Magnesium alloy and magnesium alloy member

Abstract

This magnesium alloy comprises 10 mass% to 15 mass% of Al and 0.1 mass% to 1.0 mass% of a rare earth element, with the balance being Mg and inevitable impurities. The magnesium alloy includes magnesium phases, Mg17Al12 phases, and Al11RE3 phases. RE is a rare earth element. The diffraction intensities of the magnesium phases, the Mg17Al12 phases, and the Al11RE3 phases are measured by using an XRD method (X-ray diffraction method), and when the total of the maximum diffraction intensities of the magnesium phases is x, the total of the maximum diffraction intensities of the Mg17Al12 phases is y, and the total of the maximum diffraction intensities of the Al11RE3 phases is z, the magnesium alloy has a structure satisfying the condition that y / (x+y+z) is less than 0.25 and z / (x+y+z) is 0.02 or more.

Description

Magnesium alloys and magnesium alloy components

[0001] The present disclosure relates to magnesium alloys.

[0002] Magnesium alloys are used as materials for various cases due to their high strength and low cost, but magnesium alloys generally require chemical conversion treatment to improve weather resistance, which increases manufacturing costs.

[0003] As a countermeasure against this problem, Patent Document 1 describes that the corrosion resistance of magnesium alloys can be improved by adding aluminum to the alloys, but on the other hand, it also describes that the mechanical properties may be deteriorated if the amount of aluminum added is increased.

[0004] JP 2010-116620 A

[0005] Magnesium alloy casting materials are desired to have excellent mechanical properties at room temperature as well as high weather resistance. Poor mechanical properties, for example, can lead to problems such as magnesium alloy members produced by casting being prone to breakage during use, making design more difficult and reducing usability. Furthermore, poor weather resistance can lead to problems such as rusting during use and paint peeling, which means that the magnesium alloy members do not fulfill their intended functions.

[0006] Therefore, an object of the present disclosure is to provide a magnesium alloy and a magnesium alloy member that have excellent mechanical properties and high weather resistance.

[0007] In order to achieve the above object, the magnesium alloy according to the present disclosure contains 10% by mass or more and 15% by mass or less of Al, 0.1% by mass or more and 1.0% by mass or less of rare earth elements, the balance being Mg and unavoidable impurities, and the magnesium alloy contains a magnesium phase, Mg １７ Al １２ phase, and Al １１ RE ３ phase, RE is a rare earth element, and magnesium phase, Mg １７ Al １２ phase, and Al １１ RE ３The diffraction intensity of the magnesium phase is measured, and the sum of the maximum diffraction intensities of the magnesium phase is defined as x, Mg １７ Al １２ The sum of the maximum diffraction intensities of the phases is y, Al １１ RE ３ When the sum of the maximum diffraction intensities of the phases is z, the structure satisfies y / (x+y+z) less than 0.25 and z / (x+y+z) 0.02 or more.

[0008] The magnesium alloy structural member according to the present disclosure includes the magnesium alloy.

[0009] According to the present disclosure, it is possible to provide a magnesium alloy and a magnesium alloy member having excellent mechanical properties and high weather resistance.

[0010] 1 is a graph showing the relationship between diffraction angle and diffraction intensity by XRD method according to Example 2. FIG. 2 is a graph showing the relationship between diffraction angle and diffraction intensity by XRD method according to Comparative Example 1. FIG. 3 is a graph showing the relationship between diffraction angle and diffraction intensity by XRD method according to Comparative Example 8. FIG. 4 is a graph showing the relationship between diffraction angle and diffraction intensity by XRD method after a SunSimulation test according to Example 2. FIG. 5 is a graph showing the relationship between diffraction angle and diffraction intensity by XRD method after a SunSimulation test according to Comparative Example 1. FIG. 6 is a graph showing the relationship between diffraction angle and diffraction intensity by XRD method after a SunSimulation test according to Comparative Example 8. FIG. 7 is a diagram showing a load-stroke curve obtained by a three-point bending test according to Example 2. FIG. 8 is a diagram showing a load-stroke curve obtained by a three-point bending test according to Comparative Example 1. FIG. 9 is a diagram showing a load-stroke curve obtained by a three-point bending test according to Comparative Example 8. FIG. 10A is a diagram showing an SEM image according to Comparative Example 1, FIG. 10B is a diagram showing an SEM image according to Example 2, and FIG. 10C is a diagram showing an SEM image according to Comparative Example 8. 10A is a diagram showing the observation location of an SEM image after a three-point bending test for Comparative Example 8, and FIG. 10B is a diagram showing an SEM image after a three-point bending test for Comparative Example 8.

