KR20090092413A - Methods of coloring magnesium material and the magnesium material colored by the same - Google Patents

Abstract

A method of coloring magnesium material and a magnesium material colored by the same are provided to improve the corrosion resistance of the magnesium material by adding water-soluble metal salt to basic electrolyte including potassium hydroxide and sodium silicate and electro-oxidizing the basic electrolyte with plasma. A method of coloring magnesium material comprises following steps. In the basic electrolyte, a magnesium material is electro-oxidized with the plasma. The basic electrolyte includes the water-soluble metal salt, the potassium hydroxide and sodium silicate. The water-soluble metal salt includes one metal or metal ion selected from the group consisting of the vanadium, the cobalt, the copper, the nickel and the tin. The pH of the basic electrolyte is over 11.5. The plasma electrolytic oxidation is performed in a plasma electrolyzing apparatus. The plasma electrolyzing apparatus comprises an electrolytic cell(1), electrolyte(2), a cathode(3), an anode(4) and a power supply source(5). The plasma electrolyzing apparatus includes a mixer(6), a filter(7) and a cooling system(8). The basic electrolyte includes potassium hydroxide, the sodium silicate and ammonium phosphate when water-soluble metal salt is the vanadium.

Description

Method of coloring magnesium material and colored magnesium material by this TECHNICAL FIELD

The present invention relates to a method for coloring magnesium materials and magnesium materials colored thereby, and more particularly, magnesium and magnesium alloys that can not only color magnesium and magnesium alloys in various colors without a separate coating process, but can also improve corrosion resistance at the same time. A method of coloring an alloy and thereby colored magnesium and magnesium alloys.

Recently, plastic materials and metal materials are widely used as materials for electric and electronic components such as mobile phone case parts. The double plastic material has advantages in that it is easy to manufacture in a complicated shape, is light in weight, and is easily implemented in various colors by coloring. Conventional techniques for imparting color to plastic parts are performed using oil-based and water-based paints, and the coating process is performed by two coats or three coats of undercoat and top coat. The coating process is mostly carried out by spray coating, which is a method of first applying a coat containing a pigment having a desired color to a plastic injection molding, and then applying a transparent top coat to realize various colors. The spray coating method has been widely used until now due to its advantages in mass production, inexpensiveness, and various colors. However, this method has the disadvantage that it is not environmentally friendly and the color is not beautiful by using an oily solvent. Recently, water-based paints have been applied, but they are only about 70-80% higher than oil-based paints in terms of color diversity and especially high brightness in metal colors. In addition, these plastic materials are poor in wear resistance, weak to heat, discolored by sunlight, and the color does not have a metallic gloss, which is not beautiful.

On the other hand, metal materials have excellent wear resistance, are resistant to heat and sunlight, and are environmentally friendly. However, they are difficult to manufacture in a complicated shape, are heavy, and have a metallic luster, but have various disadvantages in implementing various colors. Among these metal materials, magnesium is the lowest electrochemically metal among practical metals, which is extremely active, and thus, it is generally characterized by corrosion very rapidly in the air or in a solution when it is not surface treated. Therefore, in order to put a magnesium product into practical use, a technology for chemically, electrochemically or physically treating the surface of the product to increase the corrosion resistance and to color the magnesium product in a desired color is inevitably required.

An anodizing process is provided by the method of coloring magnesium and magnesium alloys. In particular, in the magnesium anodizing process, the formation of the coating layer (barrier layer) is formed by physical rupture, and the electrical resistance rapidly increases as the thickness of the oxide film increases. As a result, higher voltages are required as compared to aluminum anodizing processes. In particular, in the case of aluminum in which anodizing process is more commonly used, the anodizing product is mainly in the form of aluminum oxide, but in the case of magnesium, the barrier layer is composed of more complex species. Therefore, it is very difficult to selectively color magnesium to a desired color in terms of forming a barrier layer in a complicated form of the electrolyte composition, and in particular, a technique for coloring magnesium to a desired color while improving corrosion resistance has not been disclosed at all. There is no situation.

Korean Patent Application No. 10-2002-0051005 (hereinafter referred to as “Technology 1”) is a prior art for describing a method of coloring by magnesium electrolysis. The cited technique 1 discloses a method of coloring a magnesium material in a pearl color by adding a pearl pigment to a basic electrolyte and then anodizing magnesium. However, the cited technique 1 discloses only a method of coloring magnesium material using only a pearl pigment, and does not disclose a selective coloring method for various colors due to the characteristics of magnesium constituting the barrier layer in a complex form of an electrolyte solution. Furthermore, the improvement in corrosion resistance of the choice of water soluble metal salts and solvents is not disclosed or even implied at all.

