JP2014125639A - High-corrosion-resistance magnesium-based material and production method thereof, and surface treatment method for magnesium-based material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnesium-based material provided with a film having a corrosion resistance improving effect, its production method and a surface treatment method capable of coping with large members at low costs.SOLUTION: A magnesium-based material consists of a substrate composed of magnesium or a magnesium alloy and a film formed on the surface of the substrate. The film is composed of magnesium hydroxide (Mg(OH)) and an Mg-Al type laminar double hydroxide. For diffraction peaks in an X-ray diffraction of the surface of the film, the ratio (Y/X) of the peak intensity (Y) of the (003) plane of the Mg-Al type laminar double hydroxide to the peak intensity (X) of the (101) plane of the magnesium hydroxide is 0.05-0.3.

Description

  The present invention relates to a magnesium-based material with improved corrosion resistance, a method for producing the same, and a surface treatment method for the magnesium-based material. Specifically, a magnesium-based material having a film having a high anticorrosion effect and excellent adhesion, and a surface of a magnesium-based material that can effectively form such a film and can be applied to a large-sized member at low cost The present invention relates to a treatment method and a method for producing a magnesium-based material including the surface treatment method.

  Magnesium and magnesium alloys (in the present specification, these may be collectively referred to as magnesium-based materials) are extremely light alloys among various metal materials that have been put into practical use. Is larger than aluminum, steel, etc., and is used for structural members of aerospace equipment. In addition to the above-mentioned advantages, there is a possibility of recycling, and in recent years, it has been used for cellular phones, cameras, notebook computer cases, automobile parts, building structural members, and the like.

  The magnesium-based material is a metal material having many advantages as described above, but is a very active metal, and this is a problem. That is, the magnesium-based material has a surface inferior to other metal materials in terms of corrosion resistance, and has a drawback that the surface is easily corroded by oxidation or the like. Therefore, various methods have been studied in order to improve the corrosion resistance of the magnesium-based material.

  The simplest method for improving the corrosion resistance of a magnesium-based material is to directly apply a paint such as an acrylic organic resin to the material. However, such a countermeasure by applying a paint is not fundamental. Magnesium-based materials are highly active, and are often already oxidized at the coating application stage. Even if the coating is applied in this state, the adhesion of the coating film is poor and peeling occurs. Therefore, the application of the paint is useful for finishing the appearance, but cannot itself be a treatment for improving the corrosion resistance. Therefore, various chemical conversion treatments and anodization treatments are known as treatment methods for forming a film in consideration of adhesion to a magnesium-based material.

  For example, Patent Documents 1 and 2 describe a surface treatment method using a treatment liquid containing phosphate as a chemical conversion treatment of a magnesium-based material. In this method, a member made of a magnesium-based material to be treated is immersed in a treatment solution containing a phosphate (diammonium hydrogen phosphate (Patent Document 1), metaphosphoric acid, pyrophosphoric acid, etc. (Patent Document 2)). The film is formed by heating or the like. The chemical conversion treatment using these phosphates as the treatment liquid does not require the use of harmful chromate treatments compared to the chromate treatment, which has been performed for a long time. It is possible.

  Patent Document 3 discloses surface treatment of a magnesium-based material with water vapor. In this surface treatment method, a magnesium-based material is cured with steam at a predetermined temperature to form a film made of magnesium hydroxide on the surface without performing pretreatment such as blast treatment.

JP-A-11-29874 JP 2002-322567 A JP 2010-7147 A

  However, there are still improvements in the conventional surface treatment methods for magnesium-based materials. That is, in the surface treatment methods of Patent Documents 1 and 2, since impurities derived from phosphate remain in the treatment liquid after the surface treatment, it is difficult to reuse, and the cost increases due to the treatment of the used treatment liquid. In addition, since the irregular portion is also attached to the processed material after processing, cleaning processing is necessary. On the other hand, the method described in Patent Document 3 does not have the above-described problems because it uses pure water and is a gas phase treatment using water vapor instead of a solution. However, in the method described in this document, it is difficult to control the film thickness of the film. Therefore, it is difficult to form a uniform film on a large material to be processed.

  In addition, regarding the corrosion resistance of the magnesium-based material produced by the conventional surface treatment method, the film formed by immersion in the treatment liquid as in Patent Documents 1 and 2 is soft and easy to peel off, and its film thickness Is insufficient, and may not act as a sufficient anticorrosion film. Moreover, although the film formed by the method described in Patent Document 3 can be expected to have an anticorrosive effect in terms of applying a water-insoluble film called magnesium hydroxide, there is room for improvement from the uniformity of the film quality as described above. In addition, further improvement of the anticorrosion effect is demanded.

