KR20140075454A - Method for surface treatment of magnesium material using plasma electrolytic oxidation, anodic films formed on magnesium thereby and solution for surface treatment of magnesium material used for plasma electrolytic oxidation - Google Patents

Abstract

The present invention relates to a method for surface treatment of a magnesium material using plasma electrolytic oxidation, a magnesium anodic oxide film formed thereby and a solution for surface treatment of a magnesium material used for plasma electrolytic oxidation. More specifically, the present invention relates to a method for surface treatment of a magnesium material using plasma electrolytic oxidation comprising the steps of: immersing a magnesium material in a solution for surface treatment of the magnesium material; and applying a pulse current for plasma electrolytic oxidation of the magnesium material to thereby form a magnesium anodic oxide film on the surface of the magnesium material, a magnesium anodic oxide film formed by the surface treatment method, and a solution for surface treatment of the magnesium material used for plasma electrolytic oxidation. The method for surface treatment of a magnesium material using plasma electrolytic oxidation according to the present invention can form a magnesium anodic oxide film which is uniform and dense on the surface of the magnesium material and has superior corrosion resistance regardless of the kinds of electrolytes used for plasma electrolytic oxidation. Moreover, the method for surface treatment of the magnesium material using plasma electrolytic oxidation according to the present invention can form a magnesium anodic oxide film which has excellent electric resistivity and outstanding hardness due to the existence of oxide particles deposited inside the film, in a case where oxide powder is contained in the electrolyte used for plasma electrolytic oxidation.

Description

TECHNICAL FIELD The present invention relates to a method for surface treatment of magnesium using plasma electrolytic oxidation, a magnesium anodizing film formed by the electrolytic oxidation and a magnesium surface treatment solution used for plasma electrolytic oxidation solution for surface treatment of magnesium metal used for plasma electrolytic oxidation}

More particularly, the present invention relates to a method for surface treatment of a magnesium material using plasma electrolytic oxidation, a magnesium anodizing film formed by the electrolytic oxidation and a plasma electrolysis The present invention relates to a magnesium material surface treatment liquid used for oxidation.

Magnesium material, which refers to magnesium or magnesium alloy, has low density, excellent non-strength and inelasticity coefficient, and is excellent in casting, machinability and dimensional stability. In addition, electromagnetic shielding and vibration damping are superior to aluminum alloy and steel Although it is widely used in automobile and aircraft parts, mobile phone case, notebook computer case, and spectacle frame, it is easily activated in oxidizing atmosphere compared to other metal chelate, so it needs to be surface treated to prevent corrosion due to its weak corrosion resistance.

As an example of such a surface treatment method of magnesium materials, anodizing, that is, anodic oxidation, in which a metal is immersed in an anode in an electrolytic solution to form a corrosion preventive film, is widely known.

However, when an anodic oxidation film is formed by the anodic oxidation, an electrolytic solution in an acidic atmosphere containing a harmful component such as sulfuric acid and chromic acid is used. Therefore, as a new environment-friendly surface treatment method, plasma eletrolytic oxidation (PEO ) Are attracting attention.

Plasma electrolytic oxidation is not only an environmentally friendly surface treatment technique because it uses an electrolytic solution in an alkaline atmosphere, but also the coating formed through it is excellent in durability, corrosion resistance and abrasion resistance and can improve the adhesion of the coating have.

However, conventional plasma electrolytic oxidation techniques for magnesium materials are mainly performed by applying direct current or alternating current. When a film is formed by applying a direct current during the plasma electrolytic oxidation treatment, local burning phenomenon There is a problem that the applicable electrolyte in the surface treatment of the magnesium material is very limited, and the above problem has been similarly accompanied by the application of the alternating current.

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a magnesium material surface treatment method capable of forming a uniform and dense oxide film on the magnesium material surface without restriction depending on the type of electrolytic solution during plasma electrolytic oxidation treatment on the surface of magnesium material, Anodic oxidation coating, and a magnesium material surface treatment liquid used for plasma electrolytic oxidation.

According to an aspect of the present invention, there is provided a method for manufacturing a magnesium-based surface treatment solution, comprising: immersing a magnesium material in a surface treatment liquid of a magnesium material; And applying a pulse current to plasma electrolytically oxidize the magnesium material to form a magnesium anodic oxide coating on the surface of the magnesium material. A method for surface treatment of a magnesium material using plasma electrolytic oxidation, An oxidation film and a magnesium material surface treatment solution used for plasma electrolytic oxidation.

