JPH01100298A - Formation of anodic oxide film on aluminum alloy casting - Google Patents

Abstract

PURPOSE:To form a uniform and dense anodic oxide film having superior corrosion resistance by alloying the surface layer of an Al alloy casting with an Al alloy having a higher alloying degree than the casting under high density heating energy and by carrying out anodic oxidation. CONSTITUTION:High density heating energy 3 such as laser beams or electron beams are projected on an alloying material 2 to simultaneously melt the material 2 and the surface layer of an Al alloy casting 1 under the material 2. In the resulting molten pool 4, the Al alloy of the surface layer of the casting 1 and the material 2 are integrated to form an alloy layer 5. The rough surface of the layer 5 is smoothened and the smoothened surface 6 is anodically oxidized. A uniform and dense anodic oxide film 7 having superior corrosion resistance can be formed.

Description

[Detailed Description of the Invention] Industrial Application Field This invention is for improving the surface properties such as wear resistance and corrosion resistance of aluminum alloy castings used for automobile parts, especially aluminum alloy castings with high alloying element content. The present invention relates to a method of forming an anodic oxide film on.

BACKGROUND OF THE INVENTION As a means of improving the surface properties of Al alloy members such as wear resistance and corrosion resistance, a method of subjecting the surface to anodizing treatment has been widely known. In other words, since the anodic oxide film formed by anodizing Al alloys is generally hard, has high wear resistance, and has excellent corrosion resistance, forming an anodic oxide film can significantly improve these surface properties. 1.

By the way, it has been conventionally attempted to improve the wear resistance, corrosion resistance, etc. of wrought A2 alloy materials by forming an anodic oxide film as described above. For example, casting defects such as pinholes, blowholes, and cavities often exist in the surface layer, and large amounts of gaseous components such as nitrogen gas are often solid-dissolved or occluded. It was considered difficult to produce a dense anodic oxide film.

In other words, if an A2 alloy casting with no casting defects as described above is directly anodized, defects such as pinholes, blowholes, and cavities will remain in the anodized film, impairing its wear resistance and corrosion resistance. It was difficult to obtain a good homogeneous and dense anodic oxide film.

In addition, gas in defects such as pinholes, blowholes, and cavities, as well as dissolved or occluded gas components, are released during the anodizing process and form gas bubbles on the surface of the Al alloy casting, resulting in gas bubbles on the surface. This prevented the electrolytic solution for anodizing treatment from coming into contact with the surface of the Al alloy casting, and the anodic oxidation reaction did not proceed in that area, making it difficult to form a homogeneous and Wi-dense anodic oxide film.

Therefore, the present inventors have already proposed in Japanese Patent Application No. 60-99375 (Japanese Unexamined Patent Publication No. 61-257496) that high-density heating energy such as a laser beam or TIG arc is applied to the surface of the area where the anodic oxide film is to be formed. This paper proposes a method for forming an anodized film on an Al alloy casting, in which the surface layer is rapidly melted and rapidly resolidified by applying an electric current, and then the surface of the resolidified portion is anodized.

According to this proposed method, rapid resolidification after rapid melting of the Al alloy casting surface layer by high-density heating energy irradiation is achieved mainly by heat transfer from the base metal side to the surface. It solidifies in a directional manner,
Therefore, casting defects such as pinholes, blowholes, and cavities that existed in the surface layer before melting are pushed out during solidification, and also occur during melting due to occluded or solid-dissolved gas components. During solidification, the air bubbles are also extruded to the outside, and as a result, the melted and resolidified surface layer has almost no casting defects and has very little solid solution or occluded gas components. Furthermore, since resolidification occurs rapidly, the structure of the surface layer becomes extremely fine. Therefore, if the surface is anodized after such rapid melting and rapid resolidification treatment, the anodic oxide film itself will have fewer defects caused by casting defects and residue components, and the film structure will become finer. An anodized film with excellent film properties can be obtained.

Problems to be Solved by the Invention According to the method disclosed in Japanese Patent Application No. 60-99375, the properties of the anodic oxide film can be significantly improved compared to the case where the surface of the aluminum alloy casting is directly anodized. It can be improved. However, in high-alloy Al alloy castings containing many alloying elements, such as S1 and M
Q, Cu, etc. are factors that deteriorate the properties of the anodic oxide film, so before anodizing high-alloy aluminum alloy castings, rapid melting and rapid resolidification by irradiation with high-density heating energy as described above is required. Although the treatment has been effective in eliminating casting defects and refining the structure, the properties of the anodic oxide film have not yet been sufficiently improved to a satisfactory degree, and therefore the wear resistance is still at an excellent level. The reality is that corrosion resistance was not achieved. That is, in high-alloy Al alloy castings, various intermetallic compounds and crystallized products of non-solid solution alloying elements (for example, hypereutectic A
In l-3i alloy castings, a large amount of primary crystal Si) is present in the surface layer, and these intermetallic compounds and the initial product part hinder the smooth progress of anodization during anodizing treatment, and the anode Even during oxidation treatment, it remains in the positive oxide film and is a factor that impairs the properties of the film, but the rapid melting and rapid resolidification treatments described above were not effective against this factor. .