Therefore, the magnesium coloring method known to date only relates to the coloring technique for a specific color, and the coloring technique which can achieve all the corrosion resistance improvement which is essential for a magnesium material is not disclosed at all.

Therefore, the first problem to be solved by the present invention is to provide a method of coloring magnesium material which can selectively color various colors on the magnesium material with improved corrosion resistance.

The second problem to be solved by the present invention is to provide a magnesium material selectively colored in a variety of colors with excellent corrosion resistance.

In order to solve the first problem, the present invention provides a magnesium material coloring method for coloring the magnesium material by plasma electrolytic oxidation of the magnesium material in a basic electrolytic solution containing a water-soluble metal salt, potassium hydroxide and sodium silicate, In one embodiment the water soluble metal salt comprises one metal or metal ion selected from the group consisting of vanadium, cobalt, copper, nickel and tin.

The plasma electrooxidation is performed by energizing the magnesium material as an anode in a time range of 150 to 600 seconds at a current density of 2 to 20 A / dm 2, and the basic electrolyte solution has a pH of 11.5 or more.

In one embodiment of the method for coloring magnesium material according to the present invention, the water-soluble metal salt is vanadium, and the vanadium has a concentration of 0.001M to 0.5M. In addition, the basic electrolyte solution contains potassium hydroxide, sodium silicate and ammonium phosphate, wherein the concentration of potassium hydroxide is 0.2 to 0.6M, the concentration of sodium silicate is 0.1 to 0.3M, the concentration of ammonium phosphate is 0.1 to 0.3M.

In another embodiment of the method for coloring magnesium material according to the present invention, the water-soluble metal salt is cobalt, and the cobalt has a concentration of 0.001 to 0.05M. In addition, the basic electrolyte solution contains potassium hydroxide, sodium silicate and ammonium phosphate, wherein the concentration of potassium hydroxide is 0.1 to 0.3M, the concentration of sodium silicate is 0.05 to 0.15M, the concentration of ammonium phosphate is 0.03 to 0.13M.

In another embodiment of the method for coloring magnesium material according to the present invention, the water-soluble metal salt is copper, and the copper has a concentration of 0.001 to 0.05M. In addition, the basic electrolyte solution contains potassium hydroxide, sodium silicate and potassium fluoride, wherein the concentration of potassium hydroxide is 0.13 to 0.21M, the concentration of sodium silicate is 0.06 to 0.12M, the concentration of potassium fluoride is 0.06 to 0.12M.

In another embodiment of the method for coloring magnesium material according to the present invention, the water-soluble metal salt includes nickel and has a concentration of 0.001 to 0.05M. In addition, the basic electrolyte solution contains potassium hydroxide, sodium silicate and potassium fluoride, wherein the concentration of potassium hydroxide is 0.13 to 0.21M, the concentration of sodium silicate is 0.06 to 0.12M, the concentration of potassium fluoride is 0.06 to 0.12M.

In another embodiment of the method for coloring magnesium material according to the present invention, the water-soluble metal salt is tin, and the tin has a concentration of 0.016M to 0.22M. In addition, the basic electrolyte solution contains potassium hydroxide and sodium silicate, wherein the concentration of potassium hydroxide is preferably 0.13 to 0.23M, the concentration of sodium silicate is 0.008 to 0.08M.

The present invention to solve the second problem is plasma electrolytic oxidation in a basic electrolytic solution containing a water-soluble metal salt, potassium hydroxide and sodium silicate, to provide a magnesium material comprising the water-soluble metal salt oxide in the coating layer, In one embodiment of the present invention, the water-soluble metal salt includes one metal or metal ion selected from the group consisting of vanadium, cobalt, copper, nickel and tin.

The method of coloring magnesium material according to the present invention not only effectively colors various colors such as black, red, blue, maroon and ocher depending on the metal used, but also on the use of selected metals and electrolytes. Corrosion resistance improvement effect can be achieved simultaneously.

1 is a schematic diagram showing a plasma electrolytic oxidation apparatus according to an embodiment of the present invention.

