JPH06330386A - Formation of hard anodic oxide film and aluminum alloy for forming the film - Google Patents

Abstract

PURPOSE:To form a high-hardness anodic oxide film uniform in the thickness direction on an aluminum alloy by using an ordinary-temp. electrolytic bath. CONSTITUTION:An aluminum alloy, e.g. Al-Mn, Al-Mn-Mg alloy, etc., in which an intermetallic compd. deposit insoluble or sparingly soluble in sulfuric acid and having 0.01-3mum particle diameter is dispersed at a density of >=1X10<4> units/mm<2> and is used as a substrate 1. The surface of the substrate 1 is anodized by a sulfuric-acid electrolytic bath kept at 12-30 deg.C to form a hard anodic oxide film 2 having >=350Hv hardness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a hard anodic oxide coating having a Hv of 350 or more for an aluminum alloy material used as a member required to have hardness and wear resistance, such as parts of various precision machinery or sliding parts. How to form,
And an aluminum alloy for forming a hard anodized film thereof.

[0002]

2. Description of the Related Art Aluminum alloy materials have been widely used for precision machinery / equipment parts, sliding parts, etc., which are mainly required to be lightweight, but in this case, they give high hardness to the surface and have good wear resistance. A hard anodized film is often formed in order to impart the property.

The hard anodic oxide film is generally referred to as an anodic oxide film having a hardness of Hv 350 or higher. As a method for forming such a hard anodic oxide film, a low temperature method has been generally adopted conventionally. . This low-temperature method uses an electrolytic bath based on sulfuric acid, sets the bath temperature to a low temperature of 10 ° C. or lower, and sets the current density to a high value of ³ to 5 A / dm ² ,
Anodization is performed in a relatively short time, and by such treatment at low temperature, high current density and short time, chemical erosion by the electrolytic bath can be suppressed and a hard anodized film can be obtained. Industrially, JIS 1000 series pure aluminum Al alloys or corrosion resistant alloys such as 5052 alloys are treated with a bath temperature of 5 ° C. and a sulfuric acid bath with a concentration of 10 to 15%, a current density of 3 A / dm ² , and a treatment. A hard anodized film having a thickness of about 50 μm can be obtained in 60 minutes, and the hardness of the hard anodized film in this case has a surface hardness of Hv 350 to 40.
0, the hardness of the coating cross section is Hv near the boundary between the coating and the metal
It will be about 400 to 450.

[0004]

When a hard anodic oxide film is formed by the low temperature method as described above, a hardness difference occurs in the thickness direction of the film, and it is possible to make the hardness uniform and high throughout the thickness direction. There is a problem that cannot be done. That is, a high hardness can be obtained inside the coating, that is, in a portion close to the base metal, but a phenomenon occurs in which hardness decreases in an upper portion of the coating, that is, a portion near the surface. Of the parts in the thickness direction of the hard anodic oxide film, the inside close to the bare metal is hard because it is not directly exposed to the electrolytic bath, but the vicinity of the surface is directly exposed to the electrolytic bath and treated. It is a phenomenon that occurs due to the fact that during the period, it is chemically and electrochemically dissolved and melted, especially at the pore part the diameter near the opening end is expanded and the part near the surface softens. This is a phenomenon that cannot be avoided by the hard anodizing treatment by the usual low temperature method.

Therefore, particularly in the case of aircraft parts and ultra-precision parts which are required to be evenly hard up to the surface, a soft surface layer is ground and removed over a thickness of, for example, about 20 μm to obtain a hard portion on the surface. Is exposed and used for these parts, but in this case an extra process is required and it will inevitably cause a significant cost increase, so it is necessary to avoid such cutting. It is strongly desired to develop a method for uniformly forming a hard anodized film that is hard in the thickness direction.

