Manufacturing method for high-strength, highly corrosion-resistant magnesium alloy materials

Abstract

A method for manufacturing a magnesium alloy material with a coating applied by steam treatment is provided, which is simpler than conventional techniques while achieving both improved corrosion resistance and increased strength. [Solution] The present invention relates to a method for producing a magnesium alloy material comprising a base material made of a magnesium alloy containing a solute element and a coating formed on the surface of the base material. In the present invention, the magnesium alloy base material is subjected to a solution treatment by heating it at a temperature of 300°C to 520°C and then rapidly cooling it, and then the base material is exposed to steam at a temperature of 130°C to 250°C to form the coating. By performing steam treatment on the magnesium alloy base material after solution treatment without performing aging treatment as in the present invention, both corrosion resistance and strength can be increased.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a magnesium alloy material having high strength and good corrosion resistance. More specifically, the present invention relates to a method for manufacturing a magnesium alloy material capable of strengthening a base material while forming a film having a corrosion prevention effect on the base material made of a magnesium alloy.

Background Art

[0002] Magnesium alloys are extremely light among various metal materials that have been put into practical use, and in addition, have the characteristic that their specific strength is greater than that of aluminum, steel, etc., and thus are used for structural members of aerospace equipment and the like. Recently, they have also come to be used for automotive materials, railway vehicle bodies, building members, and the like. In addition, the application of magnesium alloys as medical implant materials has also attracted attention. Magnesium is an essential mineral component for human metabolism, so it is decomposed and absorbed by the physiological environment in the human body, and is considered suitable as an implant that can be decomposed and disappear in the human body while having mechanical properties for fixing affected parts and expanding defects.

[0003] When using magnesium alloys for the above-mentioned various applications, matters of concern include corrosion resistance and degradability. Since magnesium is a very active metal, its surface is easily corroded by oxidation or the like in the use environment. When a magnesium alloy is applied to a structural member, such corrosion leads to a decrease in the strength of the structural member. Also, in the case of a medical implant, if the implant material decomposes earlier than expected, the implant may disappear before the treatment of the affected part is completed.

[0004] Therefore, various methods are being considered to improve the corrosion resistance of magnesium alloy materials. As one such method for improving corrosion resistance, the applicant has reported on the formation of a corrosion-preventive coating by steam treatment (Patent Document 1). The coating formation treatment by the applicant involves exposing a substrate made of magnesium alloy to steam to form a coating containing magnesium hydroxide (Mg(OH)2) on the surface of the substrate. Steam coating treatment does not require a special treatment liquid like chemical conversion treatment, and the problem of wastewater treatment is minimal. Furthermore, since steam treatment can be easily scaled up, it can be used to treat large components, making it a beneficial surface treatment method.

[0005] Furthermore, the applicant has reported a steam process that includes a pretreatment to adjust the material structure of the substrate before steam treatment in order to further enhance the corrosion protection effect of the steam treatment (Patent Document 2). This pretreatment, which the applicant calls a microstructure adjustment treatment, involves composition processing (hot or warm processing) or heat treatment of the magnesium alloy substrate at a temperature of 200°C to 500°C before steam treatment, thereby refining the compounds of solute elements contained in the magnesium alloy substrate. This microstructure adjustment treatment homogenizes the film formed by the subsequent steam treatment, resulting in higher corrosion resistance than magnesium alloy materials without microstructure adjustment treatment. In addition, since the microstructure adjustment treatment contributes to the refinement of compound particles in the magnesium alloy substrate, it leads to an improvement in strength as well as improved corrosion resistance. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 6115912 specification [Patent Document 2] Patent No. 7148992 specification [Overview of the project] [Problems that the invention aims to solve]

[0007] As described above, the improved steam treatment process developed by the applicant (Patent Document 2) is more effective in improving corrosion resistance than steam treatment alone. Furthermore, this steam treatment process also has the effect of increasing the strength required for magnesium alloy materials. However, this steam treatment process requires a microstructure adjustment step before steam treatment, which inevitably increases the number of steps. Therefore, the present invention relates to a method for producing a magnesium alloy material using a magnesium alloy as a base material and having a coating formed by steam treatment, and provides a method that is simpler than the conventional improved process while exhibiting the effects of improved corrosion resistance and increased strength. [Means for solving the problem]