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Magnesium alloys and magnesium alloy members according to embodiments of the present invention will be described below with reference to the drawings.

[0012] The magnesium alloy structural member according to the present embodiment contains a magnesium alloy and is produced by casting. Casting here includes die casting. The composition, properties, and structure of the magnesium alloy will be described below.

[0013] The magnesium alloy contains aluminum (Al) and rare earth elements as additive elements. The magnesium alloy also contains a magnesium phase, Mg １７ Al １２ phase, and Al １１ RE ３ The magnesium alloy has a phase (RE) where RE represents a rare earth element. Examples of types of magnesium alloys include AE-based alloys, AEX-based alloys, AEM-based alloys, and AEXM-based alloys, which are designated in accordance with ASTM standards.

[0014] (Al) Al has the effect of enhancing the weather resistance of a magnesium alloy member produced by casting a magnesium alloy. The Al content is 10% by mass or more and 15% by mass or less. Here, weather resistance refers to, for example, the diffraction intensity ratio of a protective film and a corrosion product in an XRD method after a SunSimulation test. When the Al content is 10% by mass or more and 15% by mass or less, the magnesium alloy member has excellent weather resistance. The Al content is a value when the total content of elements contained in the magnesium alloy is taken as 100% by mass. This also applies to the contents of rare earth elements, Zn, Ca, and Mn, which will be described later.

[0015] (Rare Earth Elements) Rare earth elements have the effect of improving the mechanical properties of magnesium alloy parts produced by casting magnesium alloys. The rare earth elements are at least one rare earth element selected from the group consisting of elements of Group 3 of the periodic table, i.e., scandium (Sc), yttrium (Y), lanthanides, and actinides, and also include misch metal (MM), an alloy containing multiple rare earth elements. Specifically, the rare earth elements preferably include Ce and La. The mechanical properties referred to here include, for example, the product of the maximum load and the stroke at the maximum load point in a three-point bending test. The total content of rare earth elements is preferably 0.1% by mass or more, more preferably 0.2% by mass or more. By doing so, Al, which has excellent plastic deformability, can be obtained. １１ RE ３ The ratio of the rare earth elements in the magnesium alloy structural member is increased, and the magnesium alloy structural member has excellent mechanical properties. The total content of the rare earth elements is preferably 1.0 mass % or less, and more preferably 0.5 mass % or less. By doing so, the weather resistance improving effect of Al is not easily reduced, and the weather resistance of the magnesium alloy structural member is not easily reduced. The reason is that Al １１ RE ３ This is because the amount of the phase is not excessively large, and therefore the formation of a protective film having the effect of improving weather resistance due to Al is unlikely to be hindered.

[0016] The magnesium alloy may further contain at least one element selected from the group consisting of Zn (zinc), Ca (calcium), and Mn (manganese) as an additive element. The magnesium alloy is also permitted to contain unavoidable impurities other than Mg (magnesium) and the additive element.

[0017] (Zn) Zn has the effect of improving the mechanical properties of a magnesium alloy structural member produced by casting a magnesium alloy. The Zn content is preferably, for example, 0.01 mass% or more and 2.0 mass% or less. When the Zn content is 0.01 mass% or more, the magnesium alloy structural member has excellent mechanical properties. This is because a high Zn content makes it easier to obtain the effects of improving strength and plastic deformability due to the inclusion of Zn. When the Zn content is 2.0 mass% or less, the mechanical properties of the magnesium alloy structural member at room temperature are less likely to deteriorate. This is because the Zn content is not excessively high, making it difficult for intermetallic compounds to form.

