DE2416012A1 - PROCESS FOR THE PRODUCTION OF COLORED OXYD FILMS ON ALUMINUM OR ALUMINUM ALLOYS - Google Patents

Description

DR. ING. E. HOFFMANN · DIPL. ING. W. 'KIlXS · DK. ii £ R. NAT. K. HOFFMANN

ΓΛΤΚΛ ΥΛΝΛν ^τ Αΐ, Τ.ΐί

D-8000 MÖNCHEN 81ARABELLASTRASSE 4 TELEPHONE (0811) 911087 2416012

25 170

Riken Light Metal Industries Co., Ltd., Shizuoka-shi / Japan

Process for the production of colored oxide films on aluminum

or aluminum alloys

The invention relates to a method for producing a colored oxide film on the surface of an aluminum material, in which the aluminum material is an electrolytic Is subjected to treatment in an aqueous solution containing sulfuric acid, whereby an aluminum oxide film is formed containing aluminum oxides and lattice vacancies, and wherein the sulfuric acid ions in the solution enter the lattice vacancies penetrate the oxide film and some or all of the sulfuric acid ions are reduced, with sulfur and sulphides are formed and the colored oxide film is formed which contains sulfur and sulphides which give the color.

The invention relates to a method for producing a colored Oxide film on the surface of aluminum or an aluminum alloy, and particularly relates to a method for the production of a colored oxide film on the surface of aluminum or an aluminum alloy by is electrolyzed in an electrolytic bath from an aqueous solution containing sulfuric acid, the aluminum or the aluminum alloy is used as an anode, or both an anode and a cathode.

It is known to make aluminum material resistant to corrosion or similar influences by making it a

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anionic oxidation treatment in an aqueous solution, which contains sulfuric acid, subjects. A coloration of the oxide film formed on the aluminum material becomes achieved by painting with a dye or similar or by electrolytically applying an alternating current between the Aluminum materials, which serve as anode and cathode, conducts in aqueous solution, the sulfuric acid and a metal salt contains. However, coloring with dyes is disadvantageous in that the dyes can decompose and upon electrolysis with alternating current, two steps of electrolyzing are required, and from an economical point of view, this process is therefore unfavorable.

Furthermore, a method has been used to produce a colored oxide film by using an aluminum material Subjected anodic oxidation treatment in an electrolytic bath containing, for example, sulfosalicylic acid and sulfuric acid or contains a metal sulfate. In this process, a colored oxide film is only obtained by electrolytic treatment Formed at room temperature, but sulfosalicylic acid is used as the electrolyte, which is expensive and difficult to obtain is, and therefore this method is too expensive. This method also has the disadvantage that the aluminum material is only used as an anode and cannot be used as an anode and cathode at the same time.

The present invention is therefore based on the object of a method for producing a colored oxide film to provide an aluminum material, wherein the aluminum material undergoes an anodic oxidation treatment in a aqueous solution containing sulfuric acid and being subjected to pulse voltage on the aluminum material applies.

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~ j -

Another object of the present invention is to provide a method for producing a colored oxide film on an aluminum material by subjecting the aluminum material to electrolytic treatment in . aqueous solution containing sulfuric acid, while applying a square pulse voltage to the aluminum material containing is used as an anode or both electrodes.

Another object of the present invention is ... to provide a method for producing a colored oxide film on an aluminum material by the ^aluminum: material is subjected to an anodic oxidation treatment in aqueous solution containing 5 to 95 wt% sulfuric acid. .

The present invention is also based on the object of a method for the simultaneous formation of a colored Oxide film on aluminum material that is used as both electrodes, alternatively using pulse voltages opposite polarities between the two electrodes in an aqueous solution containing only sulfuric acid contains, creates.

The invention relates to a method in which an AIu-

■ electrolytically treated minium material in aqueous solution

* is, where the aqueous solution contains sulfuric acid and where an oxide film is formed which contains aluminum oxides and which has defects in its crystal lattice contains (this oxide film is hereinafter referred to as "oxide film with lattice defects"), and if sulfur or sulfide are formed in the oxide film, the sulfur or sulfides act as color sources to give a colored oxide film.

