JPS602694A - Surface treatment for patterning of aluminum - Google Patents

Abstract

PURPOSE:To form satisfactorily various kinds of decorative patterns of the surface of an Al alloy with good productivity by subjecting the Al alloy formed by extrusion to a slack age hardening treatment and forming an underlying pattern thereon then subjecting the alloy to an electrochemical pigmenting treatment including oxide film reforming. CONSTITUTION:An Al alloy after extrusion is subjected to a slack age hardening treatment then a desired underlying pattern is formed thereon by a mechanical operation. An anodically oxidized film is formed on the surface of such Al alloy and in succession the alloy is subjected to AC electrolysis or DC electrolysis in a bath of an inorg. or org. acid to reform the anodically oxidized film to a double-film construction. The reformed oxide film is subjected to AC electrolysis or DC cathodic electrolysis in an electrolyte contg. an inorg. metallic salt, thereby forming a desired colored film. A difference in the density of coloring is generated between the underlying pattern part and the background by the synergistic effect of the above-mentioned surface treating stages, by which the colored pattern having the beautiful woodgrain tone, printed tone, etc. having resistance to corrosion and wear is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a surface treatment method that can clearly produce various decorative patterns such as woodgrain or printed patterns on the surface of an aluminum alloy (excluding pure aluminum) having age hardening performance. More specifically, by applying a skillful combination of incomplete age hardening treatment, mechanical operation, and electrochemical operation to the surface of aluminum alloy, it is possible to create shading differences on the surface of aluminum alloy in an extremely simple manner. Patterning of aluminum alloys, which can produce a beautiful colored pattern and a corrosion-resistant colored film, is related to a surface treatment method.

Conventional technology and its problems Conventionally, as a method of generating a colored pattern on the surface of an aluminum material using artificial age hardening treatment, there is a method described in Japanese Patent Application Laid-open No. 53
-83941 is known. This technology involves attaching a desired patterned sheet to the surface of an aluminum material, subjecting it to artificial age hardening under normal conditions, removing the patterned sheet before or after cooling, and then removing the patterned sheet from the aluminum material. This is a method of producing a colored pattern on the surface of an aluminum material by electrolytically coloring it as an anode. The generation mechanism of the colored pattern in this method is that during the age hardening treatment, heating causes a difference in the crystal structure between the areas where the patterned sheet is attached to the aluminum material and the area where it is not attached. It creates a pattern during electrolytic coloring.

However, this technique has the following drawbacks.

αNO Inside the age hardening furnace, the temperature is not necessarily uniform between the left and right, top and bottom edges and the center, and there are temperature differences, making it difficult to control the pattern of the resulting product.

b) Since aluminum material has very good thermal conductivity, it is difficult to create a temperature difference between the parts to which the patterned sheet is attached and the parts to which it is not attached. Therefore, it is difficult to generate a colored pattern with a clear difference in shading, and it is also difficult to make small patterns such as a spotted pattern, a polka dot pattern, a woodgrain pattern, etc. appear on the aluminum material.

C) The process of attaching and removing the patterned sheet is necessary, and a patterned sheeter must be prepared for each shape of the extruded shape, so the workability is extremely poor and the resulting product is expensive. become.

Furthermore, as another method for forming a patterned oxide film, the method described in Japanese Patent Publication No. 43-6365 is known. This technology uses an aluminum alloy with a specially selected At-MyL-My alloy composition, expands the aluminum alloy, applies special heat treatment during or after the processing process, and then anodizes the aluminum alloy. This method is designed to produce a contrasting black and white pattern on the surface of an aluminum alloy due to the precipitation of an Al-Mn binary compound.

The patterns obtained by this method are completely random in form, and it is not possible to obtain arbitrary patterns, and the patterns are also limited to the contrast of black and white, so it is still impossible to obtain decorative and beautiful colored patterns. There is a problem with this.

OBJECTS OF THE INVENTION Accordingly, it is an object of the present invention to provide a surface treatment method for patterning an aluminum alloy, which can produce a beautiful wood grain, print adjustment, and various desired colored patterns on the surface of an aluminum alloy.

Other objects of the present invention, in relation to the above-mentioned objects, are to produce a colored pattern that is excellent in various performances such as corrosion resistance, weather resistance, abrasion resistance, etc., and has good color contrast with differences in shading, and to produce a machined pattern for aluminum alloys. The object of the present invention is to provide a surface treatment method for patterning aluminum alloys that can impart mechanical strength through a series of steps with high productivity.

