JP2016030860A - Magnesium member comprising film with excellent conductivity and corrosion resistance, and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a magnesium member comprising a film with excellent conductivity and corrosion resistance, by a simple method.SOLUTION: A method for producing a magnesium member has a preparation step of preparing a magnesium material predominantly composed of magnesium, and a film formation step of forming a film by bringing a cyclic compound having a π electron and water into contact with at least part of the surface of the magnesium material, in an atmosphere of heating and pressurization.SELECTED DRAWING: None

Description

  The present invention relates to a magnesium-based member having a film excellent in conductivity and corrosion resistance and a method for producing the same.

  Magnesium or magnesium alloy has advantages such as light weight, high rigidity compared to resin materials, recyclable points, etc., and in recent years, mobile phones (including smartphones), portable information terminals, It is used in the case of electronic devices such as cameras and personal computers.

However, since the base metal magnesium is a highly active metal, magnesium or a magnesium alloy (hereinafter, these may be collectively referred to as “magnesium-based materials”) is susceptible to corrosion due to oxidation of the surface. 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 for a magnesium substrate that can form a highly corrosion-resistant film at a low cost, a magnesium substrate made of magnesium or a magnesium alloy is heat-treated in a humidified atmosphere to form a magnesium oxide film on the surface. A surface treatment method of a magnesium base to be formed is known (for example, see Patent Document 1).
Further, as a method for economically treating magnesium or its alloy product without causing environmental problems, a surface treatment method for treating magnesium or a magnesium alloy product with a treatment liquid containing diammonium hydrogen phosphate is known. (For example, refer to Patent Document 2).
Further, as a surface treatment method of magnesium material or magnesium alloy having high corrosion resistance without using harmful chromate, a chemical method using a neutral solution or an alkaline solution as a treatment solution on the surface of the magnesium material or magnesium alloy Alternatively, a surface treatment method of a magnesium material or a magnesium alloy that is processed in a high-pressure steam atmosphere after forming an oxide film by any one of electrochemical methods is known (see, for example, Patent Document 3).
In addition, as a surface treatment method for castings that is low-cost and has no concern about human influence, the castings made by casting magnesium, magnesium alloys, etc. are heated and pressurized in an aqueous solution such as phosphate. A casting surface treatment method for performing the surface treatment of the casting is known (see, for example, Patent Document 4).
In addition, as a surface treatment method of magnesium material or magnesium alloy that does not use chemicals and has high production efficiency, a blast treatment step of performing wet blast treatment on the surface of the magnesium material or magnesium alloy, and the magnesium material or A surface treatment method of a magnesium material or a magnesium alloy having a water vapor treatment step of heat treating a magnesium alloy at a relative humidity of 80% or more is known (for example, see Patent Document 5).
In addition, as a surface treatment method of magnesium alloy material for producing a magnesium alloy material with excellent corrosion resistance and impact resistance, the surface of the magnesium alloy is subjected to blasting, coating treatment, chemical conversion treatment, pickling treatment, rust prevention treatment, removal A surface treatment method for a magnesium alloy that forms a magnesium hydroxide film by steam curing the magnesium alloy with water without performing at least one pretreatment selected from rust treatment, oxide film removal treatment, and degreasing treatment is known. (For example, refer to Patent Document 6).
In addition, as a method for producing a magnesium or magnesium alloy product having an anodic oxide film having both electrical conductivity and excellent corrosion resistance on its surface, phosphate radicals (free phosphoric acid, phosphate, hydrogen phosphate, phosphorus Magnesium containing 0.1 to 1 mol / L of acid dihydrogen salt) and immersing magnesium or a magnesium alloy in an electrolyte having a pH of 8 to 14 and anodizing the surface Or the manufacturing method of a magnesium alloy product is known (for example, refer patent document 7).