  The present invention has been made based on the background as described above, and provides a magnesium-based material having a film having a higher effect of improving corrosion resistance than the conventional one. The present invention also provides a surface treatment method capable of forming a film having a high effect of improving the corrosion resistance and capable of dealing with a large-sized member at a low cost and a method for producing a magnesium-based material including the surface treatment method.

  The present inventor has intensively studied to solve the above problems, and has developed from a magnesium-based material having a film based on magnesium hydroxide. This is because magnesium hydroxide is a chemically stable substance and is useful as an anticorrosion film as described above. However, magnesium hydroxide is not an anticorrosive film that is not eroded at all, and erosion by anions (anions) such as chloride ions in salt water cannot be avoided.

  Therefore, the present inventor decided to add an element for improving the corrosion resistance while using magnesium hydroxide as the base of the film. And as this additional element, the effective application of the layered double hydroxide (Layered Double Hydroxide: LDH) of Al-Mg type | system | group was discovered.

  The layered double hydroxide is a compound in which a double hydroxide in which trivalent metal (Al) ions are dissolved in a divalent metal (Mg) hydroxide forms a laminated structure. In this laminated structure, since the double hydroxide base layer has a positive charge, a structure in which an anion having a negative charge is sandwiched between the layers is maintained.

  A characteristic of this layered double hydroxide is an anion exchange ability by a host-guest reaction. This is because the layered double hydroxide maintains the structure of its basic layer (host layer) when other anions and molecules such as water molecules (guest materials) are in close proximity, and the anion contained between the layers. The ion can be exchanged with the guest material, and the guest material can be taken in. Such ion exchange capacity is useful for improving the corrosion resistance of a film containing a layered double hydroxide. This is because, when the film is exposed to a corrosive environment such as salt water, it is considered that the erosion of the film can be suppressed by incorporating anions in the environment.

  However, even when the layered double hydroxide is applied to the anticorrosion film, it can be said that there is an appropriate content thereof. Therefore, the present inventor has further studied a preferred configuration and a method for forming the magnesium material having a film made of magnesium hydroxide and layered double hydroxide, and have arrived at the present invention.

That is, the present invention relates to a magnesium-based material composed of a base material made of magnesium or a magnesium alloy and a film formed on the surface of the base material, wherein the film comprises magnesium hydroxide (Mg (OH) ₂ ), The diffraction peak of the X-ray diffraction formed on the surface of the film is composed of the Mg—Al-based layered double hydroxide represented by the following formula, and the peak intensity (X) of the (101) plane of the magnesium hydroxide and the Mg -A magnesium-based material characterized in that the ratio (Y / X) to the peak intensity (Y) of the (003) plane of the Al-based layered double hydroxide is 0.05 to 0.3.

（式中、陰イオンであるＡ^ｎ−は、炭酸イオン（ＣＯ_３ ^２−）、硝酸イオン（ＮＯ_３ ⁻）、フッ素イオン（Ｆ⁻）の少なくともいずれかである）

(Wherein is ^{A n-} is an anion, carbonate ions _(CO ^{3 2-),} nitrate ion (NO ₃ ^-), fluoride ion (F ^- at least either of))

  Hereinafter, the present invention will be described in more detail. As described above, the present invention is characterized in that a film made of magnesium hydroxide and an appropriate amount of an Al—Mg layered double hydroxide is formed on a base material made of a magnesium-based material. In the following description, each of these configurations will be described.

  The magnesium-based material serving as the base material is pure magnesium or a magnesium alloy. As the magnesium alloy, a magnesium alloy containing at least 1% by mass of aluminum is preferable. In the present invention, the Al—Mg-based layered double hydroxide is an essential component because it is reasonable to supply aluminum, which is a constituent element, from the alloy base. Moreover, aluminum is an alloy element that improves strength by alloying with magnesium, and is an essential element in industrial magnesium alloys.

  An example of this magnesium alloy is an Mg—Al—Zn alloy, and more specifically, Mg— (2.5 to 3.5% by mass) Al— (0.6 to 1.4% by mass). Zn alloy (AZ31 alloy), Mg- (5.5-7.2 mass%) Al- (0.5-1.5 mass%) Zn alloy (AZ61 alloy), Mg- (7.5-9.2) Mass%) Al- (0.2 to 1.0 mass%) Zn alloy (AZ80 alloy), Mg- (8.3 to 9.7 mass%) Al- (0.35 to 1.0 mass%) Zn An alloy (AZ91 alloy) is mentioned. From the viewpoint of the characteristics of the alloy, the amount of aluminum added to the magnesium alloy is preferably 10% by mass. Aluminum is an element that is preferably added to the magnesium alloy base material, but pure magnesium or a magnesium alloy that does not contain aluminum may be the base material. This is because, as will be described later, an Al—Mg-based layered double hydroxide can be formed in the film by the surface treatment method according to the present invention. For example, an Mg—Zn alloy, an Mg—rare earth element alloy, and the like are alloys with improved magnesium strength, but these can also be applied as the base material of the present invention.

