JP2007154300A - Aluminum alloy anodic oxidation method and power source for aluminum alloy anodic oxidation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum alloy anodic oxidation method capable of enhancing film forming rate to improve productivity while keeping the quality of a coating film without applying negative voltage, and to provide a power source for aluminum alloy anodic oxidation. <P>SOLUTION: In the aluminum alloy anodic oxidation method for anodically oxidizing an aluminum alloy by applying pulse voltage, a positive electrode for anodic oxidation and a negative electrode for anodic oxidation are short-circuited when the pulse voltage is not applied. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an aluminum alloy anodizing method and an aluminum alloy anodizing power source.

Conventionally, for the purpose of improving the hardness, wear resistance and corrosion resistance of the aluminum alloy surface and coloring it, an anodized film can be formed on the surface of the aluminum alloy by anodizing in an aqueous solution of sulfuric acid, oxalic acid, phosphoric acid or the like. Has been done. This anodized film is composed of a dense barrier layer and a porous porous layer, and the composition is Al ₂ O ₃ .

  In order to obtain a film having a desired characteristic, a direct current method, a current inversion method, an AC / DC superposition method, a pulse waveform method, and the like have been reported as methods of applying electric power (Non-patent Documents 1 and 2, Patent Documents 1 and 2). .

  When a high voltage is applied to flow a large current in order to obtain a high film formation rate by the direct current method, the amount of Joule heat generated in the barrier layer increases, and defects occur in the oxide film called burn. Therefore, in the direct current method, it has been difficult to form a thick anodic oxide film in a short time on an aluminum cast material and an aluminum die cast material that contain a large amount of Si, Cu, Fe and the like and hardly flow current.

On the other hand, it is said that the pulse electrolysis method including the current reversal method is better than the direct current method in order to form the desired oxide film in a short time with good productivity without causing a defect called “film burn”. . For example, the following Non-Patent Document 1 reports that an anodic oxidation by current reversal method in which a negative current is intermittently passed in a sulfuric acid bath, and an oxide film can be formed at a high speed at an oxidation voltage lower than that of anodic oxidation by a direct current method. Yes. In Non-Patent Document 2, aluminum A1080P is electrolyzed in a 20 Wt% sulfuric acid + 10 g / l oxalic acid bath at 20 ° C. for 65 minutes under the conditions of a current inversion method, a frequency of 13.3 Hz, a current density of 4 A / dm ² , and a duty of 95%. To obtain a 92 μm aluminum anodic oxide film (1.4 μm / min). However, these methods have a problem that the film forming speed cannot be increased in the case of an aluminum die-cast material having a frequency of several tens of Hz, especially an alloy element having many elements. In addition, there is a problem that a positive voltage and a negative voltage must be applied, and the power source used is bipolar and complicated.

Patent Document 1 discloses an aluminum anode that is excellent in heat resistance and corrosion resistance under an electrolytic condition in which an alternating current component does not include a negative component and an alternating current component is contained by 5% or more of the direct current component by an AC / DC superimposition method in which direct current is applied to alternating current. It has been shown that an oxide film can be formed on an aluminum alloy surface. However, the preferred current density is as low as 0.1 to ^{2 A} / dm ^2, and at this current density, the film formation rate is slow, which causes problems in productivity and cost. Furthermore, this method also has a problem that an AC power source and a DC power source are required, and the power supply system becomes complicated.

Further, in Patent Document 2 below, as a method for improving the film formation rate of the aluminum anodized film from the viewpoint of productivity, a direct current is applied to a sinusoidal high-frequency current of 200 to 5000 Hz (preferably 600 to 2000 Hz) in a sulfuric acid aqueous solution bath. We have proposed a method of energizing a current with superimposed current. That is, an aluminum alloy ADC12 is formed in a 10% sulfuric acid aqueous solution at 17 ° C., a DC voltage of 19.8 V is superimposed on a sinusoidal high frequency with a frequency of 1000 Hz and a voltage of ± 20 V, and an electrolytic treatment time of 20 minutes is 22 μm. An oxide film is obtained (growth rate 1.1 μm / min). It is reported that the current density 5 minutes after the start of electrolysis was 13.8 A / dm ² . However, since the frequency is limited to 200 to 5000 Hz and the sine wave is actually used, there is a problem that the current that can flow in a short time is less than that of the rectangular wave. In addition, there is a problem that an AC power source and a DC power source are necessary, and the power supply system becomes complicated.
Metal Surface Technology, 39, 512 (1988) Kinki Aluminum Surface Treatment Research Journal, No. 1334, p. 1 (1988) JP 2000-282294 A JP 2004-35930 A

  As described above, it is known that the current reversal method or the AC / DC superimposition method is preferable for anodization of an aluminum alloy. However, for this purpose, a positive voltage and a negative voltage must be applied, and the power source used is bipolar and complicated. There was a problem of becoming.

  The present invention has been made in view of the above problems and limitations, and the problem to be solved by the present invention is to increase the deposition rate while maintaining the quality of the film without applying a negative voltage, and to improve productivity. It is an object to provide a method for anodizing an aluminum alloy and a power source for anodizing an aluminum alloy.