JP 2006-28539 A JP-A-11-29874 JP 2000-64057 A JP 2002-322567 A JP 2005-54238 A JP 2010-7147 A JP 2008-214761 A

As described above, in order to improve the corrosion resistance of the magnesium-based material, a technique for forming a corrosion-resistant film on the surface of the magnesium-based material is known (for example, Patent Documents 1 to 6 above).
However, in a magnesium-based member having a structure in which a corrosion-resistant film is formed on the surface of the magnesium-based material, the conductivity of the entire magnesium-based member may be impaired by the corrosion-resistant film. For example, when the magnesium-based member whose conductivity is impaired is used as a casing of an electronic device, charging occurs in the casing of the electronic device, and this charging may adversely affect the electronic circuit.
Further, the corrosion resistance of the coating itself may be required to be more excellent.

In view of the above-described conductivity (electric conductivity), in Patent Document 7, a magnesium-based member (magnesium or magnesium alloy product) having an anodized film on its surface that has both electrical conductivity and excellent corrosion resistance, and its manufacture. 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 complicated apparatus for anodization, and the apparatus needs to be enlarged to form a thick film.

This invention is made | formed in view of the above, and makes it a subject to achieve the following objectives.
That is, the objective of this invention is providing 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 with a simple method.
Moreover, the objective of this invention is providing the magnesium-type member provided with the film | membrane excellent in electroconductivity and corrosion resistance.

Specific means for solving the above-described problems are as follows.
<1> A preparation step of preparing a magnesium-based material containing magnesium as a main component, a cyclic compound having π electrons, and water for at least a part of the surface of the magnesium-based material in a heating and pressurizing atmosphere. And a film forming step of forming a film by bringing it into contact with each other.
<2> The contact includes bringing at least part of the surface of the magnesium-based material into contact with vapor generated from the aqueous solution containing the cyclic compound and water, and at least part of the magnesium-based material. The method for producing a magnesium-based member according to <1>, which is performed by at least one of immersion in an aqueous solution containing the cyclic compound and water.
<3> The method for producing a magnesium-based member according to <1> or <2>, wherein the pressure in the heating and pressurizing atmosphere is 0.2 MPa to 1.2 MPa.
<4> The method for producing a magnesium-based member according to any one of <1> to <3>, wherein the temperature of the heating and pressurizing atmosphere is 120 ° C to 200 ° C.
<5> Any one of <1> to <4>, wherein the cyclic compound includes at least one of a 5-membered ring structure having π electrons and a 6-membered ring structure having π electrons and a hydroxyl group in one molecule. 2. A method for producing a magnesium-based member according to item 1.
<6> The method for producing a magnesium-based member according to any one of <1> to <5>, wherein the cyclic compound includes an unsaturated lactone structure and a hydroxyl group in one molecule.
<7> The method for producing a magnesium-based member according to any one of <1> to <6>, wherein the molecular weight of the 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.
<9> The method for producing a magnesium-based member according to any one of <1> to <8>, wherein the film has a thickness of 0.5 μm to 100 μm.
<10> The film forming step is a group consisting of blast treatment, coating treatment, chemical conversion treatment, pickling treatment, rust prevention treatment, rust removal treatment, oxide film removal treatment, and degreasing treatment on the surface of the magnesium-based material. The method for producing a magnesium-based member according to any one of <1> to <9>, wherein the film is formed without performing at least one kind of pretreatment selected from:
<11> 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, comprising a composite material containing magnesium hydroxide and carbon atoms 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 with a simple method is provided.
Moreover, according to this invention, a magnesium-type member provided with the film | membrane excellent in electroconductivity and corrosion resistance is provided.

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

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

<Manufacturing method of magnesium-based member>
The method for producing a magnesium-based member of the present invention (hereinafter also referred to as “manufacturing method of the present invention”) includes a preparation step of preparing a magnesium-based material containing magnesium (Mg) as a main component, and a heating and pressurizing atmosphere. A film forming step of forming a film by bringing a compound containing a cyclic structure having π electrons into contact with water on at least a part of the surface of the magnesium-based material; The manufacturing method of the magnesium-type member of this invention may have another process as needed.

In the present invention, the “magnesium-based material” refers to an object to be subjected to a film formation process (that is, film formation).
Further, in the present invention, the “magnesium-based member” refers to a resultant product after the film-forming process (that is, film formation) 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 a magnesium-type raw material.

