JP5928664B2 - Method for anodizing aluminum material - Google Patents

Description

  The present invention relates to an anodizing method for an aluminum material in which an aluminum material made of aluminum or an aluminum alloy is anodized under a predetermined voltage in a treatment bath made of a polybasic acid aqueous solution, and a porous anodic oxide film is formed on the surface. In particular, the present invention relates to an anodizing method for an aluminum material that can suppress the occurrence of crystal grain patterns as a result of anodizing as much as possible.

As for the aluminum material, since the aluminum itself is easily attacked by acid, alkali, etc., in order to impart corrosion resistance, wear resistance, etc., the aluminum material is energized as an anode in the electrolyte solution, and aluminum oxide (Al An anodizing treatment for forming a ₂ O ₃ ) film (anodized film) is generally performed. For example, in an anodic oxidation treatment using an acid aqueous solution such as sulfuric acid, oxalic acid, phosphoric acid or the like as an electrolyte, an anodic oxidation film called a porous film is formed by this anodization treatment. It consists of a dense film on the inside (aluminum side) called a layer and a porous film called a porous layer that is formed on the outside and has many pores. Initially, a barrier layer corresponding to the treatment voltage is first generated, and then a large number of holes are generated in the barrier layer, and the large number of holes grow to form a porous layer.

  And, in the aluminum material before anodizing treatment, the pattern (crystal grain pattern) caused by the crystal grains existing in the material is usually not visible with the naked eye. Due to the difference in orientation, it appears as a crystal grain pattern.

  Regarding the crystal grain pattern in the aluminum material after this anodic oxidation treatment, we grasp this as a highly decorative one, and also propose a technology that dares to clearly show the difference in crystal orientation and reveal the crystal grain pattern by light reflection (For example, refer to Patent Document 1) Housing members such as door knobs and fences, bicycle members such as handles and cranks, vehicle members such as riding door frames and inner panels, decorations such as accessories and watches, etc. In applications such as members, members for optical products such as reflectors and cameras, printing rolls, etc., the appearance and uniformity thereof may be emphasized. If such a crystal grain pattern is prominent, the appearance will be poor. May be judged.

  The problem of the crystal grain pattern in the aluminum material after the anodic oxidation treatment becomes more obvious when the aluminum purity (Al purity) in the aluminum material is high, and the surface of the aluminum material is burnished. Even when the mirror surface treatment is performed by a mirror surface processing means such as cutting, buffing, electrolytic polishing, chemical polishing, or the like.

  Therefore, as a method for making the crystal grain pattern on the surface of the aluminum material after the anodizing treatment as described above invisible, the cooling rate can be adjusted at the time of casting the aluminum material before the anodizing treatment. Or, by performing processing such as cold forging, the size of the crystal grains present in the aluminum material is made smaller than the size that can be visually confirmed (about 100 μm), thereby making the crystal grain pattern apparently inconspicuous A method is conceivable.

  However, depending on the product, the method of processing aluminum is limited, so there is a limit to reducing the size of the crystal grains. In particular, the aluminum material is a material with high Al purity, or heat treatment is performed during its manufacture. In the required material, it is technically difficult to reduce the size of the crystal grains to 100 μm or less, and even if the size of the crystal grains can be reduced, the crystal grains in the aluminum material When the agglomerates are aggregated, they may appear in the same manner as one large crystal grain, and it is difficult to obtain a uniform appearance.

By the way, in Patent Document 2, there is a tatami-shaped streak called streak that is likely to occur during chemical etching due to a difference in crystal grain orientation, and rough processing unevenness called surface quality unevenness. In order to prevent this, a preliminary electrochemical roughening of 1 to 300 C / dm ² of electricity performed using an alternating current of a predetermined frequency in an aqueous hydrochloric acid solution (1) prior to the anodizing treatment and (2) an aqueous hydrochloric acid solution. Surface treatment was improved by performing surface treatment, (3) electrochemical roughening treatment in hydrochloric acid aqueous solution, and (4) desmutting treatment in a predetermined amount of etching treatment and / or hydrochloric acid aqueous solution. It has been proposed to produce an aluminum support for a lithographic printing plate. However, the preliminary electrochemical roughening treatment performed in this method is an etching treatment in which aluminum is electrochemically dissolved and roughened in a monobasic acid, and is porous by anodizing treatment. It does not form an anodic oxide film.