  In order to achieve the above object, the present invention provides an aluminum alloy anodizing method for anodizing an aluminum alloy by pulse power as described in claim 1, and anodizing anode and anodizing when no pulse voltage is applied. An aluminum alloy anodizing method characterized in that the cathode is short-circuited.

  According to a second aspect of the present invention, in the aluminum alloy anodizing power source for anodizing an aluminum alloy by pulse power, the terminal connected to the anodizing anode and the anodizing cathode when no pulse is generated. A power supply for anodizing an aluminum alloy is characterized in that the terminal to be connected is short-circuited.

  By carrying out the present invention, it is possible to provide an aluminum alloy anodizing method and an aluminum alloy anodizing power source capable of increasing the film forming speed and improving the productivity while maintaining the quality of the film without applying a negative voltage. Become.

The present inventors have sought a method of simply passing a negative current in order to reduce the resistance of the barrier layer and the electrolytic solution. As a result, it was found that after applying a positive voltage, a negative current flows by short-circuiting the aluminum alloy anode in the electrolytic cell and the carbon cathode of the counter electrode. In this case, as shown in Example 1 of FIG. 4, the effective current density is 5.2 A / dm ² with respect to the set current density 18 A / dm ² . Since “effective current density = set current density minus negative current density at one short circuit”, it indicates that a reverse current of 12.8 A / dm ² flows. The effective current density and the film growth rate are in a good linear relationship as shown in FIG. This is because the Al ³⁺ and O ²⁻ ion concentration gradient in the barrier layer is relaxed (or the discharge of amorphous Al ₂ O ₃ just generated as a reaction as a positive electrode agent of the battery) and the electric liquid generated at the solid-liquid interface. It is presumed that this is due to the discharge of the multilayer (particularly, in the vicinity of the carbon cathode, there are a large number of hydrogen atoms in the nascent stage, which includes electrochemically reacting with OH ⁻ and returning to H ₂ O). This negative current was found to have the same effect as applying a reverse voltage to flow a reverse current.

FIG. 2 shows a power supply configuration of the present invention. The power supply 10 includes a positive DC power supply 11, a repetition frequency generator 12, a positive pulse generator 13, a short pulse generator 14, a positive chopper gate amplifier 25, a short chopper gate amplifier 26, a positive chopper switch 15, The output terminal 18 is connected to the anode 20 and the cathode 21 in the electrolytic cell 19. A positive output voltmeter (E ₁ ) 22, an electrolytic cell voltmeter (E _B ) 23, and an electrolytic cell ammeter (A _B ) 24 are attached.

FIG. 3 shows the operating state of the power supply 10. The operation repetition period T (frequency f = 1 / T) (FIG. 3A) from the repetition frequency generator 12 (positive pulse width t ₊ (FIG. 3B) from the positive pulse generation circuit 13 is short-circuited. The short-circuit pulse width t _s (FIG. 3C) is output from the pulse generation circuit, and the positive chopper gate signal (FIG. 3D) and the short-circuit chopper gate signal (FIG. 3E) are accordingly generated. The positive chopper output (FIG. 3 (F)) and the short-circuit chopper output (FIG. 3 (G)) are output in conjunction with these, and as a result, the output voltage (E ₁ ) (FIG. 3 (H) ). The T, t ₊ , t _s , and E ₁ can be freely set within an allowable range.

Depending on the output voltage E _1, the electrolysis voltage E _B applied between the anode 20 and the cathode 21 in the electrolytic tank 19, as shown in FIG. 3 (I), also electrolytic cells flowing to the both the machining gap The current (I _B ) is as shown in FIG. Such a shape is presumed to be due to the relaxation of the ion concentration gradient in the barrier layer and the discharge of the electric double layer generated at the electrode solid-liquid interface.

  As described above, a reverse current flows due to a short circuit, the ion concentration gradient in the barrier layer is relaxed, and the electric double layer at the solid-liquid interface of the electrode is discharged and eliminated. Makes it possible to pass a large current. If a positive pulse current continues to flow without flowing a reverse current due to a short circuit, the current value decreases and the film formation rate decreases in the case of constant voltage control, and the voltage increases in the case of constant current control. This causes an increase in Joule heat and causes a burning phenomenon. As described above, in the anodic oxidation using the power source of the present invention, that is, the pulsed power, the voltage application is stopped and the anode and the cathode are short-circuited for an arbitrary time and the reverse current is allowed to flow in the situation where the anodic oxidation is in progress. By using a power source that can be used, the deposition rate can be increased and the productivity can be improved without deteriorating the quality of the anodized film such as burning. Further, since it is not necessary to apply a negative voltage, a negative power supply is not required, and the power supply configuration is simplified, which can greatly contribute to cost reduction.