According to the production method of the present invention, a magnesium-based member having a film excellent in conductivity and corrosion resistance can be produced by a simple method.
More specifically, in the film forming step of the present invention, the above “simple method”, in a heating and pressurizing atmosphere, at least a part of the surface of the magnesium-based material, a compound containing a cyclic structure having π electrons, A film can be formed by a simple method of contacting water.
Here, the concept of “water” includes not only liquid water but also gaseous water (ie, water vapor).

The reason why the film formed by the production method of the present invention is excellent in conductivity and corrosion resistance is presumed as follows.
That is, the film is a magnesium hydroxide-based film, and this magnesium hydroxide-based film is considered to contribute to corrosion resistance.
Further, this magnesium hydroxide film is a film (composite film) made of a composite material containing magnesium hydroxide and carbon atoms derived from a cyclic compound having π electrons (that is, carbon atoms having π electrons). It is considered that π electrons are included in the film. It is considered that π electrons contained in the film contribute to conductivity.

Furthermore, the film formed by the production method of the present invention is excellent in corrosion resistance as compared with a conventional magnesium hydroxide film (for example, the magnesium hydroxide film described in Patent Document 6).
This is because the film in the present invention is a composite film made of a composite material containing magnesium hydroxide particles and carbon particles (carbon particles) having a size different from that of the magnesium hydroxide particles. This is thought to be because the denseness of the film is higher than that of the film consisting only of the above.

  Furthermore, in the manufacturing method of this invention, the electroconductivity of a film | membrane can also be adjusted by adjusting the quantity of the cyclic compound which has (pi) electron in a film | membrane formation process.

Conventionally, a resin film is sometimes used as a film provided on a magnesium-based material.
Compared 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 thus has an advantage of high rigidity.

  Further, the production method of the present invention is a simple method as compared with the conventional method for forming a film by an anodic oxidation method, and more specifically has the following advantages.

  That is, the anodic oxidation method needs to be performed using a complicated apparatus including an electrode for anodic oxidation, but the manufacturing method of the present invention can be performed using a simpler apparatus.

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

Further, in the anodic oxidation method, since the film is only applied to the surface of the base material (magnesium-based material), the adhesion between the base material and the film may be poor. For example, in the anodic oxidation method, a crack may occur in the film when the substrate is bent.
On the other hand, the film in the present invention is excellent in adhesion to the base material, and the above-described cracks are difficult to occur.
The reason for this is considered that the film in the present invention grows directly from the material of the base material (magnesium-based material). In other words, it is considered that the film in the present invention is a film formed by modifying (converting) the surface layer portion of the base material (magnesium-based material).

Further, in the anodic oxidation method, when the substrate has a pipe shape, a film can be formed on the outer peripheral surface of the pipe shape, but a film cannot be formed on the inner peripheral surface of the pipe shape. Yes. In addition, the anodic oxidation method has a problem that when the substrate has a concavo-convex shape, the concave and convex portions of the concavo-convex shape cannot be surface treated.
On the other hand, in the manufacturing method of the present invention, a film can be efficiently and uniformly formed on a substrate having a complicated shape (pipe shape, uneven shape, etc.).
Furthermore, in the production method of the present invention, a film can be efficiently and uniformly formed on a large-sized substrate.

The contact in the film forming process is
Contacting at least part of the surface of the magnesium-based material with steam generated from an aqueous solution containing the cyclic compound and water (hereinafter also referred to as “operation 1” or “steam curing”); and
Immersing 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 an advantage of excellent film formation efficiency. In addition, since the operation 2 (immersion) is less likely to be restricted by the vapor pressure of the cyclic compound, there is an advantage that the range of selection of the type of the cyclic compound is wide.
The contact may be performed by either 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, either the operation 1 or the operation 2 may be performed first.

In the operation 1 (steam curing) and the operation 2 (dipping), an aqueous solution containing the cyclic compound and water is used.
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, it can be 0.2-2.0 mass% with respect to aqueous solution whole quantity, for example. .

