JP2002275687A - Coated member and surface treatment method for magnesium base material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coated member which is provided with a surface film having excellent adherence, corrosion resistance, wear resistance and seizure resistance. SOLUTION: The coated member is provided with a magnesium base material essentially consisting of magnesium(Mg), an oxidized layer formed on the magnesium base material, and a coating layer consisting of oxides or sulfides of the group VIa elements, and formed on the oxidized layer. The coating layer having high hardness is firmly bonded with the magnesium base material via the oxidized layer, and exhibits excellent adherence, corrosion resistance, wear resistance or seizure resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to adhesiveness, corrosion resistance,
The present invention relates to a coating member having a surface treatment layer having excellent seizure resistance or abrasion resistance, and a method for surface treatment of a magnesium base material.

[0002]

2. Description of the Related Art Magnesium is the lightest among practical metals, has excellent specific strength, and has abundant resources and excellent recyclability. For this reason, magnesium is a promising metal material in recent years where weight reduction and reduction of environmental load are strongly demanded, and magnesium or magnesium alloy is being used for various products in various fields. For example, in the field of vehicles such as automobiles, covers and wheels made of magnesium alloy have been developed, and efforts have been made to save energy and improve athletic performance due to weight reduction. Also, in the field of electric devices, magnesium (or an alloy thereof) is used in cases of notebook computers, mobile phones, and the like, and mobile devices are being further reduced in weight and recycled.
However, magnesium is a very active metal,
It is a metal with the lowest potential in practical metals (that is, a metal having a high ionization tendency). In addition, since the oxide has a volume fraction of less than 1, it does not itself form a dense oxide film, and is therefore a metal which is very easily corroded. Therefore, it is practically necessary to provide a coating having excellent corrosion resistance on the surface. Further, since magnesium is a metal having a low hardness, it is necessary that the film has not only corrosion resistance but also abrasion resistance and seizure resistance depending on use conditions.

[0003] As such a coating, for example, a chemical conversion coating formed chemically using a phosphate or the like, an anodic oxide coating formed by forming an oxide coating on the surface of a magnesium base as an anode, and furthermore, plating or coating There are coatings. But,
Although a chemical conversion film is often formed for the purpose of undercoating a coating, its film thickness is small and its corrosion resistance and abrasion resistance are not sufficient. In addition, although the anodic oxide film is often formed for the purpose of undercoating the coating, the corrosion resistance is still insufficient because of the presence of minute pinholes.
In addition, wear resistance and seizure resistance are not sufficient. In addition, electroplating and electroless plating also have insufficient adhesion or microcracks on the surface, failing to provide sufficient corrosion resistance. Similarly, the coating film is not sufficient in terms of adhesion, abrasion resistance, seizure resistance and the like.

[0004] Therefore, there have been proposed a number of surface treatment methods for magnesium (base material) that can further enhance the corrosion resistance and adhesion of the coating treatment layer. For example, Japanese Translation of International Patent Publication No. 11-502
No. 567, JP-A-4-254576, JP-A-61-276994, and the like. Japanese Patent Application Laid-Open No. Hei 11-502567 has a feature in an electrolytic solution used for anodizing treatment.
Japanese Patent Application Publication No. 76-276994 relates to a method of forming an Si intermediate layer by sputtering and forming an Al film on the surface thereof by ion plating.
Japanese Patent Application Publication No. JP-A-2003-110555 relates to a method of forming an Al intermediate layer by an ion plating method and plating the surface of the intermediate layer with copper, nickel, gold, or the like. In addition, JP-A-2000-345
370, JP-A-2000-309882, JP-A-10-287982, JP-A-7-10959
No. 8, JP-A-6-264292 and the like also disclose a surface treatment method of magnesium (alloy).

[0005]

However, in any method of forming an intermediate layer between a magnesium substrate and a surface layer, the adhesion between the magnesium substrate and the surface layer is insufficient. . Further, even when a hard surface film is formed, the conventional film is a thin film and has insufficient abrasion resistance. As described above, the surface film obtained by the conventional surface treatment method is not always sufficient from the viewpoints of adhesion, corrosion resistance, wear resistance, seizure resistance and the like.