  The main composition of the coating on the substrate is magnesium hydroxide. As described above, magnesium hydroxide is chemically stable and inherently useful as an anticorrosion film. This magnesium hydroxide is an Al—Mg-based layered double hydroxide matrix, but preferably in a state in which fine particles are closely bound. Magnesium hydroxide preferably has a fine crystallite diameter of 10 to 100 nm. Such suitable formation of magnesium hydroxide is achieved by the treatment temperature and pressure in the surface treatment method according to the present invention described later.

Then, the Al-Mg-based layered double hydroxide is incorporated into the magnesium hydroxide, the (A ^n-in the chemical formula ¹⁾ anion layers and carbonate ions, nitrate ions, and fluoride ions. These are targeted because they are anions capable of ion-exchange reaction with chloride ions, sulfate ions, etc. that promote the corrosion reaction.

  In the present invention, the content of the Al—Mg-based layered double hydroxide is based on the diffraction peak of X-ray diffraction performed on the film surface, and the peak intensity (X) of (101) of magnesium hydroxide, Mg— The ratio (Y / X) to the peak intensity (Y) of the (003) plane of the Al-based layered double hydroxide is set to 0.05 to 0.3. The Al—Mg-based layered double hydroxide protects the film by the above-described anion exchange ability and improves the corrosion resistance of the magnesium-based material. However, when the peak intensity ratio Y / X is less than 0.05, the amount is Since the amount is too small, the film is not effectively protected and may be eroded. On the other hand, the upper limit of the peak intensity ratio Y / X is set to 0.3 when the mixing amount of the Al—Mg-based layered double hydroxide increases, cracks and the like occur during the formation of the magnesium hydroxide film, which is the main material of the film. This is because it becomes easier to form. A more preferable range of the peak intensity ratio Y / X is 0.1 to 0.25.

  In the present invention, the peak intensity in the X-ray diffraction is used to define the content of the Al—Mg-based layered double hydroxide. The Al—Mg-based layered double hydroxide is a fine compound (electrons). This is because observation with a microscope or the like is difficult. This is because X-ray diffraction is a comparatively simple analytical means, and there is a certain reliability with respect to the quantitativeness of invisible trace substances such as the Al—Mg-based layered double hydroxide in the present invention. Here, the diffraction peak of (101) plane is applied as the diffraction peak of magnesium hydroxide, which is the standard for peak intensity ratio production, because it is the peak with the highest intensity in the film analysis. This peak of the magnesium hydroxide (101) plane is seen around 2θ = 38 °. On the other hand, the (003) plane diffraction peak is applied as the diffraction peak of the Al—Mg layered double hydroxide because it shows the strongest intensity among the diffraction peaks of the Al—Mg layered double hydroxide. is there. The position of the diffraction peak of the Al—Mg-based layered double hydroxide can be seen around 2θ = 11 °, although it varies somewhat depending on the size of the anions included.

  The film made of magnesium hydroxide and Al—Mg layered double hydroxide described above preferably has a thickness of 10 to 100 μm. If it is less than 10 μm, when a minute scratch occurs, the base material erodes therefrom. When the thickness exceeds 100 μm, the film may be cracked or peeled off due to stress or thermal shock.

  In addition, about the magnesium-type material which concerns on this invention, the shape is not limited and the thing of all shapes, such as plate shape and a tubular shape, is applicable. Moreover, there is no restriction | limiting also about a dimension. This is because, as will be described later, in the surface treatment method performed by the method for producing a magnesium-based material according to the present invention, a film can be formed without any shape limitation or dimensional limitation. Furthermore, the formation of the film may be partial, and may be either single-sided or double-sided.

  Next, the manufacturing method of the magnesium-type material which concerns on this invention is demonstrated. As described above, the present invention is a magnesium-based material formed with a film based on magnesium hydroxide. Here, Patent Document 3 discloses a method for forming a film made of magnesium hydroxide on a magnesium-based material, and the magnesium-based material is cured (exposed) with water vapor. This film formation with water vapor is useful as a treatment for effectively producing magnesium hydroxide, and can be a basic technical element in the present invention. However, the conventional method for producing a magnesium-based material based on the surface treatment method has a problem that it is difficult to control the film thickness. Further, the Al—Mg-based layered double hydroxide that is essential in the present invention is used. It is considered that an effective amount cannot be generated.

