JP6548183B2 - Method of manufacturing magnesium-based member provided with coating excellent in conductivity and corrosion resistance - Google Patents

Description

  The present invention relates to a magnesium-based member provided with a film excellent in conductivity and corrosion resistance, and a method of manufacturing the same.

  Recently, mobile phones (including smart phones), mobile information terminals, and the like have advantages in that magnesium or magnesium alloy has advantages such as light weight, high rigidity compared to resin materials, and recyclable point. It is used for housings of electronic devices such as cameras and personal computers.

However, since magnesium as a base metal is a highly active metal, magnesium or a magnesium alloy (hereinafter, these may be collectively referred to as "magnesium-based material") has a drawback that the surface is easily oxidized and corroded. There is.
Therefore, surface treatment methods for improving the corrosion resistance of magnesium-based materials have been studied.
For example, as a surface treatment method of a magnesium base material capable of forming a coating having high corrosion resistance at low cost, a magnesium base material made of magnesium or a magnesium alloy is heat treated in a humidified atmosphere to form a magnesium oxide coating on the surface. The surface treatment method of the magnesium base material to form is known (for example, refer to patent documents 1).
Also, as a method capable of economically surface-treating magnesium or its alloy products without causing environmental problems, a surface-treating method is known in which magnesium or magnesium alloy products are treated with a treatment solution containing diammonium hydrogen phosphate (See, for example, Patent Document 2).
Also, as a surface treatment method of magnesium material or magnesium alloy with high corrosion resistance without using harmful chromic acid, a chemical method using a neutral solution or alkaline solution as a treatment liquid on the surface of magnesium material or magnesium alloy Or after forming an oxide film by any method of an electrochemical method, the surface treatment method of the magnesium material or magnesium alloy processed in a high pressure steam atmosphere is known (for example, refer to patent documents 3).
In addition, as a method for surface treatment of castings at low cost with no concern for human beings, the castings made by casting magnesium, magnesium alloy, etc. are heated and pressurized in an aqueous solution such as phosphate. The surface treatment method of the cast which surface-treats the above-mentioned cast is known (for example, refer to patent documents 4).
In addition, as a method of surface treatment of magnesium material or magnesium alloy with high production efficiency without using a chemical, a blasting step of wet blasting the surface of the magnesium material or magnesium alloy, and the magnesium material or the above magnesium material after this blasting step There is known a surface treatment method of a magnesium material or a magnesium alloy having a steam treatment step of heat treating the magnesium alloy at a relative humidity of 80% or more (see, for example, Patent Document 5).
Moreover, as a surface treatment method of a magnesium alloy material for producing a magnesium alloy material excellent in corrosion resistance and impact resistance, the surface of the magnesium alloy is subjected to blast treatment, painting treatment, chemical treatment, acid pickling treatment, rust prevention treatment, removal There is known a surface treatment method of a magnesium alloy to form a magnesium hydroxide film by vapor curing the magnesium alloy with water without performing at least one kind of pretreatment selected from rust treatment, oxide film removal treatment and degreasing treatment. (See, for example, Patent Document 6).
In addition, as a method of producing a magnesium or magnesium alloy product having an anodic oxide film having both electrical conductivity and excellent corrosion resistance on its surface, phosphate root (free phosphate, phosphate, hydrogen phosphate, phosphorus Magnesium or magnesium alloy is immersed in an electrolytic solution containing 0.1 to 1 mol / L of an acid dihydrogen salt and contained at 0.1 to 1 mol / L and having a pH of 8 to 14, and the surface is anodically oxidized Alternatively, methods for producing magnesium alloy products are known (see, for example, Patent Document 7).

JP, 2006-28539, A Japanese Patent Application Laid-Open No. 11-29874 JP 2000-64057 A JP 2002-322567 A JP, 2005-54238, A JP, 2010-7147, A Unexamined-Japanese-Patent No. 2008-214761

As described above, in order to improve the corrosion resistance of magnesium-based materials, techniques for forming a corrosion-resistant film on the surface of magnesium-based materials are known (for example, Patent Documents 1 to 6 above).
However, in the case of a magnesium-based member having a structure in which a corrosion-resistant film is formed on the surface of a magnesium-based material, the conductivity of the entire magnesium-based member may be impaired by the corrosion-resistant film. For example, in the case where the above-mentioned magnesium-based member having impaired conductivity is used as a housing of an electronic device, the housing of the electronic device may be charged, which may adversely affect the electronic circuit.
Also, better corrosion resistance may be required for the corrosion resistance of the coating itself.

