KR101067744B1 - Method for conversion coating of surface to magnesium or magnesium alloy - Google Patents

Abstract

The present invention discloses a method of forming a chemical conversion layer on the outer surface of magnesium or magnesium alloy by improving the corrosion resistance by surface-treating the surface of the magnesium alloy using an acid alkali solution. By the above method, magnesium or a magnesium alloy may be provided, which may improve corrosion resistance, minimize appearance damage even after surface treatment, and maximize beauty.

Magnesium, corrosion resistance, chemical film, eco-friendly

Description

METHODS FOR CONVERSION COATING OF SURFACE TO MAGNESIUM OR MAGNESIUM ALLOY}

The present invention relates to a method of forming a chemical conversion layer on the outer surface of magnesium or magnesium alloy, and more particularly, to the magnesium or magnesium alloy outer surface of the magnesium or magnesium alloy, the chemical conversion coating layer is formed on the outer surface of the magnesium or magnesium alloy It relates to a method of forming a.

In general, magnesium is not only abundant on the earth but also has a density of about 1.74 g / cm3, which is the lightest of the structural metal materials, and thus is used in aircraft, automobiles, and portable devices.

However, magnesium alloy has a disadvantage in that corrosion resistance is poor due to the characteristics of the material, so the surface of the chemical treatment is essential, and one of the most commonly used chemical treatments is the process of finishing the coating after the formation of chemical conversion film.

The chemical conversion film formation method is one of metal surface treatments in which a film is formed by various chemical reactions on the surface of magnesium. In addition, the method of forming a chemical film is characterized by obtaining a film by using a chemical reaction occurring on the metal surface without applying electricity from the outside, unlike the electroplating to apply electricity from the outside.

Chemical conversion coating method of the magnesium alloy is generally a chromium-based chemical conversion treatment and non-chromium-based chemical conversion treatment.

The chromium-based chemical conversion treatment was developed by Dow Chemical in the 70's, and is named after Dow1 or Dow21. Representative Dow method is metal surface treatment in acidic solution based on sodium dichromate. The acid solution used in the Dow method is easy to manage and has the advantages of corrosion resistance and paint adhesion of metal after surface treatment. However, the use of hexavalent chromium in the acidic solution used is limited.

Accordingly, low chromium-based or non-chromium-based chemical treatment methods have been developed and used. Non-chromium-based chemical treatment methods mainly include manganese salts and zirconium salts. Other rare earth salts and organic salts are known, but treatment liquids are expensive or unmanageable. It has a hard disadvantage.

In addition, since the color of the chemical coating is green or reddish gray in the case of chromate, and gray or ivory in the case of non-chromium, the metallic color of magnesium cannot be expressed as it is, so the beauty of the appearance of magnesium alloy is deteriorated. .

One object of the present invention is to provide a method for forming a chemical conversion layer on the outer surface of magnesium or magnesium alloy with improved corrosion resistance.

Another object of the present invention is to provide a method for forming a chemical conversion layer on the outer surface of magnesium or magnesium alloy which is environmentally friendly.

Another object of the present invention is to provide a method for forming a chemical conversion layer on the outer surface of magnesium or magnesium alloy to minimize damage to the appearance even after the surface treatment.

Another object of the present invention is to provide a method for forming a chemical conversion layer on the outer surface of magnesium or magnesium alloy that can maximize the beauty of the appearance.

Method for forming a chemical conversion layer on the magnesium or magnesium alloy outer surface according to an embodiment of the present invention, the step of degreasing treatment on the magnesium or magnesium alloy outer surface after washing with water; Washing with water after etching to remove the oxide film from the outer surface of the magnesium or magnesium alloy; Washing with water after a smut treatment to remove smut generated on the magnesium or magnesium alloy outer surface; Washing with water after chemical conversion film formation on the outer surface of the magnesium or magnesium alloy; And coating on the chemical conversion film.

By the above method, magnesium or a magnesium alloy may be provided that may improve corrosion resistance, minimize appearance damage after surface treatment, and maximize beauty.

Degreasing treatment in the step of degreasing after washing the magnesium or magnesium alloy outer surface is less than 30 ~ 60g / L potassium hydroxide (KOH), 150 ~ 200g / L sodium hydroxide (NaOH), 20 ~ 30g / L It may be treated with a first aqueous solution composed of amine oxide, 5-10 g / L of C ₆ H ₁₁ NaO ₇ (sodium gluconate) and a wetting agent. The first aqueous solution configured as described above can easily remove the oil component of the magnesium or magnesium alloy surface, and can minimize the discoloration of the material.

In the step of washing with water after etching to remove the oxide film of the magnesium or magnesium alloy, the etching treatment includes 600 to 800 g / L nitric acid (HNO₃), 200 to 400 g / L phosphoric acid (H₃PO₄) and a wetting agent (Wetting). agent) may be treated with a mixed second aqueous solution. On the other hand, the second aqueous solution may be adjusted to less than pH 1.0 ~ 2.0 by dilution with distilled water, it may be formed within a temperature range of about 35 ~ 50 ° C. By the second aqueous solution configured as described above, the oxide film on the surface of the magnesium or magnesium alloy may be easily removed, and discoloration of the metal may be minimized.