According to a further embodiment of the invention, an aluminum material is subjected to electrolytic treatment, while applying a pulse voltage, where a

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Oxide film with lattice defects formed on the aluminum material will.

According to a further embodiment of the invention, there is at least 5> O% by weight of sulfuric acid in an electrolyte is present, forming sufficient sulfur or sulfide for coloring on the oxide film with lattice defects.

According to a further embodiment of the invention, an aluminum material containing Mg, Fe, Si, Cu, Zn, Cr, Contains Ti or other various alloying elements, an oxide film with lattice defects is formed on the aluminum material, by subjecting the latter to an electrolytic treatment and applying a pulse voltage, since the above elements, with the exception of copper, have a strong affinity for oxygen as in the case of aluminum. In the aluminum material, which contains Fe and / or Si, the element acts as a color source to the color effect of the colored Reinforce oxide film.

The drawings are explained in more detail below.

In Fig. 1 and 2 stress wave diagrams are shown, with which the system of the present invention is to be explained in more detail.

Preferred embodiments according to the invention are explained in more detail below.

Before the electrolysis, the aluminum material undergoes chemical pretreatments such as degreasing, rinsing, etc., and then it is subjected to neutralization treatment. The pretreatments can not only be of a chemical nature, but also of a mechanical nature. Since the Pretreatments are directly related to the present invention, they will not be described in detail.

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After the above pretreatments, the aluminum material is electrolyzed in an electrolyte containing at least 5.0% by weight Contains sulfuric acid, the aluminum material being used as an anode or an anode and cathode and a film from an aluminum oxide, which contains aluminum sub-oxides and other elements and which has defects in the crystal lattice, is formed on the aluminum material serving as an anode or an anode and cathode, and then the Sulfuric acid ions, i.e. the sulfate ions, in the electrolyte enter the vacancies of the film, and then in it Sulfur and / or sulfides are formed.

An oxide film containing sub-oxides of aluminum and other elements such as AlO, AlpO or the like, has an oxygen deficiency in contrast to a conventional anodic oxide film, which consists mainly of AlpO ^. At the same time, the crystal lattice of the oxide film has defects, the number of which increases in the presence of the aluminum sub-oxides. The size of the lattice defects and the radius of the sulfuric acid ions are essentially equal to each other. Therefore, there is a possibility that the sulfate ions enter the vacancies of the oxide film. Where the radius of the ions existing as alloying elements and impurity elements in the aluminum material dissolved in the electrolyte is substantially the same size as the lattice vacancies, the ions of the alloying elements and the impurity elements can also enter the lattice vacancies. Therefore, if sufficient energy is supplied during the electrolysis, the sulfuric acid ions, that is, sulfate ions, and the ions of the alloying elements and the elements present as impurities ¹ enter the lattice vacancies of the oxide film.

The sulfate ions and the other ions that are so in the lattice defects enter, lose their valence electrons in it,

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-D-

and at the same time they are reduced, taking sulfur and sulfides or sulfates of the alloying elements or impurity elements are formed. These products act as color sources and result in the colored oxide film.

To form an oxide film that contains sub-oxides of aluminum and other elements and that has lattice defects, the sulfate ions and other ions are caused to enter the lattice vacancies, and then they become during the Electrolysis is reduced to sulfur and / or sulfides, using the aluminum material as an anode or as an anode and cathode is used, and it is preferred, a pulse voltage memorize for the following reasons:

(1) In the case of using aluminum material as an anode in the electrolysis.

A rectangular pulse voltage as shown in FIG. 1 is a voltage at which a pulse from a peak voltage Ep is superimposed _{on the base voltage E 1.}

Using a voltage having a waveform as shown in Fig. 1, the aluminum material becomes by applying the basic voltage E. an aluminum oxide film is formed, and in the process in which the oxide film is formed, the rectangular voltage E ~ in a unit cycle time T is applied so that the alumina film is shocked and lattice vacancies are formed therein will. The oxide film is not sufficiently oxidized and aluminum and other elements remain in the form of suboxides, so that the film contains many suboxides. The sulfuric acid ions in the electrolyte are from. the aluminum oxide film of the above kind strongly attracted by momentarily impressing the rectangular voltage Ep, with practically no time passing, so that the sulfuric acid ions receive sufficient energy to be able to enter the lattice defects.