In view of the above-described conductivity (electrical conductivity), in Patent Document 7, a magnesium-based member (magnesium or magnesium alloy product) having an anodic oxide film having both electrical conductivity and excellent corrosion resistance on its surface and its production A method has been proposed.
However, the manufacturing method described in Patent Document 7 tends to be complicated. For example, the manufacturing method described in Patent Document 7 requires a complex apparatus for anodic oxidation, and further, the apparatus needs to be enlarged in order to form a thick film.

The present invention has been made in view of the above, and an object thereof is to achieve the following object.
That is, an object of the present invention is to provide a method of manufacturing a magnesium-based member capable of manufacturing a magnesium-based member provided with a film excellent in conductivity and corrosion resistance by a simple method.
Another object of the present invention is to provide a magnesium-based member provided with a film excellent in conductivity and corrosion resistance.

The specific means for solving the said subject are as follows.
<1> A preparation step of preparing a magnesium-based material having magnesium as a main component, a cyclic compound having π electrons with respect to at least a part of the surface of the magnesium-based material in a heating and pressurizing atmosphere, and water And a film forming step of forming a film by bringing the film into contact with one another.
<2> The contacting includes contacting at least a portion of the surface of the magnesium-based material with a vapor generated from an aqueous solution containing the cyclic compound and water, and at least a portion of the magnesium-based material, The manufacturing method of the magnesium-type member as described in <1> performed by at least one of immersing in the aqueous solution containing the said cyclic compound and water.
The manufacturing method of the magnesium-type member as described in <1> or <2> whose pressure of the <3> above-mentioned heating-pressing atmosphere is 0.2 Mpa-1.2 Mpa.
The manufacturing method of the magnesium-type member of any one of <1>-<3> whose temperature of the <4> above-mentioned heating / pressing atmosphere is 120 degreeC-200 degreeC.
<5> Any one of <1> to <4>, wherein the cyclic compound contains at least one of a 5-membered ring structure having a π electron and a 6-membered ring structure having a π electron in one molecule, and a hydroxyl group. The manufacturing method of the magnesium-type member of 1 item.
<6> The method for producing a magnesium-based member according to any one of <1> to <5>, wherein the cyclic compound contains an unsaturated lactone structure and a hydroxyl group in one molecule.
The manufacturing method of the magnesium-type member of any one of <1>-<6> whose molecular weight of the <7> above-mentioned cyclic compound is 1000 or less.
<8> The method for producing a magnesium-based member according to any one of <1> to <7>, wherein the cyclic compound is at least one of ascorbic acid and a salt thereof.
The manufacturing method of the magnesium-type member of any one of <1>-<8> whose thickness of the <9> above-mentioned film | membrane is 0.5 micrometer-100 micrometers.
<10> The film forming step is a group consisting of blasting, painting, chemical conversion treatment, pickling treatment, rust prevention treatment, rusting treatment, oxide film removal treatment, and degreasing treatment on the surface of the magnesium-based material. The manufacturing method of the magnesium-type member of any one of <1>-<9> which forms the said film | membrane, without performing at least 1 type of pre-processing selected from <1>.
<11> A composite material comprising a magnesium-based material containing magnesium as a main component, and a film covering at least a part of the surface of the magnesium-based material, the composite material comprising magnesium hydroxide and a carbon atom having π electrons. And a film having a carbon atom content of 10 atomic% to 60 atomic%.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the magnesium-type member which can manufacture the magnesium-type member provided with the film | membrane excellent in electroconductivity and corrosion resistance by a simple method is provided.
Further, according to the present invention, a magnesium-based member provided with a film excellent in conductivity and corrosion resistance is provided.

1 is an X-ray diffraction diagram of a coating of Mg alloy samples of Examples 1 to 3 and Comparative Example 1. FIG. It is a polarization characteristic of Mg alloy sample of Examples 1-3 and comparative example 1, and Mg alloy substrate 1 which is not covered with a tunic. It is an external appearance photograph before saltwater immersion of the Mg alloy sample of Example 1. FIG. It is an external appearance photograph after salt-water immersion (after immersing in salt water for 72 hours) of the Mg alloy sample of Example 1. FIG. It is an external appearance photograph before saltwater immersion of the Mg alloy sample of comparative example 1. It is an external appearance photograph after salt-water immersion (after immersing in salt water for 72 hours) of the Mg alloy sample of comparative example 1. FIG.