2A to 2C are photographs and graphs showing scanning electron micrographs and EDS analysis results of the magnesium alloy coating layer of Example 1. FIG.

3 is a graph showing the results of phase analysis of the magnesium alloy coating layer of Example 1.

4A to 4C are graphs and photographs showing scanning electron micrographs and EDS analysis results of the magnesium alloy coating layer of Example 2. FIG.

5 is a graph showing a phase analysis result of the magnesium alloy coating layer of Example 2. FIG.

6A to 6C are graphs and photographs showing scanning electron micrographs and EDS analysis results of the magnesium alloy coating layer of Example 3. FIG.

7 is a graph showing the phase analysis results of the magnesium alloy coating layer of Example 3.

8A to 8C are graphs and photographs showing scanning electron micrographs and EDS analysis results of the magnesium alloy coating layer of Example 4. FIG.

9 is a graph showing the phase analysis results of the magnesium alloy coating layer of Example 4.

10A to 10C are graphs and photographs showing scanning electron micrographs and EDS analysis results of the magnesium alloy coating layer of Example 5. FIG.

11 is a graph showing the phase analysis results of the magnesium alloy coating layer of Example 5.

12 is a photograph showing the results of the salt spray experiment of the magnesium alloy coating layer of Examples 1 to 5 and Comparative Examples 1 to 5.

13A to 13C are graphs showing electrochemical polarization curves of the magnesium alloy coating layers of Examples 1 to 5 and Comparative Examples 1 to 5;

In order to solve the first problem, the present invention provides a magnesium material coloring method characterized by coloring the magnesium material by plasma electrolytic oxidation of the magnesium material in a basic electrolytic solution containing a water-soluble metal salt, potassium hydroxide and sodium silicate. The present invention focuses on the fact that the magnesium material is greatly improved not only in colorability but also in corrosion resistance when a water-soluble metal salt is added to a basic electrolyte including potassium hydroxide and sodium silicate and then plasma electrooxidized. The simultaneous improvement effect of corrosion resistance is demonstrated in more detail in the following experimental example.

In one embodiment of the present invention, the water-soluble metal salt provides a method of manufacturing magnesium material including one metal or metal ion selected from the group consisting of vanadium, cobalt, copper, nickel and tin.

Plasma electrolytic oxidation technology of magnesium or magnesium alloy (hereinafter referred to as magnesium material) is a technique for forming a magnesium composite oxide layer by using a discharge phenomenon generated when a proper current and a relatively high voltage are applied in an electrolyte solution. It is a technology distinct from the anodization technology in which a hydroxide passivation film is formed. The plasma electrolytic oxidation process is performed by separating two different metals into a liquid (electrolyte) that can be energized, so that when a direct current or alternating current is added, the metal is separated into a cathode and an anode according to the polarity of the power source. Use the electrochemical reaction that takes place. That is, when a high voltage of more than a voltage (Dielectric Breakdown Voltage: 200 to 500 V) that is applied to the pre-formed anodized film (or dielectric film) is applied, a strong current formed locally in the gas (O ₂ or H ₂ gas) reacted inside the oxide film Arcs (arc, spark, or plasma) may be generated by the field, and these plasma energies serve to fusion the oxides formed at the moment. Thus, gaseous oxygen generation and metal oxidation reaction occur at the anode surface. This is a process of forming an ionized or oxide film on the surface of the anode. The present invention provides a method capable of simultaneously improving the corrosion resistance of the magnesium material as well as coloring the surface of the magnesium material using the plasma electrolytic oxidation process.

In general, when the plasma electrolytic oxidation process is applied to magnesium, which is a highly reactive metal, corrosion or galvanic corrosion of magnesium may occur depending on the composition of the electrolyte, and thus, very careful selection of the electrolyte is required. In particular, in order to apply the plasma electrolytic oxidation process to the magnesium material, the electrolyte solution must meet several conditions. First, since the corrosion reaction occurs at a pH of 11.5 or less, the pH of the electrolyte solution must be maintained at 11.5 or more, and at the same time, a constant electric conductivity It must be secured. In addition, the elements added to implement the color on the surface of the magnesium alloy exhibits sufficient activity even in solution conditions of pH 11.5 or more, and problems such as precipitation should not occur. Furthermore, it is most preferable that the elements not only exhibit excellent colorability when fused to the film layer of magnesium, but also show excellent corrosion resistance at the same time. The present inventors have come to the present invention based on the fact that when a water-soluble metal salt is incorporated in a basic electrolytic solution containing potassium hydroxide and sodium silicate, the magnesium material not only exhibits excellent colorability but also has excellent corrosion resistance. In particular, in view of the characteristics of magnesium, in which a barrier layer having a complex and diverse composition is formed, unlike aluminum, in the form of a hydroxide, the present invention simultaneously improves colorability and corrosion resistance according to the type of metal and electrolyte and the composition ratio therebetween. Is a very good effect of the present invention.