[0018] (Ca) Ca has the effect of improving the mechanical properties and flame retardancy of a magnesium alloy part produced by casting a magnesium alloy. The Ca content is preferably, for example, 0.1 mass% or more and 1.0 mass% or less. When the Ca content is 0.1 mass% or more, the magnesium alloy sheet has excellent mechanical properties and flame retardancy. This is because the strength improvement effect of containing Ca is easily obtained. Furthermore, the flame retardancy improvement effect of containing Ca is easily obtained. When the Ca content is 1.0 mass% or less, the mechanical properties of the magnesium alloy part at room temperature are less likely to deteriorate. This is because the Ca content is not excessively high, making it difficult for intermetallic compounds to be formed. Examples of intermetallic compounds include those composed of Al and Ca.

[0019] (Mn) Mn has the effect of improving the mechanical properties and corrosion resistance of a magnesium alloy member produced by casting a magnesium alloy. The Mn content is preferably, for example, 0.1 mass % or more and 1.0 mass % or less. When the Mn content is 0.1 mass % or more, the magnesium alloy member has excellent mechanical properties and corrosion resistance. This is because the strength improvement effect of containing Mn is easily obtained. Furthermore, when the Mn content is high, the corrosion resistance improvement effect of containing Mn is easily obtained. When the Mn content is 1.0 mass % or less, the magnesium alloy sheet has excellent mechanical properties. Because the Mn content is not excessively high, the crystal grain size is less likely to become coarse, and the formation of intermetallic compounds is easily suppressed. Examples of intermetallic compounds include those composed of Al and Mn.

[0020] The composition of the magnesium alloy can be confirmed by, for example, ICP optical emission spectrometry (Inductively Coupled Plasma Optical Emission Spectrometry).

[0021] Next, the structure of the magnesium alloy will be described.

[0022] Magnesium alloys consist of magnesium phase, Mg １７ Al １２ phase, and Al １１ RE ３ A magnesium alloy part produced by casting a magnesium alloy has a structure in which y / (x+y+z) and z / (x+y+z) each satisfy a specific range.

[0023] In the magnesium alloy according to the present embodiment, y / (x+y+z) is less than 0.25, and z / (x+y+z) is 0.02 or more. x is the maximum diffraction intensity at a diffraction angle of 32.0 to 32.6° among the diffraction lines obtained from the magnesium phase measured by the XRD method. １ , the maximum diffraction intensity at 34.4 to 35.0° is x ２ , the maximum diffraction intensity at 36.5 to 37.1° is x ３ The sum of the maximum diffraction intensities when １ +x ２ +x ３y is the Mg content measured by the XRD method. １７ Al １２ Among the diffraction lines obtained from the phase, the maximum diffraction intensity at a diffraction angle of 35.6 to 36.2° is defined as y １ , the maximum diffraction intensity at 39.7 to 40.3° is y ２ , the maximum diffraction intensity at 41.3 to 41.9° is y ３ , the maximum diffraction intensity at 43.2 to 43.8° is y ４ The sum of the maximum diffraction intensities when １ +y ２ +y ３ +y ４ z is the Al content measured by the XRD method. １１ RE ３ Among the diffraction lines obtained from the phase, the maximum diffraction intensity at a diffraction angle of 33.2 to 33.6° is defined as z １ , the maximum diffraction intensity at 33.7 to 34.1° is z ２ The sum of the maximum diffraction intensities when １ +z ２ When y / (x+y+z) is less than 0.25 and z / (x+y+z) is 0.02 or more, the magnesium alloy member has excellent mechanical properties. １７ Al １２ Al phase ratio is low and has high plastic deformability １１ RE ３ This is because the proportion of the phase is high.

[0024] As will be described in detail later, x, y, and z can be measured using the maximum diffraction intensity of the diffraction line by the XRD method.