Structure of the Invention The present invention involves subjecting an aluminum alloy to an incomplete age hardening treatment after extrusion molding, instead of the conventional complete age hardening treatment after extrusion molding, and then applying a base pattern by mechanical manipulation. After that, the aluminum alloy is subjected to an electrochemical coloring treatment including an oxide film modification treatment, and by taking advantage of the mutual effects of these treatments, the base pattern area and the background (other than the base pattern area) are This is based on the knowledge that there is a difference in the shade of color between the parts), and the base pattern is clearly exposed on the surface of the aluminum alloy.

That is, the present invention (the third invention concerned).

(3) Incomplete age hardening treatment is applied to the aluminum alloy after extrusion molding.

[Bl Next, a base pattern is applied to the surface of the aluminum alloy by a mechanical operation, (C) After that, an anodized film is formed on the aluminum alloy by a conventional method, After modifying the anodic oxide film into a double film structure by alternating current electrolysis in a bath, a coloring treatment is applied to the film.

Further, in the second invention according to the present invention, the oxide film modification step is different from the (DJ step) of the first invention, and (3) the aluminum alloy after extrusion molding is subjected to incomplete age hardening treatment, Bl Next, a base pattern is applied to the surface of the aluminum alloy by mechanical manipulation, (Cl) Thereafter, an anodic oxide film is formed on the aluminum alloy by a conventional method, and (6) The aluminum alloy is connected to a cathode and subjected to direct current electrolysis to modify the oxide film, and then subjected to (El coloring treatment).

Aspects of the Invention Next, each step of the present invention and its aspects will be explained in detail.

(3) Incomplete aging hardening treatment process First, the aluminum alloy after extrusion molding (below).

Incomplete age hardening treatment is applied to the extruded shape of aluminum alloy (abbreviated as aluminum alloy).

This age hardening treatment is performed under conditions where the aluminum alloy does not reach complete aging.

To explain age hardening treatment, for example, aluminum alloy A
In the case of -60638 material, the effects of age hardening temperature and time on the hardness of the alloy are shown in FIG. That is, at any age hardening treatment temperature, the hardness reaches its maximum value after a certain period of time, and age hardening at this stage is defined as complete age hardening. Therefore, incomplete age hardening means age hardening before reaching this stage.

Although FIG. 1 shows the state of high-temperature aging or artificial aging, incomplete aging here is not limited to this, but also includes room temperature aging or natural aging. Therefore, in an extreme case, it may be allowed to stand for a long period of time for natural aging. However, it is usually preferable to perform artificial age hardening treatment from the viewpoint of workability, etc. In this case, although it differs depending on the material of the aluminum alloy, it is generally performed at a temperature of 155 to 195 degrees Celsius.
It is best to do this for a minute to 8 hours. The appropriate range of time and temperature for incomplete age hardening treatment is shown in Figure 2. In particular, the conditions shown in the shaded area shown in FIG. 2 are preferable.

(B) Base pattern forming process As mentioned above, an extruded shape of an aluminum alloy that has been subjected to incomplete age hardening treatment (an extruded shape in a high temperature state immediately after age hardening treatment may be used, or an extruded shape at room temperature after cooling) Then, a base pattern is applied by mechanical operation.

Mechanical operations include all operations other than chemical treatments such as etching with acids and alkalis.

This base pattern can be created using, for example, a blasting method in which sand, iron powder, etc. are sprayed, a high-pressure jetting method in which a liquid such as water is injected at high pressure, a brush method in which the aluminum alloy surface is scratched with a brush, a laser beam method in which a laser beam is irradiated, and an embossing plate roll method. It is applied to the aluminum alloy surface by various mechanical operation means such as the roller method used and the press method in which a die press is used.

To be more specific, for example, with the aim of improving workability,
In a mold or metal frame (jig) that has the same shape as an aluminum alloy extrusion mold and has a certain clearance, for example, provide injection grooves (holes) for surface pressure injection at straight-grain pattern intervals, and make a water puddle 7?1. By continuously adjusting the surface (applying a base pattern) while spraying an abrasive or the like, it is possible to apply a base pattern even to complex-shaped irregularities. In this case, a desired continuous pattern (for example, a pattern with long straight grain intervals as in printing, a pattern with varying shading, etc.) can be easily provided. Alternatively, instead of the above-mentioned high-pressure injection, there is also a method in which claw-shaped metal or ceramic jigs are placed inside the mold or metal frame, for example, at intervals in a straight-grained pattern, and the aluminum alloy profile is rubbed with a constant pressure. Can be adopted.

