JP3344973B2 - How to color aluminum material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coloring an aluminum material in a rust-like red rust.

[0002]

2. Description of the Related Art Materials having various colors are used for building materials in consideration of harmony with the surrounding environment.
Recently, textures and colors such as red rust of iron have been preferred. A texture like red rust gives a calm impression with a rough surface. In addition, the color tone is based on brown to black, and the graininess is further emphasized by a fine difference in shading. When steel building materials are used, red rust develops due to natural corrosion. However, red rust resulting from the corrosion of iron does not appear at the beginning of construction, and does not have a desirable color tone after a certain number of years. When the number of years further elapses, corrosion proceeds, so that a preferable color tone cannot be maintained. In particular, in recent years when environmental pollution is serious, the progress of corrosion is remarkable, and the time period in which a predetermined color tone can be maintained by giving a color tone by red rust is short.
On the other hand, aluminum materials are used for various building materials such as sashes, curtain walls, etc., utilizing their excellent light weight, corrosion resistance and workability. When a red rust-like texture and color tone can be imparted to an aluminum material, a building structure that is rich in harmony with the surroundings can be obtained instead of a steel building material.

[0003]

For coloring an aluminum material, a method of passing through a process of alkali etching → anodic oxidation → electrolytic coloring is widely used. When the alkali-etched aluminum material is anodized, a porous film that grows in a direction perpendicular to the material surface is generated. This porous film has many micropores (hereinafter, referred to as pores) perpendicular to the material surface. When an aluminum material having a porous film formed by anodization is electrolyzed in an aqueous solution containing a metal ion source, metal is deposited on the bottom of the pore. When the surface of the aluminum material thus treated is irradiated with light, the reflected light is absorbed by the deposited metal, so that the color tone due to the absorption is observed. The light absorption increases in accordance with the amount of deposited metal, and the brightness of the observed color tone also decreases.

[0004] In this method, an aluminum material is colored in a brown-black color tone mainly called a bronze color. However, with the usual alkali etching, the gloss of the colored aluminum material is high, and a red-rust-like texture cannot be obtained. Above all, when using extruded material as a material,
A streak pattern peculiar to the extruded material called a die mark appears on the surface, and a high-grade appearance of the material cannot be obtained. Even if the aluminum material is subjected to mechanical surface roughening treatment such as shot blasting and then electrolytically colored using a nickel bath, a fine difference in shading in the form of red rust does not occur, and a favorable roughness cannot be obtained.

[0005]

SUMMARY OF THE INVENTION The present invention has been devised to solve such a problem, and has been settled by forming relatively large irregularities on the surface of an aluminum material and then performing electrolytic coloring. The purpose is to color the aluminum material in a red rust tone giving an impressive impression. The coloring method of the present invention, in order to achieve the object, after forming fine irregularities on the surface of the aluminum material by immersion in an aqueous solution containing hydrochloric acid, immersing the aluminum material in an alkaline aqueous solution to expand the irregularities, and then Anodizing treatment to form a porous film on the surface is performed on the aluminum material, and the anodized aluminum material is electrolyzed in an aqueous solution containing copper ions to precipitate metallic copper in the pores of the porous film, and further, nickel ions or It is characterized in that metallic nickel or metallic cobalt is deposited on the pores of the porous film by electrolysis in an aqueous solution containing cobalt ions.

As an aqueous solution containing hydrochloric acid, a concentration of 10 to 200 is used.
An aqueous solution containing hydrochloric acid at a bath temperature of 20 to 50 g / l is used.
It is preferable to immerse the aluminum material in a hydrochloric acid-containing aqueous solution at a temperature of 1 ° C for 1 to 20 minutes. As the alkaline aqueous solution, an aqueous solution containing sodium hydroxide at a concentration of 20 to 100 g / l is used, and it is preferable to immerse the aluminum material in an alkaline aqueous solution having a bath temperature of 30 to 70 ° C. and a pH of 13 or more for 3 to 20 minutes. As the copper ion-containing aqueous solution, an aqueous solution containing copper ions at a concentration of 2 to 10 g / l and having a pH of 2 or less is preferably used. The aqueous solution containing nickel ions or cobalt ions includes nickel ions or cobalt ions having a concentration of 20 to 40 g / l and a concentration of 10 to 40 g / l.
An aqueous solution containing boric acid of pH 4 to 6 is preferred.

