WO2008004634A1 - Method for anodically oxidizing aluminum alloy and power supply for anodically oxidizing aluminum alloy - Google Patents

Abstract

A method for anodically oxidizing an aluminum alloy is provided for forming an anodically oxidized film on the surface of the aluminum alloy by using pulse power. An anodically oxidizing anode and an anodically oxidizing cathode are short-circuited for a short-circuiting time of 15μs or shorter when a pulse voltage is not applied after a positive pulse voltage is applied. Furthermore, the cycle of waveform of the pulse power has a pulse voltage application time (T+), a dead time (Td) and a short-circuiting time (Ts) in this order. Thus, a film forming speed and productivity are improved by suppressing a negative current or by preventing the negative current from flowing.

Description

 Specification

 Aluminum alloy anodizing method and power source for anodizing aluminum alloy

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

 Background art

 [0002] Conventionally, aluminum alloys are anodized in an aqueous solution bath of sulfuric acid, oxalic acid, phosphoric acid, etc. for the purpose of improving the hardness, wear resistance, corrosion resistance, and coloring of the surface of the aluminum alloy, An oxide film is formed on the surface. This anodized film is composed of a dense barrier layer and a porous porous layer, and the composition is A10.

 2 3

 [0003] In order to obtain a film having a desired characteristic, a DC method, a current inversion method, an AC / DC superposition method, a pulse waveform method, and the like have been reported as methods for applying electric power (Metal Surface Technology, P. 512 (1988)). ), Kinki Aluminum Surface Treatment Research Journal, No. 1334, p. 1 (1988), JP 2000-28 2294, JP 2004-35930).

 [0004] 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 this is called oxidation of the film. Defects occur in the film. Therefore, with the direct current method, it was difficult to form a thick anodic oxide film in a short time on aluminum forging materials and aluminum die casting materials that contain a large amount of Si, Cu, Fe, etc., and are difficult to flow current.

[0005] On the other hand, in order to form a desired oxide film in a short time with good productivity without causing defects called "film burn", a pulse electrolysis method including a current inversion method is better than a direct current method. It is said that. For example, in the above-mentioned document, Metal Surface Technology, 39, p. 512 (1988), in an acid bath, an anodic oxidation by a current reversal method in which a negative current is intermittently applied, and an oxidation voltage lower than that by a direct current method. It has been reported that an oxide film can be formed at high speed. In addition, according to the above literature, Kinki Aluminum Surface Treatment Study Group, No. 1334, p. 1 (11988), Anoleminium A1080P IIS H4100) was added to 20 Wt% sulfuric acid + lOg / 1g at 20 ° C. In an acid bath, electrolysis was performed for 65 minutes under the conditions of a frequency of 13.3 Hz, a current density of 4 A / dm ² and a duty of 95% by a current reversal method to obtain an aluminum anodized film of 92 μΐη (1 · 4 / im / min). However, these methods apply voltage with a frequency on the order of several tens of Hz, and there is a problem that the film formation speed cannot be increased particularly for a large amount of alloying elements and aluminum die casting materials. It was. In addition, a positive voltage and a negative voltage must be applied, and there is a problem that the power supply used is bipolar and the structure becomes complicated.

[0006] In Japanese Patent Application Laid-Open No. 2000-282294, the AC component does not include a negative component and the AC component is a DC component in the AC / DC superimposition method in which a DC is applied to an AC. / ₀ or more Included electrolysis conditions, excellent moreover corrosion in heat resistance good aluminum anodic oxide film has been shown to be capable of forming the aluminum alloy surface. However, the preferred current density is as low as 0.:! To 2 A / dm ^2. At this current density, the film formation rate is slow, and there is a problem in productivity and cost. Furthermore, this method also has the problem that an AC power source and a DC power source are required and the power supply system becomes complicated.

