JPH091319A - Surface treatment method of aluminum alloy casting or aluminum alloy die casting - Google Patents

Abstract

PURPOSE: To improve the decoration effect by achieving the anode oxidation, dyeing and sealing after melting and removing Si in the surface chill layer of a product, or squeezing defective cast parts to prevent generation of blackened part or irregular dyeing when the surface treatment is achieved on an aluminum alloy casting or a die cast product. CONSTITUTION: In a grinding process, defective cast parts such as pin holes, blowholes, shrinkage cavity on or close to the surface of a work are squeezed by the blasting by the scale ball or steel grit. Then, in the surface property adjusting process, the surface of the work is treated with the solution containing fluorine acid or fluoride compounds, Si in the surface chill layer is melted and removed, the surface is smoothed by the chemical or electrolytic polishing, and then, the anode oxidation, dyeing and sealing are successively executed. The surface property treatment may be achieved using the solution containing phosphoric acid and nitric acid in addition to the treatment with fluorine acid solution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method for aluminum alloy castings or aluminum alloy die castings.

[0002]

2. Description of the Related Art In aluminum alloy castings or aluminum alloy die castings for motorcycle parts and the like, as a substitute for the coating that is common in surface treatment for ensuring the appearance and commercial viability, it is possible to obtain a luster such as glass-like luster and metallic luster. Anodizing treatment that can maintain the property for a long time is desired. However, it is common knowledge that the anodic oxidation treatment of an aluminum alloy casting or an aluminum alloy die casting is not suitable for the purpose of decoration because of the following items.

Aluminum alloy castings are manufactured by pouring molten metal into a sand mold, a mold, etc., but the portion in contact with the mold is rapidly cooled and a chill layer is generated on the surface. In this chill layer, Si added to improve the castability is present at a high density. In anodizing, this Si is left in the film without being dissolved or oxidized, resulting in a dark gray color (black ink).
Becomes

The aluminum alloy die casting is a method for injecting a molten metal into a mold at a high speed, but the generation of the chill layer and the black ink due to the chill layer is similar to that of the aluminum alloy casting.

In an aluminum alloy casting, hydrogen gas contained in the molten metal is released during solidification, so that fine holes (pinholes) exist under the chill layer near the surface of the casting. In addition, there are shrinkage cavities due to insufficient hot water during solidification, and the electrolytic solution (acid) during anodization treatment remains in casting defects such as pinholes and shrinkage cavities, resulting in defective anodic oxide coating (non-staining). To do.

Further, in the aluminum alloy die casting, as described above, the entrainment of air by the high-speed injection of the molten metal is remarkable, and unstaining due to the casting defects similar to the aluminum alloy casting occurs.

In both the aluminum alloy casting and the aluminum alloy die casting, the anodization process is defective due to the inclusion of the surface oxide (slag) of the molten metal and the deposits such as the mold coating agent and the mold release agent on the surface of the casting.

In both the aluminum alloy casting and the aluminum alloy die casting, when the gate and the burr-removed portion are selectively buffed and then subjected to anodizing treatment, the buffed portion and the other portion (the mold surface remains the same). part)
Difference in gloss and surface roughness, resulting in poor appearance and commercial properties.

However, in the prior art, the following (a) or, in order to secure uniform dyeability and glitter by anodizing an aluminum alloy casting or an aluminum alloy die casting,
(b) is adopted.

(A) After removing Si from the surface chill layer with a solution containing hydrofluoric acid or a fluorine compound, blasting is performed,
After that, anodizing treatment is applied (Japanese Patent Publication No. 1-25831).
By removing Si from the surface chill layer, generation of black ink is avoided.

(B) The surface chill layer and casting defects are mechanically cut off by cutting. As a result, black ink and non-staining are prevented from occurring.

[0012]

However, the prior art
(a) has the following problems. Since the surface of the surface chill layer from which Si has been removed is subjected to blasting, it is considered that the surface is ground by this blasting and Si is exposed again.

It is conceivable that a solution containing hydrofluoric acid or a fluorine compound remains on the surface pinholes. Then, when the pinhole opening is closed by blasting, the residual solution that is to be contained in the pinhole subsequently deteriorates the anodic oxide coating.

In the surface treatment step, the material to be treated, which is usually hung on a hanger or the like, is automatically and continuously moved in each bath for degreasing, washing, chemical polishing, anodic oxidation and the like. Therefore,
It is not preferable to insert a machining process such as a blast treatment between the hydrofluoric acid bath and the anodizing bath from the viewpoint of workability and quality. The surface cleaned with a hydrofluoric acid bath becomes dirty again due to the blast treatment, and the continuous chemical treatment is interrupted due to the blasting step after the treatment step with the solution containing hydrofluoric acid or a fluorine compound, and the object to be treated in the meantime. The surface of the material is oxidized.

