JP3657733B2 - Surface-treated film-coated member having excellent corrosion resistance and method for forming surface-treated film - Google Patents
Surface-treated film-coated member having excellent corrosion resistance and method for forming surface-treated film Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、含Siアルミニウム合金（4000系合金）表面の耐食性に優れた表面処理皮膜およびその皮膜形成方法の技術分野に属するものである。
【０００２】
【従来の技術】
従来、Al合金の耐食性を向上させる皮膜としてクロメート皮膜が広く使用されており、1000系、3000系等の合金については耐食性向上に有用な皮膜である。しかし、クロメート皮膜はその処理液中にフッ化物イオン、クロム酸イオンを含むため環境負荷が大きく、これら環境に有害なイオンを含まない処理液による処理皮膜が種々提案されている。例えば、非クロメート皮膜として、特開昭54-145337 号公報にLi塩処理皮膜や、Mg塩処理皮膜などが提案されている。
【０００３】
【発明が解決しようとする課題】
クロメート処理皮膜は1000系、3000系等のAl合金に対しては耐食性向上に有効である。しかし、4000系Al合金においては、晶出Si相とAl相が共存し、晶出Si相はAl相に比較して処理液に溶解しにくいため、晶出Si相上に形成される皮膜はAl相上の皮膜に比べて薄く、実使用環境においては、晶出Si相をカソードとしてAl相がアノード溶解するため、十分な耐食性が得られない。また、4000系Al合金においては、上記のLi塩処理皮膜やMg塩処理皮膜などの非クロメート皮膜においても同様の問題点が生じ、耐食性の向上は困難である。
【０００４】
本発明は、上記の問題点を解決するためになされたもので、環境に有害なイオンを含まない処理液を用い、4000系Al合金の表面に、Si相とAl相の両相に均一なクロメート皮膜と同等以上の耐食性に優れた表面処理皮膜を形成する方法を提供することを目的とする。
【０００５】
【課題を解決するための手段】
本発明者らは、Si相とAl相の両相に均一な表面処理皮膜を形成し、晶出Si相でのカソード反応を抑制する手段について鋭意研究した結果、Li塩処理皮膜中に Li2〔Al2(OH)6〕2 ・CO3 ・nH2Oを十分に生成させればよいという知見を得て本発明に至ったものである。
【０００６】
その要旨は、4000系Al合金部材表面の皮膜が、C を原子分率で0.05≦C/(Al+Li+C) ≦0.14、Liを原子分率で 0.2≦Li/(Al+Li+C)≦0.3 の範囲で含有するCO3 を含むLiとAlの複合酸化物を主体とする耐食性に優れた表面処理皮膜被覆部材で、さらに表面処理皮膜中に、Si、Mg、Mn、Caのうちから選んだ少なくとも１種を、原子分率で0.01≦Ｍ/(Al+Li+C+Ｍ) ≦0.05の範囲で含有する。但しＭはSi、Mg、Mn、Caのうちから選んだ元素を表す。また、表面処理皮膜の膜厚は100nm 以上である。
【０００７】
表面処理皮膜の形成方法は、 0.1〜0.2mol/lのLiイオン、 0.1〜0.5mol/lのCO3 イオンおよび 1×10-9〜 1×10-3mol/l のAlイオンを含有するpHが 9.5〜10.9の溶液中に4000系Al合金部材を浸漬することを特徴とする耐食性に優れた表面処理皮膜の形成方法で、溶液中に、さらにSi、Mg、Mn、Caのうちから選んだ少なくとも１種の塩を、 0.001〜0.5mol/lの範囲で含有する。また、4000系Al合金部材を浸漬する溶液温度は20〜60℃である。
【０００８】
従来、Li塩処理皮膜はLiH(AlO2)2、 Li2〔Al2(OH)6〕2 ・CO3 ・nH2OとAl(OH)3 の混合物であるが、4000系Al合金のような表面に共晶Siと共晶Alとが混在する材料に対しては、共晶Si部の被覆が十分でなく、耐食性を付与することが困難であった。本発明における皮膜も上記と同様な混合物であるが、皮膜中の Li2〔Al2(OH)6〕2 ・CO3 ・nH2Oの量に注目し、皮膜中に含有するC の範囲を原子分率で、0.05≦C/(Al+Li+C) ≦0.14に限定することにより、4000系Al合金のような材料に対しても優れた耐食性を付与することができる。C の含有量が原子分率で0.05未満では、皮膜は主にLiH(AlO2)2とAl(OH)3 とからなり、十分な Li2〔Al2(OH)6〕2 ・CO3 ・nH2Oが生成されないため耐食性が低下する。一方、C の含有量が原子分率で0.14を超えると、皮膜中にLi2CO3などの溶解性炭酸塩が混入するため耐食性が低下する。
【０００９】
皮膜中に含有するLiの範囲を原子分率で、 0.2≦Li/(Al+Li+C)≦0.3 に限定する。その理由は、Liの含有量が原子分率で 0.2未満では、皮膜は主にAl(OH)3 からなり、皮膜の溶解度が大きくなり耐食性が低下し、一方、 0.3を超えると、皮膜中にLiOH、Li2CO3などの溶解性の物質が混入して耐食性を示さないからである。
【００１０】