[0006] The surface treatment method for the coated member and the magnesium base material of the present invention has been made in view of such circumstances. That is, an object of the present invention is to provide a coated member in which a magnesium base is coated with a surface film having excellent adhesion, corrosion resistance, abrasion resistance, or seizure resistance. It is another object of the present invention to provide a method for treating a magnesium substrate, which can form a surface film having excellent adhesion, corrosion resistance, abrasion resistance, and seizure resistance on the magnesium substrate.

[0007]

The inventor of the present invention has made intensive studies to solve this problem, and as a result of repeated trial and error,
By forming a coating layer composed of an oxide and / or sulfide of a Group VIa element on the oxide layer formed on the surface of the magnesium base, adhesion, corrosion resistance, wear resistance or seizure resistance can be improved. They have found that an excellent surface film can be obtained, and have completed the method of surface treating a coated member and a magnesium substrate of the present invention. (Coating Member) That is, the coating member of the present invention includes a magnesium base mainly composed of magnesium (Mg), an oxide layer formed on the magnesium base, and a VIa formed on the oxide layer. And a coating layer made of an oxide and / or sulfide of a group element.

[0008] According to the coating member of the present invention, on the oxide layer (film) formed on the magnesium base material, the VIa
Since the coating layer made of the oxide and / or sulfide of the group element is formed, the coating layer not only reinforces the oxide layer by sealing small holes formed on the oxide layer, but also forms the coating layer. Is strongly adhered to the magnesium base, and the corrosion resistance of the magnesium base is improved, unlike the related art. Furthermore, the present inventors have confirmed that the surface film provided with the coating layer is excellent in wear resistance and seizure resistance. For this reason,
The covering member provided with the surface film can be used for various applications in many fields.

In the coating member of the present invention, the magnesium substrate, the oxide layer and the coating layer are not always separated clearly, and each element or particle is disturbed by diffusion at the boundary between the layers. Often. The term “coated member” in the present specification refers to a member coated with the above-described surface film,
The form of the member is not a problem, and it can take various forms and shapes such as a raw material, a casting, a forged product, and a processed product. The covering member only needs to have a magnesium base on which a surface film is formed, and the entire member does not need to be made of magnesium (alloy). For example, the inside may be made of other members such as metal or resin other than Mg. The magnesium base material contains magnesium as a main component, and the composition ratio is sufficient as long as a surface treatment is required at least from the viewpoint of corrosion resistance.
Therefore, the magnesium base material includes not only pure magnesium but also a magnesium alloy and the like.

(Method for Surface Treatment of Magnesium Substrate) Such a coated member having an excellent surface film is, for example,
It can be manufactured by the surface treatment method for a magnesium base material of the present invention. That is, the surface treatment method for a magnesium base material of the present invention includes an oxidation step of forming an oxide layer on the surface of a magnesium base material containing magnesium (Mg) as a main component, and forming an oxide layer on the oxide layer formed by the oxidation step. VIa
A coating treatment step of forming a coating layer made of an oxide and / or sulfide of a group element.

By the way, when a coating layer made of an oxide and / or sulfide of a Group VIa element is formed on the oxide layer,
It is not always clear why a surface film with excellent adhesion can be obtained. This is because, as will be described below, it has been found after the inventor's hard research and study. That is, elements of group VIa of Cr, Mo and W are:
Chromium oxide (Cr ₂ O ₃ ), molybdenum oxide (Mo
O _3), but tends to form an oxide such as tungsten oxide (WO _3), be applied like the oxides thereof directly to the magnesium substrate on the coating layer excellent in adhesiveness was not obtained.

Therefore, by changing the idea, anodizing the magnesium base material in advance to form fine irregularities on its surface and forming an oxide of magnesium on its surface, It has been found that a coating layer made of an oxide of an element and having excellent adhesion is formed. In addition, VIa
The same applies to the case of coating with a sulfide of a group element, and a coating layer having excellent adhesion was not formed even when coated alone. However, when a mixture of graphite and fluororesin was coated on the surface of the anodized layer formed by anodizing, a coating layer having excellent adhesion was obtained. Based on such circumstances, it is preferable that the above-described oxide layer be an anodized layer.
Further, the oxide of the Group VIa element is preferably at least one of chromium oxide, molybdenum oxide and tungsten oxide, and the sulfide of the Group VIa element is preferably molybdenum disulfide.

