JP2003171793A - Method of forming anodic oxidation film onto aluminum alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of forming an anodic oxidation film onto an aluminum alloy for extrusion, diecasting, casting or the like. <P>SOLUTION: An aluminum alloy is dipped into an electrolytic solution containing two or more kinds selected from inorganic acid salts, inorganic bases, organic acid salts and organic acids, and is subjected to constant-voltage electrolysis by a method where a Duty [PR (periodic reverse) wave form] power source is used, and voltage is gradually increased at 3 to 100 V/min, or is subjected to constant-voltage electrolysis after the performance of constant- current electrolysis. The electrolytic solution preferably contains two or more kinds of inorganic acid salts (phosphates and silicates) of alkali metals. Advantageously, the electrolytic treatment can be performed by using a jig made of aluminum. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for forming an anodized film on an aluminum alloy.

[0002]

2. Description of the Related Art Aluminum alloys subjected to anodizing treatment have been conventionally used as building materials such as aluminum sashes, but in recent years, aluminum alloy extruded materials, drawn materials and die cast materials are lightweight and cast. Since it is excellent in properties, suitable for thin walls and complicated shapes, and has high dimensional accuracy, it has been proposed to use them in frames for motorcycles, automobile bodies, cylinder blocks for internal combustion engines, and the like. However, compared to extruded and drawn materials, die-cast materials take into consideration wear resistance, castability, and thermal expansion, and Si (silicon)
Since it contains a large amount of 5 to 20% by weight, the anodic oxide film formed by using a conventional electrolytic solution such as sulfuric acid or oxalic acid is
Due to the action of Si, a large number of voids in which no film has been formed are generated, which is not satisfactory in terms of corrosion resistance. Further, the anodic oxide coating applied to the Si-based casting material was not satisfactory for the same reason as the die casting material.

[0003]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for forming an anodic oxide film which solves the above problems on an aluminum alloy for extrusion, die casting, casting, etc. To do.

[0004]

In order to solve the above problems, the present inventor, as a result of earnest research, devised a devised electrolytic method and an electrolytic solution suitable for the method, and completed the present invention. That is, the invention of claim 1 is an aluminum alloy,
It is dipped in an electrolytic solution containing two or more kinds of inorganic acid salts, inorganic bases, organic acid salts and organic acids, and a duty (PR waveform) power source is used to gradually increase the voltage at 3 to 100 V / min. A method for forming an anodic oxide film on an aluminum alloy, which comprises performing constant voltage electrolysis after performing constant voltage electrolysis or constant voltage electrolysis.

According to a second aspect of the present invention, there is provided a method for forming an anodic oxide coating on an aluminum alloy according to the first aspect, wherein
The forming method is characterized by immersing in an electrolytic solution containing one or more kinds of inorganic acid salts of alkali metals.

The invention of claim 3 is the method for forming an anodized film on an aluminum alloy according to claim 1 or 2, wherein the inorganic acid is sulfuric acid, nitric acid, phosphoric acid or silicic acid, and the organic acid is dicarboxylic acid or tricarboxylic acid. It is an acid, which is a forming method.

The invention according to claim 4 is the method for forming an anodized film on an aluminum alloy according to any one of claims 1 to 3, wherein the duty ratio is 20 to 99%. is there.

According to a fifth aspect of the present invention, in the method for forming an anodized film on an aluminum alloy according to any one of the first to fourth aspects, the anodized film is formed on a Si-based aluminum alloy. It is a forming method.

According to a sixth aspect of the present invention, in the method for forming an anodic oxide film on the aluminum alloy according to any of the first to fifth aspects, the titanium alloy or the aluminum jig is used to bring the aluminum alloy into the electrolytic solution. It is formed by immersing in and electrolyzing.

According to a seventh aspect of the present invention, in the method for forming an anodized film on an aluminum alloy according to the sixth aspect, after electrolytically treating using an aluminum jig, the jig used is a solution containing an inorganic base. The method is characterized in that it is soaked in water to remove the anodized film formed on the surface, and then reused in the next electrolytic treatment.