さらに、皮膜中のSi、Mg、Mn、Ca等のイオンの存在は、例えばSiは皮膜から溶出してインヒビターとして作用し、Mg、Mn、Caは皮膜中に難溶性の酸化物を形成し耐食性に寄与する。これら元素の皮膜中の含有量は原子分率で0.01≦Ｍ/(Al+Li+C+Ｍ) ≦0.05の範囲に限定する。その理由は、Si、Mg、Mn、Caのうちから選んだ少なくとも１種の含有量が原子分率で0.01未満では上記の効果を示さず、一方、0.05を超えると皮膜中での上記の効果が飽和するからである。
【００１１】
表面処理皮膜の膜厚は、100nm 未満では耐食性が十分でなく、Cl- イオン等により局所的に皮膜が破壊され、かえって深い孔食を生ずる。したがって、表面処理皮膜の膜厚は100nm 以上に限定する。
【００１２】
次に、表面処理皮膜形成方法について説明する。
既に述べたように、4000系Al合金では、耐食性向上のためには表面の晶出Si相とAl相の両相に均一に皮膜を形成することが必要であるが、従来法においては、Al相の溶解速度がSi相よりも大きいため、皮膜が不均一に形成され腐食の抑制効果が得られなかった。
【００１３】
本発明法では、CO3 イオンの水酸化アルミゲル安定化作用によるAlの溶解生成物を安定化、および溶液中にAlイオンを含有させることによりAl相の溶解を抑制することにより、腐食抑制効果を有する均一皮膜形成が可能となる。さらにLi、Mg、Mn、Ca等のイオンを溶液中に含有することにより、それらの酸化物を皮膜中に取り込むことができ、さらに耐食性を向上させることができる。
【００１４】
本発明法は１溶液処理であるため、クロメート処理等の従来法と置換し易く、かつ最終製品にも適用可能であり、処理液中に有害なイオンを含まないため、環境負荷も小さいという特徴を有する。
【００１５】
溶液中のLiイオン濃度は、0.1mol/l未満では不溶性の Li2〔Al2(OH)6〕2 ・CO3 ・nH2Oなどの皮膜が形成されず、耐食性を有する均一皮膜が形成されない。一方、0.2mol/lを超えるとその効果は飽和する。したがって、溶液中のLiイオン濃度は 0.1〜0.2mol/lの範囲に限定する。
【００１６】
溶液中のCO3 イオン濃度は、0.1mol/l未満ではAl合金近傍の水酸化アルミゲルを十分に安定化できずAl相の溶解を抑制できない。一方、0.5mol/lを超えると皮膜中にLi2CO3等の溶解性炭酸塩が生じるため、耐食性が低下する。したがって、溶液中のCO3 イオン濃度は 0.1〜0.5mol/lの範囲に限定する。
【００１７】
溶液中のAlイオン濃度は、 1×10-9mol/l 未満ではAl合金近傍で溶出Alイオン濃度が飽和するまでに要するAl相溶解量が多く、均一皮膜が形成されない。一方、 1×10-3mol/l を超えると処理液が白濁、または処理液中に沈殿が生じ液中のAlイオンが飽和するため、皮膜形成に必要なAl合金表面からのAlイオンの溶出が生じにくくなり皮膜の形成速度が小さく実用的でない。したがって、溶液中のAlイオン濃度は 1×10-9〜 1×10-3mol/l の範囲に限定する。
【００１８】
溶液のpHは、9.5 未満ではAl相の溶解が不十分で皮膜の形成が行われない。一方、10.9を超えるとAl相の溶解速度が大きくなり過ぎるため均一に皮膜が形成されない。したがって、溶液のpHは 9.5〜10.9の範囲に限定する。
【００１９】
溶液中のSi、Mg、Mn、Caのうちから選んだ少なくとも１種の塩の濃度は、0.001mol/l未満では含有の効果は認められない。Si塩は0.5mol/lを超えると溶液の粘度が増加し、かつ処理液のpHを10.9以下に維持できないために均一な皮膜が形成されない。また、Mg、Mn、Ca塩においては、0.5mol/lを超えて含有させるにはpHを 9.5未満に下げる必要がある。したがって、溶液中のSi、Mg、Mn、Caのうちから選んだ少なくとも１種の塩の濃度は、 0.001〜0.5mol/lの範囲に限定する。
【００２０】
溶液の温度は20〜60℃の範囲に限定する。その理由は、溶液の温度が上昇すると皮膜形成速度は大きくなり、60℃を超えても皮膜形成は行われるが、Al相の溶解速度も大きくなるため均一な皮膜が形成されず、また、20℃未満では皮膜形成速度が著しく小さくなり、実用的でないからである。
【００２１】
【発明の実施の形態】
以下に、実施例を挙げて本発明を説明する。
実施例１
芯材 A3003の両面にろう材BA4004をクラッドしたブレージングシートにろう付け熱処理を施した後、アルカリ脱脂（ファインクリーナー315 、70℃、5 分浸漬）→酸洗（15％硝酸酸洗、室温、30秒浸漬）後、表１に示す条件で皮膜形成処理を行い、形成された皮膜厚さ、カソード分極および塩水噴霧、湿潤、乾燥を１サイクルとするＣＣＴ試験にて耐食性を評価した。皮膜厚さ、電位-1200mVvsSCEでのカソード電流密度、およびＣＣＴ試験 300サイクル終了後の孔食深さを表２に示す。
【００２２】
表２に示すように、本発明例の番号１〜５は、クロメート処理に比較してカソード反応が抑制され、孔食深さも減少していることが分かる。また、皮膜厚さが100nm 未満の場合（番号18）および皮膜中のLi/(Al+Li+C)、C/(Al+Li+C) が本発明の限定範囲から逸脱している場合（番号６〜17）においては、カソード電流密度および孔食深さはクロメート処理（番号20）と同程度で耐食性の改善効果は認められない。
【００２３】
【表１】
【表２】
実施例２