[0007] Further, JP 2004-35930 A discloses a method of improving the deposition rate of an aluminum anodized film from the viewpoint of productivity in a sulfuric acid aqueous solution bath of 200 to 5000 Hz (preferably 600 to 2000 Hz). A method is proposed in which a current in which a direct current is superimposed on a sinusoidal high-frequency current is applied. In other words, aluminum alloy ADC 12 JIS H5302) was electrolyzed by superimposing a 19.8 V DC voltage on a sine wave with a frequency of 1000 Hz and a voltage of ± 20 V in a 10% sulfuric acid aqueous solution at 17 ° C. An anodic oxide film of 22 μm was obtained in 20 minutes (growth rate 1. l / im / min). It has been 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 be flowed in a unit time is less than that of the rectangular wave. In addition, there is a problem that the power supply system becomes complicated because an AC power supply and a DC power supply are necessary.

[0008] In addition, in JP-A-2006-83467, for the purpose of improving corrosion resistance and impact resistance, the cells of the anodized film grow in a random direction with respect to the surface of the aluminum or aluminum alloy, and the orientation is improved. A method for forming an anodic oxide film having no electrode is shown. As a specific method, an alloy containing impurities such as silicon is used, and a positive voltage is applied. The process of removing the charge is repeated, and one positive voltage application is 25 to 100 / s (frequency is 5 to 20 KHz). In the process of removing charges, the positive application is temporarily stopped and a short circuit of the pole or a negative voltage is applied. When a negative voltage is applied, it is shown that the negative voltage is applied for the same time as the brass voltage. The reason for removing the charge here is that the resistance increases substantially as the charge accumulates, and it is necessary to apply a high voltage to obtain a constant current value. This is because of a defect called “.

However, in this method, when a negative voltage is applied, the generated film is dissolved and reduced, which hinders the improvement of the film growth rate. It was also found that a negative current with a large negative current density flows even when the pole is short-circuited. For example, when the positive current density is 18 A / dm ² under certain anodizing conditions, the negative current density is 12.8 A / dm ² . Therefore, there is room for improvement in order to increase the growth rate of the film. Disclosure of the invention

 [0010] The present invention has been made in view of the above problems, and the problem to be solved by the present invention is to suppress negative current when anodizing an aluminum alloy using a pulse electrolysis method. Aluminum alloy anodizing method and aluminum alloy anodizing method that can increase the film deposition rate and improve productivity without causing “film burnt” defects by preventing or reducing the flow. It is to provide a power source for the vehicle.

 In addition, another problem to be solved by the present invention is that an aluminum alloy that can further increase the film formation rate and improve the productivity by setting the frequency at which the maximum current flows when a pulse voltage is applied. The purpose is to provide an anodizing method and a power source for anodizing aluminum alloy.

 In order to achieve the above object, the present invention provides the following invention.

 [1] In an aluminum alloy anodizing method in which pulse power is applied and an anodized film is formed on the surface of the aluminum alloy, the anode and anode for anodization are applied when no pulse voltage is applied after applying a positive nores voltage. Provided is an aluminum alloy anodic oxidation method characterized by short-circuiting an oxidation cathode with a short-circuiting time of 15 or less.

[2] The short circuit time is not less than 1 μs and not more than 15 / s. Aluminum alloy anodizing method.

 [3] The aluminum alloy anodizing method according to [1], wherein the short-circuiting time is 1 μs or more and 5 / s or less.

 [4] Cycle power of the pulse power waveform Pulse voltage application time (T), dead time

 +

 (1), [2] or [3 d s], characterized in that they are configured in the order of (T) and short-circuit time (T).

 ] The aluminum alloy anodizing method as described in the above.

 [5] The aluminum alloy anodizing method according to any one of [1] to [4] above, wherein the frequency of the pulse power is 8 to 35 KHz.

 [6] The aluminum alloy anodizing method according to any one of [1] to [4] above, wherein the frequency of the pulse power is 10 to 30 KHz.

 [7] In an aluminum alloy anodizing power source used in an aluminum alloy anodizing method for forming an anodized film on the surface of an aluminum alloy using pulse power, when no pulse voltage is applied after applying a positive pulse voltage, An aluminum alloy anodic oxidation characterized by having a pulse power generation section for generating a pulse power for short-circuiting a terminal connected to the anode for anodization and a terminal connected to the cathode for anodization with a short-circuiting time of 15 / s or less For power supply.