The present invention particularly proceeds by applying a current at a current density of 2 to 20 A / dm ² using the magnesium material as an anode in the engrafting method according to plasma electrooxidation of magnesium material. If the current density is less than the above range, sufficient electrooxidation is difficult to be achieved, and if the current density is higher than the above range, surface property deterioration (for example, pit corrosion) may occur due to excessive current application, which may improve colorability and corrosion resistance. It may be contrary to the object of the present invention to achieve this simultaneously. In addition, the process time of the plasma electrolytic oxidation is preferably a time range of 150 to 600 seconds, if the time is shorter than the time range, sufficient plasma electrolytic oxidation is difficult to achieve, and if longer than the time range, the surface characteristics due to excessive current application (pit) corrosion may occur, which may be contrary to the object of the present invention to simultaneously achieve coloring and corrosion resistance improvement.

The present invention provides a metal of any one of vanadium, cobalt, nickel, copper, and tin as a water-soluble metal salt material capable of simultaneously improving the corrosion resistance of the magnesium material to be colored simultaneously with the coloring of such magnesium material. However, the present invention is not limited to the kind of the metal. The metals presented above as inorganic pigments may also be present in ionic form in basic electrolytes, in particular when magnesium is colored black, the present invention provides vanadium as the water soluble metal salt, wherein the concentration of vanadium is from 0.001 M to Has a concentration of 0.5M. If the concentration is lower than the concentration range, it is difficult to obtain a desired color. On the contrary, if the concentration is higher than the concentration range, plasma electrooxidation is not performed. In addition, the basic electrolyte solution contains potassium hydroxide, sodium silicate and ammonium phosphate, wherein the concentration of potassium hydroxide is 0.2 to 0.6M, the concentration of sodium silicate is 0.1 to 0.3M, the concentration of ammonium phosphate is 0.1 to 0.3M desirable. In the black coloring method of magnesium material using vanadium, potassium hydroxide maintains the pH condition of the electrolyte solution above 11.5, and sodium silicate and sodium ammonium cause vanadium to appear black in the coating layer. If the sodium silicate and ammonium sodium are out of the above condition range, black color may not be realized or magnesium material corrosion during the process may occur due to a change in pH condition. Therefore, the components of the basic electrolyte solution and the ratio thereof are very important for improving the coloring and corrosion resistance of magnesium by vanadium, in particular, the present invention is to plasma the magnesium material using an electrolyte solution and a metal water-soluble metal salt in common containing potassium hydroxide and sodium silicate In consideration of the fact that the colored magnesium material has excellent corrosion resistance in the case of electrolytic oxidation, the selection and composition ratio of such an electrolyte are very important in the present invention.

When coloring magnesium with a blue color, the present invention provides cobalt with the water soluble metal salt, wherein the concentration of cobalt has a concentration of 0.001M to 0.05M. If the concentration is lower than the concentration range, it is difficult to obtain a desired color. On the contrary, if the concentration is higher than the concentration range, plasma electrooxidation is not performed. In addition, the basic electrolyte solution contains potassium hydroxide, sodium silicate and ammonium phosphate, wherein the concentration of potassium hydroxide is 0.1 to 0.3M, the concentration of sodium silicate is 0.05 to 0.15M, the concentration of ammonium phosphate is 0.03 to 0.13M desirable. In the above range conditions, the coloring of magnesium by cobalt can be maintained at an optimum condition, and also has excellent corrosion resistance of the magnesium material.

When coloring magnesium with red color, the present invention provides copper as a water-soluble metal salt, wherein the copper has a concentration of 0.001M to 0.05M, and if the concentration is lower than the concentration range, it is difficult to obtain a desired color. When the concentration is higher than the concentration range, plasma electrolytic oxidation is not performed. In addition, the basic electrolyte solution contains potassium hydroxide, sodium silicate and potassium fluoride, wherein the concentration of potassium hydroxide is 0.13 to 0.21M, the concentration of sodium silicate is 0.06 to 0.12M, the concentration of potassium fluoride is 0.06 to 0.12M Preferably, this also has the same technical significance as in the case of cobalt or vanadium.