[0025] Next, a method for manufacturing a magnesium alloy structural member will be described. The method for manufacturing a magnesium alloy structural member according to this embodiment includes a melting step, a homogenizing step, and a solidification step. In the melting step, a lump of pure magnesium and a lump of each additive element metal or a lump alloyed with the additive elements are completely melted to produce molten magnesium having the additive elements and contents described above. In the homogenizing step, the molten metal produced in the melting step is sufficiently stirred to homogenize the components. In the solidification step, the molten metal homogenized in the homogenizing step is solidified. This magnesium alloy structural member may be a cast material produced by gravity casting, continuous casting, or die casting, regardless of the casting method.

[0026] Next, the properties of the magnesium alloy member produced by casting the magnesium alloy will be described.

[0027] First, the maximum load × stroke at the maximum load point in a three-point bending test will be described. The magnesium alloy structural member of this embodiment contains the elements described above, and satisfies the following conditions: y / (x+y+z) is less than 0.25, and z / (x+y+z) is 0.02 or greater. As a result, the maximum load × stroke at the maximum load point in a three-point bending test of the magnesium alloy structural member can be 1200 N·mm or greater. A maximum load × stroke at the maximum load point in a three-point bending test of 1200 N·mm or greater indicates excellent mechanical properties. The maximum load × stroke at the maximum load point in a three-point bending test can be determined using a load-stroke curve obtained by the three-point bending test, which will be described later.

[0028] Next, the weather resistance of the magnesium alloy member will be described. The weather resistance of the magnesium alloy member can be measured by the diffraction intensity ratio between the protective film and the corrosion product in an XRD method after a SunSimulation test.

[0029] The magnesium alloy structural member according to this embodiment contains the above-described elements, and satisfies y / (x+y+z) less than 0.25 and z / (x+y+z) equal to or greater than 0.02, so that the magnesium alloy structural member can have a diffraction intensity ratio of 0.0035 or greater, measured by XRD, between the protective film and corrosion products after a SunSimulation test. A diffraction intensity ratio of 0.0035 or greater, measured by XRD, between the protective film and corrosion products after a SunSimulation test indicates excellent weather resistance. The diffraction intensity ratio of the protective film and corrosion products after a SunSimulation test, measured by XRD, can be determined by measuring a test specimen obtained by a SunSimulation test, which will be described later, by XRD.

[0030] The magnesium alloy and magnesium alloy member having the above configuration have excellent mechanical properties and high weather resistance because the Al content is 10% by mass or more and 15% by mass or less, y / (x+y+z) is less than 0.25, and z / (x+y+z) is 0.02 or more. Specifically, the excellent mechanical properties are achieved because y / (x+y+z) is less than 0.25 and z / (x+y+z) is 0.02 or more. The high weather resistance is achieved because the Al content is 10% by mass or more and 15% by mass or less, which facilitates the formation of a protective film that improves weather resistance.

[0031] The magnesium alloy member according to the present embodiment can be suitably used as a component for transportation vehicles such as automobiles, aircraft, and railways, as well as for electrical and electronic devices. In particular, the magnesium alloy member according to the present embodiment can be suitably used, for example, for head-up displays. Head-up displays made using this magnesium alloy member have excellent mechanical properties at room temperature and also high weather resistance, and therefore can be used in a variety of environments, such as environments requiring shock absorption resistance and high humidity environments, and have a wide range of applications.

[0032] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0033] Examples and comparative examples of magnesium alloy members obtained by casting magnesium alloys are described below. Here, the magnesium alloy members were subjected to a three-point bending test at room temperature, scanning electron microscope (SEM) observation before the three-point bending test, SEM observation after the three-point bending test, a SunSimulation test, and X-ray diffraction after the SunSimulation test.

[0034] The magnesium alloy structural members of each sample were produced through the same process as in the manufacturing method of the magnesium alloy structural member described above, that is, a melting step for preparing molten magnesium, a homogenizing step for homogenizing the components, and a solidification step for solidifying the molten magnesium. The types and contents of the additive elements in the cast materials of the samples of Examples 1 to 3 and Comparative Examples 1 to 8 are as shown in Table 1.