芯材 A3003の両面にろう材BA4004をクラッドしたブレージングシートにろう付け熱処理を施した後、アルカリ脱脂（ファインクリーナー315 、70℃、5 分浸漬）→酸洗（15％硝酸酸洗、室温、30秒浸漬）後、表３および表４に示す処理液にて皮膜形成処理を行い、形成された皮膜について、カソード分極および塩水噴霧、湿潤、乾燥を１サイクルとするＣＣＴ試験にて耐食性を評価した。浸漬電位におけるカソード電流密度、およびＣＣＴ試験 300サイクル終了後の孔食深さを表３および表４に併記する。
【００２６】
表３および表４に示すように、本発明例の番号１〜５は、比較例のクロメート処理（番号49）に比較してカソード反応が抑制され、孔食深さも減少していることが分かる。Liイオン濃度が0.1mol/l未満の比較例（番号６〜10）または0.2mol/l超えの比較例（番号13〜17）は、カソード電流密度および孔食深さは無処理材（番号48）やクロメート処理材（番号49）と同程度で耐食性の改善効果は認められない。
【００２７】
また、CO3 イオン濃度が0.1mol/l未満（番号11）または0.5mol/l超え（番号12）の場合においても耐食性の改善効果は認められない。Alイオン濃度が 1×10-9mol/l 未満（番号18〜22）または 1×10-3mol/l 超え（番号23〜27）の場合、およびpHが 9.5未満（番号33〜37）または10.9超え（番号28〜32）の場合は、皮膜厚さが薄く耐食性の改善効果は認められない。また、処理時の溶液温度が20℃未満（番号38〜42）または60℃超え（番号43〜47）の場合も皮膜厚さが薄く耐食性の改善効果は認められない。
【００２８】
【表３】
【表４】
実施例３
芯材 A3003の両面にろう材BA4004をクラッドしたブレージングシートにろう付け熱処理を施した後、アルカリ脱脂（ファインクリーナー315 、70℃、5 分浸漬）→酸洗（15％硝酸酸洗、室温、30秒浸漬）後、表５に示す処理液にて皮膜形成処理を行い、形成された皮膜厚さ、カソード分極および塩水噴霧、湿潤、乾燥を１サイクルとするＣＣＴ試験にて耐食性を評価した。浸漬電位におけるカソード電流密度、およびＣＣＴ試験 300サイクル終了後の孔食深さを表６に示す。
【００３１】
表６に示すように、例えば、珪酸塩を添加した本発明例の番号51〜53は、珪酸塩無添加に比較して、さらにカソード反応が抑制され、孔食深さも減少していることが分かる。この効果は、Si/(Al+Li+C+Si) が0.01未満の本発明例の番号50では認められない。また、Si/(Al+Li+C+Si) が0.05を超える比較例（番号54）の場合は、皮膜厚さが減少し、カソード電流密度、孔食深さとも無処理材（表２、番号19）と同程度である。また、これらの効果が認められる珪酸塩濃度は0.001mol/l以上、0.5mol/l以下の範囲である。Mn、MgおよびCa塩添加の場合も同様の結果である。
【００３２】
【表５】
【表６】
【発明の効果】
以上、述べたところから明らかなように、本発明は環境に有害な物質を含まない処理溶液によってAl合金部材表面に皮膜を形成し、例えば、4000系Al合金の晶出Siで生じるカソード反応を抑制することにより、クロメート処理材と同等以上の耐食性を得ることができる。このため、表面に4000系Al合金をクラッドしたブレージングシートを用いた部品（自動車用エバポレータ等）を最終製品に組み上げた後に表面処理することが可能となり、それらの耐食性を向上させることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention belongs to the technical field of a surface treatment film having excellent corrosion resistance on the surface of a silicon-containing aluminum alloy (4000 series alloy) and a method for forming the film.
[0002]
[Prior art]
Conventionally, a chromate film has been widely used as a film for improving the corrosion resistance of Al alloys, and alloys such as 1000 series and 3000 series are useful films for improving the corrosion resistance. However, since the chromate film contains fluoride ions and chromate ions in the treatment liquid, it has a large environmental load, and various treatment films using treatment liquids that do not contain ions harmful to the environment have been proposed. For example, as a non-chromate film, Japanese Patent Application Laid-Open No. 54-145337 proposes a Li salt-treated film, an Mg salt-treated film, and the like.