[0007]

When an aluminum material is immersed in an aqueous solution containing hydrochloric acid, the aluminum material is locally dissolved by hydrochloric acid penetrating from a defective portion of an oxide film on the surface of the material, and etch pits are generated. The etch pit due to hydrochloric acid is called an azimuthal pit, and the dissolution proceeds so that small angular holes overlap. Since the dissolution proceeds in the depth direction from the surface of the aluminum material, the etch pit grows thin and long. Further, the number of etch pits increases according to the immersion time. As a result, fine etch pits are observed on the entire surface of the aluminum material immersed in hydrochloric acid. The aluminum material subjected to the hydrochloric acid immersion treatment has a surface with fine irregularities, and a favorable surface with a rough feeling cannot be obtained as it is. Further, even if anodized and electrolyzed in an aqueous solution containing a metal ion source, a colored surface cannot be obtained because no metal is deposited. Incidentally, when the aluminum material treated with the aqueous solution containing hydrochloric acid is anodized, a porous film grows in a direction perpendicular to the wall surface of the etch pit at a location where angular etch pits are formed. The grown porous films collide with each other at the corners of the etch pit, complicating the pore shape. For this reason, even if the anodized aluminum material is electrolyzed in an aqueous solution containing a metal ion source, metal deposition on the bottom of the pore is prevented, and coloring due to metal deposition cannot be obtained.

Accordingly, the present inventors have conducted various investigations and studies on a method for enlarging fine irregularities generated by the hydrochloric acid immersion treatment.
As a result, they found that when immersed in an alkaline aqueous solution after the hydrochloric acid immersion treatment, the surface of the aluminum material was uniformly dissolved, and the irregularities grew greatly. The growth of the unevenness is presumed as follows. In the immersion treatment using the alkaline aqueous solution, the dissolution from the surface progresses, and simultaneously, the dissolution from the inner wall of the elongated pits formed by the hydrochloric acid immersion proceeds uniformly. As a result, the diameter of the elongated pit gradually increases, and the corners of the pit become rounded, eventually forming a deep semicircular pit. The generated semicircular pits are larger in diameter and deeper than pits formed by immersing the aluminum material only in an alkaline aqueous solution. By immersing the aluminum material in the alkaline aqueous solution after the hydrochloric acid-containing aqueous solution in this way, the surface state is adjusted to a conspicuous unevenness and a rough feeling. In the aluminum material on which the second phase particles are precipitated,
Although semi-circular pits are generated starting from the second phase particles,
Since the pits have a diameter of about 10 to 50 μm and a depth of about 1 to 10 μm, they are not perceived as uneven by visual observation.

[0009] The aluminum material immersed in the alkaline aqueous solution is then anodized. The porous film formed by the anodic oxidation treatment has a porous structure with pores grown in a direction perpendicular to the material surface. At this time, since the corners of the pits formed on the surface of the aluminum material with the aqueous solution containing hydrochloric acid are rounded with the alkaline aqueous solution, the growth directions of the porous films during anodic oxidation treatment are less likely to collide with each other, and the inner wall of the concave portion is reduced. In this case, the growth direction of the pores is substantially perpendicular to the material surface. As a result, the surface state is adjusted to be capable of electrolytic coloring using the aqueous solution containing the metal ion source.

When the surface-modified aluminum material is electrolyzed in an aqueous solution containing copper ions, metallic copper precipitates at the bottom of the pore, and the material surface is colored red derived from metallic copper. In addition, the convex portion has a light color because the amount of metallic copper deposited on the bottom of the pore of the porous film is small, and the concave portion is colored in a deep color by a large amount of metallic copper deposited. The emphasis on roughness is
This is a specific phenomenon observed in electrolytic coloring using a copper ion-containing aqueous solution, and does not occur in electrolytic coloring using an aqueous solution containing a nickel ion source or a cobalt ion source, which is generally used in electrolytic coloring treatment for building materials. The present inventors have inferred the reason why the graininess is emphasized by the deposited metal copper as follows. When the surface colored with fine shading corresponding to the unevenness is irradiated with light, the light reflected at the bottom of the concave portion is also reflected on the wall surface of the concave portion, and is also absorbed by the precipitated metal copper. This means that the reflected light at the bottom is more absorbed by the deposited metal copper as compared to the reflected light at the projections. Moreover, since the deposited metal copper has a larger absorption coefficient than nickel or cobalt, the difference in the amount of absorption is increased even by a slight difference in the number of reflections, and the difference in brightness between the convex and concave portions is increased.

