JPS6220896A - Anticorrosive bright surface treatment of aluminum casting - Google Patents

Abstract

PURPOSE:To remarkably improve the filiform erosion resistance of an Al casting and to prevent reduction in the commodity value by use for many years by machining the desired surface of the casting to form a lustrous surface, anodically oxidizing the lustrous surface to successively form a porous film and a barrier layer, and applying clear point to the anodically oxidized surface. CONSTITUTION:The desired surface of an Al casting is machined to form a lustrous surface. This lustrous surface is anodically oxidized to successively form a porous film of 0.1-3mum thickness and a barrier layer of 500-5,000Angstrom thickness. Clear paint is then applied to the anodically oxidized surface to form a transparent paint film which does not reduce the metallic luster.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a surface treatment method that maintains the metallic luster of cut surfaces of aluminum castings and has excellent film properties to prevent the formation of thread-like rust. The present invention relates to a treatment method suitable for anticorrosion brightening surface treatment of 9A wheels.

BACKGROUND OF THE INVENTION 2. Description of the Related Art Aluminum castings are used in many fields, such as interior decoration and vehicle wheels, due to their immersive properties.

For aluminum castings, a method is used in which a desired surface is cut depending on the intended use, and then anodic oxidation film treatment and clear coating are applied to give the surface a metallic luster. However, 5 to 20% silicon is added to aluminum castings in order to improve the casting properties, and this silicon remains in the sulfated coating, turning the coating gray and significantly reducing the metallic luster during cutting. This phenomenon occurs, so it is necessary to keep the thickness of the anodic oxide film below a certain limit. In this case, filamentous corrosion forms and grows under the clear paint film. Salt is applied to the road surface as a snow melting agent and the road is exposed to a harsh corrosive environment, which can lead to thread-like corrosion on the entire surface, which can lead to safety issues. Among other things, the metallic luster disappears and the appearance deteriorates. We were able to avoid losses and a decline in product value. This phenomenon is
Other aluminum casting products, such as various parts and equipment for ships.

It also occurs in fishing gear parts, high-rise parts, door handles, interior decorations, etc. It has excellent metallic luster, little deterioration of luster over time, and corrosion resistance against the thread-like rust mentioned above (hereinafter referred to as "thread-resistant"). The emergence of an anti-corrosion bright surface treatment method has been eagerly awaited.

In addition, there are methods to solve thread rust resistance with conventional painting, such as 2.
Have a round market! A two-coat/one-bake method in which the film is baked later can also be used, but this is not a preferable method because the effect is insufficient and the cost increases significantly due to an increase in the number of upstream steps. Also, [Modern Meta
ls, 1984, Volume 40, No. 7, Page 32, 3
Clear coating of aluminum wheels is described in "Page 4", but no suitable method has been proposed yet.

Means for Solving the Problems As a result of studying the above-mentioned problems, the present inventors first performed a first-stage anodic oxide coating treatment on the cut surface to form a porous layer of an appropriate thickness. A film is formed that does not reduce the brightness during cutting, and then the thickness of the barrier layer interposed between the surface porous layer and the aluminum base material is increased in the second stage of anodizing film treatment to overcome the lack of thread rust resistance. We have found that this can be addressed by - If the capacity of the base material used in the anodic oxide coating treatment, clear electrodeposition coating, etc. is small, the leakage current from the casting surface other than the cut surface is at a level that cannot be focused on, and the above-mentioned In order to effectively progress the surface treatment, masking coating and/or colored coating that substantially exhibits a masking coating effect and exhibits a desired decorative coloring effect (hereinafter referred to as "colored coating") is used as a preliminary treatment. The inventors have discovered that it is effective to perform monochrome or multicolor coating, and have completed the present invention.

That is, in the method of the present invention, a cleaned aluminum casting is subjected to masking coating and/or colored coating on the front surface or a part of the desired surface, and then cutting the desired surface to form a glossy surface. It is characterized by applying a porous anodic oxide film treatment to the stage, then applying a barrier type anodic oxide film treatment, and then applying a clear coating to the anodized surface, which has a reflectance of 10%. It is possible to form a film on the cut surface that is highly resistant to thread rust while guaranteeing the above metallic luster.

The following will explain the case where the aluminum casting is applied to a vehicle wheel, but it can be similarly applied to other products as well.

Some aluminum 9Ja wheels have the rim and disc integrally cast, and after Seishin, the disc part was integrated with the rim with bolts, etc., but they are manufactured using various convex and convex methods, and are manufactured according to the requirements. Die-cast wheels are mainly used as quality characteristics become stricter, but wheels applied to the present invention may be manufactured by any manufacturing method, but wheels made by die-casting methods (especially oxygen-substituted die-casting method, vacuum die-casting method, etc.) may be used. Preferably.