According to the method for surface treatment of a magnesium material using the plasma electrolytic oxidation according to the present invention, a magnesium anodic oxide coating having uniform and dense surface and excellent corrosion resistance on the surface of the magnesium material without restriction depending on the kind of the electrolytic solution used in the plasma electrolytic oxidation treatment Can be formed.

In addition, according to the method for surface treatment of magnesium materials using the plasma electrolytic oxidation according to the present invention, when oxide powders are included in the electrolytic solution used for the plasma electrolytic oxidation treatment, A magnesium anodic oxide film having a remarkably high hardness can be formed.

FIG. 1 is a photograph (FIG. 1 (a)) of a surface of a surface-treated magnesium alloy specimen prepared in a comparative example by a digital camera and a surface of a magnesium alloy specimen prepared in Example 1 by a digital camera (Fig. 1 (b)).
Fig. 2 is a scanning electron microscope (SEM) photograph (Fig. 2 (a)) of the surface and cross-sectional microstructures of the surface-treated magnesium alloy specimen prepared in the comparative example and the surface of the magnesium alloy specimen And a scanning electron microscope (SEM) photograph of the cross-sectional microstructure (Fig. 2 (b)).
FIG. 3 is an optical microscope photograph (FIG. 3 (a) showing the results of the salt spray test on the surface-treated magnesium alloy specimen prepared in the comparative example according to elapsed time (1 day, 2 days, 3 days, 4 days and 8 days) (1), (2), (3), (4) and (8)) showing the results of the salt spray test on the surface-treated magnesium alloy specimen prepared in Example 1 3 (b)).
4 is a scanning electron microscope (SEM) photograph of the surface microstructure of the surface-treated magnesium alloy specimen produced in Example 2. Fig.
5 is an energy dispersive X-ray analysis (EDS) result of the surface of the surface-treated magnesium alloy specimen prepared in Example 2. Fig.
6 is a graph showing the hardness (H _V ) measurement results of the surface-treated magnesium alloy specimen prepared in Example 2. FIG.
7 shows the results of measurement of changes in voltage (Fig. 7 (a)) and electric current (Fig. 7 (b)) with respect to the plasma electrolytic oxidation surface treatment time of the surface-treated magnesium alloy specimen produced in Examples 1 and 2 .

Hereinafter, the present invention will be described in detail.

A method for surface treatment of a magnesium material using plasma electrolytic oxidation according to the present invention comprises the steps of: immersing a magnesium material in a surface treatment liquid of a magnesium material; And applying a pulse current to plasma electrolytically oxidize the magnesium material to form a magnesium anodized film on the surface of the magnesium material.

Hereinafter, a method of surface-treating a magnesium material using plasma electrolytic oxidation according to a preferred embodiment of the present invention will be described in more detail.

The step of immersing the magnesium material in the magnesium material surface treatment liquid is a step of immersing the magnesium material which is required to be surface-treated in the magnesium material surface treatment liquid having a certain composition before performing the plasma electrolytic oxidation.

In this specification, magnesium refers to magnesium or a magnesium-based alloy, and the type of the magnesium alloy to which the method of surface-treating a magnesium material using the plasma electrolytic oxidation according to the present invention is applicable is not limited.

The magnesium surface treatment solution used in the present invention may be an alkaline electrolytic solution, preferably sodium phosphate (Na ₃ PO ₄ ), sodium silicate (Na ₂ SiO ₃ ), sodium sulfate (Na ₂ SO ₄ ), sodium nitrate NaNO _3), potassium sulfate (Na ₂ SO _4), potassium nitrate (NaNO _3), sodium hydroxide (NaOH), potassium hydroxide (KOH), sodium fluoride (NaF), potassium fluoride (KF), ammonium fluoride (NH ₄ F ), meta-sodium silicate (Na ₂ SiO _3), sodium citrate _{(C 6 H 5 Na 3 O} 7), potassium ferricyanide _{(K 3 Fe (CN) 6} ), oxidation sodium borate (NaBO ₂₎ and nitric acid potassium (CH ₃ COOK). For example, i) a solution containing sodium phosphate as a base, in addition to sodium phosphate, sodium sulfate, sodium nitrate, potassium sulfate, potassium nitrate, sodium hydroxide and potassium hydroxide An electrolytic solution having a pH of 12 to 13.5 or ii) an electrolytic solution containing sodium silicate The solution further contains at least one selected from the group consisting of sodium sulfate, sodium nitrate, potassium sulfate, potassium nitrate, sodium hydroxide, potassium hydroxide, sodium fluoride, potassium fluoride and ammonium fluoride, Lt; / RTI > At this time, the concentration of the components included in the base is preferably 0.1 to 1 M, and the concentration of the at least one component further included is preferably 0.01 to 1 M.

