was performed under the following conditions, and thereafter, the test material was washed with water and dried sufficiently. Condition 1 (method of the present invention) Electrolyte (150 g / L trisodium phosphate + 20 g / L)
Sodium metasilicate +10 g / L oxalic acid) at 20 ° C
, And electrolytic treatment was performed using a titanium jig for 20 minutes. The power supply uses Duty and the frequency is 5
At 0 Hz, the duty ratio was 95.24%, and the ratio of positive voltage: negative voltage was 1: 0.2. Initially the current density is 1 A / d
a constant current electrolysis m ^2, and the raised voltage when the voltage reaches 90V to 100 V, were constant voltage electrolysis at that voltage.

Condition 2 (method of the present invention) Electrolyte (150 g / L trisodium phosphate + 20 g / L)
(Sodium metasilicate + 20 g / L sodium hydroxide)
While maintaining the temperature at 20 ° C., electrolytic treatment was performed for 20 minutes using an aluminum jig. Duty was used as the power source, the frequency was 50 Hz, the duty ratio was 95.24%, and the ratio of positive voltage: negative voltage was 1: 0.2. First, constant current electrolysis was performed at a current density of 1 A / dm ² , and when the voltage reached 90 V, the voltage was increased to 100 V, and constant voltage electrolysis was performed at that voltage.

Condition 3 (method of the present invention) Electrolyte (100 g / L trisodium phosphate + 30 g / L)
Sodium metasilicate +5 g / L oxalic acid +10 g / L
While maintaining (sodium hydroxide) at 30 ° C., electrolytic treatment was performed for 20 minutes using an aluminum jig. The power supply uses Duty, the frequency is 50 Hz, and the duty ratio is 6
6.67%, and the positive voltage: negative voltage ratio was 1: 0.2. Initially, constant current electrolysis is performed at a current density of 2 A / dm ² ,
When the voltage reached 80 V, the voltage was raised to 90 V, and constant voltage electrolysis was performed at that voltage.

Condition 4 (method of the present invention) Electrolyte (100 g / L trisodium phosphate + 40 g / L)
While maintaining (sodium metasilicate) at 20 ° C., electrolytic treatment was performed for 20 minutes using a titanium jig. The power source is Duty, the frequency is 50 Hz, the duty ratio is 95.24%, and the positive voltage: negative voltage ratio is 1: 0.2.
And First, constant current electrolysis was performed at a current density of 1 A / dm ² , and when the voltage reached 90 V, the voltage was increased to 100 V, and constant voltage electrolysis was performed at that voltage.

Conditions 5 to 8 (method of the present invention) Conditions 5 to 8 adopt the above-mentioned conditions 1 to 4 of the electrolyte and the duty power supply condition, the set voltage is 100 V, and the voltage rising rate is 7, 15 , 20, 25 V / min, and soft-start constant voltage electrolysis was performed. In addition, in order to make the aging conditions of the oxide film the same, the required time in the constant voltage region of the conditions 5 to 8 was adjusted to be the same as the required time of the constant voltage electrolysis of the conditions 1 to 4, respectively.

Condition 9 (Method of Comparative Example) Electrolyte (150 g / L trisodium phosphate + 20 g / L)
Sodium metasilicate +10 g / L oxalic acid) at 20 ° C
, And electrolytic treatment was performed using a titanium jig for 20 minutes. DC power was used as the power source. First, constant current electrolysis was performed at a current density of 1 A / dm ² , and when the voltage reached 90 V, the voltage was increased to 100 V, and constant voltage electrolysis was performed at that voltage.

All the test materials subjected to the electrolytic treatment by the method of the present invention (conditions 1 to 8) had a uniform white anodic oxide film formed on the surface. On the other hand, a light brown non-uniform anodic oxide film was formed on the test material subjected to the electrolytic treatment by the method (condition 9) of the comparative example. Further, a salt spray test according to JISZ2371H was performed, and the surface condition after elapse of 48 hours, 96 hours, and 120 hours was evaluated by a corrosion test area method (rating number (RN)).