The prior art (b) has the following problems. In a casting having a complicated surface shape such as bosses or ribs protruding on the casting surface, it is difficult to cut the entire surface to have the same surface texture, and even if it is possible, the cost will be greatly increased.

An object of the present invention is to easily obtain an anodized film having uniform dyeability and luster in an aluminum alloy casting or an aluminum alloy die casting.

[0017]

The present invention according to claim 1 comprises a polishing treatment step of polishing a material to be treated, which is made of an aluminum alloy casting or an aluminum alloy die casting,
The surface texture adjusting treatment step of dissolving and removing Si in the surface chill layer of the treated material after the blasting treatment and the anodizing, dyeing and sealing treatments on the treated material after the surface texture adjusting treatment are sequentially performed. It was done.

The present invention according to claim 2 is the same as the invention according to claim 1, further comprising the step of casting the surface of the material to be treated and pin holes, blow holes, shrinkage cavities, etc. This is a process for crushing defects.

According to a third aspect of the present invention, in addition to the first or second aspect of the present invention, the polishing treatment is shot blasting with a steel ball or steel grit.

The present invention according to claim 4 provides the invention according to claims 1 to 3.
In any one of the present inventions, the surface property adjusting treatment step is a treatment with a solution containing hydrofluoric acid or a fluorine compound, and further a surface smoothing treatment by chemical polishing or electrolytic polishing.

The present invention according to claim 5 is based on claims 1 to 3.
In any one of the present inventions, the surface texture adjusting treatment step is performed with a solution containing phosphoric acid and nitric acid.

[0022]

The operation of the present invention will be described first. The direction of improvement of anodizing treatment of aluminum alloy castings or aluminum alloy die castings is mainly development to the material composition of the material to be anodized easily. Review of casting method to reduce casting defects. Anodizing solution (including pretreatment) ), And the development of the anodizing treatment bill. However, there are some products that cannot meet the above requirements in order to maintain the shape and mechanical properties, so we proceeded on the premise of existing materials and existing casting methods in the development. It is relatively easy to prevent the occurrence of black ink during dyeing by removing Si in the surface chill layer with a hydrofluoric acid bath, etc., or to secure the glitter by chemical polishing, by using various chemical agents and testing it. did it. However, problems of dyeing defects such as exposure of casting defects due to non-dyeing (roughness of material due to pretreatment such as hydrofluoric acid bath treatment for removing black ink and chemical polishing for producing glitter) have been encountered. In contrast to the contradictory phenomenon that non-staining occurs if hydrofluoric acid bath treatment for black ink prevention or pretreatment such as chemical polishing is performed to bring out the luster, when the non-staining part is investigated, corrosion products are found on the surface. Although it was present and the cause of non-staining was initially determined to be due to stains on the surface of the material, the above method developed, but it was not improved. However, the existence of microscopic pinholes in the area of 200 μm to 1 mm below the surface of the material was confirmed by observing the unstained area with an electron microscope and investigating the component distribution. Although this is extremely small at the material stage, it has been found that erosion is expanded by a treatment with a hydrofluoric acid bath for preventing black ink and a treatment such as chemical polishing for producing a glittering property. Then, the electrolytic solution (sulfuric acid, etc.) for the anodizing treatment enters the pinhole, or the electrolytic solution cannot be removed from the pinhole by washing with water after the anodizing treatment, and the electrolytic solution is used in the subsequent dyeing process. Proper concentration of dyeing solution (PH)
It is conceivable that the non-stained portion is distorted to generate an unstained portion, or that the electrolytic solution that expands due to the high-temperature staining liquid oozes out around the pinhole to enlarge the unstained portion. Therefore, it has been found that it is effective to uniformly blast the surface of the material to be processed by blasting or the like to remove and crush the casting defect portion.

Therefore, according to the present invention described in claims 1 to 3, the following actions (1) to (3) are provided. Before melting and removing Si of the casting surface chill layer of the aluminum alloy casting or the aluminum alloy die casting, shot blasting treatment, liquid honing treatment, barrel treatment, etc. are applied to remove oxides on the surface of the material, pinholes, Crushes casting defects such as blowholes and shrinkage cavities. As a result, it is possible to prevent the occurrence of non-staining due to the invasion of the electrolytic solution into the surface casting defect during the anodizing treatment.

As in the prior art (a), since the blast treatment is not performed after the Si of the casting surface chill layer is removed by melting, the Si is not exposed again after the Si is removed by dissolution. Therefore, it is possible to prevent black ink from being generated due to the presence of the surface Si. Further, it is possible to prevent the Si solution from remaining in casting defects such as pinholes, blowholes and shrinkage cavities on the surface of the material.