  As a method for manufacturing a magnesium-based material according to the present invention, the present inventor controls the pressure during treatment with water vapor as a method for solving the problem of film thickness control, and maintains the pressure within a predetermined range, thereby achieving a precise density. It was assumed that a uniform magnesium hydroxide film could be uniformly formed on the substrate.

  Moreover, about the production | generation of an Al-Mg type | system | group layered double hydroxide, it is thought that the Al-Mg type | system | group layered double hydroxide is produced | generated in a trace amount also by the conventional steam curing. The Al—Mg-based layered double hydroxide is based on a solid solution of magnesium in magnesium hydroxide. Therefore, only when the magnesium alloy base material contains aluminum, both hydroxides are formed, and by incorporating carbonate ions from the treatment atmosphere (air) as anions, Al—Mg-based layered composites are formed. It is thought that hydroxide is formed. However, the unit layer of the Al—Mg-based layered double hydroxide is a hydroxide having a positive charge, and an anion needs to be supplied in order to maintain a charge neutral state. In this regard, it cannot be considered that sufficient anions can be supplied from the processing atmosphere. Therefore, the amount of the Al—Mg-based layered double hydroxide that can be produced by simply treating with water vapor is extremely small, and an effective amount as defined in the present invention is impossible.

  Therefore, the present inventor decided to add a compound serving as a source of anions to the processing atmosphere as a means for stably generating the Al—Mg-based layered double hydroxide based on the above consideration. . As a method of adding a compound serving as an anion supply source to the treatment atmosphere, instead of using a conventional pure water vapor, an anion-containing carbonate, nitrate, or fluoride salt vapor is used. This is possible.

  From the above, the method for producing a magnesium-based material according to the present invention forms a film by bringing a base material made of magnesium or a magnesium alloy into contact with a treatment liquid vapor at a temperature of 150 to 170 ° C. and a pressure of 0.4 to 0.9 MPa. The treatment liquid is an aqueous solution containing at least one of carbonate, nitrate, and fluoride salt.

  In this method for producing a magnesium-based material, magnesium hydroxide and an Al—Mg-based layered double hydroxide are exposed on the surface of the substrate by exposing the substrate made of the magnesium-based material to the vapor of a treatment liquid at a predetermined temperature and pressure. A film made of a material is formed.

  Here, the treatment liquid is an aqueous solution containing at least one of carbonate, nitrate, and fluoride salt. These salts include salts of alkali metals (lithium, sodium, potassium, etc.) (sodium carbonate, sodium nitrate, etc.) and salts of alkaline earth metals (calcium, strontium, barium, etc.) (calcium carbonate, calcium nitrate, etc.) Noble metal salt, common metal salt, etc. can be applied. These salts can be used as a treatment liquid by combining one kind or a plurality of kinds.

  Moreover, the manufacturing method of the magnesium-type material which concerns on this invention forms a membrane | film | coat, even when it uses a magnesium alloy which does not contain pure magnesium or aluminum as a base material, and can manufacture the magnesium-type material which concerns on this invention. This is because by applying a salt containing aluminum (aluminum carbonate, aluminum nitrate) as a salt of the treatment liquid, the treatment liquid can contain aluminum (ions), which is an Al—Mg-based layered double hydroxide. It is because it becomes a constituent element. At this time, the aluminum salt serves as a supply source of both aluminum and anions, which are constituent components of the Al—Mg-based layered double hydroxide. In this case, the treatment liquid may be produced from both the aluminum salt and the other salt such as sodium carbonate.

  In the present invention, the content of the Al—Mg layered double hydroxide in the film can be controlled by adjusting the salt concentration of the treatment liquid. The hydroxide content increases. A preferable salt concentration of the treatment solution is 1 mM to 1M. This salt concentration is extremely reduced as compared with the treatment liquid used in the chemical conversion treatment with a conventional phosphate solution or the like. The present invention uses water activated by a high-temperature, high-pressure atmosphere, and the salt concentration of the treatment liquid (anion supply amount) is about the amount necessary for forming an Al—Mg-based layered double hydroxide. Because it is enough. More preferably, the salt concentration of the treatment liquid is 10 mM to 0.5M.