[0008] The microstructure adjustment process performed in the improved steam treatment process described above is intended to adjust the particle size and dispersion state of solute element compound particles in the magnesium alloy substrate, thereby achieving microstructure and compositional uniformity of the magnesium alloy substrate. This indicates that a uniform substrate surface is preferable for improving the corrosion resistance of the coating through steam treatment.

[0009] Incidentally, the magnesium alloys targeted by conventional steam treatment processes are age-hardening (precipitation-hardening) alloys that use solute element compounds as strengthening factors. Age hardening occurs when precipitates are formed by heat treatment (aging treatment) of the alloy above a certain temperature, but it is considered effective to perform solution treatment before aging treatment. Solution treatment is a process in which the alloy is heated to a high temperature to increase the solid solution concentration of solute elements, and then rapidly cooled to form a supersaturated solid solution. The alloy that has been solution-treated in this way is in a structurally and compositionally homogeneous state in which the solute elements are solid-dissolved in the matrix (magnesium). The inventors considered that the surface state of the alloy after this solution treatment is also effective as a base for film formation by steam treatment.

[0010] Furthermore, while steam treatment is characterized by its treatment atmosphere (high-temperature steam), it is fundamentally a heat treatment. Therefore, by adjusting the treatment temperature of the steam treatment on a magnesium alloy substrate after solution treatment, it is possible to achieve an effect equivalent to aging treatment. At this time, the uniform magnesium alloy substrate after solution treatment is also in a suitable state as a base for coating. Based on the above considerations, the inventors conceived the present invention by steam treatment of a magnesium alloy substrate after solution treatment, which allows for the simultaneous formation of a suitable coating and aging hardening, without the need for additional steps such as the microstructure adjustment treatment of the conventional technology.

[0011] In other words, the present invention relates to a method for producing a magnesium alloy material comprising a base material made of a magnesium alloy containing a solute element and a film formed on the surface of the base material, characterized in that the base material is subjected to a solution treatment by heating it at a temperature of 300°C to 520°C and then rapidly cooling it, and then the base material is exposed to steam at a temperature of 140°C to 250°C to form the film. The method for producing a magnesium alloy material according to the present invention and the magnesium alloy material produced by this method will be described below.

[0012] A. Method for producing magnesium alloy material according to the present invention The method for producing magnesium alloy materials according to the present invention includes a solution treatment step for the magnesium alloy substrate and a subsequent steam treatment step as essential steps. The present invention will be described below, with each of these steps explained in detail.

[0013] A-1. Base material The magnesium alloy that constitutes the base material of the present invention is a metallic material alloyed by adding elements other than magnesium as solute elements to magnesium. Specifically, the magnesium alloy that serves as the base material preferably contains at least one of the following solute elements: aluminum (Al), zinc (Zn), calcium (Ca), manganese (Mn), zirconium (Zr), and rare earth elements (scandium (Sc), yttrium (Y), lanthanides). Aluminum and zinc are solute elements of standardized magnesium alloys, and magnesium alloys containing aluminum are particularly preferred. Aluminum may form Mg-Al layered double hydroxides in the film produced by steam treatment, which have a corrosion resistance-improving effect.

[0014] The solute element content of the magnesium alloy is preferably 5% to 15% by mass for aluminum. Furthermore, zinc is preferably more than 0% but 5% or less by mass, calcium is preferably more than 0% but 5% or less by mass, and manganese is preferably more than 0% but 5% or less by mass. Additionally, zirconium is preferably more than 0% but 5% or less by mass, and rare earth elements are preferably more than 0% but 5% or less by mass.

