JP2004035930A

JP2004035930A - Aluminum alloy material and anodization treatment method therefor

Info

Publication number: JP2004035930A
Application number: JP2002192835A
Authority: JP
Inventors: Akira Ishibashi; 石橋　　亮; Nobuyuki Suzuki; 鈴木　伸行
Original assignee: Suzuki Motor Corp
Current assignee: Suzuki Motor Corp
Priority date: 2002-07-02
Filing date: 2002-07-02
Publication date: 2004-02-05

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anodization treatment method which improves the film formation rate of an anode oxide film when an aluminum material or an aluminum alloy material as the object to be treated is subjected to anodization treatment. <P>SOLUTION: In the anodization treatment method for an aluminum alloy material, an aluminum material or an aluminum alloy material as the object to be treated is dipped into an anodization treatment bath, and a high frequency electric current of 200 to 5,000 Hz is applied, so that anodization treatment is performed to the object to be treated. As the electrolytic waveform of the high frequency electric current, at least either one of sinusoidal waves, square waves and triangular waves can be used. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、アルミニウム材又はアルミニウム合金材の表面に、耐食性及び耐摩耗性に優れた陽極酸化皮膜を短時間で形成する表面処理方法に関する。
【０００２】
【従来の技術】
従来から、被処理物であるアルミニウム部材及びアルミニウム合金部材の表面に、耐食性や耐摩耗性の向上、及び被処理物の着色を目的として、陽極酸化処理と呼ばれる表面処理が行われている。該陽極酸化処理は、前記被処理物を硫酸、燐酸、蓚酸、クロム酸などのジプロトン酸等の電解浴に浸漬しつつ、電解処理を一定時間行うことによって、被処理物の表面にいわゆるアルマイト皮膜と呼ばれる酸化皮膜を形成する方法である。このアルマイト皮膜は、緻密なバリヤー層と多孔質のポーラス層から構成されており、組成は非晶質のＡｌ_２Ｏ_３からなっている。
【０００３】
しかし、アルミニウム鋳造材及びアルミニウムダイカスト材では、多量に含むＳｉ，Ｃｕ，Ｆｅ等の合金成分によって、電流が流れ難く、展伸材と同様な陽極酸化処理方法では短時間で皮膜の形成を行うことは困難であった。
陽極酸化処理を短時間で行うためには、電流密度を高める必要がある。直流法において高い電流密度をアルミニウム鋳造材及びアルミニウムダイカスト材で得るために、高電圧を印加すると、電圧を高めたことにより、前記バリアー層で発生するジュール熱の発熱量が大きくなる。これにより、「酸化皮膜の焼け」と呼ばれる、酸化皮膜が形成されない部分が発生しやすくなる。従って、直流法では、アルミニウム鋳造材及びアルミニウムダイカスト材に対して短時間で正常な厚い陽極化皮膜を形成することは、一般に困難であった。
【０００４】
