JP2003003274A - Black chemical conversion treatment solution for magnesium alloy, treating method using the same, and magnesium-alloy member using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a black chemical conversion treatment solution and a black chemical conversion treating method by which the surface of the casings and parts made of magnesium alloy can be economically treated while taking an environmental pollution problem, an environmental problem, etc., into consideration and maintaining the bare corrosion resistance, adhesion of coating and corrosion resistance of coating which are comparable with those of the chemical conversion coatings obtained by the conventional chromium-type chemical conversion treating method or non-chromium-type chemical conversion treating method using manganese containing solution and also a uniform black chemical conversion coating which cannot be obtained by the conventional chromium-type chemical conversion treating method or non-chromium-type chemical conversion treating method can be formed on the surface of the casings and parts made of magnesium alloy and also to provide black chemical conversion treated articles. SOLUTION: Phosphoric acid and a strontium compound are incorporated into the black chemical conversion treatment solution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to bare corrosion resistance and coating adhesion that are equal to or higher than those of a product obtained by treating a magnesium alloy with a chromium-based chemical conversion treatment liquid or a non-chromium-based chemical conversion treatment liquid containing manganese. The present invention relates to a black chemical conversion treatment liquid capable of imparting coating corrosion resistance and the same treatment method. A field to which the present invention can be applied particularly effectively is surface treatment of casings and parts made of magnesium alloys such as automobiles, aircraft and electronic devices.

[0002]

2. Description of the Related Art In recent years, notebook personal computers, mobile phones, video cameras, and the like have become widespread. With the widespread use, magnesium alloys are often used in these casings and parts. Magnesium alloy has advantages such as physical strength, lightness, recyclability, electromagnetic wave shielding property, and heat dissipation property, and is therefore attracting attention as a material that can replace plastic materials. However, this magnesium alloy has the drawback of being highly corrosive. For this reason, most of the magnesium alloy casings and parts are painted after the chemical conversion treatment. As a surface treatment method for magnesium alloys, chromium-based chemical conversion treatment methods such as JIS H 8651 and MIL-M-3171 have been put into practical use. The coating film formed by such a chromium-based chemical conversion treatment has excellent corrosion resistance and coating film adhesion.

[0003]

However, since hexavalent chromium is contained in the treatment liquid, it is desired to use a treatment liquid containing no hexavalent chromium in view of waste water treatment and working environment. Further, as a chromium-free chemical conversion treatment for magnesium alloys, a method of treating with an aqueous solution containing phosphoric acid, manganese ion and amine compound under acidic pH (JP-A-7-126858), phosphoric acid, calcium ion under acidic pH as well. , A method of treating with an aqueous solution containing manganese ions (JP-A-11-131255) has been developed. However, the waste liquid containing the manganese compound cannot be flushed into the sewage without a high degree of post-treatment.

Further, in many cases, the magnesium alloy parts used inside the product are also subjected to a chemical conversion treatment on the surface and then a coating treatment on the whole or a part thereof. That is, despite having sufficient bare corrosion resistance by chemical conversion treatment,
It is painted due to the appearance requirements. However, in such a part, if it has sufficient corrosion resistance and has a certain degree of appearance, that is, if it is applied to a uniform colored surface,
Painting should not always be necessary. Nevertheless,
The fact that the paint is applied prevents the cost reduction.

The present invention has been made to solve the above problems, and has bare corrosion resistance and coating adhesion comparable to those of a chemical conversion coating obtained by a conventional chromium-based chemical conversion treatment method or a chromium-free chemical conversion treatment method containing manganese. It is possible to economically treat the surface of magnesium alloy casings and parts while considering the pollution problem, environmental problem, etc., while maintaining the corrosion resistance of the coating, and the conventional chromium-based chemical conversion treatment method or non-chrome To provide a black chemical conversion treatment liquid capable of economically forming a uniform black chemical conversion coating, which is not present in the system chemical conversion treatment method, on the surfaces of magnesium alloy casings and parts, the same treatment method, and the same treated product. The purpose is.

