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EP2045367A1 - Procédé d'oxydation anodique d'un alliage d'aluminium et bloc d'alimentation pour l'oxydation anodique d'un alliage d'aluminium - Google Patents

Procédé d'oxydation anodique d'un alliage d'aluminium et bloc d'alimentation pour l'oxydation anodique d'un alliage d'aluminium Download PDF

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Publication number
EP2045367A1
EP2045367A1 EP07768250A EP07768250A EP2045367A1 EP 2045367 A1 EP2045367 A1 EP 2045367A1 EP 07768250 A EP07768250 A EP 07768250A EP 07768250 A EP07768250 A EP 07768250A EP 2045367 A1 EP2045367 A1 EP 2045367A1
Authority
EP
European Patent Office
Prior art keywords
aluminum alloy
anodizing
electric power
short
pulsed electric
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP07768250A
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German (de)
English (en)
Inventor
Hiromichi Odajima
Kazuo Hayashi
Yuji Koyama
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
IDX Co Ltd
Original Assignee
IDX Co Ltd
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Filing date
Publication date
Application filed by IDX Co Ltd filed Critical IDX Co Ltd
Publication of EP2045367A1 publication Critical patent/EP2045367A1/fr
Withdrawn legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
    • C25D11/02—Anodisation
    • C25D11/04—Anodisation of aluminium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
    • C25D11/02—Anodisation
    • C25D11/024—Anodisation under pulsed or modulated current or potential