これに対し、従来から、陽極酸化処理時の電解波形を変更する方法、例えば、交流法、パルス電解法、極性反転パルス法（ＰＲ電解法）、交直重畳電解法などによって、前記焼けを防止することが行われている。これらの方法は、非定常電圧または、非定常電流で陽極酸化する方法であり、陽極酸化電流が流れていない時にバリアー層で発生するジュール熱を被処理物、及び溶液中に拡散させ、さらに反応部の電解質濃度が回復するため、成膜速度の向上が可能となる。しかし、これらの方法は、５０Ｈｚ、６０Ｈｚといった「商用周波数」で実施される場合が多く、この周波数では、特に合金元素の多いアルミニウムダイカスト材の成膜速度が遅いという問題があった。
また、交流電流とパルス状直流電流とを重畳させた電流を陽極酸化処理の電解浴に流す方法が従来から用いられている。しかし、この方法では、以下のような問題点があった。
（１）交流電流にパルス電流を重畳させるため、高い周波数領域においては波形の制御が困難となる。また、陽極酸化処理に用いる装置の構造が複雑になる。
（２）交流電流にパルス電流を重畳させるため、電解波形が複雑になり、陽極酸化において電流制御しにくくなり、最適な電解条件が求めにくい。
これらの理由から、従来の陽極酸化処理においては、低い電流密度、例えば３Ａ／ｄｍ^２程度しか得られず、成膜速度が０．５〜０．７μｍ／ｍｉｎと遅いという問題があった。
【０００５】
さらに、陽極酸化時の電解波形を変更した従来例として、特開２０００−２８２２９４公報に記載された技術がある。これは、直流電流に交流電流を重畳させた交直重畳法を適用すると共に、交流成分に負性分を含まず、かつ、交流成分が直流成分の５％以上含まれる電解条件で処理する方法である。この技術は、熱割れに強い皮膜構造を得ることを目的としており、交流成分の周波数は１００Ｈｚ以上が良好であるものの、通常は６０Ｈｚやそれ以下においても改善効果は十分効果があるとされている。しかし、次のような問題があった。
（３）電流制御での好適とされる電流密度は０．１〜２Ａ／ｄｍ^２と低く、この電流密度では、アルミニウム合金の一つであるＡＤＣ１２材に対して非常に成膜速度が遅い。
（４）電圧制御の場合、改善効果があるとされている６０Ｈｚ以下の周波数でＡＤＣ１２材に陽極酸化処理を施しても、成膜速度の速度は向上しない。
【０００６】
【発明が解決しようとする課題】
本発明は、前記課題を解決し、被処理物であるアルミニウム材又はアルミニウム合金材の表面に陽極酸化処理を施す場合に、陽極酸化皮膜の成膜速度を低コストで向上させることができる陽極酸化処理方法を提供することを目的とする。
【０００７】
【課題を解決するための手段】
本発明に係る陽極酸化処理方法は、被処理物であるアルミニウム材又はアルミニウム合金材を陽極酸化処理浴中に浸漬し、２００〜５０００Ｈｚの高周波電流を通電することによって、前記被処理物に陽極酸化処理を施す方法である。
前記処理浴は、硫酸、蓚酸、燐酸、クロム酸などのジプロトン酸の単独浴又は混合浴、また、これらの単独浴又は混合浴に、有機酸や溶存アルミニウムイオンを増加させる化合物等を添加した浴を好適に用いることができる。ジプロトン酸とは、例えば、硫酸、蓚酸、燐酸、クロム酸等の水素イオンを２つ有する酸のことであり、本発明においては、ジプロトン酸の単独浴又は混合浴、さらにこれらに有機酸や浴存アルミニウムイオンを増加させる化合物等を添加しても良い。
【０００８】
この処理方法では、電流の周波数を、従来の５０〜６０Ｈｚから２００〜５０００Ｈｚに増加させるため、被処理物に低電圧で大電流、即ち、高い電流密度で陽極酸化処理が可能となり、成膜速度が飛躍的に向上する。高い周波数で成膜速度が向上するのは、「表皮効果」によるものである。表皮効果とは周波数を高くすると電流が金属の表面付近に集中するという現象である。この効果により、陽極酸化反応が生じる被処理物の表面近傍の電流密度が特に高くなることによって、成膜速度が向上する。ジュール熱の発生量は、高電流密度であっても低電圧のため少なく、さらに熱の発生は電解液による冷却効果が高い被処理物の最表面で最も高くなるため、焼けの発生を抑制しつつ、高い成膜速度を得ることが可能となる。
しかし、周波数を高くしすぎると、ジュール熱の拡散や、電解質の濃度回復が不充分になり、成膜速度は低下する。また、多数のワークを処理する場合には数千アンペアという大電流が出力可能な電源が必要となるが、高い周波数で大電流を出力できる電源は著しく高価になる。さらに、高周波電流では配線のインピーダンスが大きくなるため、電源から被処理物間の配線での電圧ドロップが増加し、エネルギー損失が大きくなるだけでなく、電源から被処理物までの配線の長さが制限されるという問題がある。このような成膜への影響、電源製造コストやエネルギー損失を鑑みて周波数の上限は５０００Ｈｚである。