Since mold release agents adhere to the surface of cast wheels during manufacture, they are subjected to intermediate shot blasting treatment depending on the type of mold agent used, and then are subjected to alkaline degreasing, organic solvent, surfactant, etc. A degreasing and cleaning treatment using a phosphate method or the like is performed, and the sample is subjected to the treatment process of the present invention. It goes without saying that when a process such as applying partial plastic working to the wheel rim portion after casting is employed, a degreasing and cleaning treatment is performed afterwards.

First, in the present invention, in order to effectively carry out the next step of anodic oxide film treatment and electrolytic treatment during clear electrodeposition coating, surfaces other than those to which the anticorrosive light 8 surface treatment of the present invention is applied (hereinafter referred to as the main treatment surface) ( It is desirable to apply masking paint to this area.Since cutting is performed after masking paint, it is usually advantageous for on-site work to apply masking paint to the entire surface of the wheel (all surfaces including the back side).For masking Any suitable paint can be used as long as it is acid-resistant, alkali-resistant, has appropriate film adhesion, and is electrically insulating, but it is appropriate to use a commonly used synthetic cloth layer paint. Appropriate conventional means such as spray painting, electrodeposition painting, etc. can be applied to the coating method, and depending on whether the paint used is a drying type or a baking type, a usual post-treatment such as heat fixation treatment is performed.Masking coating In the treatment process of the present invention, it acts as a masking material, but after that it can function as a protective film during handling and use, and it is also possible to use the same type of paint as the clear paint, in which case There is no particular need to peel off the film at the end of the process of the present invention.

In addition, in order to enhance the aesthetic appearance of the wheel, we formed a metallic glossy surface on the disc surface and painted the wheel windows (openings formed on the disc surface) in black, white, silver, etc.
Colored coating may be applied in some cases, but in this case, the nine-color coating can also be used as the masking coating described above. In this case, it is possible to apply colored paint to some parts and apply overly bright masking paint to others, but
Paints obtained by adding pigments depending on the coloring to the same synthetic resin paints used for clear paints, such as carbon,
Paints containing pigments such as titanium oxide and aluminum gold powder are applied. In addition, for surfaces that actively require angular coating, commonly used coating base treatments such as chemical coating methods such as chromate treatment, phosphoric acid chromate treatment, and boehmite treatment, or sulfuric acid, chromic acid, and phosphoric acid treatment are applied. What is the effect of pre-treatment such as anodic oxidation, etc., on improving the adhesion of colored paints?

Following masking painting, cutting is performed on the main treated surface,
A cut surface is formed on the cast surface to give it a desired pattern of metallic luster. Cutting is done as appropriate depending on the product shape of the aluminum casting and the desired luster of the metal scraps.

This is done by applying turning means, and the reflectance at the end of machining is 2.
A cut surface having a glittering property of 5% or more is formed. For wheels, diamond lathes, etc. 8! Mechanical cutting means are preferred. After cutting, the cut surface is degreased, but
Degreasing methods using non-etching degreasers, such as organic solvent methods and surfactant methods.

Alkaline degreasing, phosphate degreasing, and the like are preferred in order to prevent loss of metallic luster during cutting, and after degreasing, washing with water is performed by a conventional method.

Next, a two-step anodic oxide coating treatment is performed on the cut surface.

First, in order to obtain a film that can prevent as much as possible the reduction in metallic luster during cutting, a porous transparent anodic oxide film treatment was performed to create a highly transparent film with an α of 1 to 3 μm (reflectance of 15
% or more) and then, in order to further form a film with excellent thread rust resistance underneath, a barrier type anodic oxidation film treatment is performed to form a dense barrier layer with a thickness of 500 to 5000 A.

As a porous type anodic oxide film treatment method, it is preferable to use sulfuric acid, phosphoric acid, or a mixed bath of both in order to obtain a highly transparent film, but other known methods such as oxalic acid, chromic acid, sulfamic acid, and malonic acid can also be used. A bath of acids such as, a mixed bath of these and sulfuric acid, or a bath of sodium hydroxide, sodium phosphate, etc. can also be used. For example, sulfuric acid bath method Teha, 50-5oog/l sulfuric acid (H2sO4
] Electrolysis voltage of 8 to 20 V in the bath, preferably 12 to 18 V, bath temperature of 15 to 30 °C, preferably 20 to 25 °C, 05
The treatment is carried out at a current density of ~1.5 A/dm2.

In addition, in the phosphoric acid bath method, phosphoric acid (II3PO4) of 5 to 3 oog/l, preferably 30 to 80 g/l, 15 to
At a bath temperature of 40°C, preferably 18-35°C, ()2-1
．． 5A/am preferably α3-1. OA/dm
It is desirable to carry out the electrolytic treatment using a constant current electrolytic method in the range of 2 or a constant voltage electrolytic method at 10 to 100 V, preferably 20 to 50 V. By performing these treatments, a porous film consisting of bores with a pore diameter of 100 to 300 mm is formed on the cut surface, but if the film is allowed to grow to a thickness of 3 μm or more, the film becomes gray and the transparency of the film decreases. This is not desirable as it will cause damage.