When coloring magnesium in the same color, the present invention provides nickel as the water-soluble metal salt, wherein the concentration of nickel is preferably 0.001M to 0.05M. If the concentration is lower than the concentration range, it is difficult to obtain a desired color. On the contrary, if the concentration is higher than the concentration range, plasma electrooxidation is not performed. When nickel is used as the water-soluble metal salt, the basic electrolyte solution preferably contains potassium hydroxide, sodium silicate and potassium fluoride, wherein the concentration of potassium hydroxide is 0.13 to 0.21M, the concentration of sodium silicate is 0.06 to 0.12M, potassium fluoride The concentration of is preferably 0.06 to 0.12M, which is the same as described above.

When coloring magnesium with ocher color, the present invention provides tin as a water-soluble metal salt, and the concentration of tin is preferably 0.016 to 0.22M. In addition, when tin is used as the water-soluble metal salt, the basic electrolyte solution preferably contains potassium hydroxide and sodium silicate, the concentration of potassium hydroxide is preferably 0.13 to 0.23M, and the concentration of sodium silicate is 0.008 to 0.08M. Since the composition of the electrolyte is in the range that allows tin to have sufficient activity in the basic electrolyte and have excellent colorability and corrosion resistance, it may cause problems such as precipitation or corrosion of magnesium when out of the above range.

In order to solve the second problem, the present invention provides a colored magnesium material according to the above-described method, the magnesium material according to the present invention is one metal oxide selected from the group consisting of vanadium, cobalt, copper, nickel and tin on the surface It has a coating layer containing.

The coloring method of the magnesium material according to the present invention can not only color the magnesium material in various colors such as black, red, blue, ocher and maroon, but also improve the corrosion resistance of the colored magnesium material.

Hereinafter, the present invention will be described in detail using examples. However, the following examples and the like are only for illustrating the present invention, and do not limit the present invention.

Example  One

Preparation of Magnesium Alloy Specimen

Magnesium alloy of AZ91 (8.29% by weight, 0.83% by weight of zinc, 0.31% by weight of manganese, balance Mg) was cooled after homogenizing heat treatment at 350 ° C for 12 hours, and after the heat treatment, the specimen was 30mm long, 40mm long and 2mm thick. Made with. Before performing plasma electrolytic oxidation, the surface of the sample was uniformly polished using SiC paper # 1000, washed with alcohol, and dried.

plasma Electrolytic oxidation

As the water-soluble metal salt, the magnesium alloy specimen was immersed in a basic electrolyte solution (pH = -12) containing 0.09 M of ammonium vanadate, 0.36 M of potassium hydroxide, 0.14 M of sodium silicate, and 0.15 M of ammonium phosphate. Plasma electrolytic oxidation was performed using the apparatus of FIG. 1 having an output voltage and a stirring and cooling device.

Referring to FIG. 1, the plasma electrolytic oxidation apparatus according to the present invention includes an electrolyzer 1, an electrolyte 2, a cathode 3, an anode 4, a power supply 5, a stirrer 6, and a filter 7. And a cooling system (8), wherein the magnesium alloy specimen is placed at the anode, and the stainless steel is placed at the cathode, and then subjected to plasma electrooxidation for 10 minutes at a current density of 10 A / dm ² using an AC power source. At this time, the temperature of the electrolyte was maintained at 20 ℃ .

Example  2

Water-soluble metal salt containing 0.01M cobalt nitride, potassium hydroxide 0.18M, sodium silicate 0.09M, ammonium phosphate 0.08M basic electrolyte solution (pH = ~ 12) for 450 seconds at a current density of 10 A / dm ² Plasma electrolytic oxidation was performed in the same manner as in Example 1 except that plasma electrolytic oxidation was performed.

Example  3

It is a water-soluble metal salt containing 0.01M copper nitride, containing 0.18M potassium hydroxide, 0.09M sodium silicate and 0.09M potassium fluoride, and plasma for 600 seconds at a current density of 5 A / dm ² in a basic electrolyte solution (pH = -12). Plasma electrolytic oxidation was carried out in the same manner as in Example 1 except that the electrolytic oxidation was performed.