Further, when a hard anodic oxide film is formed by the low temperature method as described above, volume expansion occurs when the oxide film grows at a low temperature, so that formation of minute cracks in the film is avoided. I don't get it. When a material having minute cracks in the coating is used for sliding parts, smooth sliding motion may be hindered, and the cracked portion becomes the starting point of corrosion generation, so corrosion resistance is There is a problem that the original function as a hard anodic oxide film cannot be fully exhibited, such as deterioration.
Further, as described above, minute cracks in the coating also adversely affect heat resistance. That is, although the harder the anodic oxide film is, the more easily cracks occur, but if the anodic oxide film with minute cracks as described above is exposed to a high temperature of about 150 ° C. or higher, the cracks suddenly increase due to so-called heat shock. , And not only the mechanical properties deteriorate, but also the electrical properties such as electrical insulation deteriorate.
Various problems occur such as deterioration of chemical properties such as corrosion resistance.

Further, in forming the hard anodic oxide film by the low temperature method as described above, a cooling device for cooling the electrolytic solution to a low temperature, a heat insulating structure for keeping the electrolytic bath at a low temperature, etc. are required, Therefore, there is a problem that the facility cost and running cost must be high.

On the other hand, in order to solve the above-mentioned drawbacks of the low temperature method, various methods have hitherto been considered. For example, the chemical electrolysis force is reduced by adding an organic acid such as oxalic acid to sulfuric acid. Although a method is also known, in this case, it causes an increase in cost and a decrease in productivity,
It is not a fundamental solution. Various methods have been tried, such as changing the current waveform in the anodizing process to AC / DC superimposition waveform or other special waveform, or performing constant voltage electrolysis, but all of them have been solved to the extent that the above problems can be satisfied. It was difficult to do.

The present invention has been made in view of the above circumstances, and it is possible to form a hard anodized film having a uniform high hardness in the thickness direction of the film without causing a significant increase in cost, and further, to make the anode It is an object of the present invention to provide a method for forming a hard anodic oxide film which is less likely to cause microcracks during the oxidation treatment and has less crack generation and growth after the anodization treatment.

[0010]

Means for Solving the Problems As a result of intensive experiments and studies by the present inventors to solve the above problems, as an aluminum alloy base material on which an anodic oxide film is to be formed,
By performing anodizing treatment in a sulfuric acid electrolytic bath using an aluminum alloy in which fine precipitates composed of an intermetallic compound insoluble or at least slightly soluble in sulfuric acid are uniformly dispersed, even at a bath temperature near room temperature. It is possible to form a hard anodic oxide film having high hardness equal to or higher than that of the conventional low temperature method and having high hardness uniformly in the thickness direction, and in that case, the occurrence of cracks and growth are small. Heading out, this invention was made.

Specifically, the method of forming a hard anodic oxide film according to the first aspect of the present invention is to form an intermetallic compound precipitate that is insoluble or sparingly soluble in sulfuric acid and has a particle size of 0.01 to 3 μm. A base material is an aluminum alloy dispersed at a density of 1 × 10 ⁴ pieces / mm ² or more, and the surface of the base material is 12 ° C.
It is characterized in that a hard anodized film having a Hv of 350 or more is formed by performing anodization treatment in a sulfuric acid electrolytic bath having a bath temperature of -30 ° C.

The method of the invention of claim 2 is the method of forming a hard anodized film of the invention of claim 1, which contains 0.3 to 4.3 wt% of Mn as an aluminum alloy of the base material, and the balance is Al. And Al-M consisting of inevitable impurities
An n-based alloy is used, and the intermetallic compound precipitate is Al-Mn.
It is characterized as being of a system type.

Furthermore, the method of the invention of claim 3 is the method of claim 1.
In the method for forming a hard anodic oxide film of the invention described in,
As an aluminum alloy for the base material, Mn 0.3 to 4.3 wt
%, Mg 0.05 to 6.0 wt%, the balance is Al and Mn—Mg based alloy consisting of unavoidable impurities, and the intermetallic compound precipitate is Al—Mn based. It is characterized by that.

The inventions of claims 4 and 5 both define the aluminum alloy used for forming the hard anodic oxide film as described above.

That is, the aluminum alloy for forming a hard anodic oxide film according to the invention of claim 4 has an Mn of 0.3 to 4.3 wt%.
And the balance consists of Al and unavoidable impurities,
It is characterized in that the intermetallic compound precipitates having a particle size in the range of 0.01 to 3 μm are dispersed at a density of 1 × 10 ⁴ particles / mm ² or more.