これにより、陽極酸化皮膜の焼けを防止すると共に、処理浴の温度上昇を抑制して、高速で陽極酸化皮膜を形成することが可能となる。
このように、アルミニウム材又はアルミニウム合金材の陽極酸化処理を高速で施すことによって生産効率を大幅に向上させることができ、従って、前記被処理物を用いた防錆部材や摺動部材の製造コストを低下させることができる。なお、従来から困難とされてきた、Ｓｉ，Ｃｕ，Ｆｅ等の合金元素を多量に含むアルミニウム合金材に対する高速の陽極酸化処理が可能になる。
【０００９】
また、本発明に係る陽極酸化処理方法の一態様では、前記高周波電流の周波数を６００〜２０００Ｈｚとすることができる。
この周波数であれば、前述した２００〜５０００Ｈｚの範囲よりも更に高速で陽極酸化処理を行うことができる。
さらに、本発明に係る陽極酸化処理方法の別の態様では、前記高周波電流の電解波形として、正弦波、矩形波、三角波の少なくともいずれかを用いることができる。
そして、本発明に係る陽極酸化処理方法の更に別の態様は、前記高周波電流に直流電流を重畳させて印加する方法である。
【００１０】
また、本発明に係る陽極酸化処理方法の更に別の態様は、前記陽極酸化処理浴がジプロトン酸を含む方法である。
本発明においては、ジプロトン酸の単独浴又は混合浴、さらにこれらに有機酸や浴存アルミニウムイオンを増加させる化合物等を添加しても良い。また、処理浴の条件としては、例えば、処理浴の濃度は、硫酸浴では３〜３０％、蓚酸浴では１〜５％が好ましく、処理浴の温度は、硫酸浴では−５〜４０℃、蓚酸浴では１０〜６０℃が好ましい。
さらに、本発明に係る陽極酸化処理方法の更に別の態様は、前記ジプロトン酸として、硫酸、蓚酸、燐酸、クロム酸の少なくともいずれかを含む方法である。なお、本発明は、前述されたいずれかの方法によって処理されたアルミニウム材又はアルミニウム合金材である。
【００１１】
【発明の実施の形態】
本発明の陽極酸化処理方法は、被処理物であるアルミニウム材又はアルミニウム合金材をジプロトン酸をベースとする電解浴中に浸漬し、２００〜５０００Ｈｚの高周波電流を通電することによって、前記被処理物に陽極酸化処理を施す表面処理方法である。電流は、２００〜５０００Ｈｚの高周波電流に直流電流を重畳させても良い。前記電解波形は、正弦波、三角波、矩形波などの種々のものを用いることができる。
【００１２】
図１に、高周波電流に直流電流を重畳させた電解波形を示す。該電解波形は、周波数が１０００Ｈｚで電圧が±２０Ｖである高周波電流に、１９．８Ｖの直流電圧を重畳させている。この電解波形は、高い周波数域での波形の乱れが発生することがなく、電流制御も容易であるため、従来の技術で説明した問題点（１）（２）に示した、電解波形や電流制御に関する課題を解決することができる。さらに、２００Ｈｚ以上の高周波電流のため、低い電圧で３Ａ／ｄｍ^２以上の高い電流密度を容易に得ることができる。このため、周波数を上げることにより最も陽極酸化皮膜の形成が困難といわれているＡＤＣ１２材でも１μｍ／ｍｉｎ以上の成膜速度で陽極酸化皮膜を生成することが可能となり、前記問題点（３）（４）に示した課題も克服することができる。
【００１３】
本発明における電解制御方法としては、電圧制御法と電流制御法のいずれも用いることができる。前述した図１は、電圧制御における電解波形の形状を示したものであり、この電圧は被処理物の材質、電解液組成、浴温を考慮して、焼けが発生しない範囲に設定する。例えば、硫酸浴で１０００Ｈｚの高周波電流により陽極酸化を行う場合、好ましい電圧の範囲は、プラス側のピーク値が３０〜７０Ｖ、マイナス側のピーク値が−１０〜０Ｖである。
そして、処理浴の浴液には、水素イオンを２つ有する酸であるジプロトン酸の単独浴又は混合浴を好適に用いることができる。即ち、ジプロトン酸、例えば、硫酸、蓚酸、燐酸、クロム酸等の単独浴又は混合浴、さらにこれらに有機酸や浴存アルミニウムイオンを増加させる化合物等を添加しても良い。これらの浴濃度及び浴温は従来技術と同程度であれば良く、硫酸浴の場合には濃度が３〜３０％、浴温が−５〜４０℃の範囲内であれば良い。また、従来から行われているような方法で浴液の攪拌し、被処理面の冷却、電解質の濃度回復、気泡の除去を行うことが望ましい。
【００１４】
【実施例】
次いで、実施例を通じて本発明を具体的に説明する。この実施例においては、高周波と直流の電圧を一定にする電圧制御により周波数を変化させて電解した場合の皮膜の成長速度を測定した。電圧制御によることで、周波数を変化させた場合における電流の流れ易さの変化を見ることができるためである。