In the present specification, a numerical range represented using “to” means a range including numerical values described before and after “to” as the lower limit value and the upper limit value.
Hereinafter, the magnesium-based member of the present invention and the method for producing the same will be described in detail.

«Method of manufacturing magnesium-based material»
The method for producing a magnesium-based member according to the present invention (hereinafter also referred to as “the production method according to the present invention”) comprises the steps of: preparing a magnesium-based material containing magnesium (Mg) as a main component; And a film forming step of forming a film by bringing a compound containing a cyclic structure having π electrons into contact with at least a part of the surface of the magnesium-based material. The method for producing a magnesium-based member of the present invention may have other steps, if necessary.

In the present invention, the “magnesium-based material” refers to an object to which the treatment of the film forming step (that is, the formation of a film) is applied.
Further, in the present invention, the term "magnesium-based member" refers to the resultant after the treatment of the film forming step (ie, the formation of a film) is performed on the magnesium-based material.
Moreover, the manufacturing method of the magnesium-type member of this invention can also be paraphrased as the surface treatment method of magnesium-type raw material.

According to the manufacturing method of the present invention, a magnesium-based member provided with a film excellent in conductivity and corrosion resistance can be manufactured by a simple method.
More specifically, in the film forming step of the present invention, a compound having a cyclic structure having π electrons with respect to at least a part of the surface of a magnesium-based material in the above-mentioned “simple method”; The film can be formed by a simple method of contacting with water.
Here, the concept of "water" encompasses not only water in the liquid state but also water in the gaseous state (i.e. water vapor).

The reason why the film formed by the manufacturing method of the present invention is excellent in conductivity and corrosion resistance is presumed as follows.
That is, the above-mentioned film is a film of magnesium hydroxide type, and it is considered that this film of magnesium hydroxide type contributes to corrosion resistance.
Furthermore, this magnesium hydroxide-based film is a film (composite film) made of a composite material containing magnesium hydroxide and a carbon atom derived from a cyclic compound having π electrons (that is, a carbon atom having π electrons). It is considered that the film contains π electrons. It is considered that π electrons contained in the film contribute to the conductivity.

Furthermore, the film formed by the manufacturing method of the present invention is excellent in corrosion resistance as compared with the conventional magnesium hydroxide film (for example, the magnesium hydroxide film described in Patent Document 6).
The reason for this is that the film in the present invention is a composite film made of a composite material containing magnesium hydroxide particles and carbon particles (carbon particles) different in size from the magnesium hydroxide particles. This is considered to be due to the high density of the film compared to the film consisting of only.

  Furthermore, in the production method of the present invention, the conductivity of the film can also be adjusted by adjusting the amount of the cyclic compound having π electrons in the film formation step.

Also, conventionally, a resin film has been used as a film provided on a magnesium-based material.
In contrast to the conventional resin film, the film produced by the production method of the present invention is a film mainly composed of an inorganic material, and therefore has an advantage of high rigidity.

  In addition, the manufacturing method of the present invention is a simple method as compared to the conventional method of forming a film by an anodic oxidation method, and has the following advantages in more detail.

  That is, although the anodizing method needs to be performed using a complicated apparatus equipped with an electrode for anodizing, the manufacturing method of the present invention can be performed using a simpler apparatus.

Further, in the anodic oxidation method, since the magnesium-based material is immersed in a solution and conducted through electricity, if the film thickness of the film on the surface of the magnesium-based material becomes large, a large voltage is required, and the device needs to be enlarged.
On the other hand, in the manufacturing method of the present invention, even if the film thickness of the film on the surface of the magnesium-based material is increased, it is not necessary to increase the size of the apparatus.
Therefore, the manufacturing method of the present invention is suitable for mass production in a fixed space (fixed apparatus footprint) as compared with the anodic oxidation method.

Moreover, in the anodic oxidation method, since the film is only applied to the surface of the substrate (magnesium-based material), the adhesion between the substrate and the film may be poor. For example, in the anodic oxidation method, the film may be cracked when the substrate is bent.
On the other hand, the film in the present invention is excellent in the adhesion to the base material, and the above-mentioned cracking hardly occurs.
The reason for this is considered that the film in the present invention is directly grown from the material of the base material (magnesium-based material). In other words, the film in the present invention is considered to be a film formed by reforming (converting) the surface layer portion of the base material (magnesium-based material).