[0003]
[Problems to be solved by the invention]
The chromate-treated film is effective for improving corrosion resistance for Al alloys such as 1000 series and 3000 series. However, in 4000 series Al alloys, the crystallized Si phase and the Al phase coexist, and the crystallized Si phase is less soluble in the processing solution than the Al phase, so the film formed on the crystallized Si phase is It is thinner than the film on the Al phase, and in an actual use environment, the Al phase is anodicly dissolved using the crystallized Si phase as a cathode, so that sufficient corrosion resistance cannot be obtained. In addition, in the 4000 series Al alloy, the same problem occurs in the non-chromate film such as the above-mentioned Li salt-treated film and Mg salt-treated film, and it is difficult to improve the corrosion resistance.
[0004]
The present invention has been made to solve the above-described problems, and uses a treatment solution that does not contain ions harmful to the environment. The surface of the 4000 series Al alloy is uniform in both the Si phase and the Al phase. It aims at providing the method of forming the surface treatment film | membrane excellent in the corrosion resistance equivalent to or better than the chromate film.
[0005]
[Means for Solving the Problems]
As a result of intensive research on means for forming a uniform surface treatment film on both the Si phase and the Al phase and suppressing the cathode reaction in the crystallized Si phase, the present inventors have found that Li 2 in the Li salt treatment film. The inventors have obtained the knowledge that [Al 2 (OH) 6 ] 2 .CO 3 .nH 2 O should be sufficiently generated, and have reached the present invention.
[0006]
The gist is that the coating on the surface of 4000 series Al alloy members has C as atomic fraction 0.05 ≦ C / (Al + Li + C) ≦ 0.14, Li as atomic fraction 0.2 ≦ Li / (Al + Li + C ) ≤ ≦ 0.3 Surface treatment film covering member with excellent corrosion resistance, mainly composed of Li and Al composite oxide containing CO 3 contained in the range, and in the surface treatment film, Si, Mg, Mn, Ca At least one selected from the group consisting of 0.01 ≦ M / (Al + Li + C + M) ≦ 0.05 in terms of atomic fraction. M represents an element selected from Si, Mg, Mn, and Ca. The film thickness of the surface treatment film is 100 nm or more.