The magnesium surface treatment solution used in the present invention may further include an oxide powder in addition to the above-mentioned components. Examples of the oxide include alumina (Al ₂ O ₃ ), silicon carbide (SiC), silicon dioxide (SiO ₂ ) , Titania (TiO ₂ ), and zirconia (ZrO ₂ ). At this time, when the oxide powder is included in the surface treatment liquid of the magnesium material, it is preferably 0.1 to 50 g / L. When the oxide powder is contained in the magnesium surface treatment solution, the oxide particles originated from the oxide powder precipitate in the oxide film formed on the surface of the magnesium material, thereby contributing to the improvement of the corrosion resistance and hardness of the oxide film.

On the other hand, the step of etching the surface to remove scratches on the surface of the magnesium material before the step of immersing the magnesium material in the magnesium material surface treatment liquid, the step of heating or pickling the magnesium material surface for activation, .

The next step is a step of plasma electrolytic oxidation of the magnesium material by applying a pulse current to form a magnesium anodized film on the surface of the magnesium material.

More specifically, after the magnesia material and the conductor (platinum, stainless steel, etc.) are connected to each other so as to have different polarities in the pulse power source device while the magnesium material is immersed in the magnesium surface treatment solution, Thereby inducing a minute discharge on the surface of the ash, thereby forming a magnesium oxide film on the surface of the magnesium material.

As described above, the plasma oxidation electrolysis is performed by applying the pulse current to the surface of the magnesium alloy using the plasma oxidation electrolysis without restriction depending on the type of the electrolyte.

At this time, the current density of the applied pulse current is 1 to 200 mA / cm ² , preferably 10 to 100 mA / cm ² . Further, the pulse duration of the applied pulse current is 0.1 to 10 milliseconds (ms), preferably 0.1 to 5 milliseconds (ms). The applied pulse current may be irregularly applied, but it may have a frequency of 100 Hz to 500 kHz, preferably 200 Hz to 300 kHz.

In addition, the applied pulse current may be a unipolar pulse current applied only in one direction of positive or negative polarity, preferably including both positive (+) and negative (-) pulses, +) And the negative (-) pulse are alternately repeated.

It is preferable that this step is performed for 10 seconds to 10 minutes. In the case of less than 10 seconds, the formation of the coating layer is weak, and when it exceeds 10 minutes, the coating having a nonuniform thickness profile is formed.

On the other hand, after the present step is carried out, a water washing step and / or a drying step may be further carried out if necessary.

Next, the plasma electrolytic oxide film according to the present invention will be described in detail below.

Since the plasma electrolytic oxide film according to the present invention is formed by the plasma electrolytic oxidation surface treatment method through the application of the pulse current described above, regardless of the type of the electrolyte used in the plasma electrolytic oxidation treatment, An oxide film is formed.

Furthermore, by using a magnesium material surface treatment solution further containing an oxide powder such as alumina (Al ₂ O ₃ ), silicon carbide (SiC), silicon dioxide (SiO ₂ ), titania (TiO ₂ ) zirconia (ZrO ₂ ) The resulting magnesium anodized coating has high electrical resistance and a remarkably high hardness.

Next, the magnesium material surface treatment solution according to the present invention will be described in detail below.

The magnesium material surface treatment solution according to the present invention is an alkaline electrolyte solution characterized in that it is used for surface treatment of a magnesium material using plasma electrolytic oxidation. Preferably, sodium phosphate (Na ₃ PO ₄ ), sodium silicate (Na ₂ SiO ₃ ), Sodium nitrate (Na ₂ SO ₄ ), sodium nitrate (NaNO ₃ ), potassium sulfate (Na ₂ SO ₄ ), potassium nitrate (NaNO ₃ ), sodium hydroxide (NaOH), potassium hydroxide (KOH) , potassium fluoride (KF), ammonium fluoride (NH ₄ F), meta-sodium silicate (Na ₂ SiO _3), sodium citrate _{(C 6 H 5 Na 3 O} 7), potassium ferricyanide _{(K 3 Fe (CN) 6} ) , Sodium borate oxide (NaBO ₂ ), and potassium acetate (CH ₃ COOK).