An aluminum material in which metallic copper is deposited in the pores of the porous film has a reddish color tone derived from metallic copper. In order to change the color tone to a red rust tone, electrolytic treatment is further performed using an aqueous solution containing a nickel ion source or a cobalt ion source. Metallic nickel or metallic cobalt deposited by the electrolytic treatment exhibits a bronze to black color tone.
This color tone overlaps with the color tone derived from metallic copper, and the aluminum material is colored reddish brown to black. In addition, the surface state in which the rough feeling is emphasized is maintained.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Materials Aluminum materials to which the present invention is applied are not particularly limited as long as an aluminum oxide film can be formed thereon.
It is an Al-Mg-Si alloy such as IS A6063, and includes a plate material, a tube material, an extruded shape material, and the like which have been conventionally used as building materials. The aluminum material is subjected to a pretreatment such as degreasing, alkali etching, or neutralization if necessary, and then is colored according to the present invention. As the pretreatment, electrolytic polishing, chemical polishing, or the like can be employed.

Immersion treatment using an aqueous solution containing hydrochloric acid By immersing an aluminum material in an aqueous solution containing hydrochloric acid, a large number of etch pits are formed on the surface of the material. The aqueous solution containing hydrochloric acid contains hydrochloric acid having a concentration of 10 to 200 g / l (more preferably 30 to 150 g / l), and has a liquid temperature of 20 to 200 g / l.
An aqueous solution at 50 ° C (more preferably 25 to 40 ° C) is preferred. At a hydrochloric acid concentration exceeding 200 g / l or a liquid temperature exceeding 50 ° C., the reaction with the material surface progresses violently, and it becomes difficult to control fine irregularities. If the hydrochloric acid concentration or the liquid temperature is too high, the working environment may be deteriorated due to generation of hydrochloric acid mist. Conversely, hydrochloric acid concentration not reaching 10 g / l or 20 ° C
When the liquid temperature is lower than the above, local dissolution becomes slow, and a long immersion treatment is required until a predetermined etch pit is generated, which lowers production efficiency.

A mineral acid such as phosphoric acid or sulfuric acid or an organic acid such as oxalic acid can be added to the aqueous solution containing hydrochloric acid in order to easily control fine irregularities. The aluminum material is preferably immersed in an aqueous solution containing hydrochloric acid for 1 to 20 minutes (more preferably 5 to 15 minutes). With immersion times less than one minute,
Local dissolution does not proceed sufficiently, and a required number of fine irregularities are unlikely to occur. Conversely, when the immersion time is longer than 20 minutes, although fine irregularities increase, local dissolution excessively proceeds, and the irregularities overlap with each other, so that a required appearance cannot be obtained. When etch pits are formed on the surface of the aluminum material by the immersion treatment, aluminum eluted from the aluminum material is accumulated in the aqueous solution containing hydrochloric acid. The amount of aluminum contained in the hydrochloric acid-containing aqueous solution is preferably suppressed to 100 g / l or less (more preferably, 50 g / l or less). As the amount of aluminum increases, the viscosity of the aqueous solution containing hydrochloric acid increases,
Workability deteriorates.