In addition, by stamping the incompletely age-hardened aluminum alloy shape into any pattern using a decoration that causes scratches or distortions, such as an embossing roll, straight grain, plate grain, etc.
Desired patterns such as letters and pictures can be easily formed, and the decorativeness can be further enhanced. Furthermore, in relation to panels, stamping using a mold press is also possible, and any complex pattern can be applied.

In addition, as a method to create a different effect from the shape of the shape, the pattern can also be imparted by making the shape itself uneven in the form of a pattern during extrusion molding, and by rubbing the surface with metal, ceramic, carbon, etc.

The means for forming the base pattern is not limited to the above methods, but any method may be used as long as it can form a decorative pattern on the surface of the aluminum alloy profile using a method with good workability.

The formation of this base pattern is caused by the interaction between the incomplete aging hardening treatment and the electrochemical coloring treatment described below, especially the oxide film modification treatment, and serves as the base or nucleus for the appearance of the colored pattern. The depth of the concave part is surface adjusted (base pattern formation)
It is not an essential element of the product, but it is sufficient to have the die mark within the range of passing the appearance, and even after the oxide film is formed, there is no performance deterioration due to the scratches even when observed under a microscope. be. Further, the same applies to the parts where distortion is applied, and there is no deterioration in performance at all.

Note that when a pattern is formed on a material immediately after extrusion molding by mechanical operation, the hardness of the material is quite soft, so there is a possibility that the shape will be defective. However, in the present invention, the formation of the base pattern is performed by incomplete age hardening. Since this is done after processing, there is almost no need to worry about this.

(C1 Anodic oxide film formation process The aluminum alloy that has gone through each of the above steps is degreased using the usual method, washed with water, smut removed if necessary (IO, etc.), and then subjected to a well-known anodic oxidation treatment to form an anode. Forms an oxide film.

Namely, 1. An electrolytic solution containing a well-known inorganic acid and/or organic acid electrolyte, such as sulfuric acid, chromic acid, phosphoric acid, etc., or a mixed acid thereof, oxalic acid, malonic acid, etc., or a mixed acid containing these or a mixed acid with an inorganic acid. The aluminum alloy is anodized in a liquid using direct current, alternating current, or similar current waveforms. The applied voltage, application time, etc. for the anodic oxidation treatment are sufficient as usual.

(Dl, (Dr) Oxide film modification step The oxide film on the surface of the aluminum alloy obtained as described above is modified by one of the methods described below. There are two methods: the quality method and the cathodic direct current electrolytic reforming method.

Each corresponds to the first invention and the second invention of the present application.

This oxide film modification treatment is a process carried out for the purpose of bringing out the contrast of the pattern more clearly, and the conditions for this include the same electrolyte as the electrolyte in (12) of the anodizing treatment, or a metal salt, etc., which will be described later. An electrolyte with additives or a different electrolyte may be used, and electrolytic treatment is performed in this electrolytic solution with alternating current or a waveform having an equivalent effect, or cathodic direct current electrolysis is performed.

Each method will be explained below.

(Dl Alternating current electrolytic reforming method: Applying current to an aluminum alloy in an electrolytic solution consisting of an inorganic acid such as sulfuric acid, phosphoric acid, chromic acid, or an organic acid such as oxalic acid in an alternating current waveform or a current waveform having properties equivalent to this. Next, the oxide film is modified into a double film structure.The electrolysis conditions are the same as the usual method, but preferably 5 to 30V, 1
The test is carried out for ~30 minutes.

This secondary anodic oxidation treatment by AC electrolysis is not intended to produce a colored film, but in conjunction with the oxide film treatment described above, is to produce an oxide film with a double film structure.

Due to the formation of this double film structure, in the colored pattern formed by the subsequent coloring process, the difference in color shading between the bare base portion and the background becomes remarkable, and the contrast of the colored pattern becomes clearer.

(D)' Cathode direct current electrolytic reforming method In an electrolytic solution consisting of an inorganic acid such as sulfuric acid or phosphoric acid, the aluminum alloy on which the oxide film is formed is connected to the cathode to generate direct current or properties equivalent to this. The aluminum alloy is energized using a current waveform.