【００１５】
［実施例１］
表１に示すように、アルミニウム合金の１種であるＡＤＣ１２材を被処理物とし、該被処理物を１０％の濃度で浴温が１７℃の硫酸単独浴に浸漬させた。この状態で、周波数が２００Ｈｚで電圧が±２０Ｖの正弦波の高周波電圧に１９．８Ｖの直流電圧を重畳させたものを５分間印加して、陽極酸化処理を行った。
［実施例２〜１６］
実施例２〜１６においては、高周波電流の周波数のみを３００〜２０００Ｈｚに変え、その他の処理条件は、前記実施例１と同様とした。
【００１６】
［実施例１７，１８］
実施例１７，１８は、電解処理時間を１０分間，２０分間にそれぞれ変え、その他の処理条件は、実施例２と同様とした。
なお、一般的に陽極酸化処理皮膜の成長速度は、電流密度に比例するといわれ、電圧制御による陽極酸化処理では、電解時間の経過に従って絶縁体の皮膜を形成していくので電流密度は低下し、成長速度も遅くなると予想される。そこで、周波数１０００Ｈｚで陽極酸化処理を行った実施例２について、電解処理時間のみを１０分間（実施例１７）又は、２０分間（実施例１８）と変化させて、処理時間に対する陽極酸化皮膜の成長速度の変化を測定した。
【００１７】
［比較例１］
また、比較例１〜４は、周波数が２００Ｈｚ未満の交流電流又は直流電流を印加して陽極酸化処理を行った。
まず、比較例１は、ＡＤＣ１２材を被処理物とし、該被処理物を１０％の濃度で浴温が１７℃の硫酸単独浴に浸漬させた。この状態で、周波数が６０Ｈｚで電圧が±１０Ｖの正弦波の高周波電圧に１５Ｖの直流電圧を重畳させたものを５分間印加して、陽極酸化処理を行った。なお、この比較例１は、特開２０００−２８２２９４号公報に記載された実施例に準じて実施したものである。
【００１８】
［比較例２］
比較例２は、印加する電圧を４０Ｖの直流電圧とし、その他の処理条件は、比較例１と同様とした。
［比較例３，４］
さらに、比較例３，４については、表１に示す条件でそれぞれ陽極酸化処理を行った。
【表１】

【００１９】
以下に、実施例と比較例の結果を説明する。
まず、成膜速度と印加電流の周波数との関係をみると、図２から明らかなように、周波数と共にほぼ直線的に成膜速度は向上することが判明した。即ち、比較例３（符号Ｕ）の周波数が５０Ｈｚでは成膜速度が０．１μｍ／ｍｉｎであるのに対し、実施例１（符号Ａ）の２００Ｈｚでは、成膜速度が０．４μｍ／ｍｉｎと上昇した。なお、図２，３における符号Ａ〜Ｖは、表１の右端欄に記載されたように、実施例１が符号Ａ、実施例２が符号Ｂとそれぞれ順に対応している。
【００２０】
また、実施例５（符号Ｆ）において、６００Ｈｚで５分間の陽極酸化処理により０．８μｍ／ｍｉｎ、実施例９（符号Ｉ）の１０００Ｈｚでは１．１μｍ／ｍｉｎ、さらに、実施例１６（符号Ｐ）の２０００Ｈｚでは１．６μｍ／ｍｉｎと周波数を上昇させれば、成膜速度は上昇することが判明した。
さらに、図３に示すように、実施例１７，１８においても、電圧制御による陽極酸化処理であることから、電解時間を長くすると成膜速度は次第に遅くなると予想されたが、結果は電解時間によらずほぼ一定であった。従って、電解時間を長くしても皮膜の成長速度は変化せず、本発明によれば、厚膜の高速成長が可能であることが確認できた。
以上をまとめると、陽極酸化処理における成膜速度は、通電する電流の周波数と最も大きな因果関係があり、６００Ｈｚ以上においては、０．８μｍ／ｍｉｎという従来法を越える成膜速度が得られることが実施例を通じて実証された。
【００２１】
【発明の効果】
本発明によれば、アルミニウム材又はアルミニウム合金材に陽極酸化処理を施す場合に、低コストでかつ容易に、陽極酸化皮膜の成膜速度を大幅に向上させることができる。
【図面の簡単な説明】
【図１】高周波電圧に直流電圧を重畳させた、陽極酸化処理に用いる印加電圧の電解波形を示す概略図である。
【図２】電流の周波数と陽極酸化処理皮膜の成膜速度との関係を示すグラフである。
【図３】陽極酸化処理の電解時間と成膜速度との関係を示すグラフである。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a surface treatment method for forming an anodic oxide film having excellent corrosion resistance and wear resistance on a surface of an aluminum material or an aluminum alloy material in a short time.