Further, in the anodic oxidation method, when the base material has a pipe shape, a film can be formed on the outer peripheral surface of the pipe shape, but there is a problem that a film can not be formed on the inner peripheral surface of the pipe shape There is. Moreover, in the anodic oxidation method, when the base material has a concavo-convex shape, there is a problem that the recessed part etc. of the concavo-convex shape can not be surface-treated.
On the other hand, according to the manufacturing method of the present invention, a film can be formed efficiently and uniformly even on a substrate having a complicated shape (pipe shape, uneven shape, etc.).
Furthermore, according to the manufacturing method of the present invention, a film can be formed efficiently and uniformly on a large substrate.

The above contact in the film forming step is
Bringing vapor generated from an aqueous solution containing the cyclic compound and water into contact with at least a part of the surface of the magnesium-based material (hereinafter, also referred to as “operation 1” or “steam curing”),
Dipping at least a part of the magnesium-based material in an aqueous solution containing the cyclic compound and water (hereinafter, also referred to as “operation 2” or “immersion”)
It is preferable to carry out by at least one of the above.

Operation 1 (steam curing) has the advantage that the contact operation can be performed more easily.
Operation 2 (immersion) has the advantage of excellent film formation efficiency. Operation 2 (immersion) also has the advantage that the selection of the type of cyclic compound is wide because it is not subject to the restriction of the vapor pressure of the cyclic compound.
The contact may be performed by any one of the operation 1 and the operation 2, or may be performed by both the operation 1 and the operation 2.
When the contact is performed by both the operation 1 and the operation 2, any of the operation 1 and the operation 2 may be performed first.

In the said operation 1 (steam curing) and the said operation 2 (immersion), all use the aqueous solution containing the said cyclic compound and water.
Although content of the said cyclic compound in aqueous solution can be suitably set according to the solubility with respect to the water of the said cyclic compound, For example, it can be 0.2-2.0 mass% with respect to the aqueous solution whole quantity. .

The pressure of the heating and pressurizing atmosphere is preferably 0.2 MPa to 1.2 MPa.
The formation efficiency of a film | membrane improves more that the said pressure is 0.2 Mpa or more.
It is advantageous in the point of productivity or cost that the said pressure is 1.2 Mpa or less. For example, when the pressure is 1.2 MPa or less, it is not necessary to use an expensive device having a pressure resistance of more than 1.2 MPa as an apparatus (for example, an autoclave) used in the film forming step. Therefore, the cost of the device can be reduced.

  The pressure is more preferably 0.5 MPa to 1.2 MPa, still more preferably 0.8 MPa to 1.2 MPa, and particularly preferably 1.0 MPa to 1.15 MPa.

The temperature of the heating and pressurizing atmosphere is 120 ° C to 200 ° C.
The formation efficiency of a film | membrane improves more that the said temperature is 120 degreeC or more.
It is advantageous at the point of productivity or cost that the said temperature is 200 degrees C or less. For example, when the temperature is 200 ° C. or less, it is not necessary to use an expensive device having high pressure resistance due to the temperature over 200 ° C. as an apparatus (for example, an autoclave) used in the film forming step. Therefore, the cost of the device can be reduced.

  As said temperature, 150 to 200 degreeC is more preferable, 170 to 200 degreeC is still more preferable, and 180 to 195 degreeC is especially preferable.

In the film forming step, as the cyclic compound having π electrons, a compound having π electrons and having a cyclic structure can be used without particular limitation.
The cyclic compound having a π electron preferably includes a cyclic structure having a π electron in one molecule, and at least one of a 5-membered ring structure having a π electron and a 6-membered ring structure having a π electron in one molecule. It is more preferable to include in one molecule at least one of a 5-membered ring structure having a π electron and a 6-membered ring structure having a π electron, and a hydroxyl group.
When the cyclic compound having a π electron has a hydroxyl group in one molecule, the solubility in water can be further improved when preparing an aqueous solution in step 1 (vapor curing) and step 2 (immersion).

The cyclic compound may be a low molecular weight compound or a high molecular weight compound.
The above cyclic compound is preferably a low molecular weight compound from the viewpoint of easily obtaining steam when performing the above-described operation 1 (steam curing).
When the cyclic compound is a low molecular weight compound, the molecular weight of the cyclic compound is preferably 1000 or less.
The molecular weight of the cyclic compound is more preferably 800 or less, still more preferably 600 or less, and particularly preferably 400 or less.