Definitions

  • the present invention relates to a method for anodizing an aluminum alloy and to a power supply for anodizing an aluminum alloy.
  • anodizing of an aluminum alloy is carried out in a bath containing an aqueous solution of sulfuric acid, oxalic acid, phosphoric acid or the like to form an oxide film or coating on a surface of the aluminum alloy for the purpose of increasing the hardness, wear resistance and corrosion resistance of the surface or coloring the surface.
  • An anodic oxide film has a dense barrier layer and a porous layer both composed of Al 2 O 3 .
  • a pulse electrolysis method including the periodic reverse electrolyzing method is better than a direct current anodizing method to form a desired oxide film free of a defect called "burning of anodic oxide coating" within a short period of time with high productivity.
  • a periodic reverse electrolyzing method in which a negative current is intermittently supplied to a sulfuric acid bath at an oxidation voltage lower than that used in a direct current anodizing method.
  • Japanese Unexamined Patent Application Publication No. 2000-282294 discloses that an aluminum anodic oxide film with a high heat resistance and a corrosion resistance can be formed on an aluminum alloy surface by a method using superimposed direct current on an alternating current under such an electrolysis condition that the AC component does not contain a negative component and the AC component is at least 5 % of the level of the DC component.
  • the current density suitably employed is as low as 0.1 to 2 A/dm 2 . With such a current density, the film formation rate is so low as to cause problems of low productivity and high cost.
  • the power supply system required for this method is also complicated since both an AC power supply and a DC power supply are required.
  • Japanese Unexamined Patent Application Publication No. 2004-35930 suggests, as a technique which can increase the formation rate of an aluminum anodic oxide film for the purpose of improving productivity, a method in which a sine wave current with a high frequency of 200 to 5000 Hz (preferably 600 to 2000 Hz) on which a DC current is superimposed is supplied to a sulfuric acid aqueous solution bath.
  • a high-frequency sine wave with a frequency of 1000 Hz and a voltage of ⁇ 20 V on which a DC voltage of 19.8 V was superimposed was supplied to aluminum alloy ADC12 (JIS H5302) in a 10% sulfuric acid aqueous solution at 17°C for an electrolytic treatment period of 20 minutes, thereby obtaining an anodic oxidation film with a thickness of 22 ⁇ m (growth rate: 1.1 ⁇ m/min). It is reported that the current density obtained five minutes after the start of electrolysis was 13.8 A/dm 2 .
  • the method is still disadvantageous in that the frequency is limited to 200 to 5000 Hz and in that, since a sine wave is used, the amount of current which can be supplied per unit time is smaller as compared to a rectangular wave.
  • the power supply system required for this method is also complicated since both an AC power supply and a DC power supply are required.
  • Japanese Unexamined Patent Application Publication No. 2006-83467 discloses a method for forming an anodic oxide film having cells which have grown in random directions relative to a surface of aluminum or aluminum alloy and thus have no orientation for the purpose of improving the corrosion resistance and impact resistance.
  • a step of applying a plus voltage and a step of removing electric charge are repeated.
  • the plus voltage is applied for 25 to 100 ⁇ s (5 to 20 KHz in terms of frequency) at a time.
  • the step of removing electric charge the application of the plus voltage is stopped and a short circuit is formed between the anode and cathode or a minus voltage is applied across the anode and the cathod.
  • the present invention has been made in view of the above problems, and it is, therefore, an object of the present invention to provide a method for anodizing an aluminum alloy and a power supply for anodizing an aluminum alloy capable of increasing the film formation rate and improving productivity without developing a defect called "burning of anodic oxide coating" by suppressing or preventing a negative current when anodizing of an aluminum alloy is carried out by a pulse electrolysis method.
  • Another object of the present invention is to provide a method for anodizing an aluminum alloy and a power supply for anodizing an aluminum alloy capable of further increasing the film formation rate to improve productivity by setting a frequency of pulse voltage that allows a maximum current to flow when the pulse voltage is applied.
  • the present invention provides the following inventions.
  • a short-circuit is formed, after application of a positive pulse voltage, between the anode for anodic oxidation and the cathode for anodic oxidation for a very short short-circuit duration during non application of the pulse voltage so that a negative current is controlled to be reduced or eliminated.
  • a method for anodizing an aluminum alloy and a power supply for anodizing an aluminum alloy that are capable of giving an effect that the film formation rate can increase and the productivity can be improved by setting the frequency of the pulse voltage to a value permitting a maximum current to flow when the pulse voltage is applied in addition to the above effect attained by the formation of a short-circuit between the anode for anodic oxidation and the cathode for anodic oxidation.
  • the present inventors have made a study for the purpose of increasing the film formation rate and found that when a short circuit is formed, after one application of a positive pulse voltage, between an anode for anodic oxidation and a cathode for anodic oxidation to cause a negative current (current which flows in a direction opposite the direction in which a current flows when the pulse is applied) to flow during non application of the pulse voltage, it is possible to reduce the concentration gradients of Al 3+ and O 2- ions in the barrier layer formed during application of the pulse voltage and to discharge the electric double layer at the solid-liquid interface so that a large current can be allowed to flow in the next application of the pulse voltage.