[0002]
[Prior art]
BACKGROUND ART Conventionally, a surface treatment called anodizing treatment has been performed on the surface of an aluminum member or an aluminum alloy member as an object to be processed for the purpose of improving corrosion resistance and wear resistance and coloring the object. The anodizing treatment is performed by immersing the object to be treated in an electrolytic bath such as diprotic acid such as sulfuric acid, phosphoric acid, oxalic acid, and chromic acid, and performing the electrolytic treatment for a certain period of time. This is a method of forming an oxide film called "Oxide film". This alumite film is composed of a dense barrier layer and a porous layer, and has a composition of amorphous Al ₂ O ₃ .
[0003]
However, in an aluminum cast material and an aluminum die-cast material, a current does not easily flow due to a large amount of alloy components such as Si, Cu, and Fe, and a film can be formed in a short time by the anodic oxidation treatment method similar to the wrought material. Was difficult.
In order to perform the anodic oxidation treatment in a short time, it is necessary to increase the current density. When a high voltage is applied in order to obtain a high current density with the aluminum casting material and the aluminum die casting material in the direct current method, an increase in the voltage causes an increase in Joule heat generated in the barrier layer. As a result, a portion where an oxide film is not formed, which is called "burning of an oxide film", is likely to occur. Therefore, in the direct current method, it is generally difficult to form a normal thick anodized film on an aluminum casting material and an aluminum die casting material in a short time.
[0004]
On the other hand, the burning has been conventionally prevented by a method of changing an electrolytic waveform at the time of anodizing treatment, for example, an AC method, a pulse electrolytic method, a polarity inversion pulse method (PR electrolytic method), an AC / DC superposition electrolytic method, or the like. That is being done. These methods are a method of anodizing with a non-stationary voltage or a non-stationary current, in which Joule heat generated in the barrier layer when no anodizing current is flowing is diffused into the object to be treated and the solution, and further reacted. Since the electrolyte concentration in the portion recovers, the film formation rate can be improved. However, these methods are often performed at a "commercial frequency" such as 50 Hz or 60 Hz, and at this frequency, there is a problem that the film forming speed of an aluminum die-casting material containing many alloying elements is particularly low.
Further, a method in which a current in which an alternating current and a pulsed direct current are superimposed is passed through an electrolytic bath for anodizing treatment has been conventionally used. However, this method has the following problems.
(1) Since the pulse current is superimposed on the AC current, it is difficult to control the waveform in a high frequency region. Further, the structure of the device used for the anodizing treatment becomes complicated.
(2) Since the pulse current is superimposed on the alternating current, the electrolysis waveform becomes complicated, the current control becomes difficult in anodic oxidation, and it is difficult to find optimal electrolysis conditions.
For these reasons, in the conventional anodic oxidation treatment, there is a problem that a low current density, for example, only about 3 A / dm ² can be obtained, and the film forming rate is as slow as 0.5 to 0.7 μm / min.
[0005]
Further, as a conventional example in which an electrolytic waveform at the time of anodic oxidation is changed, there is a technique described in JP-A-2000-282294. This is a method in which an AC / DC superposition method in which an AC current is superimposed on a DC current is applied, and an AC component does not include a negative component, and the AC component is processed under electrolysis conditions in which the DC component is 5% or more of the DC component. is there. The purpose of this technique is to obtain a film structure that is resistant to thermal cracking, and although the frequency of the AC component is good at 100 Hz or higher, the improvement effect is usually sufficient even at 60 Hz or lower. . However, there were the following problems.