Moreover, as said cyclic compound, the compound which contains unsaturated lactone structure and a hydroxyl group in one molecule is preferable.
Here, the unsaturated lactone structure is an example of a 5-membered ring structure having a π electron.

Specific examples of the cyclic compound include at least one of ascorbic acid and a salt thereof (hereinafter, also referred to as "ascorbic acid etc.").
Ascorbic acid and the like have the advantages of low environmental impact and easy availability, in addition to the advantages of excellent film formation and solubility in water.
As a salt of ascorbic acid, sodium ascorbate, potassium ascorbate, calcium ascorbate and the like can be mentioned.

  In addition, although compounds other than ascorbic acid etc. can also be used as said cyclic compound, ascorbic acid etc. are especially preferable from a viewpoint which has the advantage mentioned above.

Moreover, as for the thickness of the film formed at the said film formation process, 0.5 micrometer-100 micrometers are preferable.
When the thickness of the film is 0.5 μm or more, the effect of improving the corrosion resistance by the film is more effectively exhibited.
When the thickness of the film is 100 μm or less, peeling and cracking (cracks) of the film due to thermal shock and stress can be further suppressed.
As for the thickness of the said film, 3 micrometers-100 micrometers are more preferable, and 3 micrometers-50 micrometers are especially preferable.

The film forming step is performed on the surface of the magnesium-based material from the group consisting of blasting, painting, chemical conversion, pickling, rust prevention, rusting removal, oxide film removal, and degreasing. It is preferable to form the film without performing at least one type of pretreatment selected. Thereby, a magnesium system member can be manufactured more simply. For example, by not performing the blasting process, it is possible to suppress the scattering of the fine powder that may occur in the blasting process.
In addition, in the film forming step in the present invention, a good film can be formed without performing the pretreatment.

  Hereinafter, each process of the manufacturing method of this invention is demonstrated.

<Preparation process>
The preparation step is a step of preparing a magnesium-based material containing magnesium as a main component.
The preparation step is a step for convenience, and may be a step of preparing a magnesium-based material that has already been manufactured, or may be a step of manufacturing a magnesium-based material.

Here, "a magnesium-based material having magnesium as a main component" refers to a material in which the component having the largest content (mass%) is magnesium.
Examples of magnesium-based materials include magnesium (pure magnesium) and magnesium alloys.
The content of magnesium in the magnesium-based material is preferably 50% by weight or more, more preferably 70% by weight or more, still more preferably 80% by weight or more, and still more preferably 90% by weight or more based on the total amount of the magnesium-based material. 95% by weight or more is particularly preferred.

  Although there is no restriction | limiting in particular in metal elements other than magnesium (Mg) as a metal element contained in a magnesium alloy, For example, aluminum (Al), zinc (Zn), manganese (Mn), calcium (Ca) etc. are mentioned. Be

The shape of the magnesium-based material is not particularly limited, and may be any shape such as a substrate shape, a lump shape, a pipe shape, and a shape having unevenness.
More specifically, as the shape of the magnesium-based material, the shape of the case of electronic devices (such as mobile phones (including smart phones), portable information terminals, cameras, personal computers, etc.), and components of various displays such as plasma displays The shape, the shape of the structural member of the transport device, etc. may be mentioned.

<Film formation process>
The film forming step is a step of forming a film by bringing a compound containing a cyclic structure having π electrons into contact with water with respect to at least a part of the surface of the magnesium-based material in a heating and pressurizing atmosphere. .
The preferable aspect of a film formation process is as having mentioned above.
Although the time of the said contact can be suitably selected according to the film thickness of the film | membrane which it is going to form, it can be made into the range of 2 hours-12 hours, for example.

The production method of the present invention may have other steps other than the preparation step and the film formation step, as necessary.
Other steps include known steps such as a washing step of washing the magnesium-based material or the magnesium-based member, and a post-treatment step of post-treating the film obtained by the addition step.
However, as described above, from the viewpoint of simplifying the manufacturing process, the manufacturing method of the present invention includes blasting, painting, chemical conversion, acid pickling, rustproofing, rusting removal, oxide film removal, and the like. It is preferred not to include at least one pre-treatment selected from the group consisting of degreasing treatment.

«Magnesium based members»
The magnesium-based member of the present invention is a magnesium-based material containing magnesium as a main component, and a film covering at least a part of the surface of the magnesium-based material, and contains magnesium hydroxide and a carbon atom having π electrons. And a film comprising a composite material and having a carbon atom content of 10 atomic% to 60 atomic%. The magnesium-based member of the present invention may be provided with other members as required.
Since the magnesium-based member of the present invention is provided with a film excellent in conductivity and corrosion resistance, the entire member is excellent in conductivity and corrosion resistance.

The reason why the film in the magnesium-based member of the present invention is excellent in conductivity and corrosion resistance may be the reason described in the above description of the manufacturing method of the present invention.
In the magnesium-based member of the present invention, the preferable ranges of the magnesium-based material and the film are the same as the preferable ranges of the magnesium-based material and the film in the manufacturing method of the present invention, respectively.

In the above film, the carbon atom content refers to a value measured by an energy dispersive X-ray spectrometer.
The carbon atom content in the said film is 10 atomic%-60 atomic%.
The fact that the carbon atom content is 10 atomic% or more means that the film contains intentionally added carbon atoms in addition to the carbon atom as an impurity (see Comparative Example 1 described later). means. 20 atomic% or more is preferable and, as for carbon atom content, 25 atomic% is more preferable.
On the other hand, that the carbon atom content in the film is 60 atomic% or less means that a sufficient amount of magnesium hydroxide is contained in the film. As for carbon atom content, 50 atomic% or less is more preferable.

Further, in the film, a carbon atom having π electrons means a carbon atom having an sp 2 hybrid orbital.
In the above film, the presence of carbon atoms having π electrons can be confirmed by electron spin resonance (ESR).

  Although the method for producing the magnesium-based member of the present invention is not particularly limited, the above-mentioned production method of the present invention is preferable.

  As the applications of the magnesium-based member of the present invention and the magnesium-based member manufactured by the manufacturing method of the present invention described above, electronic devices (mobile phones (including smart phones), portable information terminals, cameras, personal computers) Etc.), components of various displays such as plasma displays, structural members of transportation equipment, and the like.

  Hereinafter, the present invention will be more specifically described by way of examples, but the present invention is not limited to the following examples.

Example 1
<Manufacturing of magnesium-based members>
(Preparation process)
As a magnesium-based material, an Mg alloy substrate 1 of 20 mm long × 20 mm wide × 1.5 mm thick was prepared. The Mg alloy base material 1 is obtained by cutting an extruded material manufactured by Kaes Technos Co., Ltd. to the above size. The material of the extruded material (i.e., the material of the Mg alloy base 1) is AZ31 (a magnesium alloy containing about 3% by mass of aluminum and about 1% by mass of zinc) specified by ASTM.

(Film formation process)
In an autoclave, 20 mL of an aqueous solution containing 0.3 g of ascorbic acid (hereinafter, also referred to as "AA" (Ascorbic Acid)) was placed, and then the Mg alloy substrate 1 was immersed in the aqueous solution.
Next, the inside of the autoclave was adjusted to a temperature of 190 ° C. and a pressure of 1.1 MPa, and heat treatment was performed at this temperature and pressure for 3 hours. Thereby, the surface layer portion of the Mg alloy base material 1 is reformed (converted) to form a film.
Thus, a Mg alloy sample (magnesium-based member) having a structure in which the surface layer portion of the Mg alloy base material 1 was reformed (converted) into a film was obtained.

<Measurement and evaluation>
(X-ray diffraction measurement of the film of Mg alloy sample)
An X-ray diffraction measurement was performed on the film of the Mg alloy sample obtained above.
The results are shown in FIG.

(Measurement of film thickness of Mg alloy sample)
The cross section of the Mg alloy sample obtained above was observed with a scanning electron microscope (manufactured by JEOL Ltd., trade name “JSM-6010LA”), and the film thickness of the film of the Mg alloy sample was measured.
The results are shown in Table 1.

(Measurement of carbon content in film of Mg alloy sample)
The carbon content in the film of the Mg alloy sample was measured using an energy dispersive X-ray spectrometer attached to the scanning electron microscope.
The results are shown in Table 1.

(Conductive evaluation of the film of Mg alloy sample)
As an evaluation of the conductivity of the film of the Mg alloy sample, the volume resistivity of the film was measured by the four-point probe method.
The results are shown in Table 1.