The effects of the present invention will be specifically described below through examples. Anodization of the aluminum alloy was performed using the above power source under the following experimental conditions.
For the test piece, A1100P material for basic characteristic evaluation, A2017P material, A6063P material, which is relatively difficult to be electrolyzed, such as an electrolysis voltage is increased by ordinary oxidation treatment, and ADC12 material, which is difficult to generate a uniform film, are used. It was. For comparison, an aluminum material having a purity of 99.99% was also used. The size of the test piece is 60 mm × 60 mm × 2 mm.
The electrolytic cell has an electrolyte amount of about 2001, liquid circulation and agitation by micro explosion, cooling by a plate heat exchanger, the cathode bar is lead, and the cathode plate is carbon. The bath composition was a free sulfuric acid concentration of about 200 g / l and a bath temperature of 10 ° C.
The anodizing conditions were: current density 6, 12, 14, 18 A / dm ² , frequency 1.0, 2.5, 5.0, 7.5, 10.0, 15.0 KHz, duty 20-20, 30- The anodic oxidation time is 15 minutes (including a soft start time of 3 minutes).
After the anodizing treatment, it was washed with running well water for about 2 minutes and subjected to forced drying with warm air.
(Examples 1 and 2)

For aluminum alloy A1100P material, current density 18 A / dm ² , frequency 10.0 KHz, duty 45-45% (T is halved, positive voltage application ratio to ½, and short circuit to remaining ½. The results of the anodic oxidation performed at the time ratio) are shown in FIG. In Comparative Example 1 in FIG. 4, a negative voltage of −4 V is applied and a reverse current is forced to flow when the duty is 45 to 45% short-circuited. In the case of a reverse current caused by a short circuit, a 20 μm thick oxide film (film growth rate: 1.33 μm / min) is obtained by anodic oxidation for 15 minutes without causing deterioration in quality such as burning. Comparative Example 1 in which a negative voltage was applied and a reverse current was forced to flow was 1.15 μm / min. That is, the film can be formed without causing burning at a film forming rate higher than that in which a reverse current is passed for the purpose of preventing burning.
(Examples 3, 4, and 5)

Aluminum alloy A2017P, which is said to be relatively difficult to electrolyze due to high electrolytic voltage in normal oxidation treatment, is 18, 12 A / dm ² , 5.0 KHz, duty 45-45% and duty 30-30%. The result of the anodization is shown in FIG. It can be seen that high-speed film formation can be achieved compared to Comparative Examples 2 and 3 in FIG. There was no deterioration in quality due to burning.
(Examples 6 and 7)

FIG. 4 shows the results of anodizing the aluminum alloy A6061P material at 18, 12 A / dm ² , 7.5, 5.0 KHz, and a duty of 30-30%. Also in this case, the high-speed film formation can be performed without causing deterioration in quality such as burning as compared with Comparative Examples 4 and 5 in the table.
(Examples 8 and 9)

Comparative Example 6 shows the results of anodizing the aluminum alloy ADC12, which is said to be difficult to form a uniform film, at a current density of 18 A / dm ² , a frequency of 5.0 KHz, a duty of 40-40%, and 30-30%. 4 together with FIG. Even in this case, film formation of 1.6 μm / min order, which is faster than Comparative Examples 6 and 7 in which a reverse current is forcibly passed to prevent burning, can be achieved without degrading quality such as burning.
(Examples 10 and 11)

For 99.99% purity aluminum, anodization is performed at a current density of 18 A / dm ² , a frequency of 5.0, 10.0 KHz, and a duty of 30-30% without applying a negative voltage and forcing a reverse current to flow. The results are shown in FIG. In the case of 5.0 KHz, a homogeneous film having a thickness of 58.4 μm (deposition rate: 3.90 μm / min) could be obtained by anodic oxidation for 15 minutes. FIG. 5 shows a cross section of this film.

It is a figure explaining the relationship between the film growth rate of this invention, and an effective current density. It is a figure explaining the power supply structure of this invention. It is a figure explaining the operating condition of the power supply of this invention. It is a table | surface explaining the experimental result of this invention. It is a photograph explaining the cross section of the aluminum anodic oxide film formed using the power supply of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Power supply for anodization, 11 ... Positive side DC power supply, 12 ... Repeat frequency generator, 13 ... Positive side pulse generation circuit, 14 ... Short circuit side pulse generation circuit, 15 ... Positive side chopper switch, 16 ... Backflow prevention diode, DESCRIPTION OF SYMBOLS 17 ... Short-circuit current control circuit, 18 ... Output terminal, 19 ... Electrolytic cell, 20 ... Anode, 21 ... Cathode, 22 ... Positive side output voltmeter, 23 ... Electrolytic cell voltmeter, 24 ... Electrolytic cell ammeter, 25 ... Positive Side chopper gate amplifier, 26 ... Short circuit side chopper gate amplifier.

Claims (2)

  An aluminum alloy anodizing method in which an aluminum alloy is anodized by pulse power, wherein the anodizing anode and the anodizing cathode are short-circuited when no pulse voltage is applied.   In an aluminum alloy anodizing power source for anodizing an aluminum alloy by pulse power, an aluminum alloy anode characterized by short-circuiting a terminal connected to the anodizing anode and a terminal connected to the anodizing cathode when no pulse is generated Power source for oxidation.

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