Immersion Treatment Using Alkaline Aqueous Solution When the aluminum material is immersed in an aqueous solution of hydrochloric acid next to an aqueous solution containing hydrochloric acid, the etch pits are enlarged by uniform dissolution of the material surface, and the surface state is adjusted to have conspicuous irregularities. As the alkaline aqueous solution, a concentration of 20 to 1
Contains sodium hydroxide of 00 g / l (more preferably 40 to 70 g / l), pH 13 or more, and liquid temperature of 30 to 70 ° C.
(More preferably 40 to 60 ° C.) is preferable. 2
At a sodium hydroxide concentration of less than 0 g / l or a liquid temperature of less than 30 ° C., uniform dissolution of the material surface does not proceed, and angular pits tend to remain. As a result, normal growth of the porous film cannot be expected in the subsequent anodic oxidation treatment, and the film cannot be colored red by electrolysis using a copper ion-containing aqueous solution. 100g /
If the concentration of sodium hydroxide exceeds 1 liter or the liquid temperature exceeds 70 ° C., the uniform dissolution proceeds intensely so that it is difficult to control, and the unevenness becomes smooth and inconspicuous. Further, a large amount of etching mist may be generated, and the working environment may be deteriorated. The time to immerse the aluminum material in the alkaline aqueous solution,
It is preferable to set within a range of 3 to 20 minutes (more preferably, 5 to 15 minutes). If the immersion time is shorter than 3 minutes, uniform dissolution does not sufficiently proceed, and angular pits remain, resulting in a surface state in which irregularities are not noticeable. As a result, a normal porous film does not grow in the subsequent anodizing treatment, and cannot be colored red by electrolysis using a copper ion-containing aqueous solution. Conversely, if the immersion time is longer than 20 minutes, the uniform dissolution proceeds excessively, and the unevenness of the material surface becomes smooth and inconspicuous.

Anodizing Treatment The anodizing treatment is not particularly limited, but an aqueous solution of sulfuric acid, oxalic acid or the like is used. Examples of the aqueous sulfuric acid solution include a sulfuric acid concentration of 100 to 200 g / l and a liquid temperature of 15 g / l.
There is an aqueous solution at ３０30 ° C. An aluminum material is immersed in the aqueous solution as an anode, and anodic electrolysis is performed using a DC power supply, an AC / DC superimposed power supply, or the like. For constant current control, set the current density to 50 to
Within the range of 300 A / m ² , the applied voltage is 1
Set in the range of 0-30V. The porous film formed by the anodic oxidation treatment preferably has a thickness of 3 to 25 μm in order to exhibit a predetermined color tone that is stable by electrolytic coloring.

Electrolytic coloring using a copper ion-containing aqueous solution The aluminum material having a porous film formed by anodizing treatment is electrolytically colored using a copper ion-containing aqueous solution. As the aqueous solution containing copper ions, an aqueous solution containing copper ions having a concentration of 2 to 10 g / l is preferable. Copper ion concentration of 2 g /
If it is less than 1, the required amount of metallic copper is less likely to precipitate, and the material surface is less likely to be colored red. The colorability decreases even when the concentration of copper ions exceeds 10 g / l. Copper ion sources include copper sulfate, copper pyrophosphate, copper carbonate, copper acetate, copper citrate and the like, and other metal ions such as Al, Mg, Ni and the like can also be contained. The aqueous solution containing copper ions is preferably adjusted to pH 2 or less by adding one or more of sulfuric acid, sulfamic acid, acetic acid, oxalic acid, citric acid and the like. As the electrolysis conditions, AC electrolysis, pulse electrolysis and the like are employed.
Further, in order to improve the uniformity of coloring, electrolytic conditions for supplying a rectangular wave alternating current after uniformizing the barrier layer below the porous film (see Japanese Patent Publication No. 58-52037) can also be adopted. The energization time is set in the range of 10 seconds to 5 minutes in order to obtain a necessary color tone. The amount of metallic copper deposited on the pores of the porous film increases in proportion to the energizing time, and gives a dark color tone to the material surface. However, if the energization time exceeds 5 minutes, it is not possible to obtain a deep color corresponding to the long energization time. Conversely, in short-time energization that does not reach 10 seconds,
Not colored to the required color.

Water containing nickel ions or cobalt ions
The aluminum material colored red by the deposition of electrolytically colored metallic copper using a solution is further electrolytically colored with an aqueous solution containing nickel ions or cobalt ions. The bronze-black color tone of the metal nickel or metal cobalt deposited by the electrolytic treatment overlaps the red color derived from the metal copper, and imparts a red rust tone to the material surface. The intensity and shade of redness are adjusted by the amount of metal copper deposited or the amount of metal nickel or metal cobalt deposited. As nickel ions or cobalt ions,
Sulfate, sulfamate, acetate, and the like are used, and the concentration is preferably adjusted in the range of 20 to 40 g / l.
Nickel or cobalt ion concentration of 20 g / l
If it is less than the required amount, the required amount of metallic nickel or metallic cobalt hardly precipitates, and the red color derived from metallic copper remains strongly. The coloring property is improved as the concentration of nickel ions or cobalt ions is increased, but is saturated at 40 g / l.