(3) The preferred current density in the current control is as low as 0.1 to ^{2 A} / dm ^2, and at this current density, the film forming rate is very slow for the ADC12 material, which is one of the aluminum alloys.
(4) In the case of voltage control, even if anodizing treatment is performed on the ADC12 material at a frequency of 60 Hz or less, which is considered to have an improvement effect, the film forming speed does not increase.
[0006]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION The present invention solves the above-described problems, and in the case where an anodizing treatment is performed on the surface of an aluminum material or an aluminum alloy material as an object to be treated, it is possible to improve the film forming speed of the anodized film at low cost. It is intended to provide a processing method.
[0007]
[Means for Solving the Problems]
The anodic oxidation method according to the present invention is characterized in that an aluminum material or an aluminum alloy material to be processed is immersed in an anodizing bath, and a high-frequency current of 200 to 5000 Hz is applied to the anodized material to thereby perform anodizing on the workpiece. This is a method of performing processing.
The treatment bath may be a single bath or a mixed bath of diprotic acids such as sulfuric acid, oxalic acid, phosphoric acid, and chromic acid, or a bath in which an organic acid or a compound that increases dissolved aluminum ions is added to these single or mixed baths. Can be suitably used. The diprotic acid is, for example, an acid having two hydrogen ions such as sulfuric acid, oxalic acid, phosphoric acid, and chromic acid. In the present invention, a diprotic acid alone or in a mixed bath, and further, an organic acid or a bath. You may add the compound etc. which increase an existing aluminum ion.
[0008]
In this processing method, the current frequency is increased from the conventional 50 to 60 Hz to 200 to 5000 Hz, so that the object to be processed can be anodized at a low voltage and a large current, that is, at a high current density. Is dramatically improved. The reason why the film formation rate is improved at a high frequency is due to the “skin effect”. The skin effect is a phenomenon in which when the frequency is increased, current concentrates near the surface of the metal. By this effect, the current density in the vicinity of the surface of the object where the anodic oxidation reaction occurs is particularly increased, so that the film formation speed is improved. The amount of Joule heat generated is low because of the low voltage even at high current density, and the heat generation is highest on the outermost surface of the object to be processed, which has a high cooling effect by the electrolytic solution. In addition, a high film forming rate can be obtained.
However, if the frequency is set too high, the diffusion of Joule heat and the recovery of the concentration of the electrolyte become insufficient, and the film formation rate is reduced. Further, when processing a large number of works, a power supply capable of outputting a large current of several thousand amps is required, but a power supply capable of outputting a large current at a high frequency becomes extremely expensive. Furthermore, since the impedance of the wiring increases with high-frequency current, the voltage drop in the wiring between the power supply and the processing object increases, which not only increases the energy loss but also increases the wiring length from the power supply to the processing object. There is a problem of being restricted. The upper limit of the frequency is 5000 Hz in consideration of such an influence on film formation, power supply manufacturing cost, and energy loss.
Thus, it is possible to form the anodic oxide film at high speed while preventing the anodic oxide film from burning and suppressing a rise in the temperature of the treatment bath.
As described above, the production efficiency can be greatly improved by performing the anodic oxidation treatment of the aluminum material or the aluminum alloy material at a high speed, and therefore, the production cost of the rust preventive member and the sliding member using the object to be treated is increased. Can be reduced. In addition, high-speed anodic oxidation of an aluminum alloy material containing a large amount of alloying elements such as Si, Cu, and Fe, which has been conventionally difficult, can be performed.
[0009]
In one embodiment of the anodic oxidation method according to the present invention, the frequency of the high-frequency current can be set to 600 to 2000 Hz.
With this frequency, the anodic oxidation treatment can be performed at a higher speed than in the range of 200 to 5000 Hz described above.
Further, in another aspect of the anodizing treatment method according to the present invention, at least one of a sine wave, a rectangular wave, and a triangular wave can be used as the electrolytic waveform of the high-frequency current.
Further, still another aspect of the anodizing treatment method according to the present invention is a method of applying a direct current superimposed on the high-frequency current.
[0010]
Still another embodiment of the anodizing method according to the present invention is a method in which the anodizing bath contains diprotic acid.
In the present invention, a single bath or a mixed bath of diprotic acids, and further, an organic acid, a compound for increasing the amount of aluminum ions present in the bath, or the like may be added. As the conditions of the treatment bath, for example, the concentration of the treatment bath is preferably 3 to 30% for a sulfuric acid bath, and 1 to 5% for an oxalic acid bath. In an oxalic acid bath, the temperature is preferably 10 to 60C.