[0015] As specific examples of magnesium alloys as described above, alloys defined by ASTM standards can be applied. For example, Mg-Al-Zn alloys (AZ alloys: AZ61, AZ91) with aluminum and zinc added as solute elements, and Mg-Al-Mn alloys (AM alloys: AM50, AM60) with aluminum and manganese added as solute elements are known. There are also Mg-Zn-Zr alloys (ZK alloys: ZK60, ZK61) with zinc and zirconium added as solute elements. Furthermore, the present invention can also be applied to Mg-Al-Zn-Ca alloys with aluminum, zinc, and calcium added as solute elements (AZX alloys: AZX611, AZX612, AZX615, AZX6112, AZX711, AZX811, AZX911, AZX1001), Mg-Al-Mn-Ca alloys with aluminum, manganese, and calcium added as solute elements (AMX alloys: AMX601, AMX701, AMX801, AMX901, AMX1001), and Mg-RE alloys with rare earth elements (RE) added as solute elements (EZ33, ZE41, WE43, EV31, etc.).

[0016] The magnesium alloy substrate targeted by this invention is made of an age-hardening magnesium alloy, but the processing and heat treatment history is not relevant when applying this invention. It may be in the state after melting and casting, or in the state after melting and casting has undergone processing and heat treatment such as forging. It may also be in an age-hardened state in which precipitates of solute element compounds are dispersed. Regardless of the state of the magnesium alloy substrate, a homogeneous supersaturated solid solution can be formed by solution treatment, and a film can be formed by steam treatment. However, since repeatedly performing solution treatment is cumbersome, the state after melting and casting and / or processing before aging treatment is preferred.

[0017] Furthermore, there are no restrictions on the shape or dimensions of the magnesium alloy substrate. This is because steam treatment allows for film formation even on substrates with complex shapes, and there are few limitations on the size of the processing equipment. The dimensions and shapes may also be those of various structural members for the aforementioned applications, or medical implants such as bone plates.

[0018] A-2. Solution treatment In this invention, the magnesium alloy substrate is required to undergo solution treatment. Solution treatment is a heat treatment in which the substrate is heated to a high temperature and then rapidly cooled to obtain a supersaturated solid solution. In this invention, magnesium alloys are the target, and the heating temperature for solution treatment should be between 300°C and 520°C. Below 300°C, it becomes difficult to increase the solid solubility of the solute elements, making it difficult to obtain a homogeneous solid solution. Furthermore, even if the temperature exceeds 520°C for magnesium alloys, the effect of the solution treatment is minimal. Excessive high-temperature heating can cause deformation and dimensional inaccuracies due to softening of the substrate, and in some cases, melting may occur. A processing temperature of 320°C or higher is more preferable for solution treatment.

[0019] To ensure sufficient solid dissolution of the solute elements into the magnesium matrix, the heating time for the solution treatment is preferably 12 hours or more and 120 hours or less. The heating atmosphere for the solution treatment may be air, an inert gas atmosphere, or a vacuum atmosphere. Preferably, it is an air atmosphere.

[0020] Solution treatment is a process to obtain a supersaturated solid solution by rapidly cooling a magnesium alloy substrate after heating it to the above temperature. Rapid cooling means cooling quickly enough so that excessive grain boundary reactions do not occur in the high-temperature range. The cooling rate is preferably 50°C / s or higher, and more preferably 150°C / s or higher. Specific methods for achieving such a cooling rate include water cooling and ice cooling. Cooling after heating is preferably carried out until the magnesium alloy substrate reaches below room temperature.

[0021] A-3. Steam treatment By contacting a magnesium alloy substrate, which has become a supersaturated solid solution through solution treatment, with steam, a magnesium alloy material with a corrosion-resistant coating can be obtained. Furthermore, the steam treatment in this invention also acts as a treatment to improve the strength of the magnesium alloy substrate by aging it and precipitation of solute element compounds. For this purpose, setting the treatment temperature is important for the steam treatment in this invention. In other words, this invention requires a treatment temperature that allows for a suitable balance between the aging treatment and film formation necessary for the magnesium alloy.