The aluminum alloy for forming a hard anodic oxide film according to the fifth aspect of the invention is Mn 0.3 to 4.3 wt%, M
g of 0.05 to 6.0 wt%, the balance of Al and unavoidable impurities, and the intermetallic compound precipitates having a grain size of 0.01 to 3 μm are 1 × 10 ⁴ pieces / mm ² or more. It is characterized by being dispersed at a density.

[0017]

[Function] When an anodizing treatment is performed in a sulfuric acid electrolytic bath on an aluminum alloy material in which fine intermetallic compound precipitates insoluble or hardly soluble in sulfuric acid are dispersed, the dispersed intermetallic compound precipitates are , Without forming dissolution voids or holes, it does not substantially dissolve and remains in the anodized film as it is.

Generally, in the process of forming an anodized film, a large number of pores are formed from the surface of the aluminum alloy material, and the growth of the oxide film (increased film thickness) is accompanied by the growth of the pores inside the aluminum alloy material. move on. In this process, in the case of a conventional general aluminum alloy, the pores grow almost perpendicularly to the surface as shown in FIGS. 2 and 3 described later, and the pore structure becomes an aligned structure. In this case, since insoluble or hardly soluble fine intermetallic compound precipitates are dispersed in the sulfuric acid electrolytic bath, refraction is performed so as to avoid the intermetallic compound precipitate particles as shown in FIG. 1 described later. The pores grow while branching finely, resulting in an unaligned pore structure. In such a non-aligned pore structure in which the pores are refracted and finely branched, cracks are less likely to occur, and even if cracks occur, their propagation and growth are prevented by the finely branched pores, and as a result, The risk of cracks and growth is reduced.

Further, during the anodic oxidation process, a portion of the intermetallic compound precipitate is not dissolved, and a large number of fine intermetallic compound precipitate particles are dispersed in the anodic oxide film finally having a desired thickness. Therefore, even if the electrolytic bath is not particularly kept at a low temperature of 10 ° C. or lower, a sulfuric acid electrolytic bath near room temperature (12 to 30 ° C.) has a sufficiently high hardness of Hv 350 or more and a uniform high hardness in the thickness direction. The anodic oxide film which it has is formed.

The reason why an anodized film having a high hardness and a uniform high hardness in the thickness direction is formed even in a sulfuric acid electrolytic bath near room temperature as described above is the reason why the conventional general hard anodized film is formed. This will be described below with reference to FIGS. 1 to 3 in comparison with the case.

FIG. 2 is a diagram showing the state of the coating and the hardness distribution in the coating thickness direction when it is assumed that an ideal hard anodic oxide coating is formed by the conventional low-temperature method, and FIG. 3 is shown by the conventional low-temperature method. FIG. 1 is a diagram showing the actual condition of the film and the hardness distribution in the film thickness direction when a hard anodized film is actually formed. FIG. 1 is the condition of the film and the film thickness when a hard anodized film is formed according to the present invention. It is a figure showing hardness distribution in the depth direction, in each figure, 1 is an aluminum alloy base material (bare metal), 2 is an anodic oxide film, 3 is a pore, and particularly in FIG.
Are intermetallic compound precipitate particles.

As shown in FIG. 2 (A), even in the conventional low temperature method, ideally, the goal is not to dissolve the vicinity of the surface of the anodic oxide film 2. In such an ideal case, As shown in FIG. 2B, the hardness distribution of the anodic oxide film 2 in the thickness direction should be at a uniformly high level. However, in practice, in the case of the conventional ordinary low temperature method, as shown in FIG.
(A), the surface of the coating film 2 is dissolved in the electrolytic bath, and especially the vicinity of the peripheral edge of the opening end of the pore 3 is dissolved, and the opening end of the pore 3 is enlarged. Especially when trying to form a thick anodic oxide film, the amount of dissolution on the film surface increases because the time for which the film surface is exposed to the electrolytic bath becomes long due to the long-term treatment. In this state, it can be said that the upper layer part (surface layer part) of the anodized film is about to collapse, and therefore, if a load is applied to the upper layer part of the film, the upper layer part will collapse. And the hardness measurement value becomes low. Therefore, the hardness distribution in the thickness direction of the coating is shown in FIG.
As shown in (B), the hardness is relatively high inside the coating, but the hardness is extremely lowered in the upper layer portion near the surface. In this case, if the concentration of sulfuric acid in the electrolytic bath is raised or the bath temperature is raised, the amount of surface dissolution during treatment increases, resulting in the formation of a thick anodic oxide film with high hardness. Becomes difficult. In this case, as described above, the pores 3 grow in an aligned state from the surface to the inside substantially vertically.