As an example of the magnesium surface-treating liquid according to the present invention, i) a solution containing sodium phosphate as a base, in addition to sodium phosphate, a solution selected from the group consisting of sodium sulfate, sodium nitrate, potassium sulfate, potassium nitrate, sodium hydroxide, And ii) a solution containing sodium silicate, sodium nitrate, potassium sulfate, potassium nitrate, sodium hydroxide, potassium hydroxide, sodium fluoride, potassium fluoride and fluorine as a solution based on sodium silicate as an electrolytic solution having a pH of 12 to 13.5 or ii) Ammonium, and an electrolytic solution having a pH of 12 to 13.5. At this time, the concentration of the components included in the base is preferably 0.1 to 1 M, and the concentration of the at least one component further included is preferably 0.01 to 1 M.

The magnesium surface treatment liquid according to the present invention may further comprise an oxide powder in addition to the above-mentioned components. Examples of the oxide include alumina (Al ₂ O ₃ ), silicon carbide (SiC), silicon dioxide (SiO ₂ ) (TiO ₂ ) and zirconia (ZrO ₂ ). When the oxide powder is included in the magnesium surface treatment solution, it is preferably 0.1 to 50 g / L. When the oxide powder is contained in the magnesium surface treatment solution, the oxide particles originated from the oxide powder precipitate in the oxide film formed on the surface of the magnesium material, thereby contributing to the improvement of the corrosion resistance and hardness of the oxide film.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in detail below on the basis of embodiments. The presented embodiments are illustrative and are not intended to limit the scope of the invention.

≪ Example 1 >

A magnesium alloy having a composition of aluminum 3 wt.%, Zinc 1 wt.% And magnesium balance was cut into a thin plate of 40 mm in width, 12 mm in length and 1 mm in thickness. The surface was polished using SiC paper, And dried to prepare a magnesium alloy specimen. Then, the specimen was immersed in an aqueous solution of 0.2 M sodium silicate (Na ₂ SiO ₃ ) maintained at 10 to 20 ° C. Next, the magnesium alloy specimen and the platinum electrode were placed on both poles of a 10-kW pulsed power source in the electrolytic aqueous solution, and then pulsed current density of 10 mA / cm ² and pulse duration An anodic oxidation film was formed on the surface of the magnesium alloy specimen by performing a plasma electrolytic oxidation treatment for 600 seconds by applying a pulse current of 1 millisecond (ms) and a pulse frequency of 3 kHz.

≪ Example 2 >

An anodic oxide film was formed on the surface of the magnesium alloy specimen in the same manner as in Example 1, except that an alumina powder having a concentration of 2 g / L was further added to the sodium silicate (Na ₂ SiO ₃ ) aqueous solution.

<Comparative Example>

A magnesium alloy having a composition of aluminum 3 wt.%, Zinc 1 wt.% And magnesium balance was cut into a thin plate of 40 mm in width, 12 mm in length and 1 mm in thickness. The surface was polished using SiC paper, And dried to prepare a magnesium alloy specimen. Then, the specimen was immersed in a 0.2 M sodium silicate (Na ₂ SiO ₃ ) electrolytic aqueous solution maintained at 10 to 20 ° C. Next, in the electrolytic aqueous solution, the magnesium alloy specimen was disposed on the positive electrode of the 1 kW direct current power source apparatus, and the platinum electrode was disposed on the negative electrode, and then the direct current power source with the current density of 10 mA / cm ² And a plasma electrolytic oxidation treatment was performed for 3600 seconds by applying a current to form a film on the surface of the magnesium alloy specimen.

<Experimental Example 1>

The surfaces of the surface-treated magnesium alloy specimens prepared in the above Comparative Examples and Examples were photographed with a digital camera and shown in Figs. 1 (a) and 1 (b), respectively. 1 (a), when the plasma electrolytic oxidation surface treatment is performed by applying the direct current, it is confirmed that the local oxidation proceeds on the surface of the specimen and the plasma electrolytic oxide film is formed unevenly. On the other hand, when the plasma electrolytic oxidation surface treatment is performed by applying the pulse current from FIG. 1 (b), it can be confirmed that the plasma electrolytic oxidation film is uniformly formed on the entire surface of the test piece.

The surface and cross-sectional microstructures of the surface-treated magnesium alloy specimens prepared in Comparative Examples and Example 1 were photographed using a scanning electron microscope (SEM: JEOL, JSM6610LV) 2 (b). From this, unlike the surface and cross-sectional microstructures (see Fig. 2 (a)) of the coating film according to the comparative example in which the plasma electrolytic oxidation surface treatment was performed by applying a direct current, plasma electrolytic oxidation surface treatment was performed by applying a pulse current It can be seen that the microstructure of the surface and the cross section of the coating film according to Example 1 (see Fig. 2 (b)) shows a much more dense structure.