Next, a coating treatment was performed on the anodic oxide film of each test material. (Undercoat): Paint (Epolac # 200HS primer white, Epolac # 100 thinner, viscosity 27 sec, manufactured by Tokyo Paint Co., Ltd.) Coating method: Baking 150 ° C. × 20 minutes (Top coat): Paint (Leather plot MT-0582M)
(Revised), Leather plot thinner, viscosity 28 sec, manufactured by Tokyo Paint Co., Ltd. Coating method: baking 150 ° C. × 20 minutes And after immersing in boiling water for 2 hours and after immersing in warm water at 60 ° C. for 4 hours, respectively A cellophane tape peeling test was performed to evaluate coating film adhesion.

The results are as follows. The anodic oxide film formed by the method of the present invention had a high rating number and excellent adhesion to the coating film. Electrolytic treatment was performed using titanium and aluminum jigs, but no trace of dissolution was seen on the titanium jig, and a thin oxide film was formed on the surface of the aluminum jig. The film was easily removed by dipping in a solution containing an inorganic base.

[0034]

[Table 1]

Further, Okuno Pharmaceutical Co., Ltd.
Was subjected to a coloring treatment using TAC BLACK-SLH (azo dye) manufactured by KK according to a standard method. The test material treated by the method had unevenness.

[0036]

The anodic oxide film formed by the method of the present invention has excellent corrosion resistance and coating film adhesion. In addition, the method of the present invention can perform electrolytic treatment while immersing a magnesium alloy in an electrolytic solution using a jig made of titanium or aluminum. These jigs can be used many times.

[Brief description of the drawings]

FIG. 1 is a time chart of voltage and current for explaining an electrolysis method.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor: Narita Nakata, 5202 Kambara, Kambara-cho, Abara-gun, Shizuoka Prefecture Inside Fuji Kogyo Co., Ltd. (72) Inventor Yoshifumi Shimajiri 2-2 Sumiyoshi-cho, Utsunomiya-shi, Tochigi S.T.C. Co., Ltd. (72) Inventor Tsuneo Kosaka 1-3-11 Nishikicho, Warabi-shi, Saitama F-term (Reference) 4K057 WA01 WB01 WE02 WE08 WE22 WK05 WN10

Claims (8)

[Claims] 1. A magnesium alloy is immersed in an electrolytic solution containing two or more of an inorganic acid salt, an inorganic base, an organic acid salt and an organic acid, and a voltage of 3 to 3 is applied using a Duty (PR waveform) power supply.
A method for forming an anodic oxide film on a magnesium alloy, wherein constant voltage electrolysis is performed by a method of gradually increasing at 100 V / min, or constant voltage electrolysis is performed after performing constant current electrolysis. 2. The method for forming an anodic oxide film on a magnesium alloy according to claim 1, wherein the anodic oxide film is immersed in an electrolytic solution containing two or more kinds of inorganic acid salts of alkali metals. 3. The method for forming an anodized film on a magnesium alloy according to claim 1 or 2, wherein the inorganic acid is sulfuric acid,
A forming method characterized in that the nitric acid, phosphoric acid or silicic acid, and the organic acid are dicarboxylic acids or tricarboxylic acids. 4. A method for forming an anodic oxide film on a magnesium alloy according to claim 1, wherein
A forming method, wherein the y ratio is 20 to 99%. 5. The method for forming an anodized film on a magnesium alloy according to claim 1, wherein the magnesium alloy is immersed in an electrolytic solution using a jig made of titanium or aluminum to perform electrolysis. A forming method characterized by the above-mentioned. 6. The method for forming an anodized film on a magnesium alloy according to claim 5, wherein the electrolytic treatment is performed using an electrolytic solution containing two or more inorganic salts of alkali metals and a jig made of aluminum. A forming method characterized by immersing a used jig in a solution containing an inorganic base to remove an oxide film formed on a surface thereof, and then reusing the jig in a subsequent electrolytic treatment. 7. The method for forming an anodic oxide film on a magnesium alloy according to claim 6, wherein the method of removing the oxide film formed on the surface by immersing the anodic oxide film in a solution containing an inorganic base is performed. A forming method characterized by removing an oxide film, performing anodizing treatment again, and reusing the film. 8. The method for forming an anodized film on a magnesium alloy according to any one of claims 1 to 7, wherein the film is colored by dipping in an inorganic dye or an organic dye, and further subjected to a sealing treatment. A forming method characterized by improving the corrosion resistance of a film.