On the other hand, in the case of the present invention, FIG.
As shown in Fig. 3, since the fine intermetallic compound precipitate particles 4 insoluble or hardly soluble in sulfuric acid are dispersed, chemical dissolution from the surface is small, and as described above, the pores 3 are refracted. In addition, the branched and non-aligned structure also contributes to delaying chemical dissolution, and as a result, a film having a substantially uniform hardness from the surface to the inside can be obtained. Also,
As described above, since the intermetallic compound precipitate particles are finely dispersed in the film, the volume between the dispersed precipitate particles and the surrounding matrix is increased due to the volume expansion of the surrounding aluminum matrix during anodization. The increase in contact pressure and the non-alignment of the pore structure in the coating as described above also contributes to the increase in contact pressure between the dispersed precipitate particles and the surrounding matrix, and as a result, the coating as a whole has a compression direction. The internal stress of the steel becomes large and it shows high hardness. Therefore, from the above, a film having a high hardness and a uniform high hardness in the film thickness direction can be obtained as shown in FIG. Then, as described above, since the presence of intermetallic compound precipitate particles that are not substantially dissolved in the sulfuric acid electrolytic bath and the resulting non-alignment of the pore structure can uniformly obtain high hardness in the film thickness direction, High hardness can be obtained even if the temperature of the bath is set to a relatively high temperature near room temperature or the sulfuric acid concentration of the electrolytic bath is increased to increase the conductivity of the bath.

Here, the grain size of the intermetallic compound precipitates is 0.
If it is less than 01 μm, the effect due to the dispersion of the precipitate particles as described above cannot be obtained, while coarse intermetallic compound precipitates exceeding 3 μm can be dispersed at a high density of 1 × 10 ⁴ particles / mm ² or more. Since it becomes difficult and the effect due to the dispersion of the intermetallic compound precipitate cannot be expected, the particle size of the intermetallic compound precipitate is set within the range of 0.01 to 3 μm. And because the distribution density of the intermetallic compound precipitates can not be obtained the effect as described above is less than 1 × 10 ⁴ cells / mm ^2, 1 × 10 ⁴ cells /
It is necessary to have a distribution density of mm ² or more.

The composition of the aluminum alloy used in the present invention is basically limited as long as it precipitates an intermetallic compound which is insoluble or hardly soluble in a sulfuric acid electrolytic bath. However, in order to surely and sufficiently exert the above-mentioned effects and also to obtain an effect of improving far-infrared radiation characteristics as described later, Al-Mn
It is preferable to use an Al-based alloy or an Al-Mn-Mg-based alloy. These Al-Mn system or Al-Mn-M
In the case of a g-based alloy, for example, Al ₆ Mn, Al ₆ (MnF
e), Al-Mn-based intermetallic compounds such as αAlMn (Fe) Si are deposited, and these are insoluble or at least hardly soluble in sulfuric acid. Therefore, as described above, the anodic oxide film is formed in the thickness direction. Contributes to uniformly increasing the hardness. Moreover, these Al-Mn system or Al-Mn
In the -Mg-based alloy, by dispersing the Al-Mn-based intermetallic compound as described above with the above-mentioned diameter and distribution density, excellent far-infrared radiation characteristics can be obtained, and far-infrared heaters and other various far-infrared radiation can be obtained. It can be suitably used for an infrared radiation member.

As the Al-Mn-based alloy, as defined in claim 2, it is appropriate that the composition of Mn is 0.3 to 4.3 wt% and the balance is Al and inevitable impurities. . Further, as the Al-Mn-Mg-based alloy, Mn0.
Containing 3 to 4.3 wt% and Mg 0.05 to 6.0 wt%,
It is suitable that the balance is a component composition consisting of Al and unavoidable impurities.