[0013]

Next, the present invention will be described in more detail with reference to embodiments. (1) Oxidation Step The oxidation step is a step of forming an oxide layer (MgO layer or the like) on the surface of a magnesium base mainly composed of Mg. As this processing method, any known method may be used. However, as described above, since the anodic oxide layer is typical as the oxide layer, it is preferable that the oxidizing step be the anodizing step of forming an anodic oxide layer on the surface of the magnesium base. This anodic oxidation step can be performed, for example, by immersing a magnesium base material in an electrolytic solution composed of an alkaline aqueous solution and applying a voltage using the magnesium base material as an anode. Although the electrolytic solution depends on the composition of the magnesium base, for example, ammonium ammonium fluoride, potassium fluoride, sodium dichromate, ethylene glycol, phosphoric acid, sodium hydroxide, sodium oxalate,
It can be produced using ammonium sulfate, potassium hydroxide and the like. In order to promote the reaction, the temperature of the electrolytic solution is set to 70
It is good to keep it at ~ 90 ° C. Also, depending on the thickness of the anodic oxide layer, the current density is set to 0.5 to 5 A / dm2,
It is good to process for 60 minutes.

Thus, the anodic oxide layer has a thickness of 10 to 100 μm.
m, more preferably 20 to 50 μm. 1
If the thickness is less than 0 μm, the adhesion to the coating layer is inferior,
If the thickness exceeds 100 μm, the anodic oxidation step requires a long time, which is uneconomical for practical use. As described above, the magnesium base material includes, in addition to the pure magnesium material, alloy materials thereof, for example, cast materials of AM60, AM212, WE43 and AZ91 (high-pressure and low-pressure cast materials, die-cast materials, thixomold materials, and the like). ), AZ31 or AZ
80 wrought materials, and magnesium sintered materials obtained by mixing magnesium powder and alloy element powder and then sintering them. In addition, each symbol showing the type of alloy is Mg of JIS.
This is based on one kind of alloy or two kinds of Mg alloy castings.

(2) Coating Step The coating step is a step of forming a coating layer made of an oxide and / or sulfide of a Group VIa element on the oxide layer. More specifically, the coating treatment step includes a coating step of applying a coating agent mixed with the oxide and / or sulfide on the oxide layer, and a step of applying the oxide and / or sulfide after the coating step. And a heating step of heating the object. An oxide of a Group VIa element on the oxide layer and / or
Alternatively, after applying a coating agent containing sulfide, by heating it at a desired temperature, the magnesium base material and the coating layer are firmly adhered to each other, and the corrosion resistance, abrasion resistance, and seizure resistance are improved. Excellent surface coating is obtained. Note that the coating step and the heating step may be appropriately repeated.

As described above, the oxide of the Group VIa element can be at least one of chromium oxide, molybdenum oxide and tungsten oxide. Specifically, Cr ₂ O ₃ , (NH ₄ ) ₂ Cr ₂ O ₇ , K ₂ Cr ₂ O ₇ ,
1 from oxide group such as NaCr ₂ O ₇ , WO ₃ and MoO ₃
The species or two or more species may be appropriately selected. The sulfide of the Group VIa element can be, for example, molybdenum disulfide (MoS ₂ ).

The coating step may be, for example, a dipping method in which the oxide layer is immersed in the coating agent, a brush coating method in which the coating agent is brush-coated on the oxide layer, or a spraying of the coating agent on the oxide layer. And spraying can be performed by any of the spray methods. According to the dipping method, the productivity can be improved. According to the brush coating method, details can be easily applied, and according to the spraying method, a uniform coating layer can be formed. It is preferable to adjust the viscosity of the coating agent and the solvent according to the method to be adopted. For example, when the dipping method is adopted, a portion of a magnesium base requiring surface treatment is immersed for a short time in a coating melt heated and melted in a container, and a part of the coating is applied to the surface of the magnesium base. You may make it simulate. In addition, this immersion is not limited to the case of so-called pickling,
The degree that the treated surface is in contact with the liquid surface of the coating agent may be sufficient.