On the other hand, in the step of washing with water after the smut treatment to remove the smut generated on the magnesium or magnesium alloy outer surface is 50 ~ 200 g / L potassium hydroxide (KOH) and 5 ~ 10 g / L It can be immersed in the third aqueous solution mixed with the leveling agent. By the composition ratio as described above it is possible to prevent the generation of a hydroxide film on the surface of the metal, it is possible to prevent the metal from being dispersed.

In addition, in the step of washing with water after the formation of the chemical film on the outer surface of the magnesium or magnesium alloy, the chemical film forming treatment is 600-800 g / L nitric acid (HNO ₃ ), 200-400 g / L phosphoric acid (H ₃ PO ₄ ) And 0.5 to 10 g / L of hydrofluoric acid (HF). In this case, the fourth aqueous solution may be diluted with distilled water to adjust the pH to 2.0 to 4.0, and the chemical conversion film may be formed in the fourth aqueous solution at 20 to 60 ° C. As such, by limiting the temperature of the fourth aqueous solution, the film formation rate may be controlled to form a film having a predetermined thickness on the metal surface, and damage to the metal appearance may be minimized.

According to the method of forming the chemical conversion film layer on the outer surface of the magnesium or magnesium alloy of the embodiment of the present invention, it is excellent in reactivity with acid alkali and strong in activity, thereby improving corrosion resistance.

According to the method of forming the chemical conversion film layer on the outer surface of the magnesium or magnesium alloy of the embodiment of the present invention, since the film is formed on the metal surface without using a material harmful to the environment such as chromic acid, it is possible to form an environmentally friendly film layer.

According to the method of forming the chemical conversion layer on the outer surface of the magnesium or magnesium alloy of the embodiment of the present invention, even after the surface treatment on the magnesium or magnesium alloy outer surface it is possible to express the color as it is magnesium.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited or limited by the embodiments. Like reference numerals in the drawings denote like elements.

1 is an enlarged view of a surface texture of a magnesium alloy plate material surface treated according to a method of forming a chemical conversion layer on the magnesium or magnesium alloy outer surface according to an embodiment of the present invention, Figure 2 is an outer surface of the magnesium or magnesium alloy of Figure 1 It is a flowchart which shows the method of forming a chemical conversion layer in the.

In the following description, an example of forming a chemical conversion layer on the surface of a magnesium alloy is described.

Referring to the drawings and [Table 1], it is possible to form a first aqueous solution capable of degreasing the surface of the magnesium alloy in order to remove fats and oils adhered to the molded magnesium alloy surface and to prevent discoloration of the metal. There is (S210).

TABLE 1

Liquid composition Processing temperature Processing time KOH NaOH Amine oxide Sodium Gluconate additive 30 to 60 g / L 150 to 200 g / L 20-30 g / L 5 to 10 g / L 3 to 5 g / L 35-50 ℃ 30 seconds-2 minutes

The additive provided in the first aqueous solution is a wetting agent, and may be a commanding agent capable of allowing the first aqueous solution to penetrate the metal surface well. The surfactant may be used a variety of wetting agents depending on the conditions required in the invention.

At this time, if the composition ratio of the first aqueous solution is out of the range shown in [Table 1], the composition ratio of the first aqueous solution is shown because the rate of removal of oil components on the surface of the magnesium alloy or the material of the metal may be discolored. It would be desirable to be within the range specified.

Using the first aqueous solution to remove the oil and foreign matter on the surface of the magnesium alloy may be washed with water (S210). The water treatment may completely remove the first aqueous solution component remaining on the magnesium alloy surface.

Since the first aqueous solution is a strong alkali component, if the first aqueous solution component remains on the magnesium alloy surface, the first aqueous solution reacts with the strongly acidic solution used in the subsequent process to lower the chemical reaction of the metal surface, and the metal surface may be unbalanced. Can be. Therefore, the first aqueous solution remaining on the metal surface may be completely removed by washing with water to improve the efficiency of the post process.

When the degreasing treatment is completed, a second aqueous solution as shown in Table 2 may be prepared to remove the magnesium oxide film on the metal surface (S220).

TABLE 2

Liquid composition Range of pH adjustment by dilution with water Processing temperature Processing time HNO₃ H₃PO₄ additive 600 to 800 g / L 200-400 g / L 5 to 10 g / L 1.0-2.0 35-50 ℃ 30 seconds-2 minutes

The infiltrating agent provided in the second aqueous solution may be provided in various ways according to the conditions required in the invention as a commanding activator to allow the solution to penetrate the metal as described above.

When the magnesium alloy surface is etched using the second aqueous solution, the oxide film on the metal surface can be removed at an appropriate speed, and discoloration of the metal can be prevented.