These Al--Mn alloys, Al--Mn--
The reasons for limiting the component composition of the Mg-based alloy will be described below.

Mn: Mn forms an Al-Mn-based intermetallic compound, which contributes to increasing the hardness of the anodic oxide film uniformly in the film thickness direction as described above, and also to improving the far-infrared characteristics. Here, if the amount of Mn is less than 0.3 wt%, it is difficult to deposit a sufficient amount of Al-Mn intermetallic compound to obtain the above-mentioned effect, while if the amount of Mn exceeds 4.3 wt%, rolling is And moldability are reduced. Therefore M
The amount of n was 0.3 to 4.3 wt%.

Mg: Mg promotes the precipitation of Al-Mn intermetallic compounds and contributes to the achievement of the above-described precipitation state. Particularly when the amount of Mn is relatively small, increasing the amount of Mg is effective for promoting the precipitation of the Al-Mn-based intermetallic compound and obtaining the above-described precipitation state. However, Mg
When the amount exceeds 6.0 wt%, rolling property and formability are deteriorated and it becomes unpractical. On the other hand, when the amount of Mg is less than 0.05 wt%, M
The above effect due to the addition of g cannot be obtained. Therefore Mg
When Mg was added, the Mg amount range was set to be in the range of 0.05 to 6.0 wt%.

The balance of the above components may basically be Al and inevitable impurities. Here, as a typical inevitable impurity in an aluminum alloy, F
e and Si, and Fe and Si may be positively added depending on the use of the alloy.
In a -Mn-based alloy or an Al-Mn-Mg-based alloy, F
It is desirable to regulate e to 0.5 wt% or less and Si to 2.0 wt% or less.

Further, in a usual aluminum alloy, a small amount of Ti alone is used for refining the crystal grains of the ingot,
Alternatively, it may be added in combination with a trace amount of B, and the Al-Mn-based alloy or Al-Mn- used in the present invention is added.
0.003 to 0.15 wt% of Ti may be added to the Mg alloy alone or in combination with 1 to 100 ppm of B.

In addition, in the aluminum alloy containing Mg, a small amount of Be has been conventionally added to prevent the oxidation of the molten metal. However, the Al--Mn alloy used in the present invention is used. Or Al-Mg-M
Even in the case of an n-based alloy, it is not particularly problematic to add Be in an amount of about 500 ppm or less.

Further, a general Al-Mn alloy or A
In the 1-Mn-Mg-based alloy, Ni, Cr, Zr,
V, Cu, Zn, etc. may be contained, and in the case of the Al-Mn-based alloy or Al-Mn-Mg-based alloy used in the present invention, Ni is less than 1.0 wt% and Cr is less than 0.3 wt%.
Zr less than 0.3 wt%, V less than 0.3 wt%, Cu 1.0 wt
%, Zn less than 1.0 wt% does not have an essential effect on the precipitation state of the intermetallic compound, so that it is acceptable to contain one or two or more kinds within these ranges.

In the method of the present invention, the anodizing treatment is carried out using a sulfuric acid electrolytic bath having a bath temperature of 12 to 30 ° C.
If the bath temperature is lower than 12 ° C, a cooling device for the electrolytic solution and a heat insulating structure for keeping the bath at a low temperature are required, which is economically disadvantageous. As described above, the greatest feature of the present invention is that an anodized film having a uniform high hardness in the film thickness direction can be formed even at a bath temperature near room temperature. It is possible to form an anodic oxide film having a high hardness equal to or higher than that of the above method and having a hardness that is much more uniform in the thickness direction than in the case of the conventional low temperature method. In an electrolytic bath having a temperature higher than 30 ° C., the dissolution phenomenon during the treatment becomes severe and the high hardness anodic oxide film intended by the present invention cannot be obtained.

The sulfuric acid electrolysis bath may be any one mainly containing sulfuric acid, and it is permissible to contain some known additives in addition to sulfuric acid. Further, as the current during the anodizing treatment, any waveform such as direct current alternating current, alternating current / direct current combination, alternating current / direct current superimposed waveform can be used, but direct current is preferable from the viewpoint of economy. Further, the current density may be in the conventional general range.