Slag, coating agent, release agent, etc. adhering to the surface of the casting are completely removed by the scouring treatment. Therefore,
There is no anodizing treatment failure due to these deposits.

Even if the gate and the burr-removed portion are selectively buffed, the subsequent polishing treatment makes the surface roughness of the casting surface uniform over the entire surface. For this reason, there is no difference in gloss and surface roughness between the buffed portion and the other portion (the portion that remains the mold surface), improving the commercialability.

The blasting treatment makes it possible to uniformly process the entire surface of a material having a complicated surface shape such as bosses or ribs protruding from the casting surface, and is excellent for such a material having a complicated shape. Anodized film can be formed.

In particular, the blasting treatment by shot blast using steel balls, steel grit, etc. causes a large compressive residual stress to remain in the material to be treated, and as a result, the fatigue resistance of the material to be treated can be improved.

A mechanical scouring treatment was carried out as a preceding step of the surface texture adjusting treatment. Therefore, the mechanical scouring treatment is not inserted between the baths in which the surface texture adjusting treatment and the anodizing treatment are successively performed, so that workability and quality can be improved.

The present invention according to claim 4 has the following effects. In the surface property adjusting treatment step, the surface smoothing treatment is performed by polishing with a solution containing hydrofluoric acid or a fluorine compound. Therefore, it is possible to dissolve and remove Si in the surface chill layer with a solution containing hydrofluoric acid or a fluorine compound to prevent black ink from being generated during the anodizing treatment of the material to be treated. Then, the surface smoothing treatment can be performed by chemical polishing or electrolytic polishing to improve the glitter of the material to be treated.

The present invention according to claim 5 has the following effects. In the surface property adjusting treatment step, the treatment is performed with a solution containing phosphoric acid and nitric acid. Therefore, the surface is dissolved with a phosphoric acid solution and Si is also removed, so that it is possible to prevent black ink generation in the anodizing treatment of the processing target material. Further, the surface oxide can be removed with a nitric acid solution to improve the glitter of the material to be treated.

[0032]

EXAMPLE An example in which the present invention is applied to an aluminum alloy cast outer tube (AC4D) for a hydraulic shock absorber forming a front fork of a motorcycle will be described.

(Example 1) In Example 1, the surface property adjusting treatment of the present invention is performed by a solution containing hydrofluoric acid or a fluorine compound and a surface smoothing treatment by chemical polishing.

(1) Abrasive cleaning The cast material to be processed is subjected to an abrasive cleaning to remove the coating agent, sand, and oxides on the surface of the material to be removed, and the sprue and deburring marks and other parts are removed. A uniform surface texture can be obtained.

Similarly, the scouring treatment can remove and collapse casting defects such as pinholes, blowholes and shrinkage cavities in the material to be treated. This is effective in preventing non-staining in the anodizing process.

Shot blasting, liquid honing, barrel polishing and the like can be used for the polishing treatment. Shot blasting and liquid honing are useful for removing casting defects and crushing, and barrel polishing is useful for improving glitter. Therefore, for the purpose of the present invention, the polishing treatment can be carried out by shot blasting only, shot blasting + barrel polishing, liquid honing + barrel polishing, or the like. In this example, 0.
Shot blasting was performed using a steel ball of 3 to 1.0 mmφ.

There are various methods of blasting, such as air, vacuum, water, and centrifugation, which may be selected according to the stains and appearance quality of the casting, but in the case of many casting defects, surface defects are removed by increasing the blasting force. You can crush internal pinholes. For example, in the outer tube, there are many pinholes under the chill layer on the surface at about 200 μm to 1 mm. Surface defects can be removed by treating with air, vacuum or centrifugal blast with steel grit or steel shot, and with water blast with silica sand or glass balls.

In the liquid honing, a fine abrasive is mixed and compressed air is sprayed from a spray gun. Finer abrasives can be used than shot blasting.

For barrel polishing, various methods may be selected depending on the stains and appearance quality of the cast article.

Hereinafter, degreasing, hydrofluoric acid and a fluorine compound, chemical polishing, anodic oxidation, dyeing and sealing are sequentially carried out, but any of the methods usually carried out for aluminum alloy castings can be adopted.

(2) Degreasing The removal of oil and its decomposition products attached to the material to be treated, abrasives, and surface corrosion products is performed by acid degreasing, bath agent degreasing, surfactant degreasing, electrolysis. Degreasing etc. The outer tube may be degreased with sulfuric acid well, and may be heated when the reaction is difficult to proceed. If a surfactant is further added, the cleaning effect will be good. It should be noted that alkaline degreasing has a strong erosive power and the treated surface becomes rough. Tables 1 and 2 show specific examples.