As described above, when the plasma electrolytic oxidation surface treatment is performed by applying the pulse current according to the present invention, a magnesium surface treatment liquid such as a sodium silicate (Na ₂ SiO ₃ ) electrolytic solution, which can not obtain a useful plasma electrolytic oxidation film at the time of application of a direct current, It can be seen that a uniform, dense and firm oxide film can be formed even when used.

<Experimental Example 2>

A salt spray test was conducted to investigate the corrosion resistance of the magnesium alloy specimens subjected to the surface treatment prepared in the comparative example and the example 1. For the saline spray test, the specimen was kept in 0.5 M sodium chloride solution for 8 days, and the changes of the surface of the specimen with 1, 2, 3, 4, and 8 days were observed under an optical microscope, 3 (a) and 3 (b).

When the plasma electrolytic oxidation surface treatment is performed by applying a direct current from FIG. 3 (a), it is confirmed that the corroded region on the surface of the specimen gradually expands over time. On the other hand, when the plasma electrolytic oxidation surface treatment is performed by applying the pulse current from FIG. 3 (b), it can be confirmed that no corrosion has occurred at all despite the lapse of time.

From the above experimental results, it can be confirmed that when the plasma electrolytic oxidation surface treatment is performed by applying the pulse current according to the present invention, an oxide film having remarkably excellent corrosion resistance can be formed as compared with the case where the DC current is applied.

<Experimental Example 3>

The surface of the magnesium alloy specimen prepared in Example 2 was observed with a scanning electron microscope (SEM: JEOL, JSM6610LV) in order to examine the change of the microstructure due to the addition of alumina powder to the magnesium alloy surface treatment liquid , And the results are shown in Fig.

Alumina precipitates in the plasma electrolytic oxide film as indicated by arrows in FIG. 4 as the alumina powder is added to the magnesium alloy surface treatment solution.

The above results are also supported by the presence of the aluminum (Al) peak shown in Fig. 5 showing the energy dispersive X-ray analysis (EDS) results on the surface of the surface-treated magnesium alloy specimen prepared in Example 2. [

<Experimental Example 4>

Vickers hardness (H _V ) was measured three times in order to examine the mechanical properties of the surface-treated magnesium alloy specimen prepared in Example 2, and the results are shown in FIG. Showed a film hardness (H _V) is 600 or more embodiments of the magnesium alloy is manufactured surface-treated in Example 2 according to the present invention, these figures are as the hardness of the film formed on the magnesium material is found to be the best value.

<Experimental Example 5>

In order to examine the effect of adding alumina powder to the magnesium alloy surface treatment liquid, the change in voltage and current with respect to the surface treatment time of the plasma electrolytic oxidation surface of the surface-treated magnesium alloy specimen prepared in Examples 1 and 2 was measured The results are shown in Figs. 7 (a) and 7 (b), respectively.

7 (a) and 7 (b), it can be seen that as the alumina powder is added to the magnesium alloy surface treatment solution, the voltage increases more rapidly under the initial constant current condition and the current decreases more rapidly after reaching the constant voltage condition have. This seems to be because the alumina particles impregnated into the plasma electrolytic oxide film increase the resistance of the coating.

Claims (25)