This current treatment causes a dissolution effect on the oxide film on the aluminum alloy surface, but at this time, because the amount of current flowing is different between the base pattern and other parts (background), there is a difference in the quality of the film between the two. Get out. As a result, the contrast of the colored pattern becomes more noticeable through the subsequent coloring process.

The concentration of the electrolytic solution, the applied voltage, the time, etc. are the same as in the conventional method, and are preferably performed under the conditions of 3 to 20 V and 20 seconds to 10 minutes.

(El coloring treatment step) The oxide film modified by either of the above (Dl current electrolytic reforming method or (D)' cathode cathode direct current electrolytic reforming method) is then placed in an electrolytic solution containing an inorganic metal salt. A colored film is formed by AC electrolysis or DC cathode electrolysis. Examples of inorganic metal salts include sulfates of nickel, cobalt, chromium, copper, cadmium, titanium, manganese, molybdenum, tin, magnesium, silver, lead, etc., and hydrochloric acid. Various conventionally known salts such as salts, oxalates, tartrates, chromates, and phosphates can be used, and conventional electrolytic conditions are sufficient.

Through this coloring treatment, a colored film with excellent corrosion resistance, weather resistance, and various other properties is formed on the aluminum alloy surface, and the background pattern area (scratches or dents) also improves the background (non-patterned area) area. It is darkly colored, and the underlying pattern applied to the aluminum alloy surface by mechanical manipulation appears as a colored pattern.

The aluminum alloy thus colored is sent to a painting process, if necessary, and is painted and baked by a well-known method. Depending on the alloy composition of the aluminum alloy, it may be difficult to completely age the aluminum alloy due to drying in a hot air oven after or before the anodizing process (15) or the coloring process in the oxide film modification process 1. In such cases, it is preferable to carry out painting and baking treatment, as baking after painting will result in complete aging. Also, in such cases,
One measure is to increase the aging hardness to a certain level in the baking furnace used in the extrusion molding process of aluminum alloys.

Material Although pure aluminum is excluded in the present invention, various aluminum alloys can be used. Aluminum alloy is an alloy whose strength is increased by quenching and tempering, that is, Ctb and Mg+8i are the main additives.

A preferred example is one containing ZrL+My, but it is not limited to this. The color tone of the colored pattern and the contrast of the pattern can be adjusted by combining the additional elements, work hardening, heat treatment conditions, etc. Further, in order to enhance the heat treatment effect and shorten the treatment time, the amount of added elements can be changed (16). For example, ht-M! 1-si alloy or Mg-5i-Fe alloy.

Depending on the combination of addition amounts, for example, excessive f3i can promote age hardening. Therefore,
For the purpose of improving color tone, pattern contrast, workability of processing steps, etc., it is possible to use an aluminum alloy with an alloy component suitable for the processing steps and conditions.

Effects of the Invention As described above, the patterning of the aluminum alloy according to the present invention can be achieved by surface treatment methods such as incomplete age hardening treatment, formation of a base pattern by mechanical operation, anodizing treatment, oxide film modification treatment, Due to the mutual effects of each step of the coloring process, a difference in color shading occurs between the base pattern and the background, giving the aluminum alloy surface excellent performance such as corrosion resistance, weather resistance, and abrasion resistance, as well as a woodgrain finish. , print mediation can produce various desired beautiful colored patterns. Naturally, such effects are due to the mutual effects of the above-mentioned processes, and in particular, the addition of the oxide film modification process makes the contrast of the colored pattern sharper and improves the coloring property. An extremely excellent colored pattern can be obtained.

Furthermore, according to the method of the present invention, in addition to the advantage that colored patterns can be generated in a series of steps with high productivity, mechanical strength, especially hardness, can be imparted to aluminum alloys compared to conventional extrusion molding. It is advantageous from the viewpoint of energy saving because it is performed not by complete age hardening treatment but by using the incomplete age hardening treatment and drying in a hot air oven in the anodic oxidation treatment step, or further paint baking treatment.

In addition, since the underlying pattern appears as a colored contrast pattern, the racking form in the surface treatment process can be either horizontally or vertically hung, and there is no element that requires the addition of new technology, which is currently standardized. This has the advantage that it can be dealt with in a sufficient manner.