Example  4

As a water-soluble metal salt, it contains 0.01M nickel nitride, 0.18M potassium hydroxide, 0.09M sodium silicate and 0.08M potassium fluoride in a basic electrolyte solution (pH = -12) at a current density of 5 A / dm ² for 300 seconds. Plasma electrolytic oxidation was performed in the same manner as in Example 1 except that plasma electrolytic oxidation was performed.

Example  5

As a water-soluble metal salt, 0.04 M sodium stannate is contained, and 0.18 M potassium hydroxide and sodium silicate are subjected to plasma electrolytic oxidation for 500 seconds at a current density of 10 A / dm ² in a basic electrolyte solution (pH = -12) containing 0.03 M. Plasma electrolytic oxidation was carried out in the same manner as in Example 1 except that.

Comparative example  1 to 5

Plasma electrolytic oxidation was performed on the electrolyte solution of the same composition which does not contain the water-soluble metal salt of Examples 1-5, and the white magnesium material was manufactured.

Experimental Example  One

Surface analysis

Experimental Example  1-1

2A to 2C are surface SEM photographs, EDS analysis results, and side SEM photographs of the coating layer of the black colored magnesium alloy of Example 1. FIG. 2A to 2C, the coating layer of Example 1 having a black surface includes metal elements of Mg, Al, O, Si, and V, wherein the thickness of the coating layer is about 29.3 μm.

Referring to FIG. 3, it can be seen that the coating layer of Example 1 according to the present invention contains a metal oxide of MgO, Mg ₂ SiO ₄ , and Mg ₂ V ₂ O ₇ forms.

Experimental Example  1-2

4A to 4C are surface SEM photographs, EDS analysis results, and side SEM photographs of the coating layer of the blue colored magnesium alloy of Example 2. FIG. 4A to 4C, the coating layer of Example 1 having a black surface includes metal elements of Mg, Al, O, Si, and Co, wherein the thickness of the coating layer is about 26.6 μm.

5, it can be seen that the coating layer of Example 2 according to the present invention contains a metal oxide of MgO and Co ₂ P ₂ O ₇ forms.

Experimental Example  1-3

6A to 6C are surface SEM photographs, EDS analysis results, and side SEM photographs of the coating layer of the red colored magnesium alloy of Example 3. FIG. 6A to 6C, the coating layer of Example 3 having a red surface includes metal elements of Mg, Al, O, Si, and Cu, wherein the thickness of the coating layer is about 9.3 μm.

Referring to FIG. 7, it can be seen that the coating layer of Example 3 according to the present invention contains metal oxides of MgO, Mg ₂ SiO ₄ , and MgCu ₄ O ₅ forms.

Experimental Example  1-4

8A to 8C are surface SEM photographs, EDS analysis results, and side SEM photographs of the coating layer of the magnesium alloy colored in the same color of Example 4. FIG. 8A to 8C, the coating layer of Example 3 having a maroon surface includes metal elements of Mg, Al, O, Si, and Ni, wherein the thickness of the coating layer is about 11.3 μm.

9, it can be seen that the coating layer of Example 4 according to the present invention contains MgO, Mg ₂ SiO ₄ , and MgNiO ₂ metal oxides.

Experimental Example  1-5

10A to 10C are surface SEM photographs, EDS analysis results, and side SEM photographs of the coating layer of the ocher colored magnesium alloy of Example 5. FIG. 10A to 10C, the coating layer of Example 3 having an ocher color surface includes metal elements of Mg, Al, O, Si, and Sn, wherein the thickness of the coating layer is about 5.7 μm.

11, it can be seen that the coating layer of Example 5 according to the present invention contains metal oxides of MgO, Mg ₂ SiO ₄ , and Mg ₂ SnO ₄ .

Experimental Example  2

Salt spray measurement

The salt spray measurement was performed for 120 hours on the magnesium alloys of Examples 1 to 5 and Comparative Examples 1 to 5 in a 3.5 wt% NaCl solution, and the results are shown in FIG. 12.

Referring to FIG. 12, it can be seen that pit corrosion occurred on the surface of the white magnesium alloy plasma-oxidized in the same basic electrolyte solution without addition of the inorganic pigment metal according to the present invention. However, it can be seen that when the metal ions, especially tin and copper, are added to the electrolyte as the inorganic pigment metal, the coating layer of the ocher and red colored magnesium alloys exhibits smooth surface characteristics in which the pit corrosion is significantly removed. .