Japanese Patent Laid-Open No. 2005-097,735 JP 2001-011,699

Therefore, as a result of repeated investigations and investigations regarding the cause of the appearance of the crystal grain pattern due to the anodizing treatment, the present inventors have found that the aluminum metal (Al) / barrier layer (Al ₂ O) in the aluminum material after the anodizing treatment It was found that the shape at the interface of ₃ ) was different for each crystal grain with different orientation. That is, according to the study by the present inventors, in the anodizing treatment, a barrier layer is first formed at the initial stage of film formation, and then holes begin to open in the formed film, but there are differences in orientation of crystal grains. Then, due to the difference in orientation of the crystal grains, a difference occurs at the time of generation of holes, and due to this, a large number of holes formed at the interface of the aluminum metal (Al) / barrier layer (Al ₂ O ₃ ) are formed. In addition, fine differences are formed in the unevenness, and the fine differences in the formed many holes are also reflected in the porous layer formed by growing many holes thereafter. And even if the difference is very slight, the fine difference in the numerous holes of the anodic oxide film formed in this way is emphasized when light is applied to the surface, and is manifested as a crystal grain pattern. It becomes a cause that a uniform external appearance is not formed in the aluminum material after the anodizing treatment.

Based on the results of this study, the present inventors made as many pores as possible generated at the interface of the aluminum metal (Al) / barrier layer (Al ₂ O ₃ ) as uniform as possible regardless of the crystal orientation. As a result of further investigations on the method for achieving this, prior to the anodizing treatment at a target voltage of 10 V or higher, anodizing treatment is performed in advance to a predetermined electric quantity at a low voltage, thereby preliminarily forming the surface of the aluminum material. By forming a pre-film having a large number of fine and uniform holes, a porous layer having holes with a uniform shape can be formed in the subsequent anodizing treatment at the target voltage. The present inventors have found that it is possible to prevent the crystal grain pattern from becoming apparent in the aluminum material as much as possible.

  Accordingly, an object of the present invention is to form a porous porous anodic oxide film at a treatment voltage of 10 V or more without making a crystal grain pattern as manifest as possible to an aluminum material made of aluminum or an aluminum alloy. An object of the present invention is to provide a method for anodizing an aluminum material.

That is, in the present invention, an aluminum material made of aluminum or an aluminum alloy is anodized under a treatment condition of a target voltage of 10 V or more in a treatment bath made of a polybasic acid aqueous solution, and a porous anodic oxide film is formed on the surface of the aluminum material. The anodizing treatment method for the aluminum material is a pretreatment of the anodizing treatment, and the anode is treated until the amount of electricity reaches 0.05 C / cm ² or more under the treatment condition of a voltage of 6 V or less in the treatment bath made of polybasic acid aqueous solution. An aluminum material anodizing method characterized by performing an oxidation treatment to form a porous pre-coating on the surface of the aluminum material.

  In the present invention, the aluminum material made of aluminum or an aluminum alloy to be anodized is not particularly limited, and is anodized under a treatment condition of a target voltage of 10 V or more in a treatment bath made of a polybasic acid aqueous solution. When a porous type anodic oxide film is formed on the surface, the crystal grain pattern becomes obvious due to the crystal grains present in the aluminum material. Particularly, the Al purity is high and exists in the material. Examples thereof include a material having a high Al purity in which the crystal grain size is 100 μm or more and the crystal grain pattern is easily manifested, for example, a high-purity aluminum material having a purity of 99.99% or more. In addition, since the surface of the aluminum material is easily mirror-finished by a mirror-finishing means such as buffing, electrolytic polishing, cutting, and chemical polishing, the surface of the aluminum material is easily manifested. Thus, the aluminum material whose surface is mirror-finished is also effective.