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When the sulfuric acid ions in the lattice defects of the aluminum oxide have occurred accordingly as described above, since the suboxide of the aluminum that is in the film is contained, has a strong reducing effect that reduces sulfuric acid ions, and it v / earths sulfur and Sulphides are formed and a golden yellow oxide film is obtained, for example.

(2) Use of aluminum materials in electrolysis as anode and cathode.

Since it is necessary to electrolyze both aluminum materials at the same time, a rectangular pulse voltage, as shown for example in Fig. 2 and changed its polarity at predetermined time intervals is applied.

In the electrolysis, in which the rectangular shown in FIG Pulse voltage is used, the polarity of the aluminum materials that serve as anode and cathode will be for example "positive" and "negative" changed, each with two periods. During each of the aluminum materials is embossed with positive rectangular pulse voltage, is accordingly, the aluminum material is oxidized, forming an aluminum oxide film thereon, the sub-oxides of aluminum and other elements and the lattice defects and the sulfuric acid ions in the electrolyte enter the vacancies of the film as above have been described in (1). However, contrary to the case of (1), the positive rectangular pulse voltage becomes during impressed in a very short time, so that the reduction described in (1) above takes place very little. The decrease in sulfuric acid ions is mainly during the impression of the negative square pulse voltage and the sulfur and / or sulfides are formed in the films and serve as a source of color, and thus colored oxide films are created on both aluminum materials at the same time.

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The following is a description of the appropriate range of characteristic voltage values of the waveforms, as shown in Figs. 1 and 2, given. You can go with. any pulse voltages other than the stresses shown in Figs. 1 and 2 can easily obtain a colored oxide film or films as long as their characteristic values are within the appropriate ranges described below.

Basic stresses E ^ and E.:

The positive basic voltage E ^ takes part in the formation of the aluminum oxide film; in order to form a sufficiently thick film, it is preferred to increase the positive fundamental voltages as high as possible. However, if the basic voltage E _{1 is} too high, the films can break off, so that the positive basic voltage E _{1 is} preferably 40 V or less.

Even if a positive basic voltage E ^ is not applied, An alumina film is formed to some extent because of the rectangular pulse voltage E2 described below is created. Accordingly, a colored oxide film can be formed even if the positive fundamental voltage E>, Is zero.

The negative basic voltage E ^ increases in the reduction of the Sulfuric acid ions part, and this also applies to the case when aluminum materials, which act as anode and cathode are used, can be electrolyzed at the same time. If the basic voltage is too negative, the aluminum oxide film can loosen .will and cancel, and it is preferable to negative ^ Base voltages in the range from -40 to 0 V are to be used. When the negative base voltage is zero, it becomes as follows will be described in more detail, a rectangular pulse voltage Ep imprinted to the reduction of sulfuric acid ions activate so that even if the negative fundamental voltage is zero and the fundamental voltage; is not used,

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Sulfur and / or sulfides are formed in the aluminum oxide film and a colored oxide film on both aluminum materials result.

The values Eg and Eg of the pulse voltage: With a positive value Eg, sufficient energy is supplied thus the sulfuric acid ions on the alurainium oxide film are attracted and enter the lattice vacancies of the oxide film, and at the same time adhere to the oxide film a shock is applied in order to suppress the growth of the oxide film, whereby an aluminum oxide film is formed, the sub-oxides of aluminum such as AlO, AIgO and others.

In the present invention, therefore, it is necessary to select the value Eg large enough so that the alumina film can provide sufficient shock that lattice voids are formed therein and that as many sulfuric acid ions as possible penetrate deeply into the lattice voids. From that point of view it is preferred that the value Eg be as large as possible, but to large values lead to the destruction of the aluminum oxide film. The value Eg is preferably 120 V or less. If the Eg value is about 5 V, the above effect can be satisfactory can be obtained.