In addition, the aluminum alloy shapes treated according to the present invention showed no deterioration in performance even after being given a base pattern, no defects were observed when observing the oxide film or colored film under a microscope, and various tests showed that the aluminum alloy shapes were not colored by electrolytic coloring. It is no different from shaped materials and can be used freely for the same purpose, without any restrictions on interior or exterior use.

Examples Example 1 An aluminum alloy (A-60638) shape after extrusion molding is subjected to incomplete age hardening treatment under the conditions of 170° C. A base pattern was formed by spraying water under the condition of +20022.

After that, the aluminum alloy shape is degreased.

Etching and smut removal were performed, followed by immersion in a 19 W/V% sulfuric acid aqueous solution and anodizing at a current density of 1.2 A/dηt (voltage approximately 12.5'l, liquid temperature 21°C, 35 minutes). Then, as an oxide film modification treatment, a current density of 2 was applied to a carbon counter electrode at the same concentration and temperature as in the anodic oxidation treatment bath.
．． Perform AC electrolysis for 7 minutes at 8 A/d co(+9) (voltage approximately 7.1 E V),
Afterwards, as a coloring process, the length is 200v, the width is +50 fins,
A container with a height of 150 mm and a carbon counter electrode placed at one end of the container.
The aluminum alloy shape having a width of 70 +u, a width of 70 + + + a, and a thickness of 1.3 mm was immersed in an electrolytic solution having the following composition at a temperature of 16°C, with the distance between the electrode and the carbon counter electrode set at 180. When AC electrolysis was carried out for 5 minutes at an applied voltage of , initial current density IA/d, and 10VO, the base pattern was colored darker than the background, and a beautiful ocher decorative pattern was exposed.

Electrolyte bath composition: sulfuric acid 40' I/, sodium trithionate If/, stannous sulfate 4 g/
Except that the aluminum alloy profile was connected to the cathode and subjected to direct current electrolysis at a voltage of about 5 V) for 2 minutes.

When the entire aluminum alloy (2ω) profile was treated in exactly the same manner as in Example 1, a beautiful ocher decorative pattern with a difference in shading between the base pattern on the surface of the profile and the background appeared. .

Example 3 After cooling an extruded aluminum alloy (A-60638) shape to room temperature, it was subjected to incomplete age hardening at 170°C x 3 hr, and then cooled to room temperature. On the surface, 1011s/? ec
A laser beam with a frequency of 3.0 KI (Z, +6 A) was fully irradiated at a speed of
The shape was immersed in a sulfuric acid aqueous solution of +gW/W, and the current density was 1. Anodic oxidation was carried out under the conditions of 1A/dpi (voltage approximately +2V), liquid temperature 20° C., and time 30 minutes to form an anodic oxide film of approximately 10 μm. Next, as an oxide film modification treatment, Example 2
With the same equipment and the same concentration bath, the current density was 1.2A/dyf.
(ilj pressure of about 6 V) for 1 minute and 30 seconds by connecting the aluminum alloy shape to the cathode and performing direct current electrolysis. Next, as a coloring treatment, using the same apparatus as in Example 1, immersed in an electrolytic solution having the following composition at a bath temperature of 20°C, and subjected to AC electrolysis at an applied voltage of IIV for 5 minutes and 30 seconds. , the base pattern was colored much darker than the background, resulting in a clear olive-colored decorative pattern.

Electrolyte composition: sulfuric acid 20ml/nickel sulfate 30g/1 sulfuric acid 57/l cresonyl sulfon e 109/l Example 4 Aluminum alloy (A-60638) shape after extrusion molding at 160°C After performing an incomplete age hardening treatment under the conditions of 7 hours, and then once cooling to room temperature, a base pattern was formed by bringing uneven carbon into contact with the surface of the aluminum alloy shape. After that, the aluminum alloy shape was degreased, etched, and smut removed, and then 19W/V%
sulfur.

It was immersed in an acid aqueous solution and anodized at a current density of 1.2 A/d (voltage of about 12.5 V) and a solution temperature of 21° C. for 35 minutes to form an anodic oxide film of about 11 μm. Subsequently, as an oxide film modification treatment, a current density of 2.5% was applied to the counter electrode carbon under the same concentration and temperature conditions as the anodic oxidation treatment bath. AC electrolysis was carried out for 7 minutes using FEA/drll (voltage approximately 'Z8V), and then, as a coloring treatment, using the same apparatus as in Example 1, the pieces were immersed in an electrolytic solution having the following composition at a temperature of 20°C. , for 2 minutes at an applied voltage of 15V.