  In the present invention, the “target voltage” as the treatment conditions for the anodizing treatment is, for example, a corrosion-resistant film on the surface of an aluminum material using a treatment bath comprising a 10-20 wt% -sulfuric acid aqueous solution as a polybasic acid aqueous solution, In the case of forming a dyeing film, a decorative film, etc., a DC voltage of about 10 to 20 V is usually applied, and a treatment bath comprising a 0.01 to 4 wt% oxalic acid aqueous solution is used as the polybasic acid aqueous solution. When a corrosion-resistant film, an abrasion-resistant film, a decorative film, etc. are formed on the surface of an aluminum material, a DC voltage of about 10 to 600 V is usually applied. Thus, a predetermined treatment bath is used for a predetermined purpose. This means the voltage applied during the anodizing process performed in the above.

  In the present invention, the size of the crystal grains present in the aluminum material is determined by, for example, polishing the surface of the aluminum material (for example, buffing) to obtain a cross section, And the surface of the sample cross-section is dissolved so that the crystal grains can be seen visually, and then the cross-section is photographed with a microscope or an inverted microscope. A line of a certain length (for example, 50 mm, 20 mm) is drawn, the number of crystal grains on the line segment is counted, and the line segment length (L) is divided by the number of crystal grains (N) to obtain L / The value of N is obtained, and the obtained value of L / N is used as the size (length) of crystal grains, which is generally referred to as “cutting method”.

In the present invention, in the pretreatment performed prior to the anodic oxidation treatment at the target voltage, the amount of electricity becomes 0.05 C / cm ² or more under the treatment conditions of a voltage of 6 V or less in the treatment bath made of a polybasic acid aqueous solution. An anodizing treatment is performed to form a pre-coating on the surface of the aluminum material.
Here, as the polybasic acid constituting the treatment bath, usually, mineral acids such as sulfuric acid, phosphoric acid and chromic acid, and organic acids such as oxalic acid, tartaric acid and malonic acid can be mentioned, preferably the treatment rate. Sulfuric acid, phosphoric acid and the like, and the polybasic acid concentration of the treatment bath using these polybasic acids (polybasic acid aqueous solution) may be the same as that used in normal anodizing treatment, For example, in the case of sulfuric acid, it is 10% by weight or more and 20% by weight or less, preferably 14% by weight or more and 18% by weight or less.

In the pretreatment of the present invention, it is necessary to maintain the voltage at 6 V or less and to perform anodization until the amount of electricity reaches 0.05 C / cm ² or more. When the voltage rises above 6 V, This makes it difficult to suppress the difference in the opening of holes due to the difference in crystal grain orientation. As a result, when anodizing is performed at a target voltage of 10 V or higher, the crystal grain pattern becomes apparent. In this pretreatment, if the amount of electricity during the pretreatment is less than 0.05 C / cm ² even if the voltage is maintained at 6 V or less, the pre-film formed In some cases, a large number of fine and uniform holes may not be formed, and it may not be possible to prevent the appearance of crystal grain patterns when anodizing is performed at a target voltage of 10 V or higher. Here, there is no particular lower limit on the voltage during the pretreatment, but if the voltage is 1 V or less throughout the pretreatment, it may take a long time to form the pre-coating. Also, there is no particular upper limit for the amount of electricity, but the effect is almost the same even if the amount of electricity is greatly increased. For example, when the amount of electricity exceeds 5 C / cm ² , the film thickness of the pre-coating is several μm or more. In the case where the pre-film is removed in the subsequent process, the treatment time is lost, which is not preferable.

Here, as for the voltage during the pretreatment of the present invention, a constant voltage of 6 V or less may be applied from the beginning to the end of the pretreatment, and gradually in a range of 6 V or less from the beginning to the end of the pretreatment. Further, it may be gradually lowered in the range of 6 V or less from the beginning to the end of the pretreatment, and the pretreatment time is about 0.05C during the pretreatment. / cm and up to ² is reached, further, the treatment temperature during the pre-treatment, like a normal anodic oxidation treatment, for example in the case of sulfuric acid may range from 5 ° C. or higher 35 ° C. or less.