This invention was made against the background of the above circumstances, and
In forming an anodized film on l-alloy castings, we not only aim to improve the properties of the anodized film by reducing casting defects and refining the structure, as in the case of the proposal mentioned above, but also to improve the properties of the anodic oxide film on high-alloy aluminum alloy castings. Even in some cases, it is possible to eliminate the influence of alloying elements on anodizing treatment and form an anodic oxide film with extremely excellent film properties, that is, an anodic oxide film that is uniform, dense, and has extremely excellent wear and corrosion resistance. The purpose is to provide a method.

Means for Solving the Problems In the present invention, when forming an anodic oxide film on the surface of an aluminum alloy casting, high-density heating energy is used to coat the surface layer of the area where the anodic oxide film is to be formed with pure Al or Al-containing material. It is characterized by alloying an Al alloy with a higher amount than the aluminum alloy casting, and then subjecting the surface of the alloyed layer to anodizing treatment.

Function: Using high-density energy to form pure A! Alternatively, by alloying an Al alloy with a higher Al content than the Al alloy casting, the alloyed surface layer has an increased Al content but a reduced concentration of alloying elements. Therefore, when performing anodizing treatment afterwards, the anodizing treatment is performed on the part where the concentration of alloying elements is lower than that of the base material part of the Al alloy casting. There is less risk that the properties of the anodic oxide film will deteriorate. In other words, pure A! Alternatively, reducing the concentration of alloying elements in the surface layer by alloying an Al alloy with a high He1 content means that the amount of intermetallic compounds and non-dissolved alloying element crystallized substances in the surface layer decreases. , the possibility that the progress of anodic oxidation is hindered by crystallized substances such as these intermetallic compounds or that these crystallized substances remain in the anodic oxide film is reduced, resulting in a uniform anodic oxide film. It is now possible to do so.

Again'd! When alloying AN or A2 alloy with high Al content, these alloying materials are placed on the surface of the Al alloy casting, and high-density heating energy such as laser TIG arc, plasma arc, or electron beam is applied from above. And the alloyed material and its lower A! The surface layer of the alloy casting is simultaneously melted and alloyed, and then re-solidified, but the cooling and solidification during this re-solidification is performed in the same manner as in the method of Japanese Patent Application No. 60-99375 mentioned above. This is done rapidly and directionally from the casting base metal side to the surface: Therefore, casting defects such as pinholes, blowholes, and cavities that existed in the casting surface layer before alloying are pushed out to the surface. In addition, air bubbles generated during melting due to occluded or dissolved gas components are extruded from the surface to the outside during solidification, and as a result, there are almost no casting defects in the alloyed layer formed by resolidification. The state is such that there is very little solid solution or occluded gas component. Furthermore, since the resolidification is performed by rapid cooling and solidification as described above, the structure of the resolidified surface layer is extremely fine. If the surface layer, which has almost no casting defects and has a fine structure, is anodized, the resulting anodic oxide film will have almost no defects and will have a fine structure. .

Therefore, by alloying pure Al or an Al alloy with a high Al content into the surface layer of an Al alloy casting using high-density heating energy, the concentration of alloying elements in the surface layer decreases, as described above. This, combined with the reduction of casting defects in the surface layer and the effect of finer structure,
A uniform, dense, and excellent anodic oxide film can be formed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 to 5 show step by step an example of a situation in which the method of the invention is implemented.

First, as shown in FIG. 1, pure Al or an Al alloy with a high He1 content is placed as an alloying material 2 on the surface 1A of the Al alloy casting 1 to be treated where an anodized film is to be formed. do. As a method for arranging this alloyed material 2, for example, a method of simply leaving the powder still, a method of applying or spraying the powder as a slurry, a method of thermally spraying the powder, etc. Applicable and not particularly limited. Although pure Al is optimal as the alloying material, it is possible to use materials with a higher He2 concentration than the Al alloy castings to be treated, or in other words, materials with lower alloying element concentrations than the Al alloy castings to be treated. is.