The invention of claim 8 is the method of forming an anodized film on an aluminum alloy according to claim 7, which is a method of removing the anodized film formed on the surface by immersing it in a solution containing an inorganic base. It is a forming method characterized by using an anodized aluminum alloy, removing the anodized film, performing anodizing again, and reusing.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A method for forming an anodized film on an aluminum alloy will be described. The aluminum alloy, which is the base material, can obtain suitable results even if it is a Si-based die-cast material containing a large amount of Si and for castings, which has not been able to form a satisfactory anodic oxide film in the past.

Regarding the die casting material, ADC1, ADC3 and A of the aluminum alloy base metal series for die casting are used.
DC5, ADC6, ADC10, ADC10Z, ADC
12, ADC12Z, ADC14 are illustrated. ADC
5 and ADC6 are all Al-Si based, Si
Contains at least 7.5% by weight. Furthermore, AC1A, AC1B of aluminum alloy ingot series for casting,
AC2A, AC2B, AC3A, AC4A, AC4B,
AC4C, AC4CH, AC4D, AC5A, AC7
A, AC8A, AC8B, AC8C, AC9A, AC9
B is illustrated. This series also contains many Al-Si systems.

The Si-based aluminum alloy preferably has a Si content of 15% by weight or less. Incidentally, the present invention is not limited to the above materials, and other than that, suitable results can be obtained by applying the method of the present invention to an aluminum alloy having an anodized film formed using an electrolytic solution such as sulfuric acid or oxalic acid. Needless to say.

The electrolytic solution contains two or more kinds of inorganic acid salt, inorganic base, organic acid salt and organic acid, and is colorless and transparent. Preferably, the inorganic acid of the inorganic acid salt is sulfuric acid, nitric acid, phosphoric acid, or silicic acid. The inorganic base is preferably an alkali metal hydroxide 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, such as dicarboxylic acid or tricarboxylic acid. More preferably, the organic acid is a dicarboxylic acid having two or more carboxyl groups.

The salt may be added directly 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, two or more kinds of inorganic acid salts of alkali metals are contained,
More preferably, it contains a phosphate and a silicate. When the anodic oxide film formed on the aluminum alloy is defective, there is an advantage that the film can be removed by immersing it in a solution containing an inorganic base.

The pH of the electrolytic solution is preferably 11-14. The temperature of the electrolytic solution is preferably 0 to 40 ° C, more preferably 15 to 25 ° C.

The electrolysis is carried out according to the method shown in the time chart of the two kinds of voltage and current shown in FIG. Figure 1 (A)
[Fig. 3] is a time chart when constant voltage electrolysis is performed after constant current electrolysis. When constant current electrolysis is started, formation of an insulating anodic oxide film (coarse film) starts, the resistance value increases, and the voltage increases linearly. When switching to constant voltage electrolysis, the rough film is aged during that time and the current density exponentially decreases. Switching from constant current electrolysis to constant voltage electrolysis may be performed when the voltage has risen to a specified voltage value, or may be performed when a specified time has elapsed according to a time chart created in advance based on preliminary experiments.

The current density value in 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 . The constant current electrolysis is preferably performed until the final voltage reaches the range of (constant voltage −15 V) to constant voltage in the constant voltage electrolysis.

FIG. 1B is a time chart in the case where constant voltage electrolysis in which the voltage is gradually increased (hereinafter referred to as "soft start constant voltage electrolysis") is performed. The voltage in the constant voltage region is set to the same value as the voltage in the constant voltage electrolysis shown in FIG. In the case of soft-start constant-voltage electrolysis, the voltage is gradually increased to 3 to 100 V / min, so that the occurrence of film defects due to current concentration on the aluminum alloy defect part is prevented. The voltage rise speed range is
It is preferably 12 to 27 V / min. When the constant voltage electrolysis of soft start is started, the voltage gradually increases linearly and the current density also linearly increases in the voltage increase region. Then, normally, the formation of the anodic oxide film (coarse film) starts at about 70 V or higher.