Immersing a magnesium material in a magnesium material surface treatment liquid; And
And applying a pulse current to plasma electrolytically oxidize the magnesium material to form a magnesium anodic oxide coating on the surface of the magnesium material. The method according to claim 1, wherein the pulse current is a positive pulse only. The method according to claim 1, wherein the pulse current includes positive (+) and negative (-) pulses. 4. The method of claim 3, wherein the pulse current is alternately applied with positive (+) and negative (-) pulses. 2. The method of claim 1, wherein the pulse duration of the pulse current is 0.1 to 5 milliseconds (ms). The method according to claim 1,
The magnesium material surface treatment liquid is prepared by mixing i) sodium phosphate (Na ₃ PO ₄ ) and ii) sodium sulfate (Na ₂ SO ₄ ), sodium nitrate (NaNO ₃ ), potassium sulfate (Na ₂ SO ₄ ), potassium nitrate (NaNO ₃ ) , Sodium hydroxide (NaOH) and potassium hydroxide (KOH), and has a pH of 12 to 13.5. The method of claim 6, wherein the concentration of sodium phosphate is 0.1 to 1 M. 7. The method of claim 6, wherein the surface treatment liquid of the magnesium material further comprises an oxide powder. The method of claim 8, wherein the oxide powder is one selected from the group consisting of alumina (Al ₂ O _3), silicon carbide (SiC), silicon dioxide (SiO _2), titania (TiO ₂₎ and zirconia (ZrO ₂₎ Wherein the surface of the magnesium material is a powder of an oxide. The magnesium material surface treatment liquid according to claim 1, wherein the magnesium material surface treatment liquid comprises i) sodium silicate (Na ₂ SiO ₃ ) and ii) sodium sulfate (Na ₂ SO ₄ ), sodium nitrate (NaNO ₃ ), potassium sulfate (Na ₂ SO ₄ ) And at least one selected from the group consisting of potassium nitrate (NaNO ₃ ), sodium hydroxide (NaOH), potassium hydroxide (KOH), sodium fluoride (NaF), potassium fluoride (KF) and ammonium fluoride (NH ₄ F) wherein the pH of the surface of the magnesium material is in the range of 12 to 13.5. The method according to claim 10, wherein the concentration of sodium silicate is 0.1 to 1 M. The method according to claim 10, wherein the magnesium material surface treatment liquid further comprises an oxide powder. The method of claim 12, wherein the oxide powder is one selected from the group consisting of alumina (Al ₂ O _3), silicon carbide (SiC), silicon dioxide (SiO _2), titania (TiO ₂₎ and zirconia (ZrO ₂₎ Wherein the surface of the magnesium material is a powder of an oxide. The method according to claim 9 or 13, wherein the oxide powder is alumina (Al ₂ O ₃ ) powder and is contained in the magnesium material surface treatment liquid at a concentration of 0.1 to 50 g / L. Magnesium material surface treatment method. A magnesium anodic oxide film formed on a surface of a magnesium material by the method of surface treatment of a magnesium material using the plasma electrolytic oxidation as set forth in any one of claims 1 to 13. A magnesium anodic oxidation film formed on the surface of a magnesium material by the method of surface treatment of a magnesium material using the plasma electrolytic oxidation method according to claim 14, characterized in that the film contains alumina (Al ₂ O ₃ ) film. i) sodium phosphate (Na ₃ PO _4), and ii) sodium sulfate (Na ₂ SO _4), sodium nitrate (NaNO _3), potassium sulfate (Na ₂ SO _4), potassium nitrate (NaNO _3), sodium hydroxide (NaOH) and And potassium hydroxide (KOH), and has a pH of 12 to 13.5, and is used for surface treatment of a magnesium material using plasma electrolytic oxidation. The magnesium material surface treatment liquid according to claim 17, wherein the concentration of sodium phosphate is 0.1 to 1 M. 18. The magnesium material surface treatment liquid according to claim 17, wherein the magnesium material surface treatment liquid further comprises an oxide powder. 20. The method of claim 19 wherein the oxide powder is one selected from the group consisting of alumina (Al ₂ O _3), silicon carbide (SiC), silicon dioxide (SiO _2), titania (TiO ₂₎ and zirconia (ZrO ₂₎ Wherein the powder is an oxide powder. i) sodium silicate (Na ₂ SiO ₃ ) and ii) sodium nitrate (Na ₂ SO ₄ ), sodium nitrate (NaNO ₃ ), potassium sulfate (Na ₂ SO ₄ ), potassium nitrate (NaNO ₃ ) And at least one selected from the group consisting of potassium hydroxide (KOH), sodium fluoride (NaF), potassium fluoride (KF), and ammonium fluoride (NH ₄ F), having a pH of 12 to 13.5, A magnesium material surface treatment liquid characterized by being used for ash surface treatment. The magnesium material surface treatment liquid according to claim 21, wherein the concentration of sodium silicate is 0.1 to 1 M. 22. The magnesium material surface treatment liquid according to claim 21, wherein the magnesium material surface treatment liquid further comprises an oxide powder. 24. The method of claim 23, wherein the oxide powder is selected from the group consisting of Al ₂ O ₃ , SiC, SiO ₂ , TiO ₂ , and ZrO ₂ . Wherein the powder is an oxide powder. The magnesium material surface treatment liquid according to claim 20 or 24, wherein the oxide powder is alumina (Al ₂ O ₃ ) powder and is contained in the magnesium material surface treatment liquid at a concentration of 0.1 to 50 g / L .

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