When direct current electrolysis was carried out using the aluminum alloy profile as a cathode, the base pattern was colored considerably darker and blackish brown compared to the background, revealing a clear bronze-colored decorative pattern.

Electrolyte composition: Nickel sulfate 30 P/boric acid 20
Ammonium sulfate 15 Li/l pH 4,5 Example 5 As the base pattern forming treatment of Example I, a thick stainless steel plate of 0 and 1 pi was etched to form an embossed pattern with unevenness of about 3 Q Ilm. A plate is made, placed on an aluminum (23) alloy profile so that the pattern part is in contact with the profile surface, and stamped from above with a roller to form a pattern on the aluminum alloy surface. When the aluminum alloy profile was treated in exactly the same manner as in Example 1, a beautiful decorative pattern with a difference in shading between the base pattern and the background was revealed on the surface of the profile.

Example 6 Aluminum alloy shape after extrusion molding (A-60638)
After cooling to room temperature, it was subjected to incomplete age hardening at 190°C for 2 hours, and then stainless steel cut wire (grains 1100) was injected at an air pressure of 2'Yl from a 6.4mmφ nozzle while still at high temperature.

A base pattern was formed. Next, the shape was degreased, etched, and smut removed, and the shape was immersed in a 117 W/V% sulfuric acid aqueous solution at a current density of 1.2 A/d (voltage approximately 12.5 V).
, anodized at a liquid temperature of 20°C for 1 hour and 35 minutes, approximately 10
, a 5 μm anodic oxide film was formed. Next, as an oxide film modification treatment, a current density of 1.2 A/d (voltage of about 6 V) was applied.
) for 1 minute and 30 seconds to connect the aluminum alloy shape to the cathode (2
4) Then, DC electrolysis was performed. Next, as a coloring treatment, Example 1
When the same container was immersed in an electrolytic solution having the following composition at a bath temperature of 28°C and subjected to AC electrolysis for 3 minutes at an applied voltage of IIV, only the sandblasted surface became blackish brown. The surface that is not sandblasted will be light brown,
Beautiful shapes and cutlets with different colors depending on the side of the shape.

Electrolyte composition: Nickel sulfate 25 f/l Magnesium sulfate 15 'I/l ammonium sulfate 30 l/l Boric acid 20 f/l Ammonium thiosulfate ty7t pH 5,5 Comparative example] Example 1 except that the oxide film modification treatment was omitted When treated in the same manner as in Example 1, it turned pale yellow, and the underlying pattern was slightly darker than the background, but it was much less clear than in Example 1 and could hardly be called a pattern. Ta.

[Brief explanation of drawings]

Figure 1 shows aluminum alloy (A-60638) (1
') is a graph showing the influence of age hardening treatment temperature and treatment time on hardness, and FIG. 2 is a graph showing the appropriate range of time and temperature for incomplete age hardening treatment. Applicant Yoshida Kogyo Co., Ltd. Agent Patent Attorney Masaaki Yonehara Patent Attorney Tadashi Hamamoto

Claims (1)

[Claims] 1. (At) An incomplete age hardening treatment is applied to the aluminum alloy after extrusion molding. (Bl) A base pattern is then applied to the surface of the aluminum alloy by a mechanical operation; (C) After sintering, An anodic oxide film is formed on the aluminum alloy by a conventional method, and then the anodic oxide film is modified into a double film structure by alternating current electrolysis in an inorganic acid and/or organic acid bath. Patterning of aluminum alloy is a surface treatment method characterized by coloring the film and clearly exposing the base pattern on the aluminum alloy surface. 2 (4) There are no defects in the aluminum alloy after extrusion molding. A complete age hardening treatment is performed, (Bl) Next, a base pattern is applied to the surface of the aluminum alloy by mechanical manipulation. (C) After aging, an anodic oxide film is formed on the aluminum alloy by a conventional method. (Dl) After the aluminum alloy is connected to a cathode in an inorganic acid and/or organic acid bath and the oxide film is modified by direct current electrolysis, the base pattern is clearly formed on the surface of the aluminum alloy by applying coloring treatment. The patterning of aluminum alloys is a method of surface treatment to make them appear.