[0022] As the treatment temperature of this steam treatment, the temperature of the steam shall be 130°C or higher and 250°C or lower. In the steam treatment at a temperature lower than 130°C, age hardening in the magnesium alloy base material hardly occurs. On the other hand, for the film formed at a temperature exceeding 250°C, although the film thickness increases, the film is poor in density and has a low corrosion prevention effect. The steam temperature is preferably 170°C or higher, and more preferably 200°C or higher.

[0023] The pressure of the steam is preferably in the range of 0.1 to 10 MPa. The pressure is more preferably 0.2 to 3 MPa. When applying pressurized steam, a two-phase equilibrium state of saturated steam and subcritical water is achieved, and it becomes possible to promote the reactivity with respect to film formation. By keeping the pressure of the steam constant during the treatment, a uniform film can be formed.

[0024] The treatment time with steam should be appropriately set according to the shape and dimensions of the base material and is not particularly limited. However, when the steam treatment requires the functions of film formation and aging treatment as in the present invention, the preferable treatment time is 12 hours or more and 48 hours or less. In the steam treatment for less than 12 hours, age hardening in the magnesium alloy base material hardly occurs. On the other hand, when it exceeds 48 hours, although the film thickness increases, the film is poor in density and has a low corrosion prevention effect. Furthermore, over-aging occurs in the magnesium alloy base material, inducing a decrease in strength.

[0025] Steam for steam treatment is generated by heating and vaporizing water. Industrial water or tap water can be used as the steam source, and the use of pure water is also preferable. Aqueous solutions containing appropriate salts can also be used. When using pure water, ion-exchanged water, distilled water, or ultrapure water with an electrical conductivity of 1 mS / m or less is preferred. As for aqueous solutions containing salts, steam from aqueous solutions of carbonates, nitrates, sulfates, and fluoride salts can be used. These salts include alkali metal salts (lithium, sodium, potassium, etc.) (sodium carbonate, sodium nitrate, etc.), alkaline earth metal salts (calcium, strontium, barium, etc.) (calcium carbonate, calcium nitrate, etc.), as well as salts of precious metals and common metals. Aqueous solutions of one or more of these salts can be used. The treatment atmosphere may be in the atmosphere or in a container purged with an inert gas. There are no shape or dimensional restrictions on the material to be treated in this steam treatment.

[0026] There are no particular limitations on the method of bringing the magnesium alloy substrate into contact with steam. Steam treatment may be performed by exposing the magnesium alloy to be treated to steam in a closed space such as a reactor or container. Specifically, treatment can be carried out by placing the substrate in a container with water and exposing the substrate to a steam atmosphere generated by controlling the temperature and pressure. Alternatively, the treatment may be carried out by directly spraying steam onto the material to be treated.

[0027] The magnesium alloy material obtained by the steam treatment described above may be subjected to post-treatment such as washing as appropriate, but is not required. Furthermore, the treated magnesium alloy material can be painted.

[0028] B. Magnesium alloy material manufactured according to the present invention The magnesium alloy material obtained by the magnesium alloy material manufacturing method according to the present invention described above consists of a magnesium alloy substrate and a coating formed on its surface.

[0029] The composition of the magnesium alloy substrate is as described above. According to the present invention, the magnesium alloy substrate has a material structure in which particles of solute element compounds are dispersed, with a solid solution of magnesium or a magnesium alloy as the matrix. The particles of the solute element compounds are particles of compounds of one or more solute elements and magnesium. For example, in the above-mentioned ASTM standard magnesium alloy, In AM alloys, the α-Mg solid solution contains MgAl compounds (Mg 17 Al 12 It exhibits a eutectic structure in which (etc.) are dispersed. AZ alloys exhibit a similar structure to AM alloys, but the Mg(Al,Zn) compound (Mg) is affected by the Zn content. 32 (Al,Zn) 49 (etc.) may also be dispersed.