Still another embodiment of the anodizing treatment method according to the present invention is a method including at least one of sulfuric acid, oxalic acid, phosphoric acid, and chromic acid as the diprotic acid. The present invention is an aluminum material or an aluminum alloy material processed by any of the above-described methods.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
The anodizing treatment method of the present invention is characterized in that an aluminum material or an aluminum alloy material to be treated is immersed in an electrolytic bath based on diprotic acid, and a high-frequency current of 200 to 5000 Hz is applied to the object to be treated. Is a surface treatment method for performing anodizing treatment on the surface. As the current, a DC current may be superimposed on a high-frequency current of 200 to 5000 Hz. As the electrolysis waveform, various waveforms such as a sine wave, a triangular wave, and a rectangular wave can be used.
[0012]
FIG. 1 shows an electrolytic waveform in which a DC current is superimposed on a high-frequency current. In the electrolysis waveform, a DC voltage of 19.8 V is superimposed on a high-frequency current having a frequency of 1000 Hz and a voltage of ± 20 V. This electrolysis waveform does not cause disturbance of the waveform in a high frequency range, and the current control is easy. Therefore, the electrolysis waveform and the current shown in the problems (1) and (2) described in the related arts are used. Problems related to control can be solved. Further, a high current density of 3 A / dm ² or more can be easily obtained at a low voltage because of a high frequency current of 200 Hz or more. For this reason, it is possible to generate an anodic oxide film at a deposition rate of 1 μm / min or more even with ADC12 material, which is said to be most difficult to form an anodic oxide film by increasing the frequency. The problem described in 4) can be overcome.
[0013]
As the electrolysis control method in the present invention, any of a voltage control method and a current control method can be used. FIG. 1 described above shows the shape of the electrolysis waveform in the voltage control. This voltage is set in a range in which burning does not occur in consideration of the material of the object to be processed, the composition of the electrolytic solution, and the bath temperature. For example, when anodic oxidation is performed with a high-frequency current of 1000 Hz in a sulfuric acid bath, the preferred voltage range is a positive peak value of 30 to 70 V and a negative peak value of -10 to 0 V.
As the bath solution of the treatment bath, a single bath or a mixed bath of diprotic acid, which is an acid having two hydrogen ions, can be suitably used. That is, a single bath or a mixed bath of diprotic acid, for example, sulfuric acid, oxalic acid, phosphoric acid, chromic acid, and the like, and further, an organic acid and a compound that increases the amount of aluminum ions in the bath may be added. The bath concentration and bath temperature may be the same as those in the prior art, and in the case of a sulfuric acid bath, the concentration may be 3 to 30% and the bath temperature may be in the range of -5 to 40 ° C. It is also desirable to stir the bath solution, cool the surface to be treated, recover the concentration of the electrolyte, and remove bubbles by a method conventionally used.
[0014]
【Example】
Next, the present invention will be specifically described through examples. In this example, the film growth rate was measured when the frequency was changed by voltage control to keep the high-frequency and DC voltages constant. This is because the change in the ease of current flow when the frequency is changed can be seen by the voltage control.
[0015]
[Example 1]
As shown in Table 1, ADC12 material, which is one kind of aluminum alloy, was used as a workpiece, and the workpiece was immersed in a sulfuric acid single bath at a bath temperature of 17 ° C. at a concentration of 10%. In this state, a sine wave high-frequency voltage having a frequency of 200 Hz and a voltage of ± 20 V with a DC voltage of 19.8 V superimposed thereon was applied for 5 minutes to perform anodizing treatment.
[Examples 2 to 16]
In Examples 2 to 16, only the frequency of the high-frequency current was changed to 300 to 2000 Hz, and the other processing conditions were the same as those in Example 1.
[0016]
[Examples 17 and 18]
In Examples 17 and 18, the electrolytic treatment time was changed to 10 minutes and 20 minutes, respectively, and the other treatment conditions were the same as in Example 2.