  The pre-film formed by the pretreatment of the present invention has a large number of holes and is fine, and the shape of the holes is uniform as a whole, compared with the anodized film formed by anodizing treatment at the target voltage. The film thickness varies depending on the type and concentration of the polybasic acid in the polybasic acid aqueous solution used as the treatment bath. For example, when a 15 wt% -sulfuric acid aqueous solution is used as the polybasic acid aqueous solution, the film thickness is approximately 25 nm or more. is there.

In the present invention, the pre-film formed by the above pretreatment has a smaller number of holes and a larger number than the anodic oxide film formed by anodization treatment at the target voltage. Since the unevenness at the Al) / aluminum oxide (Al ₂ O ₃ ) interface is kept low, and the number of holes is large and the unevenness is kept low, the shape and size of the holes formed in this pre-coating are crystalline. Regardless of the grain orientation, it becomes constant and uniform, and an anodic oxide film with relatively uniform holes can be formed in the subsequent anodization treatment at the target voltage (10 V or more). It can suppress as much as possible that the crystal grain pattern becomes obvious.

  In the present invention, the anodizing treatment at a voltage of 10 V or higher performed after the pretreatment can be carried out in the same manner as the conventional anodizing treatment for forming a porous anodic oxide film, and is used as a treatment bath. The acid aqueous solution and the treatment conditions may be the same as those of the conventional anodizing treatment, and it has a relatively uniform hole in the anodizing treatment at the target voltage (10 V or more) and forms a uniform anodized film without crystal grain patterns. can do.

  In the present invention, the treatment bath used in the pretreatment and the treatment bath used in the anodizing treatment may be the same polybasic acid aqueous solution or different polybasic acid aqueous solutions. Furthermore, the polybasic acid concentration of the polybasic acid aqueous solution may be the same or different. In the pretreatment and the anodizing treatment, using the same kind and the same concentration of the polybasic acid aqueous solution has an advantage that the treatment bath does not need to be replaced when the anodizing treatment is shifted from the pretreatment. When it is necessary to use a polybasic acid aqueous solution with a relatively slow treatment speed as a treatment bath in an anodic oxidation treatment at a voltage (10 V or higher), use different types and / or different concentrations of polybasic acid aqueous solution. By using a polybasic acid aqueous solution having a high treatment speed as a pretreatment bath, the entire treatment time can be shortened.

Furthermore, in the present invention, when anodizing is performed on the aluminum material at a target voltage (10 V or higher), a pre-film formed by pretreatment is performed during or after the anodizing treatment, if necessary. You may perform the pre film removal process which removes.
Here, as the pre-film removal treatment performed during the anodizing treatment, for example, when anodizing the aluminum material after the pretreatment, the amount of electricity applied during the pretreatment is usually 50 times or more, A method of removing the porous pre-coating film formed during the pretreatment by dissolving it in an anodizing treatment bath by performing an anodizing treatment of preferably 80 times or more can be exemplified. In this method, if the amount of electricity in the anodizing treatment is lower than 50 times, the pre-coating is not sufficiently dissolved in the anodizing treatment, and the porous pre-coating remains undissolved on the surface and may remain. .

  Further, as the pre-film removal treatment performed after the anodizing treatment, for example, the porous pre-film remaining on the surface during the anodizing treatment is performed by immersing the anodized aluminum material in an aqueous solution of acid or alkali. A method of chemically dissolving and removing can be exemplified.

  Thus, by removing the porous pre-film formed in the pre-treatment during or after the anodizing treatment, the target pore diameter is uniform when viewed from the surface. Thus, it is possible to obtain a film in which porous holes are uniformly opened from the bottom to the top of the hole, that is, a film similar to the film whose structure is processed only by the target voltage (normal anodizing treatment). The advantage is that

  Furthermore, when anodizing the aluminum material after the pre-treatment, the pre-coating that dissolves the porous pre-coating formed on the pre-treated aluminum material under the treatment conditions in which 10% or more of the wall thickness remains. As the partial dissolution treatment of the pre-coating, for example, a test sample substantially the same as the pre-treated aluminum material is prepared, and the pre-coating of the pre-coating is performed using this test sample. An example is a method in which a treatment condition in which the inter-hole wall thickness remains 10% or more is obtained, and the pre-treated aluminum material is treated under this pre-determined treatment condition. In this way, by carrying out partial dissolution treatment of the pre-coating in advance and adjusting the inter-hole wall thickness of the pre-coating, a porous anodic oxide coating in which a porous layer is uniformly formed without any pre-coating remaining on the surface is obtained. Can be obtained.