  In the present invention, in addition to the temperature, the pressure control is an essential component for the film formation treatment with the vapor of the magnesium-based material. By controlling the pressure at a high pressure and processing at a constant pressure, the activity of water molecules is increased, and the reaction efficiency between the substrate and water is improved. Thereby, a dense film can be formed with good adhesion. Moreover, a uniform film can be formed by keeping the pressure constant.

  In the present invention, the treatment is performed with a treatment liquid vapor at a temperature of 150 to 170 ° C. and a pressure of 0.4 to 0.9 MPa. When the treatment temperature is set to 150 to 170 ° C., dense magnesium hydroxide is not formed at a temperature lower than 150 ° C., and the generation of Al—Mg-based layered double hydroxide is insufficient. On the other hand, when the temperature exceeds 170 ° C., the amount of the layered double hydroxide decreases, so this is the upper limit. With respect to the treatment pressure, if it is less than 0.4 MPa, dense magnesium hydroxide is not formed. On the other hand, if it exceeds 0.9 MPa, the reaction rate of the film formation becomes too fast, so that cracks are likely to be formed when the film is formed. Preferred treatment conditions are a temperature of 155 to 165 ° C. and a pressure of 0.5 to 0.8 MPa.

  The treatment time of the treatment liquid with water vapor is preferably 3 to 8 hours. There is a correlation between the treatment time and the film thickness, and the film becomes thicker as the treatment time increases. In order to form a film having a suitable thickness, the above time is preferable. still. There is no particular limitation on the method for contacting the water vapor of the treatment liquid with the substrate. For example, the substrate can be disposed in a pressure vessel together with the treatment liquid, and the substrate can be exposed to a water vapor atmosphere generated by controlling temperature and pressure.

  The magnesium-based material subjected to the above treatment may or may not be appropriately subjected to post-treatment such as washing. This is because the amount of impurities adsorbed on the surface of the magnesium-based material after the treatment is reduced because the salt concentration in the treatment liquid is low. Moreover, you may perform coating about the magnesium-type material after a process.

  In addition, for the production of the magnesium-based material according to the present invention, pretreatment such as oxide film removal treatment, degreasing treatment, pickling treatment, rust prevention treatment, and rust removal treatment is not required for the base material before the film formation treatment. is there. This is because, in the present invention, high-temperature and high-pressure steam is applied to the surface of the base material, so even if impurities adhere to the surface of the base material, they are removed by the cleaning action of water vapor.

  And the manufacturing method of the magnesium-type material demonstrated above centers on performing surface treatment about the base material which consists of magnesium-type materials using the water vapor | steam of the process liquid containing a predetermined salt. This surface treatment method is also useful for members, structures and the like made of a magnesium-based material. That is, by performing the steam treatment using these members as a base material, a suitable film can be formed and the corrosion resistance can be improved.

  And although the surface treatment method according to the present invention is possible by bringing water vapor into contact with the base material, although there is a regulation of pressure, there is no shape restriction or dimensional restriction on the material to be treated. Further, as described above, this pretreatment method is highly useful because pretreatment such as washing is unnecessary.

  As described above, the magnesium-based material according to the present invention is suitable for magnesium hydroxide having high chemical stability by using an Al-Mg-based layered double hydroxide capable of incorporating anions that cause corrosion in the environment. The film has a combined amount, and this film has high corrosion resistance. The surface treatment method for a magnesium-based material according to the present invention is simple but highly effective, can be used for large-sized members and structures, and further requires no pretreatment such as cleaning, so that it can be widely used. Can be expected.

The figure explaining the structure of the steam curing apparatus used by this embodiment. The polarization curve measured about Example 1 and the comparative example 1. FIG. The result of the X-ray diffraction analysis performed about the film | membrane of Examples 1, 2 and Comparative Example 2. FIG. Polarization curves measured for Examples 1 and 2 and Comparative Example 2. The result of the X-ray diffraction analysis performed about the membrane | film | coat of Example 3 and 4. FIG.

  Hereinafter, about an embodiment of the present invention, an example is described with a comparative example.

First embodiment : In this embodiment, a magnesium alloy is used as a magnesium-based material as a test material, and this is surface-treated to form a film, and the corrosion resistance of the magnesium alloy after treatment is compared with that not subjected to treatment. While evaluating. The test material was an A31 alloy extruded material (manufactured by Kieste Knos Co., Ltd.), which was cut into 20 × 20 mm and a thickness of 1.5 mm as a test piece.