Further, a binder such as water, water glass, colloidal silica, polyamide resin or an aqueous solution of ethyl silicate is added to the oxide and / or sulfide to form a viscous paste. May be applied to the surface. In order to prevent the applied paste from peeling or flowing out, the viscosity of the paste may be adjusted by adjusting the amount of a binder such as water. Also,
As the binder for the paste, an organic liquid such as glycerin or alcohol may be used in addition to the above-mentioned ones. Furthermore, the finer the powder of each component to be compounded and added as a paste (coating agent), the higher the adhesive strength, and a paste that can be easily applied can be obtained. Also, the more the amount of coating agent applied,
Preferred coating layers tend to be obtained. Therefore, when a brush coating method or a spray method (spray coating method) is used, it is preferable to form a thick coating film by applying multiple layers.

However, it is conceivable that the viscosity of the coating material decreases during the heating step described below, and the coating material flows down from the surface of the magnesium base material. Therefore, the film thickness of the coating agent is set to 0.1.
It is preferable to set it to 01 to 3 mm. However, the present inventors have confirmed that when the heating step is performed in a non-oxidizing atmosphere, a good coating layer can be obtained even when the amount of the coating agent is reduced. After the application of the coating agent, a drying step of driving out the binder such as water from the coating agent and drying the coating agent may be performed prior to the heating step as the next step. This drying step may be natural drying or heat drying. In addition, this drying step can also serve as the heating step.

The coating agent may be a mixture of a resin dissolved in a solvent and the oxide and / or sulfide, or a mixture of a solvent and the oxide and / or sulfide. For example, a viscous paste obtained by kneading a solvent such as water, alcohol, acetone, hexane, hexafluoroisopropanol, methyl ethyl ketone, and sodium acetate and powders of oxides and sulfides thereof, or a polyamideimide may be used. Or the like, and a powder of an oxide or sulfide thereof and a mixture thereof to form a slurry. The resin such as polyamideimide is decomposed by the subsequent heating and remains as carbon or oxide. It is preferable that the coating agent further contains at least one of a fluororesin (Teflon (registered trademark) -based resin), boron nitride (BN), and graphite. and/
Alternatively, mixing and kneading with a sulfide powder are facilitated. Fluororesin and graphite have the effect of reducing sliding resistance,
When they are included in the coating layer, the wear resistance and seizure resistance of the surface of the coating member can be improved. Also, when boron nitride is included in the coating layer, since it has a high hardness,
The wear resistance of the covering member can be improved.

The viscosity of the coating agent is preferably determined according to the method of the coating process. For example, when the applied coating agent flows down from the surface of the magnesium base, alumina (Al2O3), antimony oxide (SbO2) ₂ ) and a high melting point inert material such as boron nitride (BN) may be added to increase the viscosity of the coating composition. The oxide and / or sulfide of the Group VIa element is preferably used in an amount of 1 to 70 parts by weight, more preferably 5 to 30 parts by weight, based on 100 parts by weight of the entire coating composition. You may consider including the said fluororesin, boron nitride, or graphite in the compounding quantity.
If the amount of these components is too small (for example, less than 1 part by weight), the rate of forming the coating layer composed of oxides and sulfides becomes slow, which is not practically preferable. On the other hand, if the amount is too large (for example, if it exceeds 70 parts by weight), the formation of the coating layer becomes uneven, which is not practically preferable.

The heating step is a step of heating the oxide and / or sulfide applied on the oxide layer to form a coating layer. The heating may be performed in an air atmosphere or in a non-oxidizing atmosphere such as argon or nitrogen.
When it is desired to form a coating layer on the entire surface or most of the surface of the magnesium base, it is efficient to use a furnace capable of heating the entire member. Conversely, when it is desired to form a coating layer only on a part of the surface of the magnesium base, it is preferable to use a burner capable of locally heating, a high-frequency induction heating, or the like. Needless to say, when forming the coating layer locally, it is only necessary to apply a coating material such as a paste only to the local portion.