The value Eg, in the negative direction contributes to the formation of Sulfur and / or sulfides, by reducing the sulfur ions in the lattice defects, if aluminum materials are used at the same time, which are used as an anode and a cathode, is electrolyzed. The larger the value Eg, the stronger is the reduction of sulfuric acid ions and the sulfuric acid ions that are present in the deep lattice defects are completely reduced, whereby the discoloration of the aluminum oxide is improved. Too large values for Eg lead to dissolution of the alumina film and for this reason

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it is preferred that the value Ep be in the range from -5 to 120 V is.

The periods T and T and the pulse duration i, and i :

It is necessary to precisely determine the period T and the duration. If they are not selected correctly, the effect of the impulse voltage impression is lost. It is preferred that when the time T is in the range of 0.2 to 120 seconds, the duration V is selected to be in the range of 0.1 to 60 seconds.

If the period T has a value less than 0.2 seconds, even if the duration C is less than 0.1 seconds, a colored oxide film can be formed. It is preferred that the period T and the duration T * be so selected

a a

as in the case of period T and duration ¹ T.

Average current density:

In the present invention, either when electrolyzing and using the aluminum material as an anode or when electrolyzing and using the aluminum materials as an anode and a cathode, it is so that an aluminum oxide film is formed while a positive voltage is impressed on the aluminum material and that the film is shocked or impacted so that a film is formed which has lattice defects or defects. In the present invention, therefore, it is necessary to form an alumina film having substantially the same thickness as that obtained by conventional anodic oxidation treatment, and the positive and negative current densities must both be in the range of 0.5 to 20 A / dm ² .

Duration of the electrolysis:

Too short a duration of the electrolysis causes the aluminum oxide film grows insufficiently, and if the duration is too long

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the film grows too strong. If the film is too thick, the film is easily cracked in the sealing treatment. For this reason, it is generally suitable that the electrolysis time in the range of 30 to 90 minutes is preferred in the range ^ from 30 to 60 minutes.

Influence of the positive and negative current density in the simultaneous electrolysis of aluminum materials which can be used as anode and cathode: While a positive pulse voltage is being impressed on the

Aluminum material, an aluminum oxide is formed and while the negative pulse voltage is impressed, sulfuric acid ions are reduced and the film dissolves. Accordingly, it is necessary to keep the mean current density 1 and i of both aluminum materials at the appropriate value given above and to maintain positive or negative pulse voltage impressing times t or t _o on the product and to keep the mean current density i or i in such a way.

mm "^ gL

len that the positive or negative charge density on the Aluminum material has a suitable value. According to the experiments, it was found that the appropriate values

the mean current density i and i in the range from 0.5 to p ~~ "" ■ * a

7.0 A / dm even if a pulse voltage is impressed by any waveform. Besides, the ratio is the positive charge density and the negative charge density as well as the magnitude of the absolute value of the positive or negative charge density. If the positive charge density is higher than the negative charge density, so is formation of sulfur and / or sulfides, which is effected by reduction of sulfuric acid ions, insufficient and in the opposite In this case, the formation of aluminum oxide is insufficient, too much aluminum oxide film dissolves. It was found that in the present invention, the ratio of positive charge density and negative charge density is preferably as follows

i while positive χ t .

i while negative χ t

CL

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Bath temperature:

The bath temperature is preferably in the range of 0 Ms 30 ° C. For example, a colored oxide film may form at room temperature of 15 ⁰ C as well. A low bath temperature facilitates the formation of sub-oxides of the aluminum and a cooling device may be required if necessary, and it is desirable to choose the bath temperature so that it is at room temperature of about 15 ^° C.

Experiments have found that when the above conditions all adhered to, a colored oxide film, with which one can detect any voltages of the following waveforms impresses in addition to the waveforms shown in FIGS. 1 and 2, can be formed electrolytically:

■ (1) Alternative use of positive and negative DC voltages. In this case, the DC voltages include a full-wave rectified voltage, the contains some small waves.

(2) Alternative use of positive DC voltage and AC voltage.

(3) application of a positive DC voltage one after the other, an AC voltage and a negative DC voltage in the order given.