[0006]

[Means for Solving the Problems] As a result of extensive studies on means for solving the above problems, a magnesium alloy casing and parts were treated with a black chemical conversion treatment liquid containing phosphoric acid and a strontium compound. It has been found that the above problems can be solved by carrying out. The black chemical conversion treatment liquid for magnesium alloys of the present invention is characterized by containing phosphoric acid and a strontium compound. Further, it is desirable to contain a calcium compound. Furthermore, it is desirable to contain a film formation accelerator. The magnesium alloy chemical conversion treatment method of the present invention is characterized by using the above black alloy chemical conversion treatment liquid. The magnesium alloy member of the present invention is a magnesium alloy member treated by the above chemical conversion treatment method.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The composition of the magnesium alloy to which the present invention is applied is not particularly limited, and any magnesium alloy industrially used can be used. Particularly preferred magnesium alloys are magnesium alloys containing aluminum AZ92, AZ91, AZ80, AZ63, AZ6.
1, AZ31, AM100, AM60, AM50, AM
20, AS41, AS21, AE42 mold castings, sand castings, die castings, injection moldings, wrought materials,
Forged products, etc.

According to the present invention, a chemical conversion film is formed on a magnesium alloy by a black chemical conversion treatment liquid containing phosphoric acid and a strontium compound. As phosphoric acid, orthophosphoric acid, condensed phosphoric acid, phosphorous acid, hypophosphorous acid and the like can be used, but it is preferable to use orthophosphoric acid having a low pH, good liquid stability and inexpensive. The phosphoric acid concentration in the black chemical conversion treatment liquid is preferably 0.1 to 100 g / L. 0.1 g /
If it is less than L, a chemical conversion film is formed but corrosion resistance and coating adhesion may be poor. Further, if the amount is more than 100 g / L, a chemical conversion film is formed, but the corrosion resistance and coating adhesion may be poor. As the strontium compound, strontium nitrate, strontium carbonate, strontium chloride and the like can be used, but it is preferable to use strontium nitrate excellent in solubility, liquid stability and color development. The concentration of the strontium compound in the black chemical conversion treatment solution is 0.1 to 10
0 g / L is preferred. If it is less than 0.1 g / L, a chemical conversion film is formed, but a problem occurs in color development, and a uniform and good black film may not be formed. If the amount is more than 100 g / L, a chemical conversion film is formed, but the corrosion resistance and coating adhesion may be poor. The pH of the black chemical conversion treatment liquid is 1 to
It is preferably adjusted to 3. When the pH is out of this range, the etching amount becomes excessive and the dimensional accuracy deteriorates.
Further, a coating having sufficient performance cannot be obtained, and bare corrosion resistance and the like are also reduced. Phosphoric acid and sodium hydroxide are preferably used for adjusting the pH of the black chemical conversion treatment liquid.

It is desirable that the black chemical conversion treatment liquid further contains a calcium compound. This is because the inclusion of the calcium compound further improves the corrosion resistance. As the calcium compound, calcium nitrate, calcium sulfate, calcium phosphate, calcium hydroxide, calcium carbonate, calcium chloride or the like can be used, but calcium nitrate having high solubility is preferably used. Concentration of calcium compound is 0.1-100g
/ L is preferred. If it is less than 0.1 g / L, a chemical conversion film is formed, but corrosion resistance and coating adhesion may be poor. Further, if the amount is more than 100 g / L, a chemical conversion film is formed, but the corrosion resistance and coating adhesion may be poor. Further, it is desirable that the black chemical conversion treatment liquid contains a film formation accelerator. Examples of the film formation accelerator include nitric acid and salts thereof, nitrous acid and salts thereof, hydrogen peroxide, chloric acid and salts thereof, nitrobenzenesulfonic acid and salts thereof, boric acid and salts thereof, sulfuric acid and salts thereof, metavanadic acid and salts thereof. , Metaxylene sulfonic acid and its salt, molybdenum acid and its salt, paratoluene sulfonic acid and its salt, sulfamic acid and its salt, bisulfuric acid and its salt can be used, but it is preferable to use sodium chlorate. . The concentration of the film formation accelerator is preferably 0.01 to 50 g / L. Fifty
If it is more than g / L, a chemical conversion film is formed, but the corrosion resistance and coating adhesion may be poor.

The surface treatment of the magnesium alloy is preferably performed through the following steps. First, degreasing treatment with an organic solvent or an alkaline solution is performed. This is for removing the release agent, cutting oil, processing oil, lubricating oil, abrasive, blast material, foundry sand, etc. on the surface of the magnesium alloy. Examples of the organic solvent include trichloroethylene, ethanol, methanol, acetone and the like. Examples of the alkaline solution include aqueous solutions containing hydroxide, carbonate, phosphate, silicate, surfactant and the like. Degreasing treatment using this alkaline solution is more preferable. After that, it is preferable to perform an etching treatment with an acid. This is because the segregation layer made of aluminum or zinc on the surface of the magnesium alloy is removed. Further, the release agent, cutting oil, processing oil, lubricating oil, abrasive, blast material, and foundry sand that could not be removed by the degreasing treatment are also removed. As the acid, nitric acid, phosphoric acid, sulfuric acid or the like is used. However, since etching with an acid usually requires a large amount of etching, it is necessary to pay attention to what requires dimensional accuracy of the work.