After completing the porous anodic oxide film treatment, wash with water.
Subjected to barrier type anodic oxide coating treatment.

Barrier type anodized skin that aims to grow Barrier 1.

Membrane treatment uses boric acid, borax, citric acid, and tartaric acid.

Using a bath consisting of IM or two or more salts such as phthalic acid, triethylamine, and ammonium borate, 01-
1. The treatment is carried out by constant current electrolysis in the region of OA/dm2, and is terminated when the bath voltage reaches 100 to 200 V, followed by washing with water and/or hot water. In this case, if the thickness of the barrier layer exceeds 500OA,
A phenomenon in which dielectric breakdown occurs and discharge occurs during film formation is observed, and only power consumption increases (because of this, 5,000
It is desirable to keep the film growth below A;
If the thickness is less than A, the effect of improving thread rust resistance will be insufficient; therefore, a film thickness of preferably 1000 to 3500 A is appropriate.

In this way, the treated surface (cut surface) that has been subjected to two-stage anodic oxide coating treatment will have a reflectance of 5% or less if sufficient corrosion protection is to be achieved with only porous oxide coating treatment. However, it ensures a brightness with a reflectance of 15 to 25% and is highly resistant to thread rust.

After the anodic oxide film treatment has been completed, the treated surface is then coated with a clear coating that provides a transparent coating that does not reduce its metallic luster. Clear coating (normal air spray coating, electrostatic coating, powder coating, coating methods, etc. are also commonly used, but electrodeposition coating methods are generally easier to obtain in terms of quality, and their coating thickness is is approximately 5 to 40 μm.In addition, since masking coating and/or corner coating is applied to surfaces other than the main treatment surface, only the main treatment surface has conductivity even if electrical treatment is performed, so it is efficient. can be painted.

In the clear coating method, for example, in the air spray method, a method is adopted in which a thermosetting acrylic resin paint is applied to a thickness of 20 to 30 μm (when dry), and then baked at 150 to 180° C. for 20 to 40 minutes. In the electrodeposition coating method, paints that are generally used for clear coating of building materials are commonly used, such as acrylic/melamine water-soluble paints with a constant voltage of 100 to 250 V or 20 to 8
Treated with constant current electrolysis at 0 mA/dm2, 10-3
170-190°C after forming a film of 0 μm (dry)
Perform the baking process for about 30 minutes.

By going through the above steps, it is possible to form a clear coating finish layer having a shiny surface (for example, a reflectance of 10% or more) with excellent thread rust resistance and a metallic luster on the desired cut surface of the aluminum casting. By using aluminum alloys, etc., which have a smoother cut surface than those obtained using the cutting method, and which can easily form a glittering film, it is possible to form a film that is excellent in -H in terms of glitter and corrosion resistance. The best effect is exhibited when applied as an anti-corrosion treatment method for aluminum vJa wheels, which are particularly prone to filamentous corrosion, but it can also be applied as a bright anti-corrosion treatment method for products with more relaxed usage conditions. Needless to say.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples.

Examples Example 1 Commercially available DX-30 alloy (Si9 heavy dragon, semi-α2 weight%,
Die-cast one-piece aluminum wheel (outer diameter 39
After cleaning the surface of the wheel (spoke type with a 0 mm disc surface) using an alkaline degreasing method, chromate treatment was performed, and then black paint (acrylic resin paint containing carbon pigment AL100O, manufactured by Kansai Paint Co., Ltd.) was spray-painted over the entire surface of the wheel. A baking treatment was performed at 170° C. for 25 minutes.

Next, about 70% of the area ratio of the front surface of the disk was subjected to diamond turning to cut the cast surface to obtain a metallic luster surface in which the aluminum base surface was exposed as a donut, and then trichlene degreasing was performed.

As the second stage anodic oxidation coating treatment, sulfuric acid 180g/l,
Processed for 3 minutes at a bath temperature of 25°C and a bath voltage of 14V.
A porous anodic oxide film of 5 μm was formed, and after washing with water, a second stage of anodization film treatment was performed using 30 g/E of boric acid and 20 g/E of borax.
anode current density α5A/dm in a bath containing g/l
2 and electrolyzed to form a barrier layer of 2000A, followed by washing with water and hot water (60°C).

Furthermore, a bake-curable acrylic/melamine resin paint (manufactured by Nippon Paint Co., Ltd., Power Mite 30001) was spray-painted on the anodized surface and baked at 180°C for 30 minutes to form a clear coating layer with an average thickness of 20 μm. formed.