(4) Applying a voltage so that a voltage with full-wave or half-wave rectification of a single Phase or a multiphase voltage phase-controlled by a silicone leveler, a chopper or similar or alternate use of positive and negative voltages of such waveforms.

(5) Applying a voltage so that a single phase sine wave voltage through a silicone rectifier or a chopper is phase controlled or alternatively the use of positive and negative voltages of such waveforms.

(6) Application of pulse voltage, for example Saw number shape, triangular or similar wave shape or age-

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native application of positive and negative voltages such waveforms.

The following examples illustrate the invention without restricting it.

example 1

An aluminum material 6063 is degreased and rinsed with water and then anodic oxidation in one subjected to aqueous solution containing 7.0 to 30 wt.% HpSO, with the aluminum as an anode and a graphite electrode can be used as a cathode.

In this example, three types of voltages shown in Fig. 1 are applied between the two electrodes created or embossed. The results are shown in Table I below.

Table I State of voltage waveform Electrolytic bath Color d.

EE ₂ T Z current current ^H 2 ^S V ^{tem perature}

ίπ \ (λτ \ c. ™ r, ~ dense density conc.

(V) (V) sec sec _{(A) k / äa} 2 _(B) (g _e y.%) (Qq 30 40 1.1 0.1 4 10 7.0 13 deep gold yellow 20 10 5.5 0.5 2 10 17.0 14 somewhat "0 30 6 5 0 10 30.0 15 somewhat light yellow

Current density (A) shows the impression of a constant voltage E. and the current density (B) shows the impression or application of (E. + E ₂ ).

Example 2

An aluminum material 1100 is degreased and rinsed with water and then subjected to electrolytic treatment in subjected to an aqueous solution containing 15% by weight of sulfuric acid by applying pulse voltages shown in FIG are, between the aluminum material that acts as the anode

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acts, and a carbon electrode, which acts as a counter electrode, applies for 60 minutes. The bath temperature is at Maintained 25 ° C.

In this example the values of the pulse voltages are the between the aluminum material and the carbon electrode, and the color of the films in the following table II listed.

Table II

Voltage (V) ^E 2 la ^E 2a Pulse width (see) T T
a \ Proportions
d.Charging
density
in the
Polarite. •
5-
colour 86 -28 -61 T 1 2 1 0.5 very bright
yellow 1 4a 6? -18 -56 2 1 2 1 1.0 light yellow 2 51 115 -52 -76 5 1 2 1 1.5 yellow 5 56 69 -18 -58 5 2 2 1 4.0 easy
greyish.-"
Brown 4th 54 10

Example 5

The fourteen aluminum materials listed in Table III were subjected to electrolytic treatment in an aqueous solution containing 7% by weight of sulfuric acid by taking the voltage of FIG Cathode was used, using the following conditions: E ₁ = 30 V, E ₂ = 40 V, T = 1.1 sec, Z = 0.1 sec, A = 4 A / dm ^, B = 10 A / dm, bath temperature = 15 ⁰ C. the properties of the colored oxide films are shown in Table IV.