[0007]
The surface treatment film is formed by pH 0.1 to 0.2 mol / l Li ion, 0.1 to 0.5 mol / l CO 3 ion and 1 × 10 −9 to 1 × 10 −3 mol / l Al ion. Is a method of forming a surface-treated film with excellent corrosion resistance, characterized by immersing 4000 series Al alloy members in a solution of 9.5 to 10.9, selected from Si, Mg, Mn, and Ca in the solution. At least one salt is contained in the range of 0.001 to 0.5 mol / l. Moreover, the solution temperature which immerses a 4000 series Al alloy member is 20-60 degreeC.
[0008]
Conventionally, the Li salt treatment film is a mixture of LiH (AlO 2 ) 2 , Li 2 [Al 2 (OH) 6 ] 2 .CO 3 .nH 2 O and Al (OH) 3 , but like 4000 series Al alloys. For a material in which eutectic Si and eutectic Al are mixed on a rough surface, the eutectic Si portion is not sufficiently covered, and it is difficult to impart corrosion resistance. The film in the present invention is a mixture similar to the above, but paying attention to the amount of Li 2 [Al 2 (OH) 6 ] 2 .CO 3 .nH 2 O in the film, the range of C contained in the film is determined. By limiting the atomic fraction to 0.05 ≦ C / (Al + Li + C) ≦ 0.14, excellent corrosion resistance can be imparted even to materials such as 4000 series Al alloys. When the C content is less than 0.05 in atomic fraction, the film is mainly composed of LiH (AlO 2 ) 2 and Al (OH) 3, and sufficient Li 2 [Al 2 (OH) 6 ] 2 .CO 3. Since nH 2 O is not generated, corrosion resistance is reduced. On the other hand, if the C content exceeds 0.14 in atomic fraction, the corrosion resistance deteriorates because soluble carbonates such as Li 2 CO 3 are mixed in the film.
[0009]
The range of Li contained in the film is limited to 0.2 ≦ Li / (Al + Li + C) ≦ 0.3 in terms of atomic fraction. The reason for this is that when the Li content is less than 0.2 in atomic fraction, the film is mainly composed of Al (OH) 3 , so that the solubility of the film increases and the corrosion resistance decreases. This is because soluble substances such as LiOH and Li 2 CO 3 are mixed and do not exhibit corrosion resistance.
[0010]
Furthermore, the presence of ions such as Si, Mg, Mn, and Ca in the film, for example, Si elutes from the film and acts as an inhibitor, and Mg, Mn, and Ca form a poorly soluble oxide in the film, resulting in corrosion resistance. Contribute to. The content of these elements in the film is limited to the atomic fraction of 0.01 ≦ M / (Al + Li + C + M) ≦ 0.05. The reason is that when the content of at least one selected from Si, Mg, Mn, and Ca is less than 0.01 in terms of atomic fraction, the above effect is not exhibited. Is saturated.
[0011]
If the film thickness of the surface-treated film is less than 100 nm, the corrosion resistance is not sufficient, and the film is locally destroyed by Cl - ions or the like, and deep pitting corrosion occurs. Therefore, the film thickness of the surface treatment film is limited to 100 nm or more.
[0012]
Next, the surface treatment film forming method will be described.
As already mentioned, in the 4000 series Al alloy, it is necessary to form a uniform film on both the crystallized Si phase and the Al phase on the surface in order to improve the corrosion resistance. Since the dissolution rate of the phase was higher than that of the Si phase, the film was formed unevenly, and the effect of inhibiting corrosion was not obtained.
[0013]
The method of the present invention stabilizes the Al dissolution product by stabilizing the aluminum hydroxide gel of CO 3 ions, and suppresses the dissolution of the Al phase by containing Al ions in the solution, thereby suppressing the corrosion effect. It is possible to form a uniform film. Furthermore, by containing ions such as Li, Mg, Mn, and Ca in the solution, these oxides can be incorporated into the film, and the corrosion resistance can be further improved.