  About the said test piece, the surface treatment for film formation was performed using the steam curing apparatus shown in FIG. The steam curing apparatus in FIG. 1 is a horizontal autoclave, and a processing liquid serving as a steam source is injected into the lower part. A plurality of test pieces can be suspended from the upper part of the apparatus. In the surface treatment, an aqueous solution obtained by dissolving 1 mM sodium carbonate in 1 L of water was used as a treatment liquid, and the surface treatment was performed at a temperature of 160 ° C., a pressure of 0.7 MPa, a treatment time of 6 hours, and the temperature and pressure maintained.

  And about the magnesium test piece after surface treatment, and the magnesium test piece which has not performed surface treatment, the corrosion resistance evaluation and the adhesiveness of the film were evaluated. In the corrosion resistance evaluation, first, a corrosion test was performed. In the corrosion test, each test piece was immersed in 5% by weight salt water (manufactured by Kanto Chemical Co., Inc.), and the liquid temperature was maintained at 35 ° C. for 72 hours. About each test piece after immersion, the presence or absence of corrosion generation | occurrence | production was judged visually, the state which has no corrosion was set to "(double-circle)", and the case where corrosion generate | occur | produced was determined to be "x". In addition, as a corrosion resistance evaluation, a polarization curve using a potentiostat was measured. For the polarization measurement, a 5 wt% NaCl aqueous solution was used, the measurement temperature was 25 ° C., and the potential sweep rate was 0.5 mV / s.

  For the evaluation of the adhesion of the film, an adhesion test kit (Elcometer 107 Cross Hatch Cutter) was used. In this test, the surface of a test piece after film formation is cut into a grid shape, a tape is applied thereon with a load of 40 N, the tape is peeled off after a predetermined time, and the peeled state of the film is observed and observed. . And when there was no peeling at all, it was determined as “◎”, and when peeling occurred, it was determined as “x”. In addition, about the membrane | film | coat, the film thickness is previously measured by optical microscope observation.

  The results of the above corrosion test and the results of the film adhesion evaluation are shown in Table 1. The measured polarization curve is shown in FIG.

From Table 1, it can be seen that the corrosion resistance of the magnesium alloy is dramatically improved by the surface treatment using the sodium carbonate solution as the treatment liquid. This can also be confirmed from the polarization curve of FIG. 2, and the corrosion potential of the magnesium test piece without surface treatment of Comparative Example 1 is −1.484 V (vs. SCE), whereas that of Example 1 The corrosion potential of the surface-treated magnesium test piece is -1.074 V (vs. SCE). Further, the corrosion current density at this corrosion potential is 7.2 × 10 ⁻⁵ A / cm ² in Comparative Example 1, whereas Example 1 is 8.5 × 10 ⁻⁹ A / cm ² . That is, Example 1 is 400 mV or more noble than Comparative Example 1, and the corrosion current density is 4 digits or more smaller. Therefore, it can be confirmed that the corrosion resistance is remarkably improved by the film formation of Example 1. And about Example 1, the adhesiveness of the formed membrane | film | coat is also excellent.

Second Embodiment : In this embodiment, the same magnesium alloy as that in the first embodiment is used as a test piece, and the film formation is performed by changing the composition of the treatment liquid and the surface treatment conditions for film formation, and the corrosion resistance evaluation is performed. Went.

  As Example 2, the sodium carbonate concentration of the treatment liquid was set to 100 mM, and the film formation treatment was performed under the same apparatus and conditions as in the first embodiment. In Comparative Example 2, pure water was applied to the treatment liquid, and film formation was performed using the same apparatus and conditions as in the first embodiment. Further, as Comparative Example 3, the same treatment liquid as in the first embodiment (sodium carbonate concentration: 1 mM) was used, and the surface treatment conditions were a temperature of 140 ° C. and a pressure of 0.35 MPa.

  The test pieces steam-cured in Example 2 and Comparative Examples 2 and 3 were first subjected to corrosion resistance evaluation, film thickness measurement, and film adhesion evaluation by a corrosion test. These evaluation methods are the same as those in the first embodiment. The results are shown in Table 2. Table 2 also shows the results of Example 1 and Comparative Example 1 of the first embodiment.

  From Table 2, it can be confirmed that even if the salt concentration of the treatment liquid is changed, it is possible to form a film having good corrosion resistance and adhesion. On the other hand, even when the pure water of Comparative Example 2 was used as the treatment liquid, it can be said that a film having good corrosion resistance was formed in the corrosion test. However, in the case of Comparative Example 2, there was a problem in that discoloration of the film occurred although it could not be determined visually that corrosion occurred.