 [8] The aluminum alloy anodic oxidation power source according to [7], wherein the pulse power generation unit generates pulse power having the short circuit time of 1 μs to 15 μs.

 [9] The aluminum alloy anodic oxidation power source according to [7], wherein the pulse power generation unit generates pulse power having the short circuit time of 1 μs to 5 μs.

 [10] The pulse power generator generates a waveform force S pulse voltage application time (Τ), dead time (

 +

 S), short-circuit time (Τ) is generated in the order of pulse power, and d S

The power source for anodizing an aluminum alloy according to any one of [7] to [9].

[11] The aluminum alloy anodizing power source according to any one of [7] to [10], wherein the pulse power generation unit generates pulse power having a frequency of 8 to 35 KHz. [12] The aluminum alloy anodic oxidation power source according to any one of [7] to [10], wherein the pulse power generation unit generates pulse power having a frequency of 10 to 30 KHz.

 [0012] According to the present invention, when forming an anodic oxide film on the surface of an aluminum alloy using pulse power, it is possible to achieve a very short short-circuit time when no pulse voltage is applied after applying a positive pulse voltage. Since the anode for anodic oxidation and the cathode for anodic oxidation are short-circuited, the film formation rate can be reduced without causing negative film current to occur, or by preventing the current from flowing. It is possible to provide an aluminum alloy anodizing method and an aluminum alloy anodizing power source that can improve productivity and productivity. Further, according to the present invention, by setting the frequency at which a large current can flow when a no-less voltage is applied, in addition to the effect caused by the short circuit between the anode for anodization and the cathode for anodization, it is possible to further increase the frequency. It is possible to provide an aluminum alloy anodizing method and an aluminum alloy anodizing power source capable of increasing the deposition rate and improving the productivity.

 Brief Description of Drawings

 FIG. 1 is a diagram for explaining the relationship between the film growth rate and the effective current density in an aluminum alloy anodizing method using pulse power. Here, the effective current density is the difference between the positive current density when a pulse voltage is applied and the negative current density that flows when no pulse is applied (effective current density = positive current density minus negative current density).

 FIG. 2 is a diagram for explaining the configuration of a power source and an electrolytic cell used for anodizing of an aluminum alloy according to the present invention.

 FIG. 3 is a diagram for explaining pulse setting conditions and actual voltage / current waveforms corresponding thereto.

 FIG. 4 is a diagram for explaining a steady state of film growth by anodization.

 FIG. 5 is a diagram for explaining the relationship between the current waveform and frequency of pulse power used in the present invention.

 FIG. 6 is a table for explaining the experimental results of Examples and Comparative Examples of the present invention.

 FIG. 7 is a diagram for explaining a relationship between a short circuit time and a negative current according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION [0014] Hereinafter, the present invention will be described in detail.

For the purpose of improving the deposition rate, the present inventors have short-circuited the anode for anodization and the cathode for anodization when a pulse voltage is not applied after applying a positive pulse voltage, and a negative current (when a pulse is applied). and the electric current) flowing in the opposite direction, the [alpha] 1 ³⁺ and 〇 ² ion concentration gradient of one layer in the barrier formed at the pulse voltage is applied to discharge the electric double layer relaxation and the solid-liquid interface, the following Roh ^ It has been found that a large current can flow when applying a low voltage. However, as described above, the force S has a problem that the magnitude of the negative current is larger than the magnitude of the positive current when the pulse voltage is applied, and this point was further investigated.

 [0015] In the aluminum alloy anodic oxidation method using pulsed power, the present inventors have used the technique of short-circuiting the anodic oxidation anode and the anodic oxidation cathode when no pulse voltage is applied. (Fig. 1). However, when trying to increase the effective current density, there was a conflicting problem that the negative current also increased.