This wheel was divided into eight parts symmetrically and used as test pieces.
After making cross cuts with a knife on the clear coating film, IN
Immersed in hydrochloric acid aqueous solution for 10 minutes, relative humidity 80%, 40
It was kept in a constant temperature bath at °C for 144 hours.

As a result, filamentous corrosion with an average length of 05 mm or more from the cut part was observed within an average of 10 pieces per 1 cm of the cut part length, and the rate of decrease in metallic luster is expressed by the following formula: rate of decrease = [ (Reflectance immediately after cutting) - (Reflectance after clear coating) ÷ (Reflectance immediately after cutting lX100
(%) was 18%.

Comparative Example 1 Chromic acid chromate bath (
Nippon Paint Co., Ltd., Allodin 100019 trowel The same treatment as in Example 1 was carried out, except that a film treatment with chromium adhesion of 15 mg/m2 was carried out, and the same test was conducted. An average of 11 threads of filamentous corrosion were observed. However, the reduction rate of metallic luster is 13
%Met.

Comparative Example 2 In Example 1, the second stage barrier type anodic oxide film treatment was not carried out, but after the first stage porous type anodic oxide film treatment,
A clear coat was applied and the same evaluation test was conducted. In this case, an average of nine filamentous corrosions with an average diameter of 1-5 mm were observed per 1 cm of the cut length, and the rate of decrease in metallic luster was 15%.

Example 2 AC40 alloy (7 wt.% Si, 35 wt.% Mg0.

A wheel disk for a passenger car (mesh type with an outer diameter of 280 mm) was produced using 4% by weight of Feα and the remainder Al by a low-pressure cleaning method, and after removing the mold release agent by shot blasting with alumina particles, it was subjected to alkaline degreasing and cleaning.

Next, after performing polar oxidation treatment in a sulfuric acid bath to prepare the base for painting, a white electrodeposition coating bath (manufactured by Nippon Paint Co., Ltd., acrylic/melamine resin paint containing titanium oxide pigment, Power Mite 6000H1) is applied to the entire surface in white. Form a coating film, heat at 180℃,
Baking treatment was performed for 20 minutes.

A diamond cutting process was performed on a 35% area ratio of the front surface of the disk to expose the aluminum base surface having metallic luster, and the surface was degreased with a surfactant and washed with water.

Next, in the first stage, sulfuric acid 20 g/1. Phosphoric acid 80g/
l using a bath with a bath temperature of 20°C1 anode current density α
Electrolytically treated for 15 minutes at 3A/c1m2, 05μm
After washing with water, a porous film of 30 g/l of ammonium tartrate was used as the second step, and the bath temperature was 2.
Condition of 5°C9 anode current density α3 A/dm2 ″c
After electrolytic treatment for ls minutes, a barrier layer of about 150 OA was formed.

After washing with water and hot water at 70°C, the bath temperature was 20°C in an acrylic/melamine grease-based paint bath (manufactured by Honey Kasei Co., Ltd., Vanilite NH30001).

After being treated with constant current electrolysis at 40 mA/dm2 for 5 minutes, baked at 180°C for 30 minutes, and cured, 20 mA/dm2
A µm clear coating film was formed.

The wheel manufactured in this way was made in the same manner as in Example 1 and 3'1! When we conducted a test, we found that the cut length was 1.
An average of nine filamentous corrosions with an average length of α7+nm per cm were observed. At this time, the reduction in metallic luster was 13%.

Effects of the Invention According to the conventional method, maintenance of metallic luster during cutting and improvement of thread rust resistance were contradictory requirements, and this could not be adequately met, resulting in the occurrence of thread corrosion on clear coated parts of aluminum castings. However, according to this Hatsuro method, it is possible to increase the metallic gloss of the clear coated part of aluminum castings from the conventional method with a reflectance of about 5% to 10% or more, as well as improve thread rust resistance. This can be significantly improved, thereby preventing a decrease in product value due to use over time, and improving product safety.

Claims (1)

[Claims] 1. A desired surface of an aluminum casting is cut to form a glossy surface, a porous anodic oxide film treatment is applied to the cut surface, a barrier type anodic oxide film treatment is then performed, and the anodic oxidation process is performed. An anti-corrosion brightening surface treatment method for aluminum castings, which is characterized by applying a clear coating to the treated surface. 2. The anti-corrosion brightening surface treatment method for aluminum castings according to claim 1, wherein the cutting is performed after masking and/or colored coating on the entire or partial desired surface of the aluminum castings. 3. The porous film thickness obtained by the porous type anodic oxide film treatment is 0.1 to 3 μm, and the barrier layer thickness obtained by the barrier type anodic oxide film treatment is 500 to 5000 Å. anti-corrosion bright surface treatment method for aluminum castings.