The aqueous coloring solution may contain 20 to 40 g / l of an organic acid such as boric acid, malic acid, oxalic acid and citric acid, in addition to nickel ions or cobalt ions. The pH of this coloring aqueous solution is adjusted to a range of 4 to 6. As the electrolysis conditions, AC electrolysis, pulse electrolysis and the like are employed. Further, in order to improve the uniformity of coloring, it is also possible to employ an electrolysis condition for supplying a rectangular wave alternating current after uniformizing the barrier layer below the porous film. The energization time is set in the range of 10 seconds to 5 minutes in order to obtain a necessary color tone. The deposition amount of metallic nickel or metallic cobalt deposited on the pores of the porous film increases in proportion to the energization time, and gives a dark color tone to the material surface. However, if the energization time exceeds 5 minutes, it is not possible to obtain a deep color corresponding to the long energization time. Conversely, if the current is supplied for a short time that does not reach 10 seconds, the required color tone is not obtained.

The aluminum material having the post-processing target color tone is subjected to a sealing treatment, an electrodeposition coating, a spray coating, or the like, if necessary, to obtain a product.

[0021]

[Example 1] JIS A6063 aluminum alloy
It was immersed in a 0% hydrochloric acid aqueous solution (liquid temperature: 30 ° C.) for 5 minutes to form many fine pits on the alloy surface. Then, 50g /
When the alloy surface was immersed in an aqueous solution of sodium hydroxide (solution temperature: 50 ° C.) for 10 minutes, the surface of the alloy was uniformly dissolved, the pits were greatly enlarged in a semicircular shape, and the surface was adjusted to a surface with conspicuous irregularities. The surface-modified aluminum alloy was immersed in a sulfuric acid bath having a concentration of 160 g / l and a liquid temperature of 20 ° C., and subjected to anodizing treatment at a constant current of 150 A / m ² for 25 minutes. Observation of the anodized alloy surface revealed that a porous film having a thickness of 10 μm was formed. After anodizing, the concentration is 15 g / l, p
H1.3, the aluminum alloy was immersed in an aqueous solution of copper sulfate at a liquid temperature of 25 ° C., and a voltage of 15 V was applied to perform AC electrolysis for 1 minute. Then, nickel sulfate 150 g / l, boric acid 30 g
/ L, pH 4.8, aqueous solution at a liquid temperature of 25 ° C, and a voltage of 1
5V was applied and AC electrolysis was performed for 1 minute. The surface of the electrolytically colored aluminum alloy was given a rust-like red rust color tone (L ^* : 30.5, a ^* : 5.2, b ^* : 4.0). The constant current rectangular wave alternating waveform voltage _{15V (t a / t c =} 0.1,10Hz) current density 20A /
A similar color tone was obtained when electrolysis was performed at m ² .

[0022]

Example 2 The same aluminum alloy as in Example 1 was prepared using hydrochloric acid 1
After immersion for 5 minutes in an aqueous solution containing hydrochloric acid containing 100 g / l, sulfuric acid 100 g / l and a liquid temperature of 35 ° C., a concentration of 50 g / l and a liquid temperature of 50
It was immersed in an aqueous solution of sodium hydroxide at 10 ° C. for 10 minutes. Then, anodizing treatment was performed for 25 minutes at a constant current of 150 A / m ² using a mixed acid bath of 160 g / l sulfuric acid and 10 g / l oxalic acid at a liquid temperature of 20 ° C. to form a porous film having a thickness of 10 μm. Anodized aluminum alloy with a concentration of 15 g /
1, pH 1.3, immersed in an aqueous solution of copper sulfate at a liquid temperature of 25 ° C. and subjected to electrolysis at an alternating voltage of 15 V for 1 minute. AC voltage was applied for 2 minutes while applying a voltage of 15 V. The surface of the electrolytically colored aluminum alloy has a red-rust-like color tone (L ^* : 32.5, a ^* : 7.
8, b ^* : 5.6).