Thereafter, a chemical conversion treatment using the above-mentioned black chemical conversion treatment liquid according to the present invention is performed. The above black chemical conversion treatment liquid is brought into contact with a magnesium alloy. During the chemical conversion treatment, the temperature of the black chemical conversion treatment liquid is preferably maintained in the range of 20 to 90 ° C. When the temperature of the black chemical conversion treatment solution is out of this range, the bare corrosion resistance is deteriorated. Further, the time of contact with the black chemical conversion treatment liquid has a correlation with this temperature. When the liquid temperature is lower than 70 ° C., the contact time is preferably 5 to 20 minutes. On the other hand, when the liquid temperature is 70 ° C. or higher, the contact time is preferably 0.5 minutes to 10 minutes. When the temperature of the black chemical conversion treatment liquid is low and the contact time is short, the formation of the black chemical conversion coating becomes insufficient. Further, when the liquid temperature is high and the contact time is long, the chemical conversion film is eluted. Therefore, it is preferable that the temperature and contact time of the black chemical conversion treatment liquid be within the above range.

It is preferable to carry out washing with water after each treatment step. The washing with water is preferably performed twice, or appropriately, more than once or once. Furthermore, the coating process can be performed by washing with water after the chemical conversion treatment, followed by draining and drying. Further, as a method of contacting each treatment liquid and washing water in the present invention, there are an immersion method and a spray method.
The treatment can be carried out by any contact method, but the treatment by an immersion method is preferable.

The coating process is not particularly limited. Known paints such as solvent-based paints, water-soluble paints and powder paints may be used, but powder paints are preferred. In the case of the magnesium alloy casing and parts surface-treated by the method of the present invention, even one coating often has sufficient coating film performance, but coating twice or more is preferable. The coating process may be performed on all the surfaces, or only a part of the necessary surfaces may be coated. For example, in the case of electronic and electrical equipment enclosures, only the outer surface may be painted and the inner surface may be left chemically treated by the method of the present invention.

The members targeted by the present invention are all products and parts manufactured from magnesium alloys. Examples thereof include electronic device casings and parts such as laptop computers, video cameras, and mobile phones, and casings and parts such as automobiles and aircrafts and bicycles. In the present invention, the conventional chromium-based chemical conversion treatment method without causing environmental problems, or comparable to the chemical conversion coating obtained by the non-chromium-based chemical conversion treatment method containing manganese, or more bare corrosion resistance, coating adhesion, A case and a part made of a magnesium alloy on which a black chemical conversion coating having corrosion resistance is applied are realized. In particular, according to the present invention, since the chemical conversion film is black, it is possible to provide a uniform black appearance without coating it. Therefore, the coating process can be omitted in a portion having a good black appearance, such as an interior component, and a significant cost reduction can be achieved.

[0015]

EXAMPLES The present invention will be described more specifically by showing Examples and Comparative Examples below. However, the present invention is not limited to the following examples. As surface-treated magnesium alloy materials, JIS H 5303 and JIS H 22
22 magnesium alloy (ASTM AZ9
1D) was used. This was molded to a size of 150 × 100 × 2 mm by a thixomolding method to obtain a test material α.
Further, a test material β was formed by molding into a die of 150 × 70 × 2 mm. For each sample, a surface-treated plate was prepared according to the following treatment steps. (1) Degreasing treatment → (2) Water washing → (3) Acid etching treatment → (4) Water washing → (5) Chemical conversion treatment → (6) Water washing → (7) Drying treatment

(1) Degreasing treatment Commercially available alkaline degreasing agent ("MG-CLEAN 67")
3% aqueous solution of Toei Kasei Co., Ltd.) was used. 60 ° C
And heated for 5 minutes. (2) Washing with water Immersion in deionized water at room temperature for 1 minute. (3) Acid Etching Treatment Commercially available acidic etching agent (“MG-ACID FP-
1 "Toei Kasei Co., Ltd.) 2% aqueous solution was used. It was immersed at room temperature for 1 minute. (4) Washing with water Immersion in deionized water at room temperature for 1 minute. (5) Chemical conversion treatment The black chemical conversion treatment liquids shown in Table 1 were used for treatment under the conditions shown in Table 2. (6) Washing with water Immersion in deionized water at room temperature for 1 minute. (7) Drying treatment It was put in a hot air dryer at 110 ° C for 15 minutes to be dried.