[0035]

[0036] [Structural Analysis] Measurement pieces for structural analysis of Examples 1 to 3 and Comparative Examples 1 to 8 were prepared from magnesium alloy members. The magnesium alloy members were made of a magnesium phase, Mg １７ Al １２ phase, and Al １１ RE ３ RE denotes rare earth elements. Here, RE includes Ce and La. Using an X-ray diffractometer, magnesium phase, Mg １７ Al １２ phase, and Al １１ RE ３ The phases were detected and texture analysis was carried out.

[0037] Prior to polishing, the test specimens were cut into 20 mm × 20 mm × 5 mm. The 20 mm × 20 mm surface was used as the polishing surface, and the test specimens were polished using polishing paper with silicon carbide abrasive grains. Three types of polishing paper were used: #100, #1000, and #4000. After polishing, the surface was washed with ethanol to prepare test specimens for structural analysis.

[0038] Each test piece was measured using a MiniFlex 600 X-ray diffractometer manufactured by Rigaku Corporation. The target material was Cu. The measurement conditions were room temperature, tube voltage of 40 kV, tube current of 15 A, step width of 0.02°, scanning speed of 1° / min, and measurement range of diffraction angle (2θ) of 30 to 50°.

[0039] Next, the magnesium phase, Mg, in the magnesium alloy members of Examples 1 to 3 and Comparative Examples 1 to 8 was １７ Al １２ phase, and Al １１ RE ３ To perform the phase structure analysis, x, y, and z were determined as follows: Mg １７ Al １２ The ratio of the phases is y / (x+y+z), Al １１ RE ３ The phase ratio was calculated by z / (x+y+z).

[0040] From the graph showing the relationship between the diffraction angle and the diffraction intensity measured by the XRD method (X-ray diffraction method), the maximum diffraction intensity at a diffraction angle of 32.0 to 32.6° is １ , the maximum diffraction intensity at 34.4 to 35.0° is x ２ , the maximum diffraction intensity at 36.5 to 37.1° is x ３ The sum of the maximum diffraction intensities x = x １ +x ２ +x ３ and the maximum diffraction intensity at a diffraction angle of 35.6 to 36.2° is y １ , the maximum diffraction intensity at 39.7 to 40.3° is y ２ , the maximum diffraction intensity at 41.3 to 41.9° is y ３ , the maximum diffraction intensity at 43.2 to 43.8° is y ４ The sum of the maximum diffraction intensities when １ +y ２ +y ３ +y ４ and the maximum diffraction intensity at a diffraction angle of 33.2 to 33.6° is z １ , the maximum diffraction intensity at 33.7 to 34.1° is z ２ The sum of the maximum diffraction intensities z = z １ +z ２and were calculated to determine y / (x+y+z) and z / (x+y+z).

[0041] The values ​​of y / (x+y+z) and z / (x+y+z) thus determined are shown in Table 2. When y / (x+y+z) is less than 0.25 and z / (x+y+z) is 0.02 or more, the magnesium alloy part has excellent mechanical properties. This is because Mg, which is likely to reduce plastic deformability, １７ Al １２ Al phase ratio is low and has high plastic deformability １１ RE ３ This is thought to be because the proportion of the phase is high.

[0042] [Evaluation of Mechanical Properties] The mechanical properties of the magnesium alloy members of Examples 1 to 3 and Comparative Examples 1 to 8 were evaluated by measuring the maximum load × stroke at the maximum load point in a three-point bending test of the magnesium alloy members as follows. Test specimens measuring 35 mm in length, 25 mm in width, and 3 mm in thickness were prepared from each sample magnesium alloy member. Imada Corporation's MX2-1000N motorized test stand, ZTA-5000N digital force gauge, and BT-5000N three-point bending test jig were used. The shaft diameter of the bending test jig was 10 mm. A load was applied at room temperature so that the bending axis was perpendicular to the longitudinal direction of each test specimen. Measurement began when the load reached 5 N. Three magnesium alloy members of each sample were evaluated, and the maximum load × stroke at the maximum load point was calculated using the average values ​​of the maximum load and stroke at the maximum load point. The calculated values ​​are shown in Table 2.

[0043] [Weather Resistance Evaluation] The weather resistance of the magnesium alloy members of Examples 1 to 3 and Comparative Examples 1 to 8 was evaluated by a SunSimulation test and X-ray diffraction after the SunSimulation test. The SunSimulation test is a test for evaluating light resistance, moisture resistance, and heat resistance, as defined by the German Industrial Standard "DIN 75220 (Z-In-1)." Specifically, the SunSimulation test is an accelerated environmental test in which UV irradiation at high temperature (80°C) is performed for 15 days, followed by wetting at low temperature (-10°C), UV irradiation at high temperature, and wetting at low temperature are repeated for 10 days.

[0044] First, a 50 mm x 50 mm x 10 mm test piece was prepared from each sample magnesium alloy part. Next, a SunSimulation test was conducted, with the 50 mm x 50 mm surface of each test piece being the exposed surface. Each sample was measured using the above-mentioned X-ray diffraction device, with the exposed surface being the measurement surface. Diffraction rays at diffraction angles of 11 to 12° and 23 to 24° were considered to be diffraction from the protective film, and diffraction rays at diffraction angles of 18 to 19° were considered to be diffraction from the corrosion products. Since the diffraction from the corrosion products has a broadening effect, the sum of the diffraction intensity at a diffraction angle of 18 to 19° was taken as A. The value obtained by dividing the maximum diffraction intensity at a diffraction angle of 11 to 12° by the average diffraction intensity was taken as B. １ The maximum diffraction intensity at a diffraction angle of 23 to 24° divided by the average diffraction intensity is B. ２ When this is the case, (B １ +B ２ ) / A is shown in Table 2.

[0045]

[0046] As shown in Table 2, the magnesium alloy structural members of Examples 1 to 3 had an Al content of 10% by mass or more and 15% by mass or less, and satisfied all three requirements: y / (x + y + z) < 0.25 and z / (x + y + z) ≥ 0.02. Furthermore, the magnesium alloy structural members of these samples had a maximum load × stroke at the maximum load point of 1200 N·mm or more in a three-point bending test. This indicates that the magnesium alloy structural members of these samples had excellent mechanical properties at room temperature. Furthermore, the magnesium alloy structural members of these samples had an Al content of 10% by mass or more and 15% by mass or less, and the diffraction intensity ratio of the protective film and corrosion products after the SunSimulation test was 0.0035 or more in an XRD method, indicating that they had excellent weather resistance.

[0047] In contrast to these samples, the magnesium alloy member of Comparative Example 1 satisfied the relationship y / (x + y + z) < 0.25, but did not satisfy the relationship z / (x + y + z) ≥ 0.02. This indicates that the magnesium alloy member had poor mechanical properties. Furthermore, since the magnesium alloy member of Comparative Example 1 had an Al content of less than 10% by mass, the diffraction intensity ratio of the protective film and corrosion products measured by the XRD method after the SunSimulation test was less than 0.0035. This indicates that the magnesium alloy member had poor weather resistance.

[0048] The magnesium alloy structural members of Comparative Examples 2 and 3 satisfied the Al content of 10 mass % or more and 15 mass % or less, but did not satisfy the other two requirements of y / (x + y + z) < 0.25 and z / (x + y + z) ≥ 0.02. That is, it was found that the magnesium alloy structural members of Comparative Examples 2 and 3 had poor mechanical properties.

[0049] The magnesium alloy members of the samples of Comparative Examples 4 and 5 satisfied the two requirements of y / (x + y + z) < 0.25 and z / (x + y + z) ≥ 0.02, but did not satisfy the requirement of an Al content of 10 mass%. Furthermore, the magnesium alloy members of the samples of Comparative Examples 4 and 5 had diffraction intensity ratios of less than 0.0035 in the XRD analysis of the protective film and corrosion products after the SunSimulation test. That is, it was found that the magnesium alloy members of the samples of Comparative Examples 4 and 5 had poor weather resistance.

[0050] The magnesium alloy structural member of Comparative Example 6 satisfied the requirements of an Al content of 10% by mass to 15% by mass and z / (x + y + z)≧0.02, but did not satisfy y / (x + y + z)<0.25. The magnesium alloy structural member of Comparative Example 7 satisfied the requirements of y / (x + y + z)<0.25, but did not satisfy the requirements of an Al content of 10% by mass to 15% by mass and z / (x + y + z)≧0.02. The magnesium alloy structural member of Comparative Example 8 satisfied the requirements of an Al content of 10% by mass to 15% by mass and z / (x + y + z)≧0.02, but did not satisfy the requirements of y / (x + y + z)<0.25. Furthermore, the magnesium alloy structural members of Comparative Examples 6 to 8 had a maximum load × stroke at the maximum load point of less than 1200 N·mm in a three-point bending test. This indicates that the magnesium alloy structural members of Comparative Examples 6 to 8 have poor mechanical properties.

[0051] As representative examples, graphs showing the relationship between the diffraction angle and the diffraction intensity measured by the XRD method for Example 2, Comparative Example 1, and Comparative Example 8 are shown in Figures 1 to 3, respectively. １７ Al １２ phase, and Al １１ RE ３ Specifically, diffraction at diffraction angles of 32.0 to 32.6°, 34.4 to 35.0°, and 36.5 to 37.1° indicates the presence of a magnesium phase, and diffraction at diffraction angles of 35.6 to 36.2°, 39.7 to 40.3°, 41.3 to 41.9°, and 43.2 to 43.8° indicates the presence of a Mg phase. １７ Al １２ The maximum diffraction intensity at diffraction angles of 33.2 to 33.6° and 33.7 to 34.1° indicates the presence of Al phase. １１ RE ３ The larger the value obtained by dividing the sum of the maximum diffraction intensities corresponding to a specific phase by the sum of the maximum diffraction intensities corresponding to all phases, the greater the content of the specific phase.

[0052] As shown in FIG. 1, in Example 2, the diffraction intensity x corresponding to the magnesium phase １ , x ２ , x ３ is Mg １７ Al１２ Diffraction intensity y corresponding to the phase １ , y ２ , y ３ , y ４ It was relatively larger than Al. １１ RE ３ Diffraction intensity z corresponding to the phase １ , z ２ Therefore, it is considered that Example 2 satisfied the conditions y / (x+y+z)<0.25 and z / (x+y+z)≧0.02 as described above, and the Al content was 10% by mass or more and 15% by mass or less, and therefore resulted in excellent mechanical properties and weather resistance.

[0053] As shown in FIG. 2, in Comparative Example 1, the diffraction intensity x corresponding to the magnesium phase １ , x ２ , x ３ , and Mg １７ Al １２ Diffraction intensity y corresponding to the phase １ , y ２ , y ３ , y ４ However, Al １１ RE ３ Diffraction intensity z corresponding to the phase １ , z ２ is extremely small, and Al １１ RE ３ Therefore, it is considered that Comparative Example 1 did not satisfy z / (x+y+z)≧0.02, resulting in poor mechanical properties.

[0054] As shown in FIG. 3, in Comparative Example 8, the diffraction intensity x corresponding to the magnesium phase １ , x ２ , x ３ was smaller than those in Comparative Example 1 and Example 2. Furthermore, Mg １７ Al １２ Diffraction intensity y corresponding to the phase １ , y ２ , y ３ , y ４ was larger than those in Comparative Example 1 and Example 2. Therefore, it is considered that Comparative Example 8 did not satisfy y / (x+y+z)<0.25, resulting in poor mechanical properties.

[0055] 4 to 6 show graphs showing the relationship between diffraction angle and diffraction intensity by the XRD method after the SunSimulation test for Example 2, Comparative Example 1, and Comparative Example 8. Each graph shows the presence of a protective film and corrosion products after the SunSimulation test by diffraction. Diffraction at diffraction angles of 11.0 to 12.0° and 23.0 to 24.0° indicates the presence of a protective film, and diffraction intensity B １ , B ２ The larger the diffraction intensity B at diffraction angles of 18.0 to 19.0°, the easier it is for a protective film to form, and the higher the weather resistance. Diffraction at diffraction angles of 18.0 to 19.0° indicates the presence of corrosion products. If corrosion products are present, the diffraction intensity in this range will be larger overall, and the higher the diffraction intensity, the lower the weather resistance. That is, the diffraction intensity B at diffraction angles of 11.0 to 12.0° and 23.0 to 24.0° １ , B ２ The larger the value obtained by dividing the sum of the diffraction intensities (A) at diffraction angles of 18.0 to 19.0°, the higher the weather resistance.

[0056] In Example 2 shown in FIG. 4 and Comparative Example 8 shown in FIG. 6, the diffraction intensity B corresponding to the protective film １ , B ２ The diffraction intensity A corresponding to the corrosion product was small, and the diffraction intensity B １ , B ２ The values ​​obtained by dividing the sum of these by A were 0.00374 and 0.00481, which were 0.0035 or more, and therefore it was found that the weather resistance was high.

[0057] In contrast, as shown in FIG. 5, in Comparative Example 1, the diffraction intensity B １ , B ２ However, the diffraction intensity A corresponding to the corrosion product was also relatively large, and the diffraction intensity B １ , B ２ The value obtained by dividing the sum of these by A was 0.00261, which is less than 0.0035, and therefore it was found that the weather resistance was low.

[0058] Next, the load-stroke curves of Example 2, Comparative Example 1, and Comparative Example 8 measured by a three-point bending test are shown in Figures 7 to 9, respectively. In each curve, there is a point where the load drops significantly, and the load at that point is called the maximum load. The maximum load and the stroke at the maximum load point are indicators of mechanical properties, and the larger the value obtained by multiplying them, the more excellent the mechanical properties.

[0059] 7, Example 2 had a large maximum load and a large stroke at the maximum load point, and the product of these was also large at 3005 N mm, which was greater than 1200 N mm. In other words, Example 2 was found to have excellent mechanical properties.

[0060] In Comparative Example 1 shown in Fig. 8 and Comparative Example 8 shown in Fig. 9, the maximum load and the stroke at the maximum load point were small, and the value obtained by multiplying these values ​​was less than 1000 N mm. In other words, it was found that Comparative Example 1 and Comparative Example 8 had poor mechanical properties.

[0061] [SEM Observation] Fig. 10(A) is an SEM image of Comparative Example 1, Fig. 10(B) is an SEM image of Example 2, and Fig. 10(C) is an SEM image of Comparative Example 8. In Comparative Example 1, the magnesium phase in the dark gray part and the Mg １７ Al １２ However, since it does not contain rare earth elements, the Al phase in the white part １１ RE ３ In Example 2 and Comparative Example 8, the magnesium phase in the dark gray portion and the Mg phase in the light gray portion were not observed. １７ Al １２ phase, and Al in the white part １１ RE ３ Comparative Example 8 does not satisfy the requirement of y / (x+y+z)<0.25, and therefore has a lower Mg content than Example 2, which satisfies the requirement of y / (x+y+z)<0.25. １７ Al １２ It was found that the area of ​​the Mg phase was larger than that of the Mg phase in Example 2. １７ Al １２ For the phase, Al １１ RE ３Because the proportion of this phase is high, extra energy is required for crack propagation, which is thought to improve the mechanical properties of magnesium alloy members.

[0062] [SEM Observation After Three-Point Bending Test] Fig. 11(B) shows an SEM image of the observation location shown in Fig. 11(A) after the three-point bending test of Comparative Example 8. In Comparative Example 8, the magnesium phase is shown in the dark gray area, and the Mg １７ Al １２ phase, and Al in the white part １１ RE ３ The black parts are cracks that occurred during the three-point bending test. １７ Al １２ The Al in the white part occurs inside the phase. １１ RE ３ This also indicates that the Mg １７ Al １２ For the phase, