JPH0633502B2 - Method for forming anodized film on cast aluminum alloy - Google Patents

Description

The present invention relates to an aluminum alloy (hereinafter referred to as “Al alloy”) member used for automobile parts and the like, in particular, a surface of an Al alloy casting, which has surface characteristics such as wear resistance and corrosion resistance. The present invention relates to a method of forming an anodized film for improvement.

Conventional technology In recent years, with the main purpose of improving fuel efficiency in automobiles,
Conventionally, with regard to automobile parts that have been mainly made of iron-based materials, the materials are often converted to lightweight Al alloys. However, Al alloys are inferior in wear resistance to iron-based materials and are not necessarily sufficient in corrosion resistance. Therefore, development of a method for improving wear resistance and corrosion resistance of Al alloy members is strongly desired.

By the way, as a method for improving surface properties such as wear resistance and corrosion resistance of an Al alloy member, a method of subjecting the surface to anodization has been widely known. That is, since an anodized film formed by anodizing an Al alloy is generally hard, rich in abrasion resistance, and also excellent in corrosion resistance, the formation of the anodized film significantly improves these surface characteristics. Can, especially A
In the wrought material of the 1-alloy, these surface characteristics can be reliably and sufficiently improved, and therefore, this method has been widely used for the wrought material of the Al alloy.

Problems to be Solved by the Invention As described above, it has been widely practiced that an anodic oxide film is formed on an wrought material of an Al alloy in order to improve surface properties such as wear resistance and corrosion resistance. A as it is
Since it is difficult to form a homogeneous and dense anodic oxide coating on an l-alloy member, that is, an Al-alloy cast material, as described below, the fact is that it has hardly been carried out.

That is, in the Al alloy casting, defects such as pinholes, blowholes, and cavities are often present in the surface layer, and a large amount of gas components such as nitrogen gas are solid-solved or occluded. When such an Al alloy casting is anodized, defects such as pinholes, blowholes and cavities remain in the anodized film,
It was difficult to obtain a uniform and dense anodic oxide film with good wear resistance and corrosion resistance. In addition, gas in defects such as pinholes, blowholes, and cavities, and gas components that are solid-solved or occluded are released during the anodization process and adhere to the Al alloy casting surface as gas bubbles. The contact of the electrolytic solution for the anodizing treatment with the surface of the Al alloy casting was hindered, and the anodizing reaction did not proceed at that portion, and as a result, it was difficult to form a uniform and dense anodized film.

Of course, applying special casting means such as vacuum casting,
The above problems can be solved to some extent by preparing an Al alloy casting that has few defects such as pinholes, blowholes, and cavities and less solid solution gas and occlusion gas. However, when vacuum casting is applied, the cost increases significantly, so it is economically impossible to apply it to actual operations, especially the production of mass-produced products, and therefore it cannot be said that it is a practical solution. Is.

The present invention has been made in view of the above circumstances. It is possible to form a uniform and dense anodic oxide film on an Al alloy casting without causing the above-mentioned problems, and to improve the wear resistance of the Al alloy casting. It is an object of the present invention to provide a method for surely and sufficiently improving surface characteristics such as corrosion resistance.

Means for Solving the Problems As a result of repeated studies by the present inventors in order to achieve the above-mentioned object, as a result of performing the anodizing treatment on the surface of the Al alloy casting, the area where the anodized film should be formed By irradiating the surface with high-density heating energy such as TIG arc, laser, electron beam, etc., and rapidly melting and rapidly solidifying the surface layer at that portion, defects such as pinholes, blowholes, and nests as described above can be obtained. It is possible to remove gas components that are solid solution or occluded from the casting surface layer, and as a result, a uniform and dense anodic oxide film is generated by the subsequent anodic oxidation treatment, resulting in sufficient wear resistance and corrosion resistance. They have found that they can be given and have completed the present invention.

Therefore, according to the present invention, when forming an anodized film on the surface of an aluminum alloy casting, the entire surface of the part where the anodized film is to be formed is previously irradiated with high-density heating energy in advance to rapidly melt and rapidly re-solidify the surface layer. The surface of the re-solidified portion is then subjected to an anodic oxidation treatment to form an anodic oxide film having a thickness equal to or less than the depth of the re-solidified portion.

DETAILED DESCRIPTION OF THE INVENTION The method of the present invention will be described in more detail below with reference to FIGS. 1 to 4.

First, as shown in FIG. 1, an Al alloy casting 1 to be treated
The surface layer 2A of the portion of the surface where the anodic oxide film is to be formed is irradiated with high-density heating energy 3 such as TIG arc, electron beam, or laser to melt the surface layer 2A. In the melting at this time, since the high-density heating energy source as described above is used as a heating source, only the surface layer 2A of the Al alloy casting 1 is locally and rapidly heated before the temperature of the entire Al alloy casting 1 is raised. Thus, only the surface layer 2A is rapidly melted. Then, if the irradiation is stopped by moving the high-density heating energy source or stopping the driving of the energy source, the molten portion is immediately re-solidified by the heat dissipation to the side of the base material which is still low in temperature. This state is shown in FIG. Since this re-solidification is mainly performed by heat transfer to the base metal side, it will solidify with directivity from the base metal side to the surface side, and therefore pinholes and blowholes existing before melting, Defects such as cavities are in a state of being extruded to the outside during solidification, and bubbles generated at the time of melting due to gas components that have been occluded or solid-dissolved are also in a state of being extruded to the outside at the time of solidification. In the solidified portion 2B, there are almost no defects such as pinholes, blowholes, and cavities, and the solid solution or the stored gas component is extremely small.
Further, as described above, rapid solidification by unidirectional solidification also miniaturizes the structure of the portion 2B.

Since the surface of the portion 2B that has been melted and re-solidified by the irradiation with the high-density heating energy in this way usually has a relatively large number of irregularities, the surface is smoothed by machining or polishing. The smoothed state is shown in FIG.

Next, as described above, the surface of the portion 2B that has been rapidly melted and resolidified is subjected to anodizing treatment. This anodic oxidation treatment may be performed according to a conventional method, but in order to further improve wear resistance, it is desirable to form a so-called hard anodic oxide film by a method such as using a low temperature electrolytic bath. The state in which the anodic oxide coating 4 has been formed in this manner is shown in FIG. After the anodizing treatment, if necessary, a sealing treatment is performed according to a conventional method.

Here, since there are few defects such as pinholes, blowholes, and cavities in the casting surface layer (melting / resolidifying portion 2B) before anodizing treatment, and a small amount of gas components are dissolved or occluded, The anodized film obtained by the anodizing process itself has extremely few defects such as pinholes and blowholes, and the local anodizing reaction is not hindered by the generation of gas bubbles on the casting surface during the anodizing process. The anodic oxidation reaction proceeds uniformly, so that a uniform and dense anodic oxide film is formed. Further, as described above, the fine structure of the surface layer before the anodizing treatment also contributes to the densification of the anodized film itself. Therefore, finally, an anodic oxide film having sufficient hardness, high wear resistance and sufficient corrosion resistance can be obtained.

The composition of the Al alloy to which the method of the present invention is applied is not particularly limited, and the point is that it is applicable to all Al alloys known for casting.

Further, in carrying out the method of the present invention, the depth of the melting / resolidifying layer due to irradiation with high-density heating energy can be controlled by adjusting the moving speed of the energy source so that the intensity of the energy can be controlled. The depth may be set so that the depth of the re-solidified layer after polishing is thicker than the thickness of the anodized film to be produced.

Furthermore, in actually applying the method of the present invention,
Of course, electrolytic coloring may be performed after the anodizing treatment, or a hard colored film may be formed by adding a metal salt to the electrolytic solution used during the anodizing treatment.

Example JIS AC2C alloy (Cu3.1%, Si6.32%, Mg
0.34%, Zn0.01%, Fe0.43%, Mn0.30%, balance A
In forming the anodized film on the casting material of 1), the following treatment was performed. That is, the portion of the outer peripheral surface of the disc-shaped test piece having an outer diameter of 30 mm and a thickness of 10 mm made of the above alloy casting was irradiated with a TIG arc to melt and re-solidify it. The TIG arc irradiation conditions are as follows.

Peak current / base current: 120A / 90A Voltage: 15V Torch moving speed: 3 to 15mm / sec (however, the torch moving speed is adjusted to have a uniform melting width) Bead number: 2 Argon flow rate: 25 / min After that, The surface of the melted / resolidified portion was polished and smoothed.
Then, a hard anodic oxidation treatment by a sulfuric acid method was performed under the following conditions.

Electrolyte composition: Sulfuric acid 10 to 20% Current density: ^{2 to} 4 A / dm ² (direct current) Voltage: 60 to 80 V Temperature: 0 ± 2 ° C. The hardness of the obtained anodic oxide film was Hv450.
It was found that the film had a high hardness of ˜550 and was a uniform and dense film. The base material surface layer of the test piece before melting / resolidification had a pinhole area ratio of 1.1%, whereas the surface layer after melting / resolidification had no pinholes.

On the other hand, for comparison, for the same test piece as above,
Without performing melting and re-solidification processing by TIG arc,
Anodizing treatment was performed under the same conditions as above. The resulting anodic oxide film is porous and has a hardness of Hv 300 to 3
It turned out to be as low as 50.

EFFECTS OF THE INVENTION As is apparent from the above-described embodiments, according to the method of the present invention, defects such as pinholes, blowholes, and cavities, and Al alloy castings containing a large amount of dissolved or occluded gas components, Also, it is possible to form a uniform and dense anodic oxide film. Therefore, by applying the method of the present invention, the surface properties such as wear resistance and corrosion resistance of the Al alloy casting material can be dramatically improved. .

[Brief description of drawings]

1 to 4 are cross-sectional views for showing the method of the present invention step by step, FIG. 1 is a cross-sectional view showing the state at the time of high-density heating energy irradiation (during rapid melting), and FIG. 2 is melting. -A sectional view showing the situation after re-solidification, FIG. 3 is a sectional view showing the situation after smoothing, and FIG. 4 is a sectional view showing the situation after anodizing treatment. 1 ... Al alloy casting, 2A ... surface layer, 2B ... melting
Resolidified part, 3 ... High-density heating energy, 4 ... Anodic oxide film.

Claims (1)

[Claims] 1. When forming an anodic oxide film on the surface of an aluminum alloy casting, the entire surface of the site where the anodic oxide film is to be formed is sequentially irradiated with high-density heating energy in advance and the surface layer is rapidly melted and rapidly resolidified. And then forming an anodized film having a thickness equal to or less than the re-solidified depth by subjecting the surface of the re-solidified portion to an anodizing treatment. .