In the heating step, when the coating agent containing the oxide or sulfide of the Group VIa element and a solvent such as acetone or polyamideimide is heated, the solvent is decomposed. And
The fine solid agent such as the oxide, sulfide or carbon is dispersed in a binder such as a decomposed or changed resin or an oxide thereof to form a fixed coating layer structure. The binder decomposed by the heat treatment and changed, such as a resin or an oxide, firmly adheres to the oxide layer formed by the base treatment. This heating temperature is a temperature within a range in which the magnesium base does not dissolve.
It is good to be 0-450 degreeC, More preferably, it is 200-350 degreeC. Below 150 ° C, alcohol, acetone,
Solvents such as resins such as polyamideimide and PTFE hardly decompose, and a sound coating layer may not be obtained.
If the temperature exceeds 0 ° C., the magnesium base material is softened, and the dimensional change may increase with a change in the base structure. The heating time depends on the employed heating means, the size of the object to be heated, the thickness of the coating layer, and the like, and thus cannot be determined uniformly, but can be, for example, about several minutes to 30 hours. In order to prevent thermal distortion, structural transformation, and the like, it is preferable to perform heat treatment in a short time. Therefore, for example, it is preferable to use high-frequency induction heating because the temperature of the object to be heated can be raised to a high temperature in a short time. Therefore, particularly when a coating layer is locally formed, the occurrence of thermal distortion of the coating member can be reduced. It is preferred.

(3) Use The coating member according to the present invention is characterized in that a coating layer having high hardness is firmly bonded to a magnesium base via an oxide layer, and has excellent adhesion, corrosion resistance, wear resistance, and the like. Since it has seizure resistance, it can be used not only for various products in various fields conventionally used, but also for a wide variety of products in a wide range of fields.
For example, it is preferable that automobile parts such as a piston, a throttle body, a shaft, and a mandrel, a computer, a camera, a housing of an electronic device, a tool, a mechanical part, and the like be constituted by the covering member according to the present invention.

[0025]

EXAMPLES Next, the present invention will be described in more detail with reference to examples. (Example 1) Cast magnesium alloy (AM60: 6% A
1-0.5% Mn-balance Mg: unit is% by mass (the same applies hereinafter), thickness 50 mm, width 40 mm, length 15
A test piece of 0 mm was produced (magnesium base material). Na
An OH-containing alkaline aqueous solution (NaOH: 30%, ethylene glycol: 10%, balance: water) was immersed in a 70 ° C. electrolyte solution using the test piece as an anode and a stainless steel plate as a cathode, and 2 A / dm ^2. Anodizing treatment was performed under electrolysis conditions of × 30 min (anodizing step). FIG. 1 shows the results of line analysis performed on the cross section of this test piece using an X-ray microanalyzer. The horizontal axis of FIG. 1 is the measurement distance (μm), and the vertical axis is the element concentration (%).

From FIG. 1, it can be seen that the anodic oxide layer has a thickness of about 30 μm, and a large amount of O is detected in the anodic oxide layer with the decrease of Mg. It turns out that it consists of oxides mainly composed of Mg. Next, 20% (mass) of molybdenum disulfide (MoS ₂ ) and polytetrafluoroethylene (Teflon PTFE) powders were added to a polyamideimide (PAI) resin dissolved in a solvent (methyl ethylene ketone), respectively. The mixture was sufficiently stirred, mixed and dispersed to prepare a coating solution (coating agent). This coating solution was put in a spray can and spray-coated on the surface of the test piece subjected to the anodizing treatment described above (coating step). Its thickness was about 10 μm. The test piece after the application step was placed in a box-type heat treatment furnace in an air atmosphere and heated at 200 ° C. for 60 minutes (heating step).