[0030] In the present invention, the average particle size of the compound particles is preferably 0.1 μm or more and 5 μm or less. By making the compound particles finer and more highly dispersed, the strength and hardness of the magnesium alloy material are increased. The steam treatment described above also contributes to making the particle size of the compound particles appropriate. The material structure of the magnesium alloy substrate and the state of the compound particles can be observed using an optical microscope or an electron microscope. If the particle size of the compound particles is greater than the resolution of the observation instrument used, it can be distinguished from the magnesium matrix using a normal observation method. The average particle size of the compound can then be calculated from the image captured during observation using appropriate image analysis software. While there are no specific methods for observing the material structure, in the magnesium alloy material of the present invention, the compound can be observed even at relatively low magnification, making observation and imaging with an optical microscope convenient.

[0031] The coating on the magnesium alloy material according to the present invention is mainly composed of magnesium hydroxide (Mg(OH)2). Magnesium hydroxide is chemically stable and is the main component of the corrosion-preventive coating in this invention. In addition to magnesium hydroxide, the coating may also contain oxides and hydroxides derived from the solute elements of the magnesium alloy substrate. For example, it may contain aluminum hydroxide oxide (AlO(OH)) derived from aluminum. It may also contain Mg-Al layered double hydroxides disclosed in the prior art (Patent Documents 1 and 2). Since Mg-Al layered double hydroxides are produced when aluminum is included as a solute element in the magnesium alloy substrate and under certain conditions of steam treatment, they are not an essential component of the coating on the magnesium alloy material according to the present invention. When the coating contains compounds other than magnesium hydroxide, such as aluminum hydroxide oxide or Mg-Al layered double hydroxides, the structure of the coating is presumed to consist of magnesium hydroxide as the matrix, encompassing the other components. Furthermore, while the prior art (Patent Document 2) requires the formation of Mg-Al layered double hydroxides to improve the corrosion resistance of the coating, this is not the case in the present invention. Even a coating without Mg-Al layered double hydroxides exhibits good corrosion resistance. The constituent components of the coating can be confirmed by known analytical methods such as X-ray diffraction analysis (XRD).

[0032] In this invention, the thickness of the coating is preferably 5 μm or more and 100 μm or less. If it is less than 5 μm, the corrosion protection effect is insufficient, and there is a risk that the substrate may be corroded by minute scratches. If it exceeds 100 μm, cracks and peeling may occur in the coating due to stress or thermal shock. [Effects of the Invention]

[0033] As described above, the method for manufacturing magnesium alloy materials according to the present invention can achieve improved corrosion resistance (film formation) and increased strength (age hardening) of magnesium alloy substrates through a simpler process compared to the conventional technology. [Brief explanation of the drawing]

[0034] [Figure 1] A diagram illustrating the configuration of the steam curing apparatus used in the embodiment. [Figure 2] XRD diffraction patterns of magnesium alloy materials from Examples 1 to 5 and Comparative Examples 1 to 2. [Figure 3] SEM images showing the surface morphology of the magnesium alloy coatings in Examples 1 to 5. [Figure 4] SEM images showing the surface morphology of the coatings on magnesium alloy materials in Comparative Examples 1 and 2. [Figure 5] Anode polarization curves of magnesium alloy materials from Examples 1 to 5 and Comparative Examples 1 to 2. [Modes for carrying out the invention]

[0035] The embodiments of the present invention will be described below with reference to examples and comparative examples. In this embodiment, AZ91D alloy (Mg-9%Al-1%Zn) was used as the magnesium alloy base material. After solution treatment, steam treatment was performed at various temperatures to form a film and age harden.

[0036] Examples A commercially available AZ91D alloy plate (70 x 30 mm, 3.0 mm thick: aged) was prepared as the base material for the test specimen, and solution treatment was performed. The base material was placed in a muffle furnace and heated and held at 400°C in air for 24 hours, after which the base material was removed and rapidly cooled by immersing it in ice water to complete the solution treatment.