  In the partial dissolution treatment of the porous pre-coating, if the inter-pore wall thickness of the pre-coating is dissolved to less than 10% of the inter-hole wall thickness when the pre-coating is formed in the pretreatment, the porous pre-coating becomes brittle. In some cases, the base material at a part of the substrate is exposed during the subsequent anodic oxidation treatment, and anodization occurs preferentially from the exposed part of the base material, so that a uniform anodic oxide film may not be formed.

  According to the method of the present invention, a porous porous anodic oxide film is formed on an aluminum material made of aluminum or an aluminum alloy at a processing voltage of 10 V or more without making the crystal grain pattern as manifest as possible. It can be used for applications such as housing members, bicycle members, vehicle members, decorative members, optical product members, printing rolls, etc. where the crystal grain pattern is not visible and the appearance uniformity is important. The anodized aluminum material can be easily manufactured industrially.

FIG. 1 shows an SEM photograph (upper photo) in which the upper cross section of the test piece obtained in Example 1 was observed at a magnification of 3,000, and the upper cross section of the anodized film of the same test piece at a magnification of 50,000. It is the SEM photograph (lower photograph) observed by magnification.

FIG. 2 was obtained in Example 14 by interrupting the anodizing treatment 1 minute after the start of anodizing of the pretreated aluminum material obtained by forming a pre-coating in the pretreatment. It is the SEM photograph which observed the cross-section upper part of the reference test piece at a magnification of 100,000 times.

  Hereinafter, preferred embodiments of the present invention will be described more specifically based on examples and comparative examples.

[Examples 1 to 20]
As the aluminum material, an Al purity plate material or a type of plate material shown in Table 1 is used, and an aluminum piece having a size of 50 mm × 50 mm × 10 mm is cut out from these plate materials, and the surface roughness Rt <200 nm by the mirror finishing means shown in Table 1. The aluminum piece after the mirror treatment was subjected to a pretreatment to form a porous pre-film under the polybasic acid aqueous solution and treatment conditions shown in Table 1, and the polybasic acid aqueous solution shown in Table 1 Anodizing treatment was carried out at the target voltage under the treatment conditions, and further washed with water and dried to obtain aluminum pieces (test pieces) after the anodizing treatment of Examples 1 to 19.

[Evaluation of crystal grain pattern by surface observation]
About the test piece obtained in each Example 1-20, what looked at a crystal grain pattern when visually observing under the fluorescent lamp of illuminance 1,500Lux or more and 2,500Lux or less was set as x, and illuminance 1,500Lux When the crystal pattern is not visible when visually observed under a fluorescent lamp of 2,500 Lux or less, ◯ is indicated. Further, when the crystal is visually observed under a video light with an illuminance of 15,000 Lux or more and 20,000 Lux or less, crystals are observed. Surface observations where the grain pattern was not visible were evaluated as ◎, and the crystal grain pattern in each test piece was evaluated.
The results are shown in Table 1.

[States of pre-film and anodized film by SEM observation]
In FIG. 1, the upper photograph is an SEM photograph obtained by observing the cross-sectional upper part of the test piece obtained in Example 1 at a magnification of 3,000 times by SEM, and the lower photograph is the same as in Example 1. It is the SEM photograph which observed the cross-sectional upper part of the anodized film of the obtained test piece at a magnification of 50,000 times, and the pre-coating disappeared during the anodizing, and a uniform porous anodic oxide film was formed. ing.