 [0016] Therefore, as a result of pursuing a method for further increasing the film growth rate in order to improve productivity, the present inventors have found that the anode can be used only for a very short time when no pulse voltage is applied after the positive pulse voltage is applied. When the anode for oxidation and the cathode for anodization are short-circuited, unexpectedly, the negative current is suppressed and reduced, or the defect of “film burn” that does not flow negative current occurs without causing the next positive It was found that a large current can be passed by applying a pulse voltage of. It was also found that making the applied panelless voltage within a specific frequency range can greatly contribute to the improvement of the film growth rate. The present invention has been made based on such knowledge.

[0017] In the aluminum alloy anodic oxidation method of the present invention, a short-circuit time of 15 μs or less between the anodic oxidation anode and the anodic oxidation cathode when pulse voltage is applied and no pulse voltage is applied after positive pulse voltage is applied. It is characterized by short-circuiting. The short-circuiting time is preferably 1 μs or more and 15 as or less than force S, more preferably 1 μs or more and 5 μs or less, and particularly preferably 1 μs or more and 3 μs or less. . The preferred range of the short-circuiting time varies depending on the type of aluminum alloy to be treated and the conductivity, but if it is within the above range, the negative current can be greatly reduced to suppress the negative current or the next current that does not flow. Since a large current can be applied by applying a positive pulse voltage, the film generated by the negative current is not reduced. In addition, the growth rate of the film can be greatly improved without causing “film burn” defects. Up to now, in order to prevent the occurrence of defects called “film burn” and increase the film growth rate,

 It was considered necessary to remove all charges accumulated in the system by applying a short circuit or negative voltage before applying the Norres voltage. However, the inventors made extensive studies and found that the barrier layer interface part (Al / AlO interface, AlO / electric interface) during the formation of the oxide film was formed.

 (2 3 2 3) (resolved liquid interface) can be used to achieve a state in which the electrical resistance is substantially reduced, which is necessary for the formation of a good film when the next positive pulse voltage is applied. It was found that a large current can flow. In this way, it was found that the growth rate of the film can be significantly improved by melting the generated film and reducing it with a large negative current.

 [0018] Further, in the present invention, the cycle of the waveform of the pulse power is expressed by the pulse voltage application time (T),

 + It is desirable that the dead time (T) and the short circuit time (T) are configured in this order. This place

 d

 In order to improve the deposition rate, the pulse voltage application time (T) should be about 20 to 100 μs.

 +

 The preferred dead time (Τ) is about 5-10 / is.

 d

 In the present invention, the frequency of the pulse power is preferably 8 to 35 KHz, more preferably 10 to 30 KHz. When the frequency is within the above range, it becomes possible to form a film by supplying an amount of electricity that further improves the growth rate of the film. The growth rate can be improved.

FIG. 2 shows the configuration of the power source and the electrolytic cell used for the aluminum alloy anodization of the present invention. Power supply P is sequencer 10, positive side DC power source 11, repetition frequency generator 12, positive side pulse generator circuit ₁₃ , short side pulse generator circuit 14, positive side chopper gate amplifier (GA) 25, short side chopper gate amplifier (GA ) 26, a positive chopper switch 15, a backflow prevention diode (D) 16, and a short-circuit current control circuit 17, and its output terminal 18 is connected to the anode 20 and the cathode 21 in the electrolytic cell 19. Further, a positive output voltmeter (E) 22, an electrolytic cell voltmeter 23) and an electrolytic cell ammeter (A) 24 are attached. 27 is the power

 B B

 It is a solution.

The sequencer 10 repeats the frequency generator 12, the positive pulse generator 13, the short pulse generator 14, and the positive pulse generator in order to make the pulse power waveform used in the present invention into a predetermined shape. Side DC power supply 11 is controlled. The positive side DC power supply 11 generates the DC power necessary for applying the positive pulse voltage or the positive pulse current set by the sequencer 10. The repetitive frequency generator 12 generates a reference repetitive frequency necessary for generating the pulse power and supplies it to the positive side panelless generating circuit 13 and the short circuit side pulse generating circuit 14. The positive side pulse generation circuit 13 generates a pulse having a time width of T, and the short-circuit side pulse generation circuit 14 generates a noise having a time width of T. The dead time (T) is set by the sequencer 10. Positive

