JP2000064092A - Aluminum-based alloy member and its anodic oxidation method and use - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of yellowing of oxide film by forming an oxide film composed essentially of aluminum oxide on the surface of a member made of aluminum-base alloy containing specific amounts of Si and constituting this oxide film of a porous inner layer and a surface layer denser than the inner layer. SOLUTION: An oxide film composed essentially of aluminum oxide is formed on the surface of a member made of aluminum-base alloy containing 7.5-18 wt.% Si. This oxide layer consists of a porous inner layer and a surface layer denser than the inner layer, and the porosity of the outer layer and that of the inner layer are regulated to <=30 vol.% and >30-50 vol.%, respectively. Further, the thickness of the outer layer and that of the inner layer are regulated to 0.06-0.3 μm and 3-70 μm, respectively, and the surface of the aluminum- base alloy member is subjected to boehmite treatment and then to anodic oxidation treatment in a solution containing sulfuric acid, oxalic acid, phosphoric acid, or the like. By this method, the oxide film capable of keeping dimensional accuracy and having uniform dark gray color can be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel aluminum alloy member, its anodizing method and its use.

[0002]

2. Description of the Related Art In recent years, the production volume of aluminum alloy die castings has tended to increase more and more due to the rapid growth in automobile applications. This is mainly due to the following characteristics of the aluminum alloy die casting.

(1) Light weight.

(2) It has excellent castability and is suitable for thin and complex shapes.

(3) Good dimensional accuracy.

(4) Good productivity.

By type of alloy, the ADC 12 of Al-Cu-Si alloy accounts for most of the production. ADC1
No. 2 contains 9.6 to 12 wt% of Si for improving wear resistance and die casting property and reducing thermal expansion coefficient, and contains 1.5 to 3.5 wt% of Cu for improving mechanical properties. 1 shows the alloy composition. Generally, it is widely used for various parts such as housings, covers and supporting materials of industrial machines, measuring machines and transportation equipment.

[0008]

[Table 1]

This alloy may require surface treatment due to problems in corrosion resistance and appearance, and like other aluminum materials, methods such as anodic oxidation, chemical conversion treatment, plating and painting are used. Above all, anodizing treatment which is excellent in corrosion resistance and abrasion resistance is desired.

However, Al-C represented by ADC12
u-Si system, Al-Si system and Al-Si-Mg
Alloys such as Si, 7.5 to 18.0 wt%
In the case of the contained alloy, some problems occur in the surface treatment, particularly in the anodic oxidation, due to the influence of Si existing at high density in the quenched structure near the surface called the chill layer. One of them is the localized yellowing of the anodized film. That is, there is a problem in that the color develops black gray as a whole while a part of the color exhibits yellow, resulting in poor appearance.

Conventionally, with respect to this problem, 1) examination from the material side such as reducing the amount of addition of alloy components, 2) improvement of casting conditions and casting method for reducing casting defects, 3) pretreatment Studies have been conducted from three directions such as improvement of the anodizing method including the above. However, with respect to 1), it is difficult to change the alloy composition from the present condition in view of the characteristics of the above-mentioned aluminum alloy die casting, particularly castability, dimensional accuracy, productivity and mechanical properties, and also with respect to 2), Due to such restrictions, we have not reached the point where the problem is solved. Therefore, it is most important at present to study 3) how to surface-treat conventional materials and casting materials.

In connection with this, Japanese Patent Laid-Open No. 9-1319 introduces that the anodic oxidation treatment is performed after the cleaning treatment, the hydrofluoric acid and fluorine compound treatment, and the chemical polishing are sequentially performed. By physically or chemically scraping the surface to make the surface properties uniform, an anodized film having uniform dyeability and glitter is formed.

As described above, in the prior art, the steps such as blasting and other machining, hydrofluoric acid bath treatment, and chemical polishing are included as pretreatments when anodizing the aluminum alloy die casting.

Further, Japanese Patent Laid-Open No. 9-184093 discloses Al
Or after boehmite treatment for Al alloy, 0.07-0.3μ
It is disclosed to form a non-porous anodic oxide coating of m thickness.

[0015]

However, in the above-mentioned conventional method, if the process is complicated, the workability and the economical efficiency are deteriorated, and the dimensional accuracy characteristic of the aluminum alloy die casting is caused by the repeated scouring and polishing treatment. May cause an error. Therefore, it is required to prevent yellowing of the anodic oxide film by a method that is simple and can maintain dimensional accuracy. Furthermore, the latter method does not show a treatment method for the particular alloy according to the invention.

An object of the present invention is Al-S containing a large amount of Si.
It is an object of the present invention to provide an aminium alloy which prevents yellowing, which is a new problem in the i alloy, and an anodic oxidation method and use thereof.

[0017]

The present invention is based on Si 7.5-
An aluminum-based alloy characterized in that an oxide film mainly composed of aluminum oxide is formed on the surface of an aluminum-based alloy member containing 18% by weight, and the oxide film comprises a porous inner layer and a surface layer denser than the inner layer. It is in the member.

It is preferable that the outer layer has a porosity of 30% by volume or less and the inner layer has a porosity of more than 30% and 50% by volume or less.

It is preferable that the outer layer has a thickness of 0.06 to 0.3 μm and the inner layer has a thickness of 3 to 70 μm.

According to the present invention, an aluminum alloy containing 7.5 to 18.0 wt% of Si is subjected to boehmite treatment,
The anodic oxidation treatment maintains the dimensional accuracy and forms an oxide film having a uniform black gray color.

Further, the aluminum alloy is Al--C.
It is any one of u-Si based alloy, Al-Si based alloy and Al-Si-Mg based alloy. In particular, for the purpose of improving mechanical strength and castability, Cu is 0.6 to 5.0 wt% and Mg is 0.3%.
˜0.7 wt%, Mn 0.3˜0.5 wt%, Zn less than 3.0 wt%, Fe 1.3 w
It can be contained at t% or less.

Further, in the present invention, the aluminum alloy die casting is obtained by subjecting a part or the whole of the aluminum alloy die casting to machining or chemical treatment after casting.

In the present invention, the boehmite treatment is carried out by immersing the boehmite in boiling water or bringing it into contact with boiling steam. By this method, the surface of the aluminum alloy die casting is covered with a hydrated oxide film of aluminum called a boehmite film so that the unevenness of the composition of the surface is reduced, and the anodic oxide film thereafter grows uniformly.

The boehmite treatment is preferably performed at a treatment temperature and a treatment time of 80 to 200 ° C. and 5 to 30 minutes, respectively. By this method, after forming a dense boehmite film having a thickness of 0.06 to 0.3 μm, a thicker anodic oxide film is formed.

The anodic oxidation treatment is carried out by electrolysis in a solution containing at least one of sulfuric acid, oxalic acid, phosphoric acid and chromic acid by the direct current method, alternating current method, alternating current superposition method, waveform control method or the like. It is a thing. By this method,
Corrosion resistance can be improved by forming a thick porous anodic oxide film.

As the electrolytic solution for the anodizing treatment, the above acid is contained in a concentration of 2 to 30 wt%, and the bath temperature is 10 to 42 ° C.
The electrolysis voltage is DC 10-50V, AC 30-120V
It is preferable to energize for 10 to 60 minutes. By this method, an anodized film having a film thickness of 3 to 62 μm, preferably 8 to 14 μm can be obtained.

The present invention is a fitting for a gas meter pipe made of an aluminum-based alloy member containing 7.5 to 18% by weight of Si, wherein an oxide film mainly composed of aluminum oxide is formed on the surface of the fitting, and the oxide film is formed. It is characterized by comprising a porous inner layer and a surface layer which is denser than the inner layer.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Examples FIG. 1 shows the steps of treating a film according to the present invention. FIG. 2 is a plan view of a safety valve flange for a gas meter pipe joint according to an embodiment of the present invention, and Table 2 shows its alloy components. The flange in this embodiment is manufactured by die casting the alloy shown in Table 2 with a die. FIG. 3 is a sectional view taken along line 3-3 of FIG.

[0029]

[Table 2]

FIG. 1 (a) conceptually shows the surface state in a cross section of the material 1 to be treated, which is die-cast with the alloy of Table 2, in which the internal structure 2 and the chill layer near the surface are shown. It is composed of a rapidly solidified structure called 3 having a thickness of several μm to several tens of μm. Since the chill layer is rapidly cooled, it tends to have a fine structure, and in many cases, a eutectic of Al and an alloy element, a solid solution, and an intermetallic compound are complicatedly formed. Such non-uniformity of the structure is considered to be a main cause of non-uniform behavior during anodization, that is, unsoundness of the formed film. In particular, Si particles have a great influence such as causing blackening by being dispersed in the film. The extremely thin natural oxide film on the outermost surface is omitted.

The material 1 to be treated is degreased with acetone or the like and then subjected to boehmite treatment. In this boehmite treatment, aluminum is reacted with water by immersing it in pure water and subjecting it to boiling treatment or contact with pressurized steam to form a hydrated oxide film of Al ₂ O ₃ and H ₂ O with a thickness of 0.1. 1 μm
To produce boehmite 4 (FIG. 1b). In this embodiment, degreasing is performed by ultrasonic cleaning in acetone for 10 minutes, and after drying, boehmite treatment is performed to have a specific resistance of 7.2 MΩc.
Boiled for 10 minutes in m 2 of deionized pure water. After the boehmite treatment, the surface of the sample was slightly blackish gray while leaving a slight gloss.

The anodic oxidation conditions applied after the boehmite treatment are 15 wt% sulfuric acid solution, bath temperature 25 ° C. and current density 2A.
Electrolysis was performed for 30 minutes at dm ^-2 . After rinsing and drying, the film thickness of the anodic oxide film 5 was obtained by direct observation of the cross section, and it was about 1
It was 0 μm (FIG. 1c). The anodic oxide film treated as described above shows excellent surface observation of uniform black gray with no yellowing portion over the entire surface having a porosity of 20 to 30% by volume on the surface. Table 3 shows the results of color tone measurement using a color difference meter.
It was shown to. As a comparative example, Table 3 also shows the measurement results of the same treatment as that of the example except that the boehmite treatment before the anodizing treatment was omitted.

[0033]

[Table 3]

L, a, and b in the table represent lightness, redness, and yellowness, respectively. The larger the value, the greater the degree. It can be said that the example of the present invention has a darker color tone because L and b are smaller. Therefore, the brightness of the present invention is 20 to 35, and the redness is -0.1 to
It is preferably −0.25 and a yellowness of 0.5 to 2.0.

FIG. 3 shows the amount of corrosion of the ADC12 to which the present invention was applied after 300 hours under a salt spray test at 0.5 mol / l NaCl, 37 ° C. and 95% relative humidity. The results of either boehmite treatment or anodizing treatment alone are also shown. As shown in FIG. 3, as compared with only the boehmite treatment (about 15.5 g / m ² ) or the anodization (about 0.4 g / m ² ), the effect of the boehmite treatment and the anodization were found in the examples of the present invention. The increase in film thickness is about 0.1 g / m ² or less, and the effect is synergistic to give a remarkable corrosion resistance.

In addition, the boehmite treatment step used in the present invention causes almost no problem in the shape of the material to be treated as compared with the polishing treatment step. Therefore, the safety valve flange 6 of the present embodiment
Is composed of a hole 7 for flowing gas, an inner convex portion 8 and an outer convex portion 9 provided for preventing leakage, and a bolt hole 10 for joining with a pipe. The number and the like can be appropriately changed depending on the application.

Further, in the present invention, the present invention is based on Al--C.
Although the example applied to the ADC12 of the u-Si alloy has been shown, the present invention is not limited to this and the ADC10 and Al-Si of the alloy of the same alloy are used.
System alloy ADC1, Al-Si-Mg system alloy ADC3
In addition, it can be applied to an aluminum alloy die casting containing Si in an amount of 7.5 to 18.0 wt%.

The material to be treated according to the present invention can distinguish between the chill layer near the surface and the internal structure in the above embodiment, but the structure is not limited to this and the chill layer and the internal structure cannot be clearly distinguished. The structure in which the chill layer exists on the surface of an extremely small amount, or these structures may be mixed.

The present invention can also be applied to a material to be processed which has been subjected to processing such as machining or chemical polishing after casting.

[0040]

According to the present invention, an aluminum-based alloy member containing 7.5 to 18% Si, especially a die-cast member, has a highly corrosion-resistant anode having an excellent surface appearance of a uniform black gray with no yellowing portion. An oxide film can be obtained.

In addition, according to the present invention, the motor housing made of the above-mentioned aluminum alloy die casting member, the blade of the exhaust fan, the sample holder of the analyzer for medical use, the flange of the washing machine dehydrator, the main body of the car stereo speaker. ， It can be applied to the stepladder lever, security camera body, heat sink cover, etc.

[Brief description of drawings]

FIG. 1 is a diagram showing a treatment process of a film according to the present invention.

FIG. 2 is a plan view of a safety valve flange that is an embodiment of the present invention.

3 is a sectional view of the safety valve flange of FIG.

FIG. 4 is a bar graph showing the corrosion test results of the coating of the present invention.

[Explanation of symbols]

1 ... Material to be treated, 2 ... Internal structure, 3 ... Chill layer, 4 ... Boehmite film, 5 ... Anodized film, 6 ... Safety valve flange, 7
... hole, 8 ... inner convex portion, 9 ... outer convex portion, 10 ... bolt hole.

Claims (9)

[Claims] 1. An oxide film mainly composed of aluminum oxide is formed on the surface of an aluminum-based alloy member containing 7.5 to 18% by weight of Si, and the oxide film is composed of a porous inner layer and a surface layer denser than the inner layer. And an aluminum-based alloy member. 2. The aluminum-based alloy member according to claim 1, wherein the porosity of the outer layer is 30% by volume or less and the porosity of the inner layer is more than 30% and 50% by volume or less. 3. The aluminum-based alloy member according to claim 1, wherein the outer layer has a thickness of 0.06 to 0.3 μm and the inner layer has a thickness of 3 to 70 μm. 4. The aluminum alloy member is Al--Cu
The aluminum alloy member according to any one of claims 1 to 3, wherein the aluminum alloy member is any one of -Si type, Al-Si type, and Al-Si-Mg type alloys. 5. An anodizing method for an aluminum alloy member, which comprises subjecting an aluminum alloy member containing 7.5 to 18% by weight of Si to a boehmite treatment and then anodizing treatment. 6. The method of anodizing an aluminum alloy member according to claim 6, wherein the aluminum alloy member is subjected to a mechanical processing or a chemical treatment on a part or the whole after casting by die casting and before the boehmite treatment. 7. The aluminum alloy member according to claim 5, wherein the boehmite treatment is performed by immersing in a pure water having a specific resistance of 1 MΩcm or more and boiling treatment or contact treatment with pressurized steam. Anodizing method. 8. The anodizing treatment is to electrolyze in a solution containing at least one of sulfuric acid, oxalic acid, phosphoric acid and chromic acid by any one of the direct current method, alternating current method, alternating current superposition method and waveform control method. It is a thing, It is characterized by the above-mentioned.
8. The method for anodizing an aluminum alloy member according to any of 7. 9. A joint for a gas meter pipe, comprising an aluminum-based alloy member containing 7.5 to 18% by weight of Si,
A joint for gas meter piping, wherein an oxide film mainly composed of aluminum oxide is formed on the joint surface, and the oxide film comprises a porous inner layer and a surface layer denser than the inner layer.