[0037] Steam treatment was performed on the substrate after solution treatment. In this embodiment, the steam treatment apparatus shown in Figure 1 was used, and the magnesium alloy substrate after solution treatment was placed inside the apparatus, the apparatus was sealed, and steam treatment was performed. The steam treatment apparatus in Figure 1 has a sealed container (volume 100 mL) made of Teflon® housed inside the autoclave. A steam source is injected into the bottom of the sealed container, and a sample stage is placed on it so that the test piece does not come into direct contact with the steam source. For steam treatment, the test piece was placed on the sample stage, the sealed container was covered, and the autoclave was sealed. Then, it was heated in an electric furnace and steam treatment was performed. In this embodiment, 50 μL of ultrapure water was injected as the steam source.

[0038] In this embodiment, the steam treatment conditions were set to a pressure of 1.4 MPa to 1.7 MPa, and the heating temperature (200°C, 210°C) and heating time (12 hours, 16 hours, 20 hours) were set. Five types of magnesium alloy materials were then produced: 200°C × 12 hours (Example 1), 200°C × 16 hours (Example 2), 201°C × 12 hours (Example 3), 210°C × 12 hours (Example 4), and 210°C × 20 hours (Example 5).

[0039] Comparative Example For comparison with the above examples, magnesium alloy materials were manufactured by forming a coating using a standard treatment performed on age-hardening magnesium alloys. In this comparative example, the same magnesium alloy substrate as in the examples was prepared, and after solution treatment, it underwent aging treatment, followed by steam treatment. The solution treatment was performed in the same manner as in the examples. For the aging treatment, the heating temperature was 210°C for 12 hours (Comparative Example 1) and 16 hours (Comparative Example 2). The steam treatment performed after the aging treatment was performed at a heating temperature of 160°C for 6 hours.

[0040] The magnesium alloy materials of Examples 1 to 5 and Comparative Examples 1 to 2, manufactured using the above process, were subjected to X-ray diffraction (XRD) analysis, surface observation using SEM, corrosion resistance evaluation, and strength (hardness) measurement.

[0041] [XRD analysis] XRD measurements were performed using a Cu-Kα X-ray source at a voltage of 40kV and a current of 30mA. Figure 2 shows the XRD profiles of the magnesium alloy surface for Examples 1 to 5 and Comparative Examples 1 to 2. From Figure 2, it was confirmed that a film mainly composed of magnesium hydroxide (Mg(OH)2) was formed on all magnesium alloy materials. In addition, in the films of the magnesium alloy materials in Comparative Examples 1 and 2, the formation of aluminum hydroxide oxide (AlO(OH)) derived from Al, the solute element of the magnesium alloy substrate, was confirmed. In these comparative examples, the formation of Mg-Al layered double hydroxide (LDH) was also confirmed. It is presumed that these components observed in the comparative examples are due to the formation of Al-containing precipitates during aging treatment, resulting in localized areas with high Al concentration before steam treatment.

[0042] [SEM observation of surface morphology] Next, the surface morphology of the coatings on each magnesium alloy material was observed using a scanning electron microscope (SEM). Figures 3 and 4 are SEM images showing the surface morphology of the coatings on the magnesium alloy materials of Examples 1 to 5 and Comparative Examples 1 to 2. The magnesium alloy materials of Examples 1 and 2, which were treated with steam at a temperature of 200°C, had relatively smooth coatings. The coatings on the magnesium alloy materials of Examples 3 to 5, which were treated with a higher steam temperature (210°C), had slight surface irregularities. On the other hand, the coatings on the magnesium alloy materials of Comparative Examples 1 and 2, which were treated with steam after aging, all had uneven surface morphologies.

[0043] [Anodic polarization measurement] The polarization curves of the magnesium alloy materials of Examples 1 to 5 and Comparative Examples 1 to 2 were measured, and their corrosion resistance was evaluated. For polarization measurement, a 5 wt% NaCl aqueous solution was used as the electrolyte. After bubbling the solution with nitrogen before measurement, the polarization curve was measured using a potentiometer / galvanostat (VersaSTAT4, Princeton Applied Research).