FIG. 2 (a) shows a photograph of the processed cross section of the test piece cooled after this heat treatment enlarged 100 times by an optical microscope.
, And the results of the line analysis by the X-ray microanalyzer are shown in FIG. From FIG. 2, it was found that the surface portion of the test piece was composed of two layers, a surface layer and an intermediate layer, and had a thickness of 15 μm and 20 μm, respectively. In addition, about 30% by surface analysis with X-ray microanalyzer
In addition to Mo and 17% S, large amounts of O and C were detected in the surface layer. On the other hand, in the intermediate layer, O
Increased. Therefore, it is considered that this intermediate layer is an Mg oxide layer (anodized layer) formed by anodizing. Next, when the surface layer was subjected to X-ray diffraction, the obtained diffraction lines agreed well with the diffraction lines of MoS ₂ and C. From the above results, the surface portion of the test piece (magnesium base material) has a surface layer (coating layer) made of an oxide containing MoS ₂ and C, and an intermediate layer (anode) made of an oxide of Mg following the surface layer. Oxide layer).

(Example 2) Magnesium alloy for drawing (A
Z31: a test piece having a diameter of 20 mmφ and a length of 500 mm made of 3% AL-1.0% Zn-remainder Mg) was prepared and anodized in the same manner as in Example 1. next,
Polyamideimide (P) dissolved in the same solvent as in Example 1
AI) Molybdenum disulfide (MoS ₂ ) and polytetrafluoroethylene (Teflon PTFE) powders of 15% each, and 5% of antimony oxide (SbO ₂ ) effective for preventing oxidation of the paste were added to the resin. The coating solution (coating agent) was prepared by sufficiently stirring, mixing and dispersing.

This coating solution was put into a spray can and spray-coated on the surface of the anodized test piece (coating step). Its thickness is about 8 μm. A test piece coated in this manner is applied to a high-frequency induction heating device (oscillation frequency:
150 kHz, heating coil: 3 turns, inner diameter 30 mm
φ, the number of revolution of the test piece: 60 rpm), and while rotating the test piece, a portion 100 mm from one end of the test piece was heated at an anode voltage of 1 kV and an anode current of 0.6 A for about 30 minutes. Due to this heating, the surface portion of the test piece is about 250 ° C.
(Heating step). The cross section of the cooled test piece after the heat treatment was examined by line analysis using an optical microscope and an X-ray microanalyzer, and by X-ray diffraction from the surface. As a result, the surface of the test piece was MoS ₂ , SbO ₂
Layer (coating layer) composed of carbon and oxide containing carbon
And an intermediate layer (anodically oxidized layer) composed of Mg oxide following the surface layer.

Example 3 Cast magnesium alloy (AM
212: 2% Zn-0.5% Zr-0.5% Ca-2%
10m thick made of RE (rare earth element)-balance Mg
A test piece having a length of m, a width of 30 mm and a length of 100 mm was prepared, and anodized in the same manner as in Example 1. However, an aqueous solution comprising 30% of ammonia, 10% of sodium hydrogen phosphate and remaining water was used as the electrolyte for the anodizing treatment.
Next, the anodized test piece was immersed in a coating solution obtained by adding chromium oxide (Cr ₂ O ₃ ) to a mixed solution of a phenol resin and methyl alcohol (coating step: dipping method). Thereafter, the test piece was pulled out, and in that state, the test piece was placed in an electric furnace at 250 ° C. and heated and maintained for 1 hour.
This operation (coating step and heating step) was repeated five times to complete the surface treatment.

As in Example 1, the cross section after this treatment was observed with an optical microscope and an X-ray microanalyzer.
FIG. 3 shows the result of line analysis of the cross section by an X-ray microanalyzer. From this, it became clear that the intermediate layer was composed of an Mg oxide layer (anodized layer), and the upper surface layer was composed of a Cr oxide layer (coating layer). In the surface analysis performed from the surface, a large amount of O and about 20% of Cr were detected in the surface layer.

Example 4 After the same anodic oxidation treatment was applied to the same magnesium alloy test piece as in Example 1, the same coating liquid as in Example 3 was applied to the surface of the anodized test piece. Brush application (coating process). Then, it was kept in an electric furnace heated to 250 ° C. for 1 hour. This operation (the coating step and the heating step) was repeated five times. As in Example 1, the processed cross section of the test piece was observed with an optical microscope and an X-ray microanalyzer. FIG. 4 shows the result of line analysis of the cross section by an X-ray microanalyzer. From this, the intermediate layer is composed of an Mg oxide layer (anodized layer), and the upper surface layer is C
It became clear that each of the oxide layers (coating layers) of r was formed.