 d

 The side chopper gate amplifier (GA) 25 plays a role of amplifying the pulse signal of the pulse generation circuit 13 to a level at which the positive side chopper switch 15 can reliably operate according to the pulse width signal determined by the positive side pulse generation circuit 13. . The short-circuit side chopper gate amplifier 26 plays a role of amplifying the pulse signal of the short-circuit pulse generation circuit 14 to a level at which the short-circuit current control circuit 17 can reliably operate according to the pulse width signal determined by the short-circuit pulse generation circuit 14. . The positive chopper switch 15 performs the role of supplying the electric power from the positive DC power supply 11 to the electrolytic cell in a pulsed manner in accordance with the panel width signal determined by the positive pulse generating circuit 13. The reverse current prevention diode 16 prevents reverse power from flowing to the positive DC power supply 11 side. The short-circuit current control circuit 17 short-circuits the output terminals 18 of the anode 20 and the cathode 21 for a short-circuit time T when no pulse voltage is applied after applying a positive no-relay voltage.

 s

[0022] Anodization was performed under the following conditions using the power source shown in FIG. For the test piece, A1100P material was used as a representative of good conductivity. The size of the test piece at this time was 50 mm × 50 mm XI · 5 mm (0.53 dm ² ). ADC12 material was used as a representative of poor conductivity. The size of the test piece at this time was 50 mm × 50 mm × 3.0 mm (0.56 dm ² ). The electrolytic cell had an electrolyte volume of about 2001, liquid circulation and micro-explosive agitation, and cooling with a plate heat exchanger. The cathode bar was lead and the cathode plate was carbon. The bath composition was a free sulfuric acid concentration of about 150 g / l and a bath temperature of 10 ° C. Anodizing current density was carried out varied variously to 20A / dm ^2. In addition, after anodizing treatment, it was washed with running well water for about 2 minutes and subjected to forced drying with warm air.

 FIG. 3 shows a pulse setting condition and an actual voltage 'current waveform corresponding to the pulse setting condition. In the figure, T is the pulse voltage application time, T is the pulse voltage zero and the electrodes are short-circuited

 + d

The dead time required for the operation to be performed (becomes an open circuit state during this period), and τ is the short circuit time. The voltage waveform rises according to the T setting, falls slightly during T, and reaches zero during T.

+ d s

Show. The current waveform increases rapidly at the beginning of T, falls through the maximum, is zero during T, T

 A large negative current flows instantaneously at the moment of entering + d s, but then returns to zero immediately, hardly flows during T, the negative current increases after τ elapses, and then begins to decrease after reaching a maximum value.

 Such a waveform can be explained as follows. According to non-patent literature (Aluminum anode oxide film formation 'dissolution behavior, Masakazu Nagayama, Hideaki Takahashi, Mitsuru Koda, Metal Surface Technology, Vol. 30, No. 9, p. 438-456 (1979)) The steady state of anodic acid is shown in Fig. 4 (Fig. 4 (a) is an enlarged view of the barrier layer in the entire anodized film structure shown in Fig. 4 (c)). That is, an anode aluminum alloy and a cathode carbon are arranged with the electrolyte in between, A1 is oxidized to A10 at the anode, and H + ions are returned at the cathode.

 twenty three

Formerly H. Here, the further growth of the barrier is explained as follows:

 2

The

(1) The A1 metal in contact with the bottom of the barrier layer is anodized into Al ³⁺ ions (Fig. 4 (a) (1)):

Al → Al ³⁺ + 3e "(Formula 1)

(2) by diffusing portion Hanoch rear layer of the resulting Al ³⁺ ions migrate into the electrolyte solution (Fig. 4 (a) (2)) ₀

 (3)-On the other hand, at the interface with the electrolyte at the top of the knurled layer, Al O, which is the knoWn layer constituent material, is used.

2 3 Tsuyore, decomposed into Al ³⁺ and 0 ^2_ under the action of the electric field (FIG. 4 (a) (3)) :

Al O → 2Α1 ³⁺ + 30 ² "(Formula 2)

 twenty three

(4) Al ³⁺ generated by the above moves into the electrolyte (Fig. 4 (a) (4))

(5) The O ² — generated by the above moves in the barrier layer (Fig. 4 (a) (5)).