  • the problem is that the magnitude of negative current is large relative to the magnitude of the positive current which flows when a pulse voltage is applied.
  • the present inventors have thus conducted a further study on this issue.
  • the film growth rate is proportional to the effective current density ( FIG. 1 ), when a short circuit is formed between the anode for anodic oxidation and the cathode for anodic oxidation during non application of a pulse voltage in a method for anodizing an aluminum alloy using pulsed electric power. It has also been found, however, that a problem is caused because when the effective current density is increased, the negative current also increases.
  • the present inventors have investigated a method capable of further improving the film growth rate in order to improve productivity.
  • the present inventors unexpectedly found that when a short circuit is formed, after one application of a positive pulse voltage, between the anode for anodic oxidation and the cathode for anodic oxidation for a very short period of time during non application of the pulse voltage, the negative current can be reduced or even prevented so that a large current can be allowed to flow without developing a defect known as "burning of anodic oxide coating" when the next positive pulse voltage is applied.
  • the present inventors also found that the film growth rate can be significantly increased when the frequency of the pulse voltage to be applied is set to a value within a specified range.
  • the present invention has been made based on the above findings.
  • a method for anodizing an aluminum alloy according to the present invention is characterized in that pulsed electric power is used and that a short circuit is formed, after application of a positive pulse voltage, between the anode for anodic oxidation and the cathode for anodic oxidation for a short-circuit duration of not longer than 15 ⁇ s during non application of the pulse voltage.
  • the short-circuit duration is preferably not shorter than 1 ⁇ s and not longer than 15 ⁇ s, more preferably not shorter than 1 ⁇ s and not longer than 5 ⁇ s, still more preferably not shorter than 1 ⁇ s and not longer than 3 ⁇ s.
  • the negative current can be significantly reduced or even prevented from flowing and a large current can be allowed to flow in the next application of positive pulse voltage when the short-circuit duration is within the above range. Therefore, the film formed is not reduced by a negative current and the film growth rate can be significantly increased without developing a defect known as "burning of anodic oxide coating.” It has been considered necessary to remove all the electric charges accumulated in the system by forming a short circuit or applying a negative voltage before the next application of a positive pulse voltage in order both to prevent a defect called "burning of anodic oxide coating" and to increase the film growth rate.
  • the present inventors have found that when only the electric charges at the barrier layer interfaces (Al/Al 2 O 3 interface and Al 2 O 3 /electrolytic solution interface) at which the oxide film is being formed are removed, a substantially reduced electrical resistance state can be realized so that a large current necessary to form a good film is allowed to flow when the next positive pulse voltage is applied. With this method, the film growth rate can be significantly increased since the film formed can be prevented from being melted and reduced by a large negative current.
  • the pulsed electric power have a waveform having a cycle composed, in the order, of a pulse voltage application duration (T + ), a dead time (T d ), and a short-circuit duration (T s ).
  • the pulse voltage application duration (T + ) is preferably approximately 20 to 100 ⁇ s
  • the dead time (T d ) is preferably approximately 5 to 10 ⁇ s.
  • the pulsed electric power have a frequency of 8 to 35 KHz, more preferably 10 to 30 KHz.
  • the frequency is within the above range, a quantity of electricity that can further increase the film growth rate can be supplied to form a film, which, in conjunction with the effect of the short circuit for a very short period of time, further increases the film growth rate.
  • FIG. 2 is a view explanatory of the structure of a power supply and an electrolytic bath for use in anodizing an aluminum alloy according to the present invention.
  • a power supply P is constituted of a sequencer 10, a positive side DC power supply 11, a repetition frequency generator 12, a positive side pulse generating circuit 13, a short-circuit side pulse generating circuit 14, a positive side chopper gate amplifier (GA) 25, a short-circuit side chopper gate amplifier (GA) 26, a positive side chopper switch 15, a reverse current prevention diode (D 1 ) 16, and a short-circuit current control circuit 17, and has output terminals 18 connected respectively to an anode 20 and a cathode 21 in an electrolytic bath 19. Also provided are a positive side output voltmeter (E 1 ) 22, an electrolytic bath voltmeter (E B ) 23 and an electrolytic bath ammeter (A B ) 24. Designated as 27 is an electrolytic solution.
  • the sequencer 10 controls the repetition frequency generator 12, the positive side pulse generating circuit 13, the short-circuit side pulse generating circuit 14 and the positive side DC power supply 11 to transform the waveform of pulsed electric power for use in the present invention into a prescribed shape.
  • the positive side DC power supply 11 generates DC power necessary to apply a positive pulse voltage or positive current pulse set by the sequencer 10.
  • the repetition frequency generator 12 generates a reference repetition frequency necessary for the generation of the pulsed electric power and supplies it to the positive side pulse generating circuit 13 and the short-circuit side pulse generating circuit 14.
  • the positive side pulse generating circuit 13 generates a pulse of duration T +
  • the short-circuit side pulse generating circuit 14 generates a pulse of duration T s .
  • a dead time (T d ) is preliminarily set in sequencer 10.
  • the positive side chopper gate amplifier (GA) 25 assumes a role of amplifying the pulse signal from the pulse generating circuit 13 to such a level that the positive side chopper switch 15 can operate reliably according to a pulse width signal determined by the positive side pulse generating circuit 13.