(Example 5) Magnesium alloy for drawing (A
Z31), a test piece having a diameter of 3 mm and a length of 50 mm (Sample No. 1) was anodized in the same manner as in Example 1 (Sample No. 2). Next, the anodized test piece (sample No. 2) was subjected to the same surface treatment (coating process) as in Example 1 to obtain a sample No. 3 and the sample No. Sample No. 2 obtained by performing the same surface treatment (coating process) as in Example 4 for Sample No. 2. And 4. Thus, Sample No. without surface treatment was used. 1 and Sample No. 1 which was subjected only to the anodizing treatment. Sample No. _{2 which} was coated with MoS ₂ after anodic oxidation. Sample No. _{3 which} was coated with Cr ₂ O ₃ after anodic oxidation. 4 was prepared.

Next, according to JIS / Z-2371, 3
A salt spray test was conducted in which 5% salt water at 5 ° C. was sprayed on each sample for 100 hours. FIGS. 5 (a) to 5 (d) show each sample No. after the test. The photographs of the appearance of Nos. 1 to 4 are shown in order. From now on, the sample no. 3
And sample No. No. 4 hardly corroded even under the present test conditions, indicating that it exhibited excellent corrosion resistance.

(Example 6) Cast magnesium alloy (AM
FIG. 6 shows an appearance photograph of the test piece of No. 60) after the same salt spray test as in Example 5. The test piece used here was the sample No. without surface treatment. Sample No. 5 which was coated with MoS _{2 in} the same manner as in Example 1 without performing anodizing treatment. Sample No. 6 which was coated with MoS ₂ after anodic oxidation. 7 and the state of each sample after the test result is shown in order in FIGS. 6 (a) to 6 (c).

From the results of Example 5 and Example 6, the coated member subjected to the surface treatment according to the present invention was hardly corroded even when the magnesium base material was a cast material, like the wrought material. It was confirmed that excellent corrosion resistance was exhibited. On the other hand, when the anodic oxidation treatment was not performed in advance (in the case of Sample No. 6), it was also found that the coating layer peeled off during the test, and the magnesium base material was largely corroded. Therefore, it was also clarified that the anodic oxide layer was necessary for improving the adhesion of the coating layer.
Each of the samples described above and the test piece obtained in Example 3 (Sample N
o. FIG. 7 shows a graph comparing the surface roughness (ten-point average roughness) before and after the salt spray test with respect to 8). From this, it was found that all the test pieces according to the present invention were very excellent in corrosion resistance.

Example 7 Magnesium alloy for casting (A
M212) having a diameter of 6 mmφ and a length of 14 mm was subjected to the same anodic oxidation treatment as in Example 1, and then to the same Cr ₂ O ₃ coating treatment as in Example 3. As a result of observing the cross section of the test piece with an optical microscope,
An oxide layer (anodized layer) containing Mg and a Cr oxide layer (coating layer) having a thickness of about 5 μm were formed on the surface thereof. Then, for this test piece cross section, a load of 0.2
The Vickers hardness was measured at 5N. As a result, the hardness of the inside of the magnesium base material (the center part of the test piece) of the covering member was Hv60, whereas the hardness of the oxide layer containing Mg was Hv120 to 150. Since the outermost Cr oxide layer was as thin as about 5 μm, its hardness could not be measured directly. However, when pressed against glass, its outermost surface was hard enough to scratch the glass. It became clear that there was.

Next, using the test piece (pin) according to this embodiment and the test piece (pin) without surface treatment,
5C (disc) mating material at room temperature, no lubrication, sliding speed 0.1m / s, friction distance 250m, surface pressure 0.1MPa
A pin-on-disk test was performed under the following conditions. As a result, magnesium alloy without surface treatment (AM
In the case of (212), the abrasion amount was about 0.2 mg / mm ² , and seizure was observed from the appearance after the test.

On the other hand, in the test piece subjected to the surface treatment of this example, there was almost no wear and no trace of seizure was observed. Similarly, when a pin-on-disk test was performed on the test piece obtained in the same manner as in Example 1, under the same conditions, the test piece was hardly worn, and no trace of seizure was observed.