(6) further barrier to move one layer in the barrier (Al O) 〇 ² ions reaching the surface of ZA1 is Sakai

 twenty three

Reacts with the metal A1 at the boundary to produce Al 2 O (Fig. 4 (a) (6)):

 twenty three

2Al + 30 ² — → A1 0 + 6e "(Formula 3)

 twenty three

 (7) In addition, at the barrier layer (Al 2 O 3) / electrolyte interface above the barrier layer, H

2 3 decomposed into 2 strong under the action of the electric field H ⁺ ions and 〇 ² _ ion (FIG. 4 (a) (7)) :

H_〇 → 2H + + 〇 ² (Equation 4)

 2

Some 〇 ^2_ generated here, the (5), be involved in the generation of A1_rei through a process of (6) It is thought that.

 This is the growth of the barrier layer, and the anodic oxide film continues to grow by this process.

Here, the charges move in the form of Al ³⁺ and 0 ² _ in the NOR layer, but the transport number of Af ⁺ is about 40% and the transport number of O ² is about 60%. The transport number of Al ³⁺ decreases as the temperature decreases and the oxidation current density increases, that is, the growth rate of the film increases.

 [0025] Here, the potential gradient in the vicinity of the barrier layer is assumed to be as shown in Fig. 4 (b).

(1) The Af ⁺ concentration in the barrier layer is higher on the barrier layer ZA1 interface side and lower on the barrier layer Z electrolyte interface side (Fig. 4 (b) (A)).

(2) In addition, the ^02_ concentration in the barrier layer is lower on the non-layer / A1 interface side and higher on the non-layer / electrolyte interface side (Figs. 4 (b) and (B)).

(3) And since the diffusion rate of Al ^{3+ in} Al 2 O is limited, A1 / A1

 2 3 2

Al ³⁺ becomes stagnant at the O interface. Therefore the concentration of Al ³⁺ of the interface is further increased (Fig.

Three

 4 (b) (C)).

(4) Similarly, there is a limit to the diffusion rate of 0 ^2_ in Al ² O.

 2 3 2 3

At the / electrolyte interface, ○ ^2_ becomes stagnant. Therefore, the concentration of ○ ^{2_ at} the interface becomes high (Fig. 4 (b) (D)).

 From the above understanding, the voltage waveform and current waveform in FIG. 3 can be explained as follows.

 (1) The voltage waveform decreases slightly during T (Fig. 3 (1): The circled characters in the figure are for convenience.

It is written as a character enclosed in parentheses. The same applies below)), Al ³⁺ , A1 at the Al / Al O interface

 twenty three

O in OZ electrolyte interface ² - would to diffuse the Al side and the electrolyte side.

twenty three

 (2) The current waveform rises sharply during the period T (Fig. 3 (2)).

 +

 This is because the reactions of (Formula 1), (Formula 2), and (Formula 3) proceed rapidly.

(3) Next, the current waveform starts to decrease after reaching the maximum value (Fig. 3 (3)). As the electrolysis progresses, as shown in Fig. 4 (b), the concentration gradient (potential of the barrier layer including both interfaces) This is because the barrier is increased. (4) When the current value decreases, the applied voltage and potential barrier eventually balance and become a constant current value (Fig. 3 (4)).

 (5) Since the applied voltage is zero (open circuit) during T, the current is also zero (Fig. 3 (5) d

 ).

(6) In the gap, at the moment the electrode enters the gap and the electrodes are short-circuited, the Af ⁺ (or hole

 twenty three

), Al Ο Electrolyte interface Ο ² — (or electrons) in the form of electrification to eliminate the discharge at once

twenty three

 Current flows in a short time (Fig. 3 (6)).