The film thickness of the anodic oxide film may be determined according to the application and is not particularly limited, but it is generally at least 3 μm or more, and 10 μm or more for a member requiring abrasion resistance. It is usually done. However, in the case of the present invention, as described above, the anodic oxide film has a high hardness almost uniformly in the film thickness direction, and the hardness does not decrease sharply particularly near the surface. It is not necessary to mechanically remove the soft part of the surface layer of the anodized film to expose the high hardness part of the inner layer for use, and in that sense the film thickness during anodization is relatively thin. Will be enough.

[0037]

【Example】

Example 1 Mn 2.04 wt%, Mg 0.51 wt%, Fe 0.13 wt
%, With the balance being essentially Al. Al-Mn-
A Mg-based alloy was cast to a thickness of 7 mm by the continuous casting and rolling method, cold-rolled to a thickness of 1 mm, annealed at 400 ° C. for 2 hours, and then 1
A sample of × 100 × 100 mm was cut out to obtain a sample 1. At the same time, as a comparative material, 1 mm of commercially available JIS 1100 alloy
A sample of the same size was cut out from a thick plate to obtain Sample 2, and also as a comparative material, a commercially available JIS 5052 alloy 1 mm
A sample having the same size was cut out from a thick plate to obtain Sample 3.

Sample 1 has Al-Mn-based intermetallic compound precipitates having a grain size of 0.1 to 1.0 μm and a distribution density of 2.8.
The particles were dispersed at × 10 ⁴ particles / mm ² , while neither sample 2 nor sample 3 had substantially no intermetallic compound precipitates.

For each of these samples, 15 vol% H ₂
A SO ₄ sulfuric acid electrolytic bath is used and the bath temperature is 0 ° C., 5 ° C., 10
Different temperatures of 15 ° C, 15 ° C, 20 ° C, 25 ° C, current density 3A / dm ² , electrolysis time 60 at each bath temperature.
Anodizing treatment was performed in minutes.

Each sample 1 anodized at each bath temperature
For ~ 3, while checking the thickness of the anodized film,
The surface hardness of the anodized film and the hardness at each position of the film cross section were examined. The hardness was measured using a micro Vickers hardness meter at a load of 50 g at each position at 5 points, and the average value was obtained. The hardness at each position of the coating film cross section was measured at a position of 10 μm, a position of 30 μm, and a position of 45 μm from the boundary position with the aluminum base metal toward the surface. The results are shown in Table 1.

[0041]

[Table 1]

As is clear from Table 1, Al-Mn is suitable.
In the case of the sample 1 in which the intermetallic compound was precipitated, the surface hardness and the hardness at each position of the cross section were almost uniformly high regardless of the bath temperature during the anodizing treatment of 0 to 25 ° C. Shows. Particularly, when the bath temperature was close to room temperature such as 15 ° C, 20 ° C, and 25 ° C, in Samples 2 and 3, the parts near the surface tended to be rapidly softened, whereas in the case of Sample 1, these bath temperatures were However, it showed almost uniform high hardness.

Example 2 Al-M composed of 2.53 wt% Mn and the balance substantially Al.
With respect to the n-based alloy, Sample 4 was prepared in the same manner as Sample 1 of Example 1. This sample 4 has a particle size of 0.1 to 0.3 μm.
Al-Mn-based intermetallic compound is distributed at a density of 2.3 x 1
That are dispersed in 0 ⁴ / mm ² was confirmed.

For this sample 4, the temperature of the electrolytic bath was 20 ° C.
The other conditions were the same as in Example 1, and the anodizing treatment was performed. Table 2 shows the results of examining the film thickness and surface hardness of the anodized film, and the hardness at each position of the cross section.

[0045]

[Table 2]

As is clear from Table 2, in the case of Sample 4 which is an Al-Mn-based alloy in which the Al-Mn-based intermetallic compound is appropriately dispersed, the anodic oxidation in the electrolytic bath at 20 ° C near room temperature is also performed. By the treatment, an anodic oxide film having high hardness was obtained uniformly in the film thickness direction.