[0014]
Since the method of the present invention is a one-solution treatment, it can be easily replaced with a conventional method such as chromate treatment, can be applied to the final product, and does not contain harmful ions in the treatment solution. Have
[0015]
If the Li ion concentration in the solution is less than 0.1 mol / l, an insoluble film such as Li 2 [Al 2 (OH) 6 ] 2 · CO 3 · nH 2 O will not be formed, and a uniform film with corrosion resistance will not be formed. . On the other hand, if it exceeds 0.2 mol / l, the effect is saturated. Therefore, the Li ion concentration in the solution is limited to the range of 0.1 to 0.2 mol / l.
[0016]
If the CO 3 ion concentration in the solution is less than 0.1 mol / l, the aluminum hydroxide gel near the Al alloy cannot be sufficiently stabilized, and the dissolution of the Al phase cannot be suppressed. On the other hand, if it exceeds 0.5 mol / l, a soluble carbonate such as Li 2 CO 3 is generated in the film, so that the corrosion resistance is lowered. Therefore, the CO 3 ion concentration in the solution is limited to the range of 0.1 to 0.5 mol / l.
[0017]
If the Al ion concentration in the solution is less than 1 × 10 -9 mol / l, a large amount of Al phase is required for the elution Al ion concentration to saturate in the vicinity of the Al alloy, and a uniform film cannot be formed. On the other hand, if it exceeds 1 × 10 -3 mol / l, the treatment liquid becomes cloudy or precipitates in the treatment liquid and the Al ions in the liquid are saturated. Is difficult to occur and the formation rate of the film is small, which is not practical. Therefore, the Al ion concentration in the solution is limited to the range of 1 × 10 −9 to 1 × 10 −3 mol / l.
[0018]
If the pH of the solution is less than 9.5, the Al phase is not sufficiently dissolved and no film is formed. On the other hand, if it exceeds 10.9, the dissolution rate of the Al phase becomes too high, and a film is not uniformly formed. Therefore, the pH of the solution is limited to the range of 9.5 to 10.9.
[0019]
If the concentration of at least one salt selected from Si, Mg, Mn, and Ca in the solution is less than 0.001 mol / l, the effect of inclusion is not observed. If the Si salt exceeds 0.5 mol / l, the viscosity of the solution increases, and the pH of the treatment solution cannot be maintained at 10.9 or lower, so a uniform film is not formed. In addition, in Mg, Mn, and Ca salts, it is necessary to lower the pH to less than 9.5 in order to contain more than 0.5 mol / l. Therefore, the concentration of at least one salt selected from Si, Mg, Mn, and Ca in the solution is limited to a range of 0.001 to 0.5 mol / l.
[0020]
The temperature of the solution is limited to the range of 20-60 ° C. The reason is that when the temperature of the solution rises, the film formation rate increases, and even when the temperature exceeds 60 ° C., the film formation is performed, but since the dissolution rate of the Al phase also increases, a uniform film cannot be formed. This is because if it is less than 0 ° C., the film formation rate is remarkably reduced, which is not practical.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described with reference to examples.
Example 1
After brazing heat treatment to brazing sheet clad with brazing material BA4004 on both sides of core material A3003, alkaline degreasing (fine cleaner 315, 70 ° C, immersed for 5 minutes) → pickling (15% nitric acid pickling, room temperature, 30 After a second immersion), a film formation treatment was performed under the conditions shown in Table 1, and the corrosion resistance was evaluated by a CCT test in which the formed film thickness, cathodic polarization, salt spray, wetting, and drying were taken as one cycle. Table 2 shows the film thickness, the cathode current density at a potential of -1200 mVvs SCE, and the pitting depth after 300 cycles of the CCT test.
[0022]
As shown in Table 2, it can be seen that in Examples 1 to 5 of the present invention, the cathode reaction is suppressed and the pitting corrosion depth is also reduced as compared with the chromate treatment. In addition, when the film thickness is less than 100 nm (No. 18) and when Li / (Al + Li + C) and C / (Al + Li + C) in the film deviate from the limited range of the present invention ( In Nos. 6 to 17), the cathode current density and the pitting corrosion depth are the same as those of the chromate treatment (No. 20), and the effect of improving the corrosion resistance is not recognized.