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Al
) 5. Cu Pe - 50 Tabel Si - Mn - I. - - 15
III - M. I. - Cr Ti - Other Egg ment - - - Legie 99-99
min. 3. - .17 - 40-v
1.2 Mg 20'-
0.8 50 - - Single total
menee menee - - - tion
(AA Il 3. - 7th .70 40 3-v,
0.9 2 "V *
1.8 Zn 25th - - - 50 0. 15th 1099 rest 0. OV
6.0 0. 0 .35 0. 50x
1.2 0-v
1.5 - 25th 15th - 05 0. 15th 1100 It 0. 5.0 1. 50 .5 0. 50 0. 05 05 10 0.10 0. - 0. 05 0. 15th 2011 It 0 β-ν-
4.9 0. 70 0. 60 0. 20th 0. 1.1 0. 10 0.10 - 0. 05 0. 15th 2014
I. Il 0 20th 0. 80 0. 5-ν,
6.0 1. .10 1. 2.8 0. 25th - 20th 0. 05 0. 15th 2024 ti 0 30th 0. 7th 4th 40 0, .20-
0.7 .5'-
4.5 0. 10 - 0. - 0. 05 0, 15th 5005 ti 0 20th 0- ■ "V
naxi-
well 0. 45 0. .15-
3.45 0. .8'v
1.2 0. 25th 0.10 - 0. 05 0 .15 4045 ti 0 .10 0 0 .40 0 .15 0. .8 ο-
Ι.2 0. - 0.15--
0.55 15th 0. 05 0 .15 5005 It 0 .10 0 .0 .12 0 .10 2 .15-
0.9 0. .25 0.05
0.25 0. - 0. .05 0 .15 5052 Il 1 .07 0 0 .4- ..
3.8 0
( • 50 5 * 2.9 0 .10 - .15 0 .05 0 .15 5O86 Il 3.4O 0 0 .20-
0.6 0 0 0 * 6a 0.15-v
0.55 0 .10 0 .05 0 .15 5357 ti .10 0 0 .50 0 0 0.10 0 .20 0 .05 0 .15 6061 ti .2 ·. ·
2.0 0 0 0 0 0.18-
0.40 0
i 0 6663 2 0 0 7075 5

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Color of the film - 16 - 2416012 Table IV alloy Brown . Alloy name Color of the film (A.A.) black-brown 1100 black-brown 5052 yellowish-brown 2011 yellowish-brown 5086 black-brown 2014 black-brown 5358 greyish-brown 2024 black brown 6061 s black eg raun 3003 black-brown 6063 yellowish ^ brown 4043 7075 yellowish-brown 5045

It can be seen from Table IV that the color of the colored oxide film of the aluminum material containing much iron becomes darker as the amount of iron obtained is increased. If one examines the condition of the films, one finds that
in all films sulfur and / or sulfides are deposited in the lattice defects.

From the foregoing it can be seen that, according to the invention, a colored oxide film is obtained by
an anodic oxidation treatment is carried out in an aqueous solution containing sulfuric acid without adding coloring additives.

The present invention thus has the following advantages:

(1) The electrolytic solution has a simple composition and is economical and control

the bath can be done easily.

(2) Sulfuric acid ions, ie sulfate ions, serve as a color source and enter the lattice defects of the aluminum oxide film during its formation, the resulting color
is constant and uniform and does not degrade the properties of the film.

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(3) Electrolysis is carried out in an aqueous solution containing sulfuric acid and productivity is excellent.

As an aluminum material or an aluminum alloy in the present invention, one can also use an industrially pure one Aluminum, any other various aluminum alloys and especially aluminum alloys that are oxidizable Containing alloying elements. However, the alloys should not contain too much copper.

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Claims (6)

Claims V1 .J A process for producing a colored oxide film on an aluminum material, characterized in that the aluminum material is electrolyzed in an aqueous solution containing sulfuric acid, an aluminum oxide film containing aluminum suboxides and crystal lattice defects being formed and the sulfuric acid ions being formed in the aqueous solution Solution are drawn into the lattice defects and some or all of the sulfuric acid ions are reduced, with sulfur and sulfides being formed, which serve as color sources for the colored oxide film. 2. Method of making a colored oxide film on an aluminum material according to claim 1, characterized in that positive pulse voltage for the formation of the aluminum oxide film and for the sulfuric acid ions to lead into the lattice imperfections, is imprinted. 3. A method for producing a colored oxide film on an aluminum material according to claim 2, characterized in that characterized in that a negative pulse voltage is impressed in order to reduce the sulfuric acid ions to activate with the formation of sulfur and sulphides. 4. A method for producing a colored oxide film on an aluminum material according to claims 2 and 3, characterized in that rectangular positive and negative pulse voltages are used. 5 · Method of making a colored oxide film on an aluminum material according to claim 1, characterized in that the aqueous solution is 5 to Contains 90% by weight sulfuric acid. 409847/1022 6. Method of making a colored oxide film on an aluminum material according to claim 1, characterized in that the aluminum material uses an aluminum alloy containing an element whose affinity for oxygen is equal to or stronger than that of aluminum or stronger than that of copper. 409847/1022 Le e rs e ite