  FIG. 2 is a reference test obtained in Example 14 by interrupting the anodizing treatment for one minute after the start of the anodizing treatment on the aluminum material after the pretreatment obtained by forming a pre-coating by the pretreatment. It is the SEM photograph which observed the cross-section upper part by the magnification of 100,000 times by SEM about a piece, and a residual pre film is observed on the upper surface of a porous type anodic oxide film. In addition, in the test piece obtained in Example 14 in which the anodizing treatment was performed under the condition of a treating time of 45 minutes, the remaining pre-coating film on the upper surface of the anodizing film was not observed.

Example 21
In the same manner as in Examples 1 to 20 above, after a porous pre-film was formed as a pretreatment in a treatment bath of 15 wt% sulfuric acid (18 ° C.) under the conditions of a voltage of 5 V and an electric quantity of 0.1 C / cm ^2. In the same 15wt% -sulfuric acid (18 ° C) treatment bath as anodizing treatment, porous anodizing under conditions of voltage 15V and electric quantity 6C / cm ² (equivalent to coating thickness 3μm) (pre-film removal treatment condition) A film was formed to obtain an aluminum piece (test piece) after the anodizing treatment of Example 21.

About the obtained test piece, it carried out similarly to Examples 1-20, and evaluated the crystal grain pattern by surface observation. The results are shown in Table 1.
Moreover, when the cross section of the obtained test piece was observed by SEM, it was confirmed that the pre-coating did not remain on the upper part of the film, and the film structure was confirmed to be uniform. There was no significant difference in appearance from Example 1 where the pre-film remained.

[Example 22]
In the same manner as in Examples 1 to 20 above, after a porous pre-film was formed as a pretreatment in a treatment bath of 15 wt% sulfuric acid (18 ° C.) under the conditions of a voltage of 5 V and an electric quantity of 0.1 C / cm ^2. In the same 15 wt% -sulfuric acid (18 ° C.) treatment bath as the anodizing treatment, a porous anodized film was formed under the conditions of a voltage of 15 V and an electric quantity of 2 C / cm ² . After the amount of electricity reached ² C / cm ² , the sample was continuously immersed in the same bath for 15 minutes (pre-film removal treatment), then taken out, and the aluminum piece after the anodizing treatment of Example 22 (test piece) )

About the obtained test piece, it carried out similarly to Examples 1-20, and evaluated the crystal grain pattern by surface observation. The results are shown in Table 1.
Moreover, when the film | membrane cross section of the obtained test piece was observed by SEM, it was confirmed that the pre film | membrane does not remain on the film | membrane upper part, and it was confirmed that the film | membrane structure is uniform. The appearance was almost the same as when the pre-film removal treatment was not performed.

Example 23
In the same manner as in Examples 1 to 20 above, the same mirror-finished aluminum pieces were subjected to the same mirror treatment, and the same pretreatment was performed in a 15 wt% sulfuric acid (18 ° C.) treatment bath with a voltage of 5 V and an electric charge of 0.1 C. Two pieces of pre-treated aluminum pieces on which a porous pre-film was formed under the conditions of / cm ² were prepared.

  One of the obtained pretreated aluminum pieces was used as a test sample, and this test sample was immersed in a 10 wt% -phosphoric acid aqueous solution (20 ° C) for 2 minutes (partial dissolution treatment of the pre-coating film), and the surface was observed with an electron microscope. As a result, it was confirmed that the thickness of the inter-hole wall of the pre-coating was reduced to 15% with respect to the pre-treated aluminum piece without partial dissolution treatment.

Next, for the aluminum piece after pretreatment without partial dissolution treatment, after performing partial dissolution treatment of the pre-coating under exactly the same conditions as above, without checking the inter-hole thickness of the pre-coating, As anodizing treatment, a porous anodized film was formed in 15 wt% -sulfuric acid (18 ° C.) under conditions of a voltage of 15 V and an electric quantity of 2 C / cm ² , and an aluminum piece after the anodizing treatment of Example 23 (test piece) Got.

About the obtained test piece, it carried out similarly to Examples 1-20, and evaluated the crystal grain pattern by surface observation. The results are shown in Table 1.
Also, when the cross section of the test piece after the anodizing treatment was confirmed with an electron microscope, the pre-coating confirmed with the test piece of Example 1 was not observed on the upper part of the film, and the film structure was confirmed to be uniform. It was done.