 (7) Next, almost no current flows for Τ time (Fig. 3 (7)), and after the elapse of Τ time, the negative current increases and then starts to decrease (Fig. 3 (8)). This negative current is thought to be due to the reverse reaction of (Equation 1), (Equation 2), and (Equation 3). Also, 時 is the time constant necessary for these reverse reactions to occur, and is considered to be determined by the aluminum alloy type and the composition of the electrolyte.

 [0027] From the above, if the short-circuit time Τ is set to Τ or less, almost no negative current can flow. S τ

 The Experimentally, it was confirmed that when the A1 alloy material is A1100P with good conductivity, almost no negative current flows if the short-circuit time 時間 is about 2 s μS. In addition, it was confirmed that when the A1 alloy material is poorly conductive ADC12, the negative current hardly flows if the short-circuit time Τ is about 15 / is. Therefore, T in this case is estimated to be about 2 μs for A1100P and 15 μs for ADC12. In the case of A1100P, the negative current was negligible until 5 μs, and no negative current was observed until 2 μs. On the other hand, in the case of ADC12, negative current began to flow rapidly when it exceeded 15 / is. As described above, the preferred short circuit time varies depending on the material of the A1 alloy.

[0028] From the above, the AlZAlO interface and the AlO / electrolyte interface in the potential barrier

 2 3 2 3

As shown above, in the case of A1100P, the short-circuit time is less, preferably 1 to 5 xs, more preferably 1 By setting the length to about 3 μs, the generated film is not reduced by a negative current, so that the film growth rate can be improved. On the other hand, in the case of ADC12, the short-circuit time is set to the following, preferably:! To 15 zs, more preferably 1 to 10 xs. The growth rate can be improved.

 [0029] As shown in FIG. 1, the film growth rate is proportional to the effective current density. It has been found that the decrease in effective current due to the negative current at the time of short circuit can be reduced by extremely shortening the short circuit time as described above, and as a result, the film growth rate can be greatly improved. The film growth rate can be further improved by optimizing the film thickness.

 FIG. 5 shows details of the current waveform of FIG. Figure 5 (a) shows the case where the frequency is small (T is large)

 Fig. 5 (b) shows the case where the frequency is large (T force M, dice). However, Fig. 5 (b)

 +

 In this case, T is 2 μs, and the negative current almost flows.

 The frequency f of the pulse is

 f = 1 / (T + Τ + Τ) (Equation 5)

 (i) + G) d s

 Here i means the i-th of multiple frequencies to be tried for optimization.

 The quantity of electricity Q used for anodization is the integrated value S of the current waveform in Fig. 5.

 (i)

 If the frequency is f,

 (i)

 Q = S -f (Equation 6)

 (ϋ (ϋ (ϋ

 The larger the Q, the higher the film growth rate. T ω that gives a large Q (The range of ϋ is the area (a) = area (b) from T where the current value is maximum in Fig. 5.

+ ω + (m)

 You can think of it as between T.

 + (e)

 [0031] From the current waveform obtained from the experiment,

 T ^ 25 μ s

 + (m)

 Τ = 90μ s

 + (e)

 The corresponding frequency is as shown in Fig. 5 (b) when T = 5 zs and A1100P.

 d

 Τ = 2μs, ADC12 T = 15μs

 f = 1 / (25 + 5 + 2) = 31.3KHz

 max

min

min

It becomes. In practice, it has been confirmed experimentally that anodization can be performed without problems at 8 to 35 KHz, and more preferably 10 to 30 KHz. Example

 [0032] Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is of course not limited to these examples.

 [Example 1 and Comparative Example 1]

Anodization was performed under the following conditions using the power source shown in FIG. For the test piece, an Al 1 OOP material was used as a representative of good conductivity. The size of the test piece at this time was 50 mm × 50 mm × 1.5 mm (0.53 dm ² ). The electrolytic cell had an electrolyte volume of approximately 2001, liquid circulation, micro-explosion agitation, and cooling by a plate heat exchanger. The cathode bar was lead and the cathode plate was carbon. The bath composition was a free sulfuric acid concentration of about 150 g / l and a bath temperature of 10 ° C. Anodizing current density was carried out varied variously to 20A / dm ^2. In addition, after anodizing, it was washed with running well water for about 2 minutes and forced-dried with warm air.