[0017]

[Table 1]

[0018]

[Table 2]

About each surface-treated plate obtained, bare corrosion resistance,
The paint adhesion and paint corrosion resistance were evaluated. The evaluation results are shown in Table 3. [Naked corrosion resistance] A salt spray test method based on JIS Z 2371 was used. The corrosion state of the surface-treated plate after 12 hours and 24 hours of salt spraying was visually evaluated. The evaluation criteria are as follows. ◎: Corrosion area ratio less than 5% ○: Corrosion area ratio 5% or more and less than 10% △: Corrosion area ratio 10% or more and less than 30% ×: Corrosion area ratio 30% or more

[Coating Adhesion] The surface of the surface-treated plate is coated with an epoxy resin-based coating material so as to have a dry coating film thickness of 10 μm, and baked at 150 ° C. for 20 minutes. Next, a grid having a width of 2 mm and a size of 100 squares is placed in the center of the coated plate and immersed in ion exchange boiling water for 1 hour. After air drying the coated plate,
A peeling test using a cellophane tape was performed, and the coating corrosion resistance was evaluated by the number of remaining cross-cut squares that were not peeled at this time. The larger the number of remaining grids, the better the coating adhesion, and the evaluation criteria are as follows. ◎: Remaining number of grids is 100 ○: Remaining number of grids is 98 or more and 99 or less ×: Remaining number of grids is 97 or less [Coating corrosion resistance] Epoxy resin coating is dried on the surface of the surface-treated plate It is coated to have a thickness of 10 μm and baked at 150 ° C. for 20 minutes. Next, a cross-cut is provided at the center of this coated plate, and the coated plate is put into the salt spray test according to JIS Z2371. It was taken out of the salt spray tester after 100 and 200 hours of salt spraying, washed with water and dried, and the peeling width of the coating film was measured. The smaller the peeling width, the better the coating corrosion resistance, and the evaluation criteria are as follows. ◎: Peeling width is less than 1 mm ◯: Peeling width is 1 mm or more and less than 2 mm ×: Peeling width is 2 mm or more

[0021]

[Table 3]

As is clear from Table 3, the bare corrosion resistances of the unpainted surface-treated plates obtained in Examples 1 to 3 have performances above a certain standard. Further, it can be seen that the coating adhesion and the corrosion resistance of the surface-treated plate after coating have performances above a certain standard. In addition, each of the obtained surface-treated plates had a black color. On the other hand, Comparative Example 1 and Comparative Example 2 are the cases where the treatment liquids deviated from the present invention.
In this case, since the chemical conversion film formed during chemical conversion treatment does not have sufficient performance, it was confirmed that all the evaluation items of bare corrosion resistance, coating corrosion resistance, and coating adhesion result in extremely poor evaluation results. .

[0023]

As described above, by applying the black chemical conversion treatment solution and the same treatment method of the present invention to members such as a case and parts made of magnesium alloy, the conventional chromium-based chemical conversion treatment method or manganese-containing chemical conversion treatment is performed. Bare corrosion resistance, paint adhesion, which is equivalent to or better than the non-chromium chemical conversion treatment method
It has become possible to form a black chemical conversion coating with corrosion resistance. In addition, the black chemical conversion treatment liquid according to the present invention does not contain hexavalent chromium or manganese, the waste liquid treatment is easy, and the relatively economical surface treatment in consideration of pollution problems and working environment becomes possible. Furthermore, since it has sufficient corrosion resistance on the surface and can form a uniform black chemical conversion film, it is not necessary to perform the coating process that was conventionally performed after the chemical conversion process, and the cost can be significantly reduced. be able to.

Claims (5)

[Claims] 1. A black chemical conversion treatment liquid for magnesium alloy, which contains phosphoric acid and a strontium compound. 2. The black chemical conversion treatment liquid for magnesium alloys according to claim 1, which contains a calcium compound. 3. The black chemical conversion treatment liquid for magnesium alloys according to claim 1 or 2, further comprising a film formation accelerator. 4. A chemical conversion treatment method for a magnesium alloy, which comprises using the black chemical conversion treatment liquid for magnesium alloy according to any one of claims 1, 2, and 3. 5. A magnesium alloy member treated by the method for chemical conversion treatment of magnesium alloy according to claim 4.