[0044] Figure 5 shows the anodic polarization curves for each magnesium alloy material. For comparison, the polarization curve of the untreated magnesium alloy material is also shown in Figure 5. The corrosion potential and corrosion current density were then measured from the polarization curve results. Table 1 shows the measured corrosion potential and corrosion current density values ​​for each magnesium alloy material.

[0045] [Table 1]

[0046] Referring to the polarization curves in Figure 5 and the results in Table 1, the magnesium alloy materials of Examples 1 to 5 and Comparative Examples 1 to 2 all exhibited a nobler corrosion potential and a lower corrosion current density compared to the untreated magnesium alloy material. In other words, it can be confirmed that the corrosion resistance of all magnesium alloy materials was improved by the formation of the coating. Furthermore, comparing Examples 1 to 5 with Comparative Examples 1 to 2 based on corrosion potential, the Examples appear to have a nobler corrosion potential and better corrosion resistance than the Comparative Examples. Of Examples 1 to 5, Example 4 (steam treatment temperature 210°C, treatment time 16 hours) exhibited the best corrosion resistance.

[0047] [Hardness measurement of magnesium alloy substrates] Hardness measurements were performed on the magnesium alloy materials of Examples 1 to 5 and Comparative Examples 1 to 2. The hardness measurements were performed on magnesium alloy substrates from which the coating had been mechanically polished and removed before measurement. A micro-Vickers hardness tester (HM-103, manufactured by Mitutoyo Corporation) was used for the measurements, with a test load of 2.94 N and a loading time of 15 s. The measurement results are shown in Table 2.

[0048] [Table 2]

[0049] Table 2 shows that the magnesium alloy materials of Examples 1 to 5 have hardness equal to or greater than that of the magnesium alloy materials of Comparative Examples 1 and 2. The magnesium alloy materials of each example were obtained by steam treatment of magnesium alloy substrates after solution treatment, and it was confirmed that these materials achieved hardness equal to or greater than that of conventional aged materials. The magnesium alloy material of Example 4 (steam treatment temperature 210°C, treatment time 16 hours) had the highest hardness.

[0050] By referring to the corrosion resistance evaluation results and hardness measurement results described above, it was confirmed that both age hardening and film formation effects can be obtained by applying steam treatment immediately after solution treatment to an age-treated magnesium alloy substrate containing solute elements. In this case, depending on the steam treatment conditions, higher corrosion resistance and strength can be obtained than with conventional age hardening and film formation methods. [Industrial applicability]

[0051] As described above, the magnesium alloy material manufacturing method according to the present invention can produce a magnesium alloy material with high corrosion resistance and high strength by performing steam treatment on a substrate after solution treatment. In the method according to the present invention, pretreatment (microstructure control treatment) performed before steam treatment is unnecessary, so it is possible to manufacture magnesium alloy substrates with high efficiency by reducing the number of steps. The magnesium alloy material of the present invention is suitable for various structural materials such as automobile materials, train car housings, and building components, as well as medical materials, and other fields where both corrosion resistance and strength are required.

Claims

1. In a method for manufacturing a magnesium alloy material comprising a base material made of a magnesium alloy containing a solute element and a coating formed on the surface of the base material, After the aforementioned substrate is heated to a temperature of 300°C to 520°C and then rapidly cooled in a solution treatment, A method for producing a magnesium alloy material, characterized by exposing the substrate to water vapor at a temperature of 130°C to 250°C to form the coating.

2. A method for producing a magnesium alloy material according to claim 1, wherein the magnesium alloy constituting the base material contains at least one of the following elements as a solute element: aluminum, zinc, calcium, manganese, zirconium, and rare earth elements.

3. The method for producing a magnesium alloy material according to claim 1 or claim 2, wherein the solution treatment is a process of heating the base material for 12 hours or more and then rapidly cooling it.

4. A method for producing a magnesium alloy material according to claim 1 or claim 2, wherein the process of forming a film on the substrate after solution treatment is a process of exposing the substrate to water vapor for 12 hours or more and 48 hours or less.

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