The pressure of the heating and pressurizing atmosphere is preferably 0.2 MPa to 1.2 MPa.
When the pressure is 0.2 MPa or more, the film formation efficiency is further improved.
When the pressure is 1.2 MPa or less, it is advantageous in terms of productivity and cost. For example, when the pressure is 1.2 MPa or less, it is not necessary to use an expensive device having resistance to a pressure exceeding 1.2 MPa as an apparatus (for example, an autoclave) used in the film forming process. For this reason, the cost of an apparatus 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.
When the temperature is 120 ° C. or higher, the film formation efficiency is further improved.
When the temperature is 200 ° C. or less, it is advantageous in terms of productivity and cost. For example, when the temperature is 200 ° C. or lower, it is not necessary to use an expensive device having resistance to a high pressure due to a temperature higher than 200 ° C. as an apparatus (for example, an autoclave) used in the film forming process. For this reason, the cost of an apparatus 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 π electrons preferably includes a cyclic structure having π electrons in one molecule, and at least one of a five-membered ring structure having π electrons and a six-membered ring structure having π electrons in one molecule. It is more preferable that one molecule contains at least one of a 5-membered ring structure having π electrons and a 6-membered ring structure having π electrons, and a hydroxyl group.
When the cyclic compound having π electrons has a hydroxyl group in one molecule, the solubility in water can be further improved when preparing an aqueous solution in operation 1 (steam curing) and operation 2 (immersion).

The cyclic compound may be a low molecular compound or a high molecular compound.
The cyclic compound is preferably a low molecular 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 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.

The cyclic compound is preferably a compound containing an unsaturated lactone structure and a hydroxyl group in one molecule.
Here, the unsaturated lactone structure is an example of a 5-membered ring structure having π electrons.

Specific examples of the cyclic compound include at least one of ascorbic acid and a salt thereof (hereinafter also referred to as “ascorbic acid and the like”).
Ascorbic acid and the like have advantages such as low environmental burden and easy availability in addition to the advantages of excellent film formability and water solubility.
Examples of the salt of ascorbic acid include sodium ascorbate, potassium ascorbate, and calcium ascorbate.

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

Moreover, as for the thickness of the membrane | film | coat formed at the said membrane | film | coat 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 coating is 100 μm or less, peeling of the coating and cracking (crack) due to thermal shock or stress can be further suppressed.
The thickness of the film is more preferably 3 μm to 100 μm, and particularly preferably 3 μm to 50 μm.

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

  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 a step of manufacturing a magnesium-based material.

Here, the “magnesium-based material containing magnesium as a main component” refers to a material in which the component having the largest content (mass%) is magnesium.
Examples of the magnesium-based material include magnesium (pure magnesium) and a magnesium alloy.
The magnesium content 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, still more preferably 90% by weight or more, based on the total amount of the magnesium-based material. 95 weight% or more is especially preferable.

  The metal element contained in the magnesium alloy is not particularly limited to metal elements other than magnesium (Mg), and examples thereof include aluminum (Al), zinc (Zn), manganese (Mn), and calcium (Ca). It is done.

There is no restriction | limiting in particular in the shape of a magnesium-type raw material, It can be set as all shapes, such as a board | substrate shape, a lump shape, a pipe shape, and a shape which has an unevenness | corrugation.
More specifically, as the shape of the magnesium-based material, the shape of the casing of electronic devices (cell phones (including smartphones), personal digital assistants, cameras, personal computers, etc.), the constituent members of various displays such as plasma displays, etc. The shape, the shape of the structural member of the transportation equipment, and the like.

<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 and at least a part of the surface of the magnesium-based material in a heated and pressurized atmosphere. .
The preferred embodiment of the film forming step is as described above.
Although the time of the said contact can be suitably selected according to the film thickness of the membrane | film | coat to form, it can be set within the range of 2 hours-12 hours, for example.

The manufacturing method of this invention may have other processes other than a preparatory process and a film formation process as needed.
Other processes include known processes such as a cleaning process for cleaning the magnesium-based material or the magnesium-based member and a post-processing process for post-processing the film obtained by the adding process.
However, as described above, from the viewpoint of simplifying the production process, the production method of the present invention includes blast treatment, coating treatment, chemical conversion treatment, pickling treatment, rust prevention treatment, rust removal treatment, oxide film removal treatment, and It is preferable not to include at least one kind of pretreatment selected from the group consisting of degreasing treatments.