When the etching process of the magnesium alloy is finished, it can be washed with water (S220). As described above, the washing process may prevent the solution used in the process of forming the chemical conversion film on the metal surface remaining on the surface after the process to damage the metal appearance.

After the etching treatment and the washing treatment are finished, the third aqueous solution may be prepared as shown in Table 3 to remove the smut generated on the surface of the magnesium alloy (S230).

[Table 3]

Liquid composition Processing temperature Processing time KOH additive 50 to 200 g / L 5 to 10 g / L 35-50 ℃ 30 seconds-2 minutes

The third aqueous solution prepared at the composition ratio shown in [Table 3] is a dismert solution, and may remove stains on the metal surface, and the metal surface may be flattened by adding a leveling agent as an additive.

In addition, it is preferable that the third aqueous solution is prepared according to the composition ratio of the above [Table 3]. If the third aqueous solution is lower than the composition ratio, the metal surface may be partially formed, and if it is higher than the composition ratio, the hydroxide film may be formed on the metal surface. Therefore, it is preferable that the composition ratio of the third aqueous solution does not depart from the above range.

On the other hand, if the smut generated on the magnesium alloy surface is removed after washing the magnesium alloy (S230), it is possible to form a chemical film on the magnesium alloy outer surface (S240). A fourth aqueous solution may be prepared to form a chemical conversion film on the outer surface of the magnesium alloy, and the composition ratio of the fourth aqueous solution is as follows.

[Table 4]

Liquid composition Range of pH adjustment by dilution with water Processing temperature Processing time HNO₃ H₃PO₄ HF 600 to 800 g / L 200-400 g / L 0.5 to 10 g / L 2.0-4.0 20 ~ 60 ℃ 10 seconds-4 minutes

Magnesium alloy in which the chemical conversion film is formed by the fourth aqueous solution prepared as described above may be coated on the chemical conversion coating (S250).

In the salt water test for the corrosion resistance test of the metal after the coating treatment result after 36 hours and the adhesion test between the film and the metal was shown as follows.

TABLE 5

Process Cross cut Brine spray time R.N. One Coating after the present chemical conversion coating 100/100 24 10.0 36 9.4

The surface of the magnesium alloy formed by the method of forming a chemical conversion film as described above can maintain the metal color of magnesium as it is, it is possible to minimize the damage to the metal surface. In addition, it improves the corrosion resistance of magnesium alloy can be used as a raw material of various devices. In addition, since an toxic chemical film such as chromate and chromic acid is not used, an environmentally friendly film layer may be formed.

Although the preferred embodiments of the present invention have been described above by way of example, the scope of the present invention is not limited to these specific embodiments, and may be appropriately changed within the scope described in the claims.

1 is an enlarged view of the surface texture of a magnesium alloy plate material surface-treated in accordance with a method for forming a chemical conversion layer on the magnesium or magnesium alloy outer surface according to an embodiment of the present invention.

FIG. 2 is a flowchart illustrating a method of forming a chemical conversion layer on the outer surface of the magnesium or magnesium alloy of FIG. 1.

Claims (7)

In the method of forming a chemical conversion layer on the outer surface of magnesium or magnesium alloy, 30 to 60 g / L potassium hydroxide (KOH), 150 to 200 g / L sodium hydroxide (NaOH), 20 to 30 g / L amine oxide, 5 to 10 g / L C ₆ H ₁₁ NaO ₇ (sodium gluconate) And a degreasing treatment step of degreasing the outer surface of the magnesium or the magnesium alloy using an aqueous solution for degreasing treatment by mixing a wetting agent. After washing with magnesium or magnesium alloy after the degreasing treatment, 600 ~ 800g / L nitric acid (HNO₃), 200 ~ 400g / L phosphoric acid (H₃PO₄) and a wetting agent (Wetting agent) is mixed and mixed An etching treatment step of etching the magnesium or magnesium alloy outer surface with an aqueous solution for etching treatment adjusted to less than 1.0 to 2.0 to remove an oxide film of the magnesium or magnesium alloy outer surface; After washing the magnesium or magnesium alloy after the etching treatment step, 50 to 200 g / L potassium hydroxide (KOH) and 5 to 10 g / L leveling agent were mixed to the aqueous solution for smut treatment. A smut treatment step of removing the smut generated on the outer surface of the magnesium or magnesium alloy by immersing the magnesium or magnesium alloy; After washing the magnesium or magnesium alloy through the smelting step, 600-800 g / L nitric acid (HNO), 200-400 g / L phosphoric acid (H₃PO) and 0.5-10 g / L hydrofluoric acid (HF) A chemical composition formed by mixing and performing a chemical conversion treatment to form a chemical conversion film on the magnesium or magnesium alloy outer surface in an aqueous solution for chemical conversion treatment at 20 to 60 ° C. adjusted to pH 2.0 to 4.0; The method of forming a chemical conversion layer on the outer surface of the magnesium or magnesium alloy, characterized in that it comprises a coating step of washing the magnesium or magnesium alloy after the step of forming the chemical conversion film, the coating treatment on the chemical conversion film. delete delete delete delete delete delete

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