[0047]

As is clear from the above description, according to the method of the present invention, the hardness is substantially uniform in the film thickness direction by the anodic oxidation treatment at the bath temperature near room temperature of 12 to 30 ° C. It is possible to form a hard anodized film, and therefore, unlike the conventional low-temperature method, a cooling device for the electrolytic solution or a low-temperature holding structure of the electrolytic bath is not required, and therefore a hard anodized film can be obtained at low cost. In addition, since the obtained hard anodized film has high hardness almost uniformly in the film thickness direction, it is not necessary to mechanically remove the soft portion near the surface as conventionally applied in some parts, and in that sense Can also reduce costs. Further, according to the method of the present invention, since the pore structure of the anodic oxide film is a finely refracted and branched non-aligned structure, the generation of cracks during the anodizing treatment and the subsequent generation of cracks due to heat or external stress, growth Therefore, it is possible to obtain a hard anodic oxide film having less mechanical properties, and thus having mechanically, electrically, and chemically stable properties.

If the aluminum alloy for forming a hard anodic oxide film of the present invention is used, a hard anodic oxide film having the above-mentioned excellent properties can be stably and reliably formed.

[Brief description of drawings]

FIG. 1 is a view for explaining a hard anodized film formed by the present invention, (A) is a schematic view of a film cross-sectional structure,
(B) is a diagram showing a hardness distribution in the film thickness direction corresponding thereto.

FIG. 2 is a diagram for explaining an ideal situation when a hard anodic oxide film is formed by a conventional low temperature method, (A) is a schematic view of a film cross-sectional structure, and (B) is a film thickness corresponding to it. It is a diagram showing hardness distribution in the depth direction.

FIG. 3 is a diagram for explaining an actual situation when a hard anodized film is actually formed by a conventional low temperature method,
(A) is a schematic diagram of a coating cross-sectional structure, and (B) is a diagram showing the hardness distribution in the coating thickness direction corresponding thereto.

[Explanation of symbols]

 1 Aluminum alloy base material (bare metal) 2 Anodized film 3 Pore 4 Intermetallic compound precipitate particles

Front page continued (72) Inventor Shuichi Matsumoto 1-5-1, Kiba, Koto-ku, Tokyo Within Fujikura Ltd. (72) Inventor Kenzo Okada 4-3-1 Nibashi Muromachi, Chuo-ku, Tokyo Sky Aluminum Co., Ltd. (72) Inventor Mamoru Matsuo 4-3-18 Nihombashi Muromachi, Chuo-ku, Tokyo Sky Aluminum Co., Ltd.

Claims (5)

[Claims] 1. An aluminum alloy which is insoluble or sparingly soluble in sulfuric acid, and in which intermetallic compound precipitates having a particle size of 0.01 to 3 μm are dispersed at a density of 1 × 10 ⁴ / mm ² or more. As a base material, and the surface of the base material has a temperature of 12 ° C to 30 ° C.
Anodizing with a sulfuric acid electrolytic bath with a bath temperature of ℃,
A method of forming a hard anodic oxide film, which comprises forming a hard anodic oxide film having a Hv of 350 or more. 2. The aluminum alloy of the base material is Mn
0.3 to 4.3 wt%, with the balance being Al and inevitable impurities, and the intermetallic compound precipitate being Al
The method for forming a hard anodized film according to claim 1, which is a -Mn-based intermetallic compound. 3. The aluminum alloy of the base material is Mn
0.3-4.3 wt%, Mg0.05-6.0 wt% are contained, the balance consists of Al and unavoidable impurities, and said intermetallic compound precipitate is an Al-Mn-based intermetallic compound. Item 2. A method for forming a hard anodized film according to Item 1. 4. Mn of 0.3 to 4.3 wt% is contained, the balance is Al and inevitable impurities, and the grain size is 0.01.
An aluminum alloy for forming a hard anodic oxide film, characterized in that intermetallic compound precipitates within a range of ˜3 μm are dispersed at a density of 1 × 10 ⁴ pieces / mm ² or more. 5. Mn 0.3 to 4.3 wt%, Mg 0.05
-6.0 wt%, the balance consisting of Al and unavoidable impurities, and intermetallic compound precipitates with a particle size in the range of 0.01 to 3 μm dispersed at a density of 1 × 10 ⁴ pieces / mm ² or more. An aluminum alloy for forming a hard anodized film, which is characterized in that