≪Magnesium-based material≫
The magnesium-based member of the present invention includes 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 includes magnesium hydroxide and carbon atoms having π electrons. A film made of a composite material and having a carbon atom content of 10 atomic% to 60 atomic%. The magnesium-based member of the present invention may include other members as necessary.
Since the magnesium-based member of the present invention includes 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 can be the reason described in the description of the production 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 production 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 coating is 10 atomic% to 60 atomic%.
The carbon atom content of 10 atomic% or more means that the film contains intentionally added carbon atoms in addition to carbon atoms as impurities (see Comparative Example 1 described later). means. The carbon atom content is preferably 20 atomic percent or more, and more preferably 25 atomic percent.
On the other hand, the carbon atom content in the film being 60 atom% 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.

In the above film, a carbon atom having π electrons means a carbon atom having sp2 hybrid orbitals.
In the above film, the presence of carbon atoms having π electrons can be confirmed by electron spin resonance (ESR).

  Although there is no restriction | limiting in particular in the method to manufacture the magnesium-type member of this invention, The manufacturing method of this invention mentioned above is suitable.

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

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to a following example.

[Example 1]
<Manufacture of magnesium-based members>
(Preparation process)
As the magnesium-based material, a Mg alloy base material 1 having a size of 20 mm long × 20 mm wide × 1.5 mm thick was prepared. This Mg alloy base material 1 is obtained by cutting an extruded material manufactured by Kieste Knos Co., Ltd. into the above size. The material of the extruded material (that is, the material of the Mg alloy base material 1) is AZ31 (a magnesium alloy containing about 3% by mass of aluminum and about 1% by mass of zinc) defined by the ASTM standard.

(Film formation process)
20 mL of an aqueous solution containing 0.3 g of ascorbic acid (hereinafter also referred to as “AA” (Ascorbic Acid)) was placed in the autoclave, and then the Mg alloy substrate 1 was immersed in this 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 part of the Mg alloy base material 1 was modified (converted) to form a film.
Thus, an Mg alloy sample (magnesium-based member) having a structure in which the surface layer portion of the Mg alloy base material 1 was modified (converted) into a film was obtained.

<Measurement and evaluation>
(X-ray diffraction measurement of film of Mg alloy sample)
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 film)
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.

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

(Evaluation of corrosion resistance of Mg alloy sample film)
A 5 mass% salt aqueous solution (manufactured by Kanto Chemical Co., Inc.) was placed in a sealed container and the temperature was adjusted to 35 ° C., and the Mg alloy sample was immersed in the temperature-controlled salt aqueous solution for 72 hours.
Subsequently, the Mg alloy sample was taken out from the salt aqueous 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: Corrosion was not confirmed by visual inspection.
B: Corrosion was confirmed by visual inspection.

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

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

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

As shown in Table 1, in the Mg alloy samples of Examples 1 to 3 using an aqueous solution of ascorbic acid (AA) in the film forming step, Mg of Comparative Example 1 using water instead of the AA aqueous solution in the film forming step. Compared with the alloy sample, the corrosion resistance of the coating was excellent, and the volume resistivity of the coating was low and the conductivity was excellent.
Specifically, the film of the Mg alloy sample of Comparative Example 1 was an insulator having a volume resistivity on the order of 10 ¹¹ Ω · cm. 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 was lowered. In Examples 1 to 3, the volume resistivity tended to decrease as the amount of AA increased.
Moreover, the carbon content of the film | membrane in Examples 1-3 showed the value higher than the carbon content of the film | membrane in the comparative example 1. FIG. In Examples 1 to 3, the carbon content in the film tended to increase as the amount of AA added increased.

  The reason why the films of Examples 1 to 3 are more excellent in corrosion resistance than the film of Comparative Example 1 is that the films of Examples 1 to 3 contain magnesium hydroxide particles and It is considered that the denseness of the film was improved as compared with the film of Comparative Example 1 because the carbon (carbon) particles having different sizes were dispersed.

  The reason why the films of Examples 1 to 3 are excellent in conductivity is because the films of Examples 1 to 3 contain carbon atoms having π electrons derived from ascorbic acid (AA) as a raw material. Conceivable. The fact that carbon atoms having π electrons are contained in the film can be theoretically confirmed by an electron spin resonance (ESR) method.