From the above results, in the coated member subjected to the surface treatment according to the present invention, the coating layer constituting the surface film is firmly adhered to the magnesium base material, and the surface film has the corrosion resistance. It was also found that the abrasion resistance and the seizure resistance were also very effective.

[0041]

According to the coating member of the present invention, the coating layer, which is the surface film, is firmly adhered to the magnesium base, and exhibits excellent corrosion resistance, abrasion resistance and seizure resistance. For this reason,
The use of the covering member has been further expanded, and it has become possible to use it for various products in various fields. Further, according to the surface treatment method for a magnesium base material of the present invention, such a coated member can be efficiently obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing a result of a line analysis by an X-ray microanalyzer, showing a cross section of a test piece after an anodizing step according to Example 1.

FIGS. 2A and 2B are views showing a cross section of a test piece after a coating process according to Example 1, wherein FIG. 2A is an enlarged photograph of the cross section, and FIG. It is a graph which shows an analysis result.

FIG. 3 is a graph showing a result of a line analysis by an X-ray microanalyzer, showing a state of a cross section of a test piece after a coating process according to Example 3.

FIG. 4 is a graph showing a result of a line analysis by an X-ray microanalyzer, showing a state of a cross section of a test piece after a coating treatment step according to Example 4.

5 is a photograph showing a state of a surface after a salt spray test performed on each sample shown in Example 5. FIG.

6 is a photograph showing a state of a surface after a salt spray test performed on each sample shown in Example 6. FIG.

FIG. 7 is a graph comparing the surface roughness before and after the salt spray test performed on each sample shown in Example 7.

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[Procedure amendment]

[Submission Date] May 30, 2001 (2001.5.3)
0)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Figure 2

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Claims (11)

[Claims] 1. A magnesium base containing magnesium (Mg) as a main component, an oxide layer formed on the magnesium base, an oxide of a Group VIa element formed on the oxide layer, and / or
Or a coating layer made of a sulfide. 2. The method according to claim 1, wherein said oxide layer is an anodized layer.
The covering member as described in the above. 3. An oxide of a Group VIa element comprising at least one of chromium oxide, molybdenum oxide and tungsten oxide.
The covering member according to claim 1 or 2, wherein the sulfide of the Group VIa element is molybdenum disulfide. 4. An oxidation step of forming an oxide layer on a surface of a magnesium base material containing magnesium (Mg) as a main component, and an oxide of a Group VIa element and / or an oxide on the oxide layer formed by the oxidation step. A coating treatment step of forming a coating layer made of a sulfide; and a method of surface treating a magnesium base material. 5. The method according to claim 4, wherein the oxidizing step is an anodic oxidizing step of forming an anodic oxide layer on the surface of the magnesium base. 6. An oxide of a Group VIa element comprising at least one of chromium oxide, molybdenum oxide and tungsten oxide.
5. The method for surface treating a magnesium substrate according to claim 4, wherein the sulfide of the Group VIa element is molybdenum disulfide. 7. The method according to claim 7, wherein the coating step comprises:
5. The magnesium substrate according to claim 4, further comprising: a coating step of coating a coating agent mixed with sulfide on the oxide layer; and a heating step of heating the oxide and / or sulfide after the coating step. 6. Surface treatment method. 8. The coating step may be a dipping method in which the oxide layer is immersed in the coating agent, a brush coating method in which the coating agent is brush-coated on the oxide layer, or a spraying method in which the coating agent is sprayed on the oxide layer. The surface treatment method for a magnesium substrate according to claim 7, wherein the step is performed by using any one of spraying methods. 9. The method according to claim 7, wherein the coating agent is a mixture of a resin dissolved in a solvent and the oxide and / or sulfide. 10. The method according to claim 7, wherein the coating agent further contains at least one of a fluororesin, boron nitride (BN) and graphite. 11. The heating step comprises: adjusting the heating temperature to 150 to 4;
The method for surface treating a magnesium base according to claim 7, which is a step of setting the temperature to 50 ° C.