Next, as shown in FIG. 2, high-density heating energy 3 such as TIG arc, laser beam, plasma arc, electron beam, etc. is applied from above the alloying material 2 to heat the alloying material 2 and the Al alloy below it. The surface layer of the casting 1 is simultaneously melted. In the molten pool 4 thus formed,
The A2 alloy casting of the base material and the alloying material are fused together (alloyed). Subsequently, by moving the application position or stopping the application of the high-density heating energy 3, the molten pool 4 is rapidly cooled and solidified, mainly due to rapid heat diffusion toward the casting base material side, and becomes an alloyed layer 5. As already mentioned, this alloyed layer 5 has a higher Al content and a lower alloying element content than the Al alloy casting 1 which is the base material, and also has a rapid Cooling and solidification results in fewer casting defects and a finer structure.

The alloyed layer 5 formed in this way usually has many irregularities on its surface, as shown in FIG.
The surface is machined or polished to create a smooth surface with no irregularities. The state is shown in FIG. Next, the surface 6 of the smoothed alloyed layer 5 is anodized to form an anodized skin 11!7 as shown in FIG.
form.

This anodic oxidation treatment produces an alloyed layer 5 with a low content of alloying elements, few casting defects, and a fine structure.
Since the anodized film is applied to the surface of the anodic oxide film, the resulting anodic oxide film is uniform, dense, and has excellent film properties. Note that the anodizing treatment itself may be carried out according to a conventional method, but in order to further improve the wear resistance, it is desirable to generate a so-called hard anodic oxide film by a method such as using a low-temperature electrolytic bath.

Note that the composition of the Al alloy to which the method of the present invention is applied is not particularly limited, and in short, it is applicable to all Al alloys used for castings.
A great effect can be obtained when applied to products with a high content of alloying elements, such as 3i alloy castings.

Further, in carrying out the method of the present invention, A formed by alloying kAl or an Al alloy with a high Al content
The thickness of the alloyed layer with high l content is determined by the thickness of pure Al or Al alloy with high A/l content to be alloyed.
It can be adjusted depending on the pot, the intensity of high-density heating energy for alloying, and its moving speed (scanning speed), etc.
The thickness of this alloyed layer may be set so that the thickness of the alloyed layer after finishing is greater than the thickness of the anodic oxide film to be produced.

Example 1] JIS AC8A alloy (Cut, 1%, 8112%
, 1.1% Mg, 1.5% Ni, and the remainder Af>, in order to form a positive %Tx% coating on a casting material of 1.1% Mg, 1.5% Ni, and the balance Af>, the above-mentioned aluminum alloy casting with an outer diameter of 30# and a thickness of 10. First, pure A! was applied to the outer peripheral surface of a disc-shaped test piece using a TIG arc using bound Al powder as an alloying material. was alloyed. The TIG arc irradiation conditions at this time are as follows.

Peak current/base current: 120A/90A current
Pressure = 15V Torch movement speed (peripheral speed): 1.5 to 3s/Sec
Argon gas flow rate: 25 f/mi In this alloying treatment, the thickness of the pure Al powder layer for alloying was adjusted so that the alloying rate expressed by the following equation was 30%.

Next, the surface of the alloyed layer was finished and smoothed, and then anodized. The conditions for the anodizing treatment at this time were as follows.

Electrolyte composition: Sulfuric acid 10-20% Current density: 2-4 A/dIi (DC) Voltage: 260-80 V Temperature: 20'C ± 2°C [Example 2] Same as used in Example 1 The test piece was subjected to alloying treatment and finishing hO any polar oxidation treatment under the same conditions as in Example 1, except that the alloying treatment was performed so that the alloying rate was 50%.

(Example 3) The same test piece as used in Example 1 was alloyed under the same conditions as Example 1, except that the alloying process was carried out so that the alloying rate was 70%. −
Polar oxidation treatment was performed.

[Comparative Example 1] A test piece similar to that used in Example 1 was subjected to anodic oxidation treatment without any particular alloying treatment. The conditions for the anodizing treatment are the same as in Example 1.

Comparative Example 2] A test piece similar to that used in Example 1 was coated with T on the outer peripheral surface according to the method of Japanese Patent Application No. 60-99375.
A remelting/resolidification process was performed using an IG arc, and then a finishing process was performed, followed by an anodizing process. The TIG arc irradiation conditions in the remelting/resolidification treatment were the same as those in the alloying treatment in Example 1, and the anodizing treatment conditions were also the same as in Example 1.