When the rough film is formed, the current density is increased, and when the voltage value is increased to about 90 to 110 V, it is 7 to 10 A / d.
It may reach up to about m ² . After the formation of the rough film, the ripening period of the rough film starts and the current density decreases exponentially. In addition,
The constant voltage value in the constant voltage region is set based on preliminary experiments (constant current electrolysis + constant voltage electrolysis). Since the constant voltage electrolysis of soft start does not have the step of constant current electrolysis, there is no switching work of electrolysis, and as a result, there is an advantage that the whole electrolysis work is simplified.

The application of the constant voltage, even when electrolysis is carried out by any of the methods (A) and (B) of FIG. 1, is finished even when the value of the current being applied falls to a specified value, The process may be terminated when a prescribed time has come according to a time chart created in advance based on preliminary experiments. Power source is D
It is a duty (PR waveform) power supply. The duty ratio is preferably 20 to 99%, more preferably 50 to 95.24.
%. The frequency is preferably 1 to 500 Hz, more preferably 1 to 80 Hz. The positive voltage: negative voltage ratio is 1: 1 to 1: 0.1.

After completion of the electrolytic treatment, it is washed with water and dried sufficiently. Considering the production efficiency, the total electrolysis time is calculated by either of the methods of FIG. 1 (A) and (B).
When the upper limit voltage is about 120V, it is preferably 5 to 6
It is preferably set to 0 minutes, more preferably 30 to 50 minutes. In any of the above electrolysis methods, when the voltage rises and a certain value is reached, a crackling spark is generated, and this spark is continued until the end of electrolysis.

According to the method of the invention, D
A jig made of aluminum can be used in addition to titanium by using the uty power source. Titanium jigs do not melt and can be reused. On the other hand, an anodized film is formed on the surface of an aluminum jig during electrolysis, but it can be reused because it can be removed by immersing it in a solution containing an inorganic base. Since the jig made of aluminum is cheaper than the jig made of titanium, the use of the jig made of aluminum has an advantage that the running cost is reduced as a result.

The following steps are preferably performed in order as pretreatment. (1) Degreasing treatment step This is a preliminary treatment for removing the oil and fat adhering to the surface of the aluminum alloy that is the material to be treated. Using an organic solvent or a commercially available neutral degreasing agent, it is immersed at 50 to 80 ° C, preferably 60 to 70 ° C for about 2 to 10 minutes and then washed with water. In addition, shot blasting, barrel polishing, etc. are carried out as necessary.

(2) Activation treatment step This is a treatment for activating the surface by removing the oxide film from the surface of the aluminum alloy by etching. Using alkalis such as sodium hydroxide, acids such as nitric acid, and metal salts such as ferric chloride, preferably at 30 to 90 ° C,
It is more preferably immersed at 50 to 60 ° C., preferably for about 1 to 10 minutes, and then washed with water.

[0027]

[Examples] Using various aluminum alloys as test materials, an anodic oxide film was formed as follows. After pretreatment so that the surface roughness of the same JIS standard test material is the same, as pretreatment, degreasing treatment (chemical: neutral degreasing agent (Kizai Co., Ltd.), liquid temperature: 50 ° C, dipping time) : 5
Min) and then washed with water.

Next, an electrolytic treatment was performed under the following conditions, after which the test material was washed with water, subjected to a sealing treatment, and then sufficiently dried. The constant voltage time was all the same. Condition 1 (method of the present invention) An electrolytic solution (150 g / L trisodium phosphate + 20 g / L sodium metasilicate + 1) was added to the test material A5052.
While maintaining 0 g / L oxalic acid) at 20 ° C., electrolytic treatment was performed for 40 minutes using a jig made of titanium. Duty is used as the power source, the frequency is 60 Hz, and the duty ratio is 9
The ratio was 5.24% 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 ,
When the voltage reached 90V, the constant voltage electrolysis was switched to, and the constant voltage electrolysis was carried out at 90V as it was.

Condition 2 (method of the present invention) An electrolyte solution (150 g / L trisodium phosphate + 20 g / L sodium metasilicate + 20) was added to the test material A1050.
While maintaining g / L sodium hydroxide) at 20 ° C., electrolytic treatment was performed for 40 minutes using a jig made of aluminum.
Duty was used as the power source, the frequency was 60 Hz, the duty ratio was 95.24%, and the positive voltage: negative voltage ratio was 1: 1. 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 raised to 100 V, and constant voltage electrolysis was performed at that voltage.

Condition 3 (method of the present invention) Electrolyte solution (100 g / L trisodium phosphate + 30 g / L sodium metasilicate + 5 g) to test material ADC12
/ L oxalic acid + 10g / L sodium hydroxide) at 30 ° C
While maintaining the above, the electrolytic treatment was performed for 40 minutes using a jig made of titanium. The power source is Duty and the frequency is 6
The duty ratio was 0 Hz, the duty ratio was 66.67%, and the positive voltage: negative voltage ratio was 1: 1. Initially current density 2 A / dm ²
The constant current electrolysis was carried out at 1, and when the voltage reached 150 V, it was switched to the constant voltage electrolysis and the constant voltage electrolysis was carried out at 150 V as it was.

Condition 4 (method of the present invention) Electrolyte solution (100 g / L trisodium phosphate + 30 g / L sodium metasilicate + 5 g) to test material A1050
/ L oxalic acid + 10g / L sodium hydroxide) at 20 ° C
While maintaining the above, the electrolytic treatment was carried out for 40 minutes using an aluminum jig. The power source is Duty and the frequency is 6
0 Hz, the duty ratio was 95.24%, and the positive voltage: negative voltage ratio was 1: 1. The set voltage was 100 V and the voltage rising rate was 20 V / min, and constant voltage electrolysis with soft start was performed.

Condition 5 (Comparative Example Method) An electrolytic solution (150 g / L trisodium phosphate + 20 g / L sodium metasilicate + 10) was added to the test material A1050.
While maintaining g / L oxalic acid) at 20 ° C., electrolytic treatment was performed for 40 minutes using a jig made of aluminum. A direct current was used as a power source. At first, constant current electrolysis was performed at a current density of 1 A / dm ² , and when the voltage reached 90 V, it was switched to constant voltage electrolysis, and constant voltage electrolysis was performed at 90 V as it was.

Condition 6 (Comparative Example Method) The test material A1100 was subjected to electrolytic treatment using an aluminum jig for 40 minutes while keeping the electrolytic solution (30 g / L oxalic acid) at 20 ° C. Direct current was used as a power source, and constant current electrolysis was performed at a current density of 1 A / dm ² .

Condition 7 (Comparative Example Method) An electrolyte solution (150 g / L trisodium phosphate + 20 g / L sodium metasilicate + 10) was added to the test material ADC12.
While maintaining g / L oxalic acid) at 20 ° C., electrolytic treatment was performed for 40 minutes using a jig made of aluminum. A direct current was used as a power source. At first, constant current electrolysis was performed at a current density of 1 A / dm ² , and when the voltage reached 90 V, it was switched to constant voltage electrolysis at that voltage.

Condition 8 (Comparative Example Method) The sample material ADC12 was subjected to electrolytic treatment for 40 minutes using an aluminum jig while keeping the electrolytic solution (30 g / L oxalic acid) at 20 ° C. Direct current was used as a power source, and constant current electrolysis was performed at a current density of 2 A / dm ² .

The color, film formability and average surface roughness of the test materials electrolytically treated by the method of the present invention (conditions 1 to 4) and the method of the comparative example (conditions 5 to 8) are shown in the following table. It was as shown. In addition, a salt spray test according to JIS Z2371H was performed, and the surface condition after 48 hours and 120 hours was evaluated by a corrosion test area method (rating number (RN)).

Next, a coating treatment was applied on the anodic oxide film of each test material. (Undercoat): Paint (Epollac # 200HS primer white, Epollac # 100 thinner, viscosity 27 sec, manufactured by Tokyo Paint Co., Ltd.) Coating method: Baking 150 ° C x 20 minutes (Topcoat): Paint (Leatherplot MT-0582M)
(Modified), leather plot thinner, viscosity 28 sec, manufactured by Tokyo Paint Co., Ltd. Coating method: baking 150 ° C. × 20 minutes, and after dipping in boiling water for 2 hours and dipping in hot water at 60 ° C. for 4 hours, respectively. A cellophane tape peeling test was carried out to evaluate the coating film adhesion.

[0038]

[Table 1]

[0039]

[Table 2] * Peeling test is not performed on the test materials treated under conditions 7 to 8.

The results are as follows. The anodic oxide film formed by the method of the present invention had a high rating number and excellent coating adhesion. Although electrolytic treatment was performed using a jig made of titanium and aluminum, no trace of dissolution was found in the jig made of titanium, and a thin anodic oxide film was formed on the surface of the jig made of aluminum. But,
The film was easily removed by immersing it in a solution containing an inorganic base. On the other hand, in the case where the anodic oxide film was formed by the method of Comparative Example, the film was thin and non-uniform, or the film could not be formed in the first place, and voids were conspicuous. In addition, the surface is also strongly influenced by the surface properties of the base material and tends to become rough. Further, the jig made of aluminum had a thicker anodic oxide film than necessary and could not be used repeatedly. The anodic oxide film formed by the method of the present invention is a current treatment method (Comparative Example 6,
It showed almost the same corrosion resistance as 8).

[0041]

The anodized film formed by the method of the present invention has a very smooth surface even if the base material is an extruded material or a drawn material, and if the base material is a Si-based material, it does not form voids. A film can be formed without any treatment. Furthermore, the corrosion resistance and the adhesion of the film are also good. In the method of the present invention, an aluminum alloy can be electrolyzed while being immersed in an electrolytic solution using a jig made of titanium or aluminum. These jigs can be used over and over again. In particular, an inexpensive jig made of aluminum can be repeatedly used by removing the anodized film, which is advantageous. Further, in the method of the present invention, since an electrolytic solution that can be generally used for various aluminum alloys is used, it is advantageous that the electrolytic solution can be shared in the case of production in various small quantities.

[Brief description of drawings]

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

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C25D 17/06 C25D 17/06 J 17/08 17/08 D (72) Inventor Takayuki Aono Anbara-gun, Shizuoka Prefecture Kambara-cho Kambara 5202 Address Fuji Industrial Co., Ltd. (72) Inventor Yoshifumi Shimajiri 2-2 Sumiyoshi-cho, Utsunomiya-shi, Tochigi STC (72) Inventor Tsuneo Kosaka 1-chome Nishiki-cho, Warabi-shi, Saitama No. 3-11 Chiyoda Co., Ltd.

Claims (8)

[Claims] 1. An aluminum alloy is immersed in an electrolytic solution containing at least two kinds of inorganic acid salts, inorganic bases, organic acid salts and organic acids, and a voltage of 3 to is applied using a Duty (PR waveform) power supply.
A method for forming an anodized film on an aluminum alloy, which comprises performing constant voltage electrolysis by a method of gradually increasing it at 100 V / min, or performing constant voltage electrolysis after performing constant current electrolysis. 2. The method for forming an anodized film on an aluminum alloy according to claim 1, wherein the method is characterized by immersing the anodized film 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 an aluminum alloy according to claim 1 or 2, wherein the inorganic acid is sulfuric acid,
Nitric acid, phosphoric acid or silicic acid, organic acid is a dicarboxylic acid or a tricarboxylic acid, the formation method characterized by the above-mentioned. 4. A method for forming an anodized film on an aluminum alloy according to claim 1, wherein Dut
A forming method, wherein the y ratio is 20 to 99%. 5. The method for forming an anodized film on an aluminum alloy according to claim 1, wherein the anodized film is formed on a Si-based aluminum alloy. 6. The method for forming an anodized film on an aluminum alloy according to claim 1, wherein a titanium or aluminum jig is used to immerse the aluminum alloy in an electrolytic solution for electrolysis. A forming method comprising: 7. The method for forming an anodized film on an aluminum alloy according to claim 6, wherein after electrolytically treating using a jig made of aluminum, the used jig is dipped in a solution containing an inorganic base to form a surface. After removing the anodic oxide film formed in step 1, it is reused in the next electrolytic treatment. 8. A method of forming an anodized film on an aluminum alloy according to claim 7, wherein the method of removing the anodized film formed on the surface by immersing the anodized film in a solution containing an inorganic base is anodized aluminum. A forming method characterized by removing an anodized film from an alloy, performing anodizing treatment again, and reusing.