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 patterns in Comparative Example 1, Example 3, Example 2, and Example 1, respectively.
In each 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 °. A diffraction line was observed at the position of. These correspond to the 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 films in Examples 1 to 3 and Comparative Example 1 were films containing magnesium hydroxide.

FIG. 2 shows the Mg alloy samples of Examples 1 to 3 and Comparative Example 1 (that is, the Mg alloy coated with the film), and the Mg alloy substrate 1 that was not subjected to the film forming process (that is, the film). It is a measurement result of the polarization characteristic of Mg alloy which is not covered with.
In FIG. 2, (a) is the polarization characteristics of the Mg alloy substrate 1 (“Bare AZ31”) not covered with the film, and (b), (c), (d), and (e) are In 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 a Mg alloy sample.

2, (e) From (e) and (a), (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 coated with the coating was no less than 500 mV compared to the corrosion potential of the Mg alloy substrate 1 not coated with the coating.
Further, (e) the corrosion current of the Mg alloy sample of Example 1 and (a) the corrosion current of the Mg alloy base material 1 not covered with the film were 1.5 × 10 ⁻⁹ A / cm ² , respectively. And 8.5 × 10 ⁻⁵ A / cm ² . Thus, the corrosion current of the Mg alloy sample of Example 1 covered with the film showed a value smaller by 4 digits or more than the corrosion current of the Mg alloy substrate 1 not covered with the film.
The above results show that the Mg alloy sample of Example 1 coated with a film is superior in corrosion resistance to the Mg alloy base material 1 not coated with the film.

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

In FIG. 2, (b) (Comparative Example 1 (“AA: 0 g”)) was also confirmed to have better corrosion resistance than the Mg alloy substrate 1 not covered with the film.
However, (b) (Comparative Example 1 (“AA: 0 g”)) is equivalent to (c) (Example 3 (“AA: 0.1 g”)), (d) (Example 2 (“AA: 0.2 g”). )) And (e) (Example 1 (“AA: 0.3 g”)) were inferior in corrosion resistance.

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

Claims (11)

A preparation step of preparing a magnesium-based material containing 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 at least part of the surface of the magnesium-based material in a heating and pressurizing atmosphere;
The manufacturing method of the magnesium-type member which has this. The contact is
Contacting at least part of the surface of the magnesium-based material with vapor generated from an aqueous solution containing the cyclic compound and water; and
The manufacturing method of the magnesium-type member of Claim 1 performed by at least one of immersing at least one part of the said magnesium-type raw material in the aqueous solution containing the said cyclic compound and water.   The method for producing a magnesium-based member according to claim 1 or 2, wherein a pressure of the heating and pressurizing atmosphere is 0.2 MPa to 1.2 MPa.   The method for producing a magnesium-based member according to any one of claims 1 to 3, wherein a temperature of the heating and pressurizing atmosphere is 120 ° C to 200 ° C.   5. The method according to claim 1, wherein the cyclic compound includes at least one of a five-membered ring structure having π electrons and a six-membered ring structure having π electrons in one molecule, and a hydroxyl group. The manufacturing method of the magnesium-type member of description.   The method for producing a magnesium-based member according to any one of claims 1 to 5, wherein the cyclic compound contains an unsaturated lactone structure and a hydroxyl group in one molecule.   The molecular weight of the said cyclic compound is 1000 or less, The manufacturing method of the magnesium-type member of any one of Claims 1-6.   The said cyclic compound is at least one of ascorbic acid and its salt, The manufacturing method of the magnesium-type member of any one of Claims 1-7.   The method for producing a magnesium-based member according to any one of claims 1 to 8, wherein a thickness of the coating is 0.5 µm to 100 µm.   The film forming step is selected from the group consisting of blasting, painting, chemical conversion, pickling, rust prevention, rust removal, oxide film removal, and degreasing on the surface of the magnesium-based material. The method for producing a magnesium-based member according to any one of claims 1 to 9, wherein the coating is formed without performing at least one kind of pretreatment. A magnesium-based material mainly composed of magnesium;
A film covering at least a part of the surface of the magnesium-based material, comprising a composite material containing magnesium hydroxide and π-electron carbon atoms, and having a carbon atom content of 10 atomic% to 60 atomic% A film,
Magnesium-based member with