  On the other hand, from the results of Comparative Example 3, even when sodium carbonate is used as the treatment liquid, the corrosion resistance of the magnesium alloy is not improved when the surface treatment conditions are lower than the preferred range and low pressure. In Comparative Example 3, the film thickness is thin and the corrosion resistance is equivalent to a test piece that is not surface-treated. Moreover, although the film was formed, it peeled easily.

  From the evaluation results so far, it can be seen that, as in Examples 1 and 2 and Comparative Example 2, a film with good adhesion is formed by steam curing under suitable conditions. This film is presumed to be mainly magnesium hydroxide, but it is considered that dense magnesium hydroxide is firmly adhered to the base material by steam curing under appropriate conditions. Therefore, also in Comparative Example 2, it is considered that no clear corrosion was observed under the test conditions of the corrosion test (5% salt water immersion).

  Then, next, while examining the structure about the film | membrane formed in Example 1, 2 and the comparative example 2, while measuring the polarization curve about these, the difference in corrosion resistance was evaluated strictly. For the examination of the composition of the film, X-ray diffraction analysis was performed for each. The polarization curve measurement was performed under the same conditions as in the first embodiment. And as a result of the X-ray diffraction analysis, the peak intensity (X) of the peak identified as the (101) plane of magnesium hydroxide and the (003) plane of the Mg—Al-based layered double hydroxide are identified. The ratio (Y / X) of the peak to the peak intensity (Y) was calculated. Moreover, the corrosion potential and the corrosion current density were measured from the result of the polarization curve. FIG. 3 shows the result of X-ray diffraction, and FIG. 4 shows the result of polarization curve measurement. Table 3 shows each numerical value.

In the result of the X-ray diffraction analysis of FIG. 3, peaks near 2θ = 18.5 °, 32.8 °, 37.9 °, 50.8 °, 58.7 °, 62.1 °, 72.1 °. Respectively correspond to the (001) plane, (100) plane, (101) plane, (102) plane, (110) plane, (111) plane, and (201) plane of magnesium hydroxide. A peak near 37.9 ° is a peak on the (101) plane of magnesium hydroxide. On the other hand, peaks observed in the vicinity of 2θ = 11.3 ° and 22.6 ° are Al—Mg-based layered double hydroxide ([Mg ²⁺ _1-x Al ³⁺ _x (OH) ₂ ] [CO ₃ ²⁻ _{x / 2} · yH ₂ O]) are identified as (003) plane and (006) plane peaks. The peak near 11.3 ° is the peak of the (003) plane of the Al—Mg layered double hydroxide. From FIG. 3, it can be confirmed that the films formed in Examples 1 and 2 are composed of magnesium hydroxide and an Al—Mg layered double hydroxide. On the other hand, although the film formed in Comparative Example 2 was mainly composed of magnesium hydroxide, the peak of the Al—Mg-based layered double hydroxide was extremely low. In Comparative Example 2, the supply of carbonate ions from the treatment liquid (pure water) is small, and it is considered that a small amount of carbonate ions are taken in from the treatment atmosphere (air) to produce an Al—Mg layered double hydroxide. The amount is considered very small.

  Table 2 shows the ratio (Y / X) between the peak intensity (X) of the magnesium hydroxide (101) plane and the peak intensity (Y) of the Mg—Al-based layered double hydroxide (003) plane in each coating. As shown, in Examples 1 and 2, the peak intensity ratio Y / X is 0.06 and 0.19, whereas in Comparative Example 1, it is 0.005. From this, it can be seen that an effective Mg-Al-based layered double hydroxide was formed by adding a salt (sodium carbonate) to the treatment liquid. Moreover, it turns out that content of the Mg-Al type | system | group layered double hydroxide in a membrane | film | coat can be adjusted by adjusting the salt concentration of a process liquid.

  Further, in the results of X-ray diffraction of Examples 1 and 2, the crystallite diameter of magnesium hydroxide in the film was calculated from the half-value width of the peak of the magnesium hydroxide (101) plane, and was 25 nm. That is, it was confirmed that the coating films in these examples were extremely fine on the nano order.

Then, looking at the results of the corrosion resistance evaluation based on the polarization curve, the corrosion potentials of Examples 1 and 2 were -1.074 V (vs. SCE), and Comparative Example 2 was -1.083 V (vs. SCE). It was. Although the corrosion potentials of Examples 1 and 2 are slightly higher, the difference is not so large. However, regarding the corrosion current density, it is 8.2 × 10 ⁻⁹ A / cm ² and 3.2 × 10 ⁻¹⁰ A / cm ² in Examples 1 and ² , whereas Comparative Example 2 is 5 5 × 10 ⁻⁶ A / cm ² and the example are three orders of magnitude lower than the comparative example. Therefore, it can be said that Examples 1 and 2 have better corrosion resistance than Comparative Example 2. From the results of this polarization curve, the film containing a certain amount or more of Mg—Al-based layered double hydroxide has a large difference in initial corrosion resistance from the film containing little or no Mg—Al-based layered double hydroxide. Although there is no, it is considered that a large difference occurs when erosion by the corrosive substance (anion) in the environment starts. This difference is presumed to be caused by Mg—Al-based layered double hydroxide contained in a suitable amount taking in a corrosive substance and suppressing its erosion.

Third Embodiment : In this embodiment, a magnesium alloy similar to that of the first embodiment is used as a test piece, and a film is formed using an aluminum nitrate (Al (NO ₃ ) ₃ ) solution as a treatment liquid for film formation. The corrosion resistance was evaluated. In Examples 3 and 4, the sodium carbonate concentration of the treatment liquid was set to 2 mM and 200 mM, and film formation was performed under the same apparatus and conditions as in the first embodiment.

  The test pieces steam-cured in Examples 3 and 4 were subjected to corrosion resistance evaluation, film thickness measurement, and film adhesion evaluation by a corrosion test. These evaluation methods are the same as those in the first embodiment. Further, X-ray diffraction analysis of the film surface was performed. The results are shown in Table 4 and FIG.

  From Table 4, it can be seen that even when an aluminum salt solution is applied as the treatment liquid, a film having good corrosion resistance and adhesion is formed. In addition, from FIG. 5, the peak of Al—Mg-based layered double hydroxide (also observed in this embodiment is observed, the peak intensity (X) of the magnesium hydroxide (101) plane and the Mg—Al-based layered double hydroxide (003). The ratio (Y / X) to the peak intensity (Y) of the surface) was also a sufficient value.

As described above, the magnesium-based material according to the present invention has excellent corrosion resistance with respect to conventional magnesium-based materials subjected to various surface treatments. Although the surface treatment method according to the present invention is relatively simple, a film containing an Mg—Al-based layered double hydroxide can be efficiently formed on a magnesium-based material substrate. This surface treatment method can be applied without limiting the shape and dimensions, and can improve the corrosion resistance of a large member at low cost.

Claims (7)

In a magnesium-based material composed of a base material made of magnesium or a magnesium alloy and a film formed on the surface of the base material,
The film is composed of magnesium hydroxide (Mg (OH) ₂ ) and Mg—Al-based layered double hydroxide represented by the following formula:

(Wherein is ^{A n-} is an anion, carbonate ions _(CO ^{3 2-),} nitrate ion (NO ₃ ^-), fluoride ion (F ^- at least either of))
Regarding the diffraction peak of X-ray diffraction performed on the film surface, the peak intensity (X) of the (101) plane of the magnesium hydroxide and the peak intensity (Y) of the (003) plane of the Mg—Al-based layered double hydroxide And a ratio (Y / X) of 0.05 to 0.3.   The magnesium-based material according to claim 1, wherein the film has a thickness of 10 to 100 μm.   The magnesium-based material according to claim 1 or 2, wherein the base material is made of a magnesium alloy and is a magnesium alloy containing at least 1% by mass of aluminum. A method for producing a magnesium-based material according to any one of claims 1 to 3,
Including a step of contacting a base material made of magnesium or a magnesium alloy with a treatment liquid vapor at a temperature of 150 to 170 ° C. and a pressure of 0.4 to 0.9 MPa to form a film,
The method for producing a magnesium-based material, wherein the treatment liquid is an aqueous solution containing at least one of carbonate, nitrate, sulfate, and fluoride salt at a concentration of 1 mM to 1M.   The method for producing a magnesium-based material according to claim 4, wherein the treatment liquid is an aqueous solution containing at least one of aluminum carbonate, nitrate, sulfate, and fluoride. In a surface treatment method for forming a corrosion-resistant film on the surface of a magnesium-based material made of magnesium or a magnesium alloy,
Including the step of forming the film by bringing the magnesium-based material into contact with a treatment liquid vapor at a temperature of 150 to 170 ° C. and a pressure of 0.4 to 0.9 MPa,
The surface treatment method for a magnesium-based material, wherein the treatment liquid is an aqueous solution containing at least one of carbonate, nitrate, sulfate, and fluoride salt at a concentration of mM to 1M. The surface treatment method for a magnesium-based material according to claim 6, wherein the treatment liquid is an aqueous solution containing at least one of aluminum carbonate, nitrate, sulfate, and fluoride salt.

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