Experimental Example  3

Electrochemical Polarization  Experiment

In order to quantitatively show the excellent corrosion resistance effect of the magnesium material coloring method according to the present invention, an electrochemical polarization test was performed and the results are shown in FIGS. 13A to 13C.

Referring to FIGS. 13A to 13C, the corrosion current density of a magnesium alloy colored by plasma electrolytic oxidation in a potassium hydroxide and sodium silicate-containing electrolyte to which metal elements such as Sn, Cu, and Ni are added is equal to plasma in an electrolyte having the same composition. It can be seen that it is produced by anodization and appears to be one order slower than the corrosion current density of the magnesium alloys of Comparative Examples 1 to 5 having a white color. Therefore, the above results mean that the magnesium alloy colored according to the present invention has not only a simple specific color implementation but also high corrosion resistance.

Claims (17)

A method of coloring a magnesium material, characterized in that the magnesium material is colored by plasma electrooxidizing the magnesium material in a basic electrolytic solution containing a water-soluble metal salt, potassium hydroxide and sodium silicate. The method of claim 1, The water-soluble metal salt is magnesium material coloring method characterized in that it comprises one metal or metal ion selected from the group consisting of vanadium, cobalt, copper, nickel and tin. The method of claim 1, The basic electrolytic solution is a magnesium coloring method, characterized in that the pH is 11.5 or more. The method of claim 1, The plasma electrolytic oxidation is performed by applying a current to the magnesium material using the magnesium material as an anode. The method of claim 4, wherein Magnesium material coloring method characterized in that the application of the current proceeds in a time range of 150 to 600 seconds at a current density of 2 to 20A / dm ² . The method of claim 1, The water-soluble metal salt is vanadium, wherein the basic electrolyte solution is a magnesium material coloring method comprising potassium hydroxide, sodium silicate and ammonium phosphate. The method of claim 6, The vanadium has a concentration of 0.001M to 0.5M, the concentration of potassium hydroxide is 0.2 to 0.6M, the concentration of sodium silicate is 0.1 to 0.3M, the concentration of ammonium phosphate is 0.1 to 0.3M Coloring method. The method of claim 1, The water-soluble metal salt is cobalt, wherein the basic electrolyte solution is a magnesium material coloring method comprising potassium hydroxide, sodium silicate and ammonium phosphate. The method of claim 8, The cobalt has a concentration of 0.001M to 0.05M, the concentration of potassium hydroxide is 0.1 to 0.3M, the concentration of sodium silicate is 0.05 to 0.15M, the concentration of ammonium phosphate is 0.03 to 0.13M Coloring method. The method of claim 1, The water-soluble metal salt is copper, wherein the basic electrolyte solution is a magnesium material coloring method characterized in that it comprises potassium hydroxide, sodium silicate and potassium fluoride. The method of claim 10, The copper has a concentration of 0.001M to 0.05M, the concentration of potassium hydroxide is 0.13 to 0.21M, the concentration of sodium silicate is 0.06 to 0.12M, the concentration of potassium fluoride is 0.06 to 0.12M Coloring method. The method of claim 1, The water-soluble metal salt is nickel, wherein the basic electrolyte solution is a magnesium material coloring method comprising potassium hydroxide, sodium silicate and potassium fluoride. The method of claim 12, The nickel has a concentration of 0.001M to 0.05M, the concentration of potassium hydroxide is 0.13 to 0.21M, the concentration of sodium silicate is 0.06 to 0.12M, the concentration of potassium fluoride is 0.06 to 0.12M Coloring method. The method of claim 1, The water-soluble metal salt is tin, wherein the basic electrolyte solution is a magnesium material coloring method characterized in that it comprises potassium hydroxide and sodium silicate. The method of claim 14, The tin has a concentration of 0.016M to 0.22M, the concentration of potassium hydroxide is 0.13 to 0.23M, the concentration of sodium silicate is 0.008 to 0.08M, characterized in that the coloring method. Magnesium material, characterized in that the plasma electrolytic oxidation in a basic electrolytic solution containing a water-soluble metal salt, potassium hydroxide and sodium silicate to include the water-soluble metal oxide in the coating layer. The method of claim 16, Magnesium material, characterized in that the water-soluble metal comprises one metal or metal ion selected from the group consisting of vanadium, cobalt, copper, nickel and tin.