[Table 1]

[Table 2]

(3) Treatment with hydrofluoric acid and fluorine compound Fine Si in the chill layer existing on the casting surface is removed with hydrofluoric acid and a fluorine compound. This is effective in preventing black ink generation in anodizing treatment. A surfactant, urea or the like may be added in order to suppress the reaction so that the casting defects crushed by the blasting treatment such as shot blasting or barreling are not exposed again. Table 3 shows a specific example.

[Table 3]

(4) Chemical Polishing The chemical polishing bath may be a combination of phosphoric acid, nitric acid and sulfuric acid. The bath in which nitric acid is added to phosphoric acid smoothes fine irregularities on the surface of the material to be treated and improves the glitter. At this time, phosphoric acid dissolves on the surface, and nitric acid removes surface oxides to obtain glitter. Table 4 shows a specific example.

[Table 4]

The chemical polishing and the treatment of (3) the hydrofluoric acid and the fluorine compound may be interchanged in process order, and the chemical polishing may be performed before the treatment of the (3) hydrofluoric acid and the fluorine compound.

In addition, following the chemical polishing of (4), in order to remove stains (smut) on the surface of the material to be treated, desmutting may be performed with a liquid containing nitric acid and hydrofluoric acid.

(5) Anodizing A solution containing at least one of sulfuric acid, oxalic acid, and organic acid is anodized by a commonly used method such as direct current, alternating current, alternating-current superposition, and pulse method. Table 5 shows a specific example.

[Table 5]

(6) Dyeing Dyeing is performed using a dye for aluminum anodizing dyeing.
Table 6 shows a specific example.

[Table 6]

(7) Sealing A sealing agent containing nickel acetate as a main component is used to seal the dyed film. Table 7 shows a specific example.

[Table 7]

The article to be treated obtained as described above can have an appearance excellent in uniform dyeing property and brilliance over the entire surface without dyeing defects such as black ink and non-dyeing. In this example, the chill layer had a thickness of about 20 μm and the anodized film layer had a thickness of 5 to 7 μm.

(Example 2) Example 2 is different from Example 1 in that the surface texture adjusting treatment step of the present invention is performed with a solution containing phosphoric acid and nitric acid.

Therefore, instead of (1) the polishing step, (2) the degreasing step, (3) the treatment with hydrofluoric acid and a fluorine compound, and (4) the chemical polishing in Example 1, Table 8 shows specific examples. A phosphoric acid / nitric acid treatment was performed. Then, in Example 1, (5) anodizing, (6) dyeing, (7)
Each treatment of sealing was performed.

Phosphoric acid dissolves the surface of the material to be treated, and the surface S
The i layer is also removed. Nitric acid removes the oxide on the surface of the material to be treated and obtains glitter.

In the surface texture adjusting process of the present invention, it is not necessary to use the phosphoric acid solution alone and the nitric acid solution together.

The present invention is also extremely useful when applied to aluminum alloy die castings.

[Table 8]

[0055]

As described above, according to the present invention, in an aluminum alloy casting or an aluminum alloy die casting, an anodized film having uniform dyeability and glitter can be easily obtained.

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Claims (5)

[Claims] 1. A blasting treatment step of blasting a material to be treated consisting of an aluminum alloy casting or an aluminum alloy die casting, and a surface texture adjusting treatment to dissolve and remove Si of a surface chill layer of the material to be treated after the blasting treatment. A surface treatment method for an aluminum alloy casting or an aluminum alloy die casting, which comprises sequentially performing the steps and anodizing, dyeing and sealing treatments on a material to be treated after the surface texture adjusting treatment. 2. The aluminum alloy casting or the aluminum alloy die casting according to claim 1, wherein the polishing treatment step is a treatment for crushing casting defects such as pinholes, blowholes and shrinkage cavities on the surface and near the surface of the material to be treated. Surface treatment method. 3. The surface treatment method for an aluminum alloy casting or an aluminum alloy die casting according to claim 1, wherein the blasting treatment is a shot blasting treatment with a steel ball or steel grit. 4. The method according to claim 1, wherein the surface texture adjusting step is a step of treating with a solution containing hydrofluoric acid or a fluorine compound and further performing a surface smoothing treatment by chemical polishing or electrolytic polishing. A surface treatment method for the aluminum alloy casting or the aluminum alloy die casting as described. 5. The surface treatment method for an aluminum alloy casting or an aluminum alloy die casting according to claim 1, wherein the surface texture adjusting treatment step is a treatment with a solution containing phosphoric acid and nitric acid.