[0023]
[Table 1]
[Table 2]
Example 2
After brazing heat treatment to brazing sheet clad with brazing material BA4004 on both sides of core material A3003, alkaline degreasing (fine cleaner 315, 70 ° C, immersed for 5 minutes) → pickling (15% nitric acid pickling, room temperature, 30 After a second dipping), a film formation treatment was performed with the treatment solutions shown in Table 3 and Table 4, and the corrosion resistance of the formed film was evaluated by a CCT test with one cycle of cathodic polarization, salt spray, wetting and drying. . Table 3 and Table 4 also show the cathode current density at the immersion potential and the pitting depth after 300 cycles of the CCT test.
[0026]
As shown in Table 3 and Table 4, it can be seen that in Examples 1 to 5 of the present invention, the cathodic reaction is suppressed and the pitting depth is reduced as compared with the chromate treatment (No. 49) of the comparative example. . In the comparative examples (numbers 6 to 10) where the Li ion concentration is less than 0.1 mol / l or the comparative examples (numbers 13 to 17) where the Li ion concentration exceeds 0.2 mol / l, the cathode current density and pitting corrosion depth are not treated (number 48). ) And chromate treatment material (No. 49), no improvement in corrosion resistance is observed.
[0027]
In addition, even when the CO 3 ion concentration is less than 0.1 mol / l (No. 11) or more than 0.5 mol / l (No. 12), the effect of improving the corrosion resistance is not recognized. When the Al ion concentration is less than 1 × 10 -9 mol / l (number 18-22) or more than 1 × 10 -3 mol / l (number 23-27), and the pH is less than 9.5 (number 33-37) or In the case of exceeding 10.9 (numbers 28 to 32), the film thickness is thin and the effect of improving the corrosion resistance is not recognized. Further, when the solution temperature during the treatment is less than 20 ° C. (number 38 to 42) or more than 60 ° C. (number 43 to 47), the effect of improving the corrosion resistance is not recognized due to the thin film thickness.
[0028]
[Table 3]
[Table 4]
Example 3
After brazing heat treatment to brazing sheet clad with brazing material BA4004 on both sides of core material A3003, alkaline degreasing (fine cleaner 315, 70 ° C, immersed for 5 minutes) → pickling (15% nitric acid pickling, room temperature, 30 After a second dipping), a film formation treatment was performed with the treatment liquid shown in Table 5, and the corrosion resistance was evaluated by a CCT test in which the formed film thickness, cathodic polarization, salt spray, wetting, and drying were performed in one cycle. Table 6 shows the cathode current density at the immersion potential and the pitting depth after 300 cycles of the CCT test.
[0031]
As shown in Table 6, for example, numbers 51 to 53 of the present invention examples to which silicate was added are further suppressed in cathodic reaction and reduced in pitting depth as compared with no silicate addition. I understand. This effect is not observed in Example No. 50 of the present invention in which Si / (Al + Li + C + Si) is less than 0.01. Moreover, in the comparative example (No. 54) in which Si / (Al + Li + C + Si) exceeds 0.05, the film thickness decreases, and both the cathode current density and the pitting depth are untreated (Table 2, It is almost the same as number 19). The silicate concentration at which these effects are observed is in the range of 0.001 mol / l or more and 0.5 mol / l or less. Similar results are obtained when Mn, Mg and Ca salts are added.
[0032]
[Table 5]
[Table 6]
【The invention's effect】
As described above, as is apparent from the above description, the present invention forms a film on the surface of an Al alloy member with a treatment solution that does not contain an environmentally harmful substance, for example, cathodic reaction that occurs in crystallized Si of 4000 series Al alloy. By suppressing, corrosion resistance equivalent to or higher than that of the chromate treatment material can be obtained. For this reason, it becomes possible to surface-treat after assembling a component (such as an automotive evaporator) using a brazing sheet clad with a 4000 series Al alloy into the final product, thereby improving the corrosion resistance.
Claims (6)
但しＭはSi、Mg、Mn、Caのうちから選んだ元素を表す。The surface treatment film further contains at least one selected from Si, Mg, Mn, and Ca in an atomic fraction of 0.01 ≦ M / (Al + Li + C + M) ≦ 0.05. 1. A surface-treated film-coated member having excellent corrosion resistance according to 1.
M represents an element selected from Si, Mg, Mn, and Ca.
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| JP09906297A JP3657733B2 (en) | 1997-04-16 | 1997-04-16 | Surface-treated film-coated member having excellent corrosion resistance and method for forming surface-treated film |
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| JP09906297A JP3657733B2 (en) | 1997-04-16 | 1997-04-16 | Surface-treated film-coated member having excellent corrosion resistance and method for forming surface-treated film |
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