 Positive current conduction time T = 80 / is, dead time (circuit open time) T = 5 / is, pulse

 + d

The positive current density I was changed variously when voltage was applied, but stable anodic acid at I = 20A / dm ²

 + +

 I was able to fix it directly. The table of Fig. 6 and Fig. 7 show the results of investigating changes in the negative current when the short-circuit B temple T is changed to 2, 3, 4, 5, 10, 20, 40 s.

 Negative current hardly flows at T = 2 μs, and even when Τ <5 μs, it is negligible.When と exceeds 5 II s, the rate of increase increases, but it is acceptable up to about 15 μs. The range increased considerably beyond 20 μs.

 That is, in order to improve the film growth rate, if the short-circuit time 15 is set to about 15 μs or less, the negative current can be suppressed and reduced or hardly flow.

 [Example 2 and Comparative Example 2]

 Figure 6 shows the results of investigating the change in negative current when に お = 40 S between positive current energizing days and temples is changed to 2, 5, 10, 20, and 40 S. It is shown in the table, Fig. 7.

 Negative current hardly flows when the short-circuit time is 2 μs, but it increases rapidly as the short-circuit time increases to 10, 20, and 40 μs, but it is acceptable up to about 10 μs. When s was exceeded, it increased considerably.

[0035] (Example 3)

In Example 1, the test piece has poor conductivity, ADC12 (size is 50mm x 50mm x 3 • Omm (0.56dm ² )) is fixed at T = 80 / is, T = 5 μs, and I = 10A / dm ²

+ d +

The change in current was examined. As a result, almost no negative current flowed until T was 15 μs, and it flowed rapidly over 15 / is.

Claims

The scope of the claims  [1] Using pulse power, an aluminum alloy anodizing method for forming an anodized film on the surface of an aluminum alloy, and anodizing anode and anode when no pulse voltage is applied after applying a positive pulse voltage An aluminum alloy anodizing method characterized by short-circuiting an oxidation cathode with a short-circuiting time of 15 zs or less.  [2] The aluminum alloy anodizing method according to [1], wherein the short-circuiting time is not less than 1 μs and not more than 15 μs. [3] The aluminum alloy anodizing method according to [1], wherein the short circuit time is 1 μs or more and 5 / s or less. [4] Cycle power of the pulse power waveform Pulse voltage application time (T), dead time (T)  + d The s according to claim 1, 2 or 3, characterized by being configured in the order of short circuit time (T)  Aluminum alloy anodizing method.  [5] The aluminum alloy anodizing method according to any one of [1] to [4], wherein the frequency of the pulse power is 8 to 35 KHz.  6. The aluminum alloy anodizing method according to any one of claims 1 to 4, wherein the frequency of the pulse power is 10 to 30 KHz.  [7] Pulse power is applied to an aluminum alloy anodizing power source used in an aluminum alloy anodizing method for forming an anodized film on the surface of an aluminum alloy. An aluminum alloy characterized by having a pulse power generator that generates a pulse power that short-circuits a terminal connected to the anodizing anode and a terminal connected to the anodizing cathode at a short-circuiting time of 15 μs or less during application. Power source for anodization.  8. The power source for anodizing an aluminum alloy according to claim 7, wherein the pulse power generation unit generates pulse power having the short-circuit time of 1 μs to 15 μs.  [9] The aluminum alloy anodizing power source according to [7], wherein the pulse power generation unit generates pulse power having the short circuit time of 1 μs or more and 5 μs or less.  [10] The pulse power generator has a waveform whose pulse voltage application time (T), dead time (T), short  A pulse power configured in the order of + d entanglement time (T) is generated.  S The power source for anodizing an aluminum alloy according to any one of forces 9. The aluminum alloy anodizing power source according to any one of claims 7 to 10, wherein the pulse power generation unit generates pulse power having a frequency of 8 to 35 KHz. 11. The power source for anodizing an aluminum alloy according to claim 7, wherein the pulse power generation unit generates pulse power having a frequency of 10 to 30 KHz.