(Evaluation of corrosion resistance of coating of Mg alloy sample)
A 5% by mass aqueous salt solution (manufactured by Kanto Chemical Co., Ltd.) was placed in a closed vessel, and the temperature was adjusted to 35 ° C., and the Mg alloy sample was immersed for 72 hours in the temperature controlled salt solution.
Subsequently, the Mg alloy sample was taken out from the salt solution, visually observed for the presence or absence of corrosion, and the corrosion resistance of the film was evaluated according to the following evaluation criteria.
The results are shown in Table 1 below.
-Evaluation criteria-
A: No corrosion was confirmed by visual inspection.
B: Corrosion was confirmed by visual inspection.

(Measurement of polarization characteristics of Mg alloy sample)
The polarization characteristics of the Mg alloy sample were measured using a potentiostat. In this measurement, the sweep speed of the potential was 0.5 mV / s.
The results are shown in FIG.

Example 2, Example 3, and Comparative Example 1
The same operation as in Example 1 was carried out except that the amount of AA (0.3 g) was changed to the amount shown in Table 1 in the film formation step of Example 1.
In Comparative Example 1, the mass of AA was 0 g. That is, in the film formation step of Comparative Example 1, water was used instead of the aqueous solution of AA.
The results are shown in Table 1 and FIGS. 1 and 2.

In Table 1, “volume resistivity (Ω · cm)” indicates only the number of digits (order).
In Table 1, "at%" shows atomic%.

As shown in Table 1, in the Mg alloy samples of Examples 1 to 3 in which the aqueous solution of ascorbic acid (AA) was used in the film forming step, Mg in Comparative Example 1 using water instead of the aqueous solution of AA in the film forming step. As compared with the alloy sample, the corrosion resistance of the film was excellent, and the volume resistivity of the film was low and the conductivity was excellent.
Specifically, the film of the Mg alloy sample of Comparative Example 1 had a volume resistivity of 10 ¹¹ Ω · cm, and was an insulator. On the other hand, as shown in Examples 1 to 3, when ascorbic acid (AA) was added to water in the film forming step, the volume resistivity decreased. In Examples 1 to 3, the volume resistivity tended to decrease as the amount of AA increased.
Moreover, the carbon content of the film in Examples 1 to 3 showed a value higher than the carbon content of the film in Comparative Example 1. In Examples 1 to 3, the carbon content in the film tended to increase as the addition amount of AA was increased.

  The reason why the coatings of Examples 1 to 3 are superior in corrosion resistance to the coating of Comparative Example 1 is that, in addition to the fact that the coatings of Examples 1 to 3 contain magnesium hydroxide particles, magnesium hydroxide particles are It is considered that the fineness of the film is improved as compared to the film of Comparative Example 1 by dispersing carbon (carbon) particles having different sizes.

  The reason why the coatings of Examples 1 to 3 are excellent in conductivity is that the coatings of Examples 1 to 3 contain a carbon atom having a π electron derived from ascorbic acid (AA) which is a raw material. Conceivable. It can be theoretically confirmed by electron spin resonance (ESR) that the film contains carbon atoms having π electrons.

FIG. 1 is an X-ray diffraction diagram of films of Mg alloy samples of Examples 1 to 3 and Comparative Example 1.
In FIG. 1, (a), (b), (c) and (d) are X-ray diffraction diagrams in Comparative Example 1, Example 3, Example 2 and Example 1, respectively.
In any of (a) to (d) in FIG. 1, 2θ = 18.5, 32.8, 37.9, 50.8, 58.7, 62.1, 68.1 and 72.1 °. At the position of, a diffraction line was observed. These correspond to 001, 100, 101, 102, 110, 111, 200 and 201 diffraction lines of magnesium hydroxide (Mg (OH) ₂ ), respectively (JCPDS No. 44-1482).
From the above results, it was confirmed that the coatings in Examples 1 to 3 and Comparative Example 1 were all coatings containing magnesium hydroxide.

FIG. 2 shows the Mg alloy samples of Examples 1 to 3 and Comparative Example 1 (ie, the Mg alloy coated with the film), and the Mg alloy substrate 1 (ie, the film not subjected to the treatment of the film formation step). It is a measurement result of the polarization characteristic of Mg alloy (uncoated).
In FIG. 2, (a) is the polarization characteristic of the Mg alloy substrate 1 ("Bare AZ31") not covered by the film, and (b), (c), (d) and (e) are Comparative Example 1 (“AA: 0 g”), Example 3 (“AA: 0.1 g”), Example 2 (“AA: 0.2 g”), and Example 1 (“AA: 0.3 g”), respectively. It is a polarization characteristic of Mg alloy sample.

From (e) and (a) in FIG. 2, (e) the corrosion potential of the Mg alloy sample of Example 1 and (a) the corrosion potential of the Mg alloy substrate 1 not covered with the film are respectively: -0.955 V (vs. Ag / AgCl) and -1. 482 V (vs. Ag / AgCl). Thus, the corrosion potential of the Mg alloy sample of Example 1 covered by the film was 500 mV or more noble as compared to the corrosion potential of the Mg alloy substrate 1 not covered by the film.
Further, (e) the corrosion current of the Mg alloy sample of Example 1 and (a) the corrosion current of the Mg alloy substrate 1 not coated with the film are respectively 1.5 × 10 ⁻⁹ A / cm ^2. And 8.5 × 10 ⁻⁵ A / cm ² . Thus, the corrosion current of the Mg alloy sample of Example 1 coated with the film showed a value four orders of magnitude smaller than the corrosion current of the Mg alloy substrate 1 not coated with the film.
The above results show that the Mg alloy sample of Example 1 coated with a film has better corrosion resistance than the Mg alloy substrate 1 not coated with a film.

  Also in (c) (Example 3 (“AA: 0.1 g”)) and (d) (Example 2 (“AA: 0.2 g”) in FIG. 2, (e) (Example 1 (“AA : 0.3 g ′ ′), it was confirmed that the corrosion resistance was superior to that of the Mg alloy substrate 1 not coated with the film.

Also in (b) (comparative example 1 ("AA: 0g")) in FIG. 2, it was confirmed that it is excellent in corrosion resistance rather than Mg alloy base material 1 which is not coat | covered with the film.
However, (b) (Comparative Example 1 ("AA: 0 g")), (c) (Example 3 ("AA: 0.1 g")), (d) (Example 2 ("AA: 0.2 g") It was inferior to corrosion resistance with respect to ()) and (e) (Example 1 ("AA: 0.3 g")).

FIG. 3A is an appearance photograph of the Mg alloy sample of Example 1 before saltwater immersion, and FIG. 3B is an appearance photograph of the Mg alloy sample of Example 1 after saltwater immersion (after being immersed in salt water for 72 hours) is there.
FIG. 4A is an appearance photograph of the Mg alloy sample of Comparative Example 1 before saltwater immersion, and FIG. 4B is an appearance photograph of the Mg alloy sample of Comparative Example 1 after saltwater immersion (after being immersed in salt water for 72 hours) is there.
As apparent from the comparison between FIG. 3A and FIG. 3B, no change in appearance was observed in the Mg alloy sample of Example 1 before and after the saltwater immersion.
However, as apparent from the comparison between FIG. 4A and FIG. 4B, remarkable corrosion occurred in the Mg alloy sample of Comparative Example 1 after the saltwater immersion (FIG. 4B).

Claims (6)

A preparation step of preparing a magnesium-based material having magnesium as a main component,
A film forming step of forming a film by bringing a cyclic compound having π electrons into contact with water with respect to at least a part of the surface of the magnesium-based material under a heating and pressurizing atmosphere;
Have
The manufacturing method of the magnesium-based member whose said cyclic compound is at least one of ascorbic acid and its salt. The contact is
Bringing vapor generated from an aqueous solution containing the cyclic compound and water into contact with at least a portion of the surface of the magnesium-based material;
The method for producing a magnesium-based member according to claim 1, wherein at least a part of the magnesium-based material is performed by at least one of immersion in an aqueous solution containing the cyclic compound and water.   The pressure of the said heating-pressing atmosphere is 0.2 Mpa-1.2 Mpa, The manufacturing method of the magnesium-type member of Claim 1 or Claim 2.   The temperature of the said heating-pressing atmosphere is 120 degreeC-200 degreeC, The manufacturing method of the magnesium-type member of any one of Claims 1-3.   The thickness of the said film is 0.5 micrometer-100 micrometers, The manufacturing method of the magnesium-type member of any one of Claims 1-4.   The film forming step is selected from the group consisting of blasting, painting, chemical conversion, pickling, rustproofing, rusting, oxide film removal, and degreasing on the surface of the magnesium-based material. The method for manufacturing a magnesium-based member according to any one of claims 1 to 5, wherein the film is formed without performing at least one kind of pretreatment.