[0023]

Comparative Example 1 A JIS A6063 aluminum alloy was electrolytically colored under the same conditions as in Example 1 except that immersion in a hydrochloric acid aqueous solution was omitted. The surface of the aluminum alloy after the treatment has a highly reddish brown and glossy color tone (L ^* : 2).
8.3, a ^* : 14.0, b ^* : 5.5), but the color tone was different from the calm red rust tone.

[0024]

Comparative Example 2 JIS A6063 under the same conditions as in Example 1 except that the immersion in the aqueous sodium hydroxide solution was omitted.
The aluminum alloy was electrolytically colored. When the surface of the alloy after the treatment was observed, only fine irregularities were detected, and there was no roughness, and the alloy was not colored red.

[0025]

Comparative Example 3 JIS A60 under the same conditions as in Example 1 except that the electrolytic coloring using the aqueous solution containing copper ions was omitted.
The 63 aluminum alloy was electrolytically colored. When the surface of the alloy after the treatment was observed, irregularities were detected, but there was no fine shading or roughness, and (L ^* : 60.2, a ^* : 3.
9, b ^* : 16.5), which was a color tone different from the calm red rust tone.

[0026]

As described above, in the present invention, the pits formed on the material surface by immersing the aluminum material in the aqueous solution containing hydrochloric acid are enlarged with an alkaline aqueous solution, and the pits are modified into a surface with conspicuous irregularities. Later, metal copper and metal nickel or metal cobalt are electrolytically deposited on the bottom of the pore through an anodic oxidation treatment. The aluminum material thus given a rust-like color with a grainy feeling is used as a building material for high-quality sashes, curtain walls, doors, exteriors, etc. because it exhibits a calm feeling rich in harmony with the surroundings. You.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Ken Ebihara 1-34-1 Kambara, Kambara-cho, Anbara-gun, Shizuoka Prefecture Nippon Light Metal Co., Ltd. Group Technology Center (72) Inventor Mikio Asakura One-Osaki, Shinagawa-ku, Tokyo Chome 11-1 Inside Nippon Light Corporation (72) Inventor Takashi Iriya 1-1-11 Osaki, Shinagawa-ku, Tokyo (72) Inventor Kiyoshi Kawabata Kiyoshi Kawabata 1-1-11 Osaki, Shinagawa-ku, Tokyo No. 1 Inside Shin Nikko Co., Ltd. (56) References JP-A-58-14797 (JP, A) JP-A-8-252989 (JP, A) JP-A-58-219728 (JP, A) JP-A-58-219728 10-138658 (JP, A) JP-A-53-30935 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C25D 11/12 301 C25D 11/16 301 C25D 11/22

Claims (5)

(57) [Claims] Claims: 1. After forming fine irregularities on the surface of an aluminum material by immersion in a hydrochloric acid-containing aqueous solution, the aluminum material is immersed in an alkaline aqueous solution to enlarge the irregularities;
Next, the aluminum material is subjected to anodizing treatment for forming a porous film on the surface, and the anodized aluminum material is electrolyzed in a copper ion-containing aqueous solution to precipitate metallic copper in the pores of the porous film, and further to nickel ions Alternatively, a method for coloring an aluminum material, comprising depositing metallic nickel or metallic cobalt on pores of a porous film by electrolysis in an aqueous solution containing cobalt ions. 2. An aqueous solution containing hydrochloric acid having a concentration of 10 to 200 g /
The method for coloring an aluminum material according to claim 1, wherein the aluminum material is immersed in an aqueous solution containing hydrochloric acid at a bath temperature of 20 to 50 ° C for 1 to 20 minutes. 3. An alkaline aqueous solution having a concentration of 20 to 100 g.
/ L sodium hydroxide, bath temperature 30-70 ° C, p
Aluminum material 3 in alkaline aqueous solution of H13 or more
The method for coloring an aluminum material according to claim 1, wherein the aluminum material is immersed for up to 20 minutes. 4. Containing copper ions at a concentration of 2 to 10 g / l,
The method for coloring an aluminum material according to claim 1, wherein a copper ion-containing aqueous solution having a pH of 2 or less is used. 5. An aqueous solution containing nickel ions or cobalt ions at a concentration of 20 to 40 g / l and boric acid at a concentration of 10 to 40 g / l and having a pH of 4 to 6 is used as the aqueous solution containing nickel ions or cobalt ions. 2. The method for coloring an aluminum material according to item 1.