[Comparative Examples 1 to 10]
Using an Al purity plate or the type of plate shown in Table 2 as the aluminum material, an aluminum piece having a size of 50 mm × 50 mm × 10 mm was cut out from these plates, and the surface was roughened by mirror finishing means (puff polishing) shown in Table 2. Rt <200 nm is mirror-finished, and the resulting aluminum pieces after the mirror-finishing are subjected to pre-treatment to form a pre-film under the treatment conditions shown in Table 2, and the anode at the target voltage under the treatment conditions shown in Table 2 Oxidation treatment was performed, followed by washing with water and drying to obtain an aluminum piece (test piece) after anodizing treatment of Comparative Examples 1 to 10.

[Evaluation of crystal grain pattern by surface observation]
About the test piece obtained by each Comparative Examples 1-10, the crystal grain pattern was evaluated by surface observation similarly to the case of each said Example.
The results are shown in Table 2.

Claims (12)

Anodization of an aluminum material in which an aluminum material made of aluminum or an aluminum alloy is anodized in a treatment bath made of an aqueous polybasic acid solution at a target voltage of 10 V or more to form a porous anodic oxide film on the surface of the aluminum material. Processing method,
As a pretreatment of the anodizing treatment, anodizing treatment is performed in a treatment bath made of an aqueous polybasic acid solution under a treatment condition of a voltage of 6 V or less until the electric quantity reaches 0.05 C / cm ² or more, and the surface of the aluminum material is treated. A method for anodizing an aluminum material, comprising forming a porous pre-film.   The method for anodizing an aluminum material according to claim 1, wherein the aluminum material has a crystal grain size of 100 µm or more.   The method for anodizing an aluminum material according to claim 1, wherein the surface of the aluminum material is mirror-finished.   The method of anodizing an aluminum material according to claim 3, wherein the mirror surface treatment is performed by any one of mirror surface processing selected from buffing, electrolytic polishing, cutting, and chemical polishing.   The method for anodizing an aluminum material according to any one of claims 1 to 4, wherein the treatment bath used in the pretreatment and the treatment bath used in the anodizing treatment are the same polybasic acid aqueous solution.   The method for anodizing an aluminum material according to claim 1, wherein the treatment bath used in the pretreatment and the treatment bath used in the anodizing treatment are different polybasic acid aqueous solutions.   The method for anodizing an aluminum material according to any one of claims 1 to 6, wherein a pre-film removal treatment for removing the porous pre-film formed in the pretreatment is performed when anodizing the aluminum material.   The method for anodizing an aluminum material according to claim 7, wherein the pre-film removal treatment is performed during or after the anodizing treatment.   The pre-film removal treatment performed during the anodizing treatment is performed by anodizing 50 times or more of the amount of electricity applied during the pretreatment when anodizing the aluminum material after the pretreatment. The method for anodizing an aluminum material according to claim 8, wherein the porous pre-film formed during the pretreatment is removed by dissolving in a treatment bath for anodizing.   The pre-film removal treatment performed after the anodizing treatment is performed by immersing the aluminum material after the anodizing treatment in an aqueous solution of acid or alkali to chemically dissolve the porous pre-film remaining on the surface during the anodizing treatment. The method for anodizing an aluminum material according to claim 8, wherein the anodizing treatment is performed.   Part of the pre-coating that dissolves the porous pre-coating formed on the pre-treated aluminum material under the processing conditions in which 10% or more of the wall thickness remains when the pre-treated aluminum material is anodized. The method for anodizing an aluminum material according to any one of claims 1 to 6, wherein the dissolution treatment is performed.   For the partial dissolution treatment of the porous pre-coating, a test sample that is substantially the same as the pre-treated aluminum material is prepared, and using this test sample, the pre-coating wall thickness between the pores of the pre-coating is 10% or more. The method for anodizing an aluminum material according to claim 11, wherein the pretreated aluminum material is treated under the processing conditions determined in advance.

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