In general, the growth rate of the anodized film is said to be proportional to the current density.In the anodizing treatment by voltage control, the current density decreases because the insulator film is formed as the electrolysis time elapses, The growth rate is also expected to be slow. Therefore, in Example 2 in which the anodic oxidation treatment was performed at a frequency of 1000 Hz, only the electrolytic treatment time was changed to 10 minutes (Example 17) or 20 minutes (Example 18), and the growth of the anodic oxide film with respect to the treatment time. The change in speed was measured.
[0017]
[Comparative Example 1]
In Comparative Examples 1 to 4, the anodizing treatment was performed by applying an alternating current or a direct current having a frequency of less than 200 Hz.
First, in Comparative Example 1, an ADC12 material was used as a treatment object, and the treatment object was immersed in a sulfuric acid single bath at a bath temperature of 17 ° C. at a concentration of 10%. In this state, an anodization treatment was performed by applying a DC voltage of 15 V superimposed on a high frequency voltage of a sine wave having a frequency of 60 Hz and a voltage of ± 10 V for 5 minutes. In addition, this comparative example 1 was implemented according to the Example described in Unexamined-Japanese-Patent No. 2000-282294.
[0018]
[Comparative Example 2]
In Comparative Example 2, the applied voltage was a DC voltage of 40 V, and other processing conditions were the same as those in Comparative Example 1.
[Comparative Examples 3 and 4]
Further, for Comparative Examples 3 and 4, anodizing treatment was performed under the conditions shown in Table 1.
[Table 1]

[0019]
Hereinafter, the results of the example and the comparative example will be described.
First, looking at the relationship between the film forming speed and the frequency of the applied current, it was found that the film forming speed improved almost linearly with the frequency, as is clear from FIG. In other words, the film forming speed is 0.1 μm / min at a frequency of 50 Hz in Comparative Example 3 (reference U), whereas the film forming speed is 0.4 μm / min at 200 Hz in Example 1 (reference A). Rose. 2 and 3, as described in the rightmost column of Table 1, the first embodiment corresponds to the reference A, and the second embodiment corresponds to the reference B.
[0020]
In Example 5 (reference F), anodizing treatment was performed at 600 Hz for 5 minutes at 0.8 μm / min, and at 1000 Hz in Example 9 (reference I), 1.1 μm / min, and in Example 16 (reference P). It was found that if the frequency was increased to 1.6 μm / min at 2000 Hz, the film formation rate was increased.
Further, as shown in FIG. 3, in Examples 17 and 18, since the anodic oxidation treatment was performed by voltage control, it was expected that the film formation rate would gradually decrease as the electrolysis time was lengthened. It was almost constant regardless. Therefore, even if the electrolysis time was lengthened, the growth rate of the film did not change, and it was confirmed that a high-speed growth of a thick film was possible according to the present invention.
In summary, the film formation rate in the anodic oxidation treatment has the greatest causal relationship with the frequency of the supplied current, and at 600 Hz or more, a film formation rate of 0.8 μm / min, which exceeds the conventional method, may be obtained. This has been demonstrated through examples.
[0021]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, when performing an anodizing process to an aluminum material or an aluminum alloy material, the film-forming rate of an anodized film can be significantly improved at low cost and easily.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an electrolytic waveform of an applied voltage used for an anodizing treatment in which a DC voltage is superimposed on a high-frequency voltage.
FIG. 2 is a graph showing a relationship between a current frequency and a film forming speed of an anodized film.
FIG. 3 is a graph showing a relationship between an electrolysis time of an anodizing treatment and a film forming rate.

Claims

An aluminum alloy material characterized by subjecting an aluminum material or an aluminum alloy material to be processed to an anodizing treatment by immersing the aluminum material or aluminum alloy material in a processing bath and applying a high-frequency current of 200 to 5000 Hz. Anodizing treatment method.

2. The method according to claim 1, wherein the frequency of the high-frequency current is 600 to 2000 Hz.

3. The method according to claim 1, wherein an electrolytic waveform of the high-frequency current is at least one of a sine wave, a rectangular wave, and a triangular wave.

The method according to any one of claims 1 to 3, wherein a direct current is superimposed on the high-frequency current and energized.

5. The method according to claim 1, wherein the treatment bath contains a diprotic acid.

6. The method according to claim 5, wherein the diprotic acid includes at least one of sulfuric acid, oxalic acid, phosphoric acid, and chromic acid.

An aluminum material or an aluminum alloy material processed by the method according to any one of claims 1 to 6.