  • the short-circuit side chopper gate amplifier 26 assumes a role of amplifying the pulse signal from the short-circuit side pulse generating circuit 14 to such a level that the short-circuit current control circuit 17 can operate reliably according to a pulse width signal determined by the short-circuit side pulse generating circuit 14.
  • the positive side chopper switch 15 assumes a role of supplying the electric power from the positive side DC power supply 11 to the electrolytic bath in a pulsed manner according to a pulse width signal determined by the positive side pulse generating circuit 13.
  • the reverse current prevention diode 16 prevents reverse power from flowing to the side of the positive side DC power supply 11.
  • the short-circuit current control circuit 17 forms, after application of a positive pulse voltage, a short circuit between the output terminals 18 of the anode 20 and the cathode 21 for a short-circuit duration T s during non application of the pulse voltage.
  • Anodizing was conducted using the power supply shown in FIG. 2 under the following conditions.
  • a test piece of A1100P was used.
  • the test piece had a size of 50 mm ⁇ 50 mm ⁇ 1.5 mm (0.53 dm 2 ).
  • a test piece of ADC12 was used.
  • the test piece had a size of 50 mm ⁇ 50 mm ⁇ 3.0 mm (0.56 dm 2 ).
  • the electrolytic bath contained approximately 200 L of an electrolytic solution, which was stirred by a liquid circulation and micro-aeration system and cooled by a plate type heat exchanger. A lead cathode bar and a carbon cathode plate were used.
  • the bath liquid was free sulfuric acid solution with a concentration of approximately 150 g/L, and the bath liquid temperature was 10°C.
  • the anodizing current density was variously changed up to 20 A/dm 2 . After the anodizing, the test pieces were rinsed with flowing water for approximately two minutes and forcibly dried using hot air.
  • FIG. 3 shows a pulse setting condition and actual voltage and current waveforms corresponding to the pulse setting condition.
  • T + represents the pulse voltage application duration
  • T d represents the dead time necessary to decrease the pulse voltage to zero and to form a short circuit between the electrodes (during which the circuit is open)
  • T s represents the short-circuit duration.
  • the voltage waveform rises according to the setting for T + , drops very slightly during T d , and remains at zero during T s .
  • the current waveform rises sharply to a local maximum and then drops in an early stage of T + .
  • the current waveform remains at zero during T d .
  • FIG. 4 is an enlarged view of the barrier layer part in the overall structure of an anodic oxide film shown in FIG. 4(c) ). That is, an anode aluminum alloy and a cathode carbon are placed in an electrolytic solution. Al is oxidized to Al 2 O 3 at the anode, and H + ions are reduced to H 2 at the cathode.
  • the growth of the barrier layer is described in the document as follows:
  • the potential gradient in the vicinity of the barrier layer is considered as shown in FIG. 4(b) .
  • the film growth rate can be improved since the film generated is not reduced by a negative current.
  • the short-circuit duration is 15 ⁇ s or less, preferably 1 to 15 ⁇ s, more preferably 1 to 10 ⁇ s, the film growth rate can be improved.
  • the film growth rate is proportional to the effective current density. It was found that a decrease in effective current caused by a negative current which flows when a short circuit is formed can be reduced and consequently the film growth rate can be improved significantly by significantly shortening the short-circuit duration. In addition, according to the present invention, the film growth rate can be further improved by optimizing the pulse frequency.
  • FIG. 5 shows the current waveform shown in FIG. 3 in more detail, in which FIG. 5(a) shows a case where the frequency is low (T + is long), and FIG. 5(b) shows a case where the frequency is high (T + is short).
  • T s is set to 2 ⁇ s so that almost no negative current can flow.
  • i refers to an i-th frequency of a plurality of frequencies which are tested for optimization.
  • the quantity of electricity Q used for the anodizing is the integral S (i) of the current waveform in FIG. 5 .
  • T + m ⁇ 25 ⁇ s T + e ⁇ 90 ⁇ s T + m ⁇ 25 ⁇ s T + e ⁇ 90 ⁇ s .
  • anodizing can be carried out without any problems in a frequency range of 8 to 35 KHz, preferably 10 to 30 KHz.
  • anodizing was carried out under the following conditions.
  • a test piece of A1100P was used.
  • the test piece had a size of 50 mm ⁇ 50 mm ⁇ 1.5 mm (0.53 dm 2 ).
  • the electrolytic bath contained approximately 200 L of an electrolytic solution, which was stirred by a liquid circulation and micro-aeration system and cooled by a plate type heat exchanger.
  • a lead cathode bar and a carbon cathode plate were used.
  • the bath liquid was a free sulfuric acid solution with a concentration of approximately 150 g/L, and the bath liquid temperature was 10°C.
  • the anodizing current density was variously changed up to 20 A/dm 2 .
  • the test piece was rinsed with flowing water for approximately two minutes and forcibly dried using hot air.
  • the positive current supply duration T + was 80 ⁇ s
  • the dead time (circuit open period) T d was 5 ⁇ s.
  • the negative current was measured at short-circuit duration T s of 2, 3, 4, 5, 10, 20 and 40 ⁇ s. The results were summarized in a table of FIG. 6 and in FIG.
  • Example 2 An experiment was conducted under the same conditions as those in Example 1 except that the positive current supply duration T + was 40 ⁇ s, and that the negative current was measured at short-circuit durations T s of 2, 5, 10, 20 and 40 ⁇ s. The results were summarized in a table of FIG. 6 and in FIG. 7 . Although almost no negative current flowed when the short-circuit duration was 2 ⁇ s, the negative current increased rapidly as the short-circuit duration T s increased to 10, 20 and 40 ⁇ s. The negative current was in an allowable range when T s was not longer than approximately 10 ⁇ s. When T s exceeded 20 ⁇ s, the negative current significantly increased.