Table 1 shows the results of examining the underlying condition of each @polar oxide film and the properties of each anodic oxide film obtained in Examples 1 to 3 and Comparative Example 1.2.

Note that the base of the anodic oxide film is the alloyed layer obtained by alloying treatment in Examples 1 to 3, the casting as it is in Comparative Example 1, and the remelted/resolidified layer in Comparative Example 2. . In Table 1, DAS is the dendrite arm spacing (
Dendrite Arm Spacing>
The degree of fineness of the tissue is measured.

Table 1 As is clear from Table 1, Example 1 in which alloying treatment of pure Al was performed before anodizing treatment according to the method of the present invention to reduce the content of alloying elements in the base of the anodized coating. ~3, the hardness of the anodic oxide film is Hv 450~5
It is clear that the hardness is as high as 50 and the film properties are also excellent. On the other hand, in Comparative Example 1 in which pure Al was not alloyed, the underlying structure was coarse and had many casting defects, and the alloying element content was high, so the hardness of the anodic oxide film was 280 Hv. The film properties were also porous.

In addition, in Comparative Example 2, which was subjected to re)melting and resolidification treatment, Comparative Example 1
Although higher hardness was obtained and the film properties were slightly better than in the case of The hardness was lower than that of Examples 1 to 3, and the film properties were also inferior.

[Example 41 As shown in Figures 6 and 7, JIS AC8A alloy (
In order to improve the wear resistance near the top ring slot 11 of an internal combustion engine piston 10 made of an aluminum alloy casting (the specific composition of which is the same as in Example 1), an anodic oxide film 7 is formed on the upper and lower surfaces thereof. For this purpose, the following process was performed.

That is, TIG is applied to the upper and lower surfaces of the top ring slot 11.
Pure Al is alloyed using an arc under the same conditions as in Example 2 to form an alloyed layer 5 in which the content of alloying elements is lower than that of the base material, and then finishing processing is performed and then under the same conditions as in Example 1. An anodic oxidation treatment was performed to form an anodic oxide film 7.

Insert the treated piston into a 2000CC 14-cylinder diesel engine with a turbocharger,
Full load 4000 rpm x 30 at high water temperature and high oil temperature
A 0-hour continuous high-speed durability driving test was conducted.

As a result, the anodized coating 7 of the ring slot 11 is hardly worn out and has good wear resistance.
a? It was done. For comparison, the upper and lower surfaces of the ring slot 11 were remelted and remelted by TIG arc under the same conditions as Comparative Example 2.
A similar continuous high-speed durability test was conducted on pistons that had been resolidified and anodized, and in this case it was found that part of the anodized film on the ring slot had disappeared due to wear.

Effects of the Invention According to the method of this invention, A to form an anodic oxide film
l The surface of the alloy casting is heated in advance using high-density heating energy such as TIG arc to form pure A! Alternatively, by alloying an Al alloy with a high Al content, anodizing is performed with the alloying element content in the surface layer reduced.
Even if the alloy casting itself has a high content of alloying elements, the properties of the positive FF1M coating will not deteriorate due to the alloying elements, and the above-mentioned alloying can be achieved by rapid melting and rapid melting using high-density heating energy. Since this is done by resolidification, the casting defects that existed on the surface of the casting are reduced and the structure is made finer, so that the anodic oxide film itself has fewer defects and has a finer structure. Therefore, by combining these factors, according to the method of the present invention, it is possible to obtain an anodic oxide film with excellent film properties, that is, an anodic oxide film that is uniform, dense, and has good wear resistance and corrosion resistance. When forming an anodic oxide film on an aluminum alloy casting with a high element content, a remarkable effect of 1q can be achieved.

[Brief explanation of the drawing]

Figures 1 to 5 are schematic cross-sectional views showing step-by-step an example of a situation in which the method of the present invention is implemented, and Figure 6 is an example of applying the method of the present invention to a piston of an automobile engine. FIG. 7 is an enlarged vertical cross-sectional view of section A in FIG. 6. 1... Al alloy casting, 2... Alloying material (pure 2
or an Al alloy with a high A/l content), 3... High-density heating energy, 5... Alloyed layer, 7... Anodic oxide film. Applicant Toyota Motor Corporation

Claims (1)

[Claims] In forming an anodic oxide film on the surface of an aluminum alloy casting, pure Al or an Al alloy with a higher Al content than the aluminum alloy casting is alloyed using high-density heating energy on the surface layer of the part where the anodic oxide film is to be formed. ,
A method for forming an anodic oxide film on an aluminum alloy casting, the method comprising: thereafter subjecting the surface of the alloyed layer to an anodic oxidation treatment.