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  • Chemical & Material Sciences (AREA)
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  • Chemical Kinetics & Catalysis (AREA)
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  • Materials Engineering (AREA)
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EP07768250A 2006-07-05 2007-07-05 Procédé d'oxydation anodique d'un alliage d'aluminium et bloc d'alimentation pour l'oxydation anodique d'un alliage d'aluminium Withdrawn EP2045367A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2006210325 2006-07-05
PCT/JP2007/063501 WO2008004634A1 (fr) 2006-07-05 2007-07-05 ProcÉdÉ d'oxydation anodique d'un alliage d'aluminium et bloc d'alimentation pour l'oxydation anodique d'un alliage d'aluminium

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US (1) US20080087551A1 (fr)
EP (1) EP2045367A1 (fr)
JP (1) JPWO2008004634A1 (fr)
CN (1) CN101126172A (fr)
TW (1) TW200804629A (fr)
WO (1) WO2008004634A1 (fr)

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JP5207124B2 (ja) * 2008-03-24 2013-06-12 スズキ株式会社 陽極酸化処理方法
JP5691135B2 (ja) * 2009-03-31 2015-04-01 スズキ株式会社 陽極酸化皮膜及び陽極酸化処理方法
CN102471915B (zh) * 2009-07-23 2015-05-20 开利公司 在钎焊的制品上形成氧化物层的方法
FR3040712B1 (fr) * 2015-09-03 2019-12-13 Montupet S.A. Procede ameliore de formation d'un revetement de conduit de culasse et culasse ainsi obtenue
EP3430185B1 (fr) 2016-04-27 2023-02-22 Bang & Olufsen A/S Surfaces en al anodisé hautement réfléchissantes à contenu diffus et spéculaire adapté
CN113981500B (zh) * 2021-12-09 2023-03-28 陕西宝成航空仪表有限责任公司 硬铝合金壳体零件的草酸阳极氧化工艺方法

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US5268235A (en) * 1988-09-26 1993-12-07 The United States Of America As Represented By The Secretary Of Commerce Predetermined concentration graded alloys
US5520791A (en) * 1994-02-21 1996-05-28 Yamaha Hatsudoki Kabushiki Kaisha Non-homogenous composite plating coating
US6461678B1 (en) * 1997-04-29 2002-10-08 Sandia Corporation Process for metallization of a substrate by curing a catalyst applied thereto
JP2000282294A (ja) 1999-03-31 2000-10-10 Kobe Steel Ltd 耐熱割れ性および腐食性に優れた陽極酸化皮膜の形成方法並びに陽極酸化皮膜被覆部材
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JP2004035930A (ja) 2002-07-02 2004-02-05 Suzuki Motor Corp アルミニウム合金材及びその陽極酸化処理方法
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JPWO2008004634A1 (ja) 2009-12-03
US20080087551A1 (en) 2008-04-17
CN101126172A (zh) 2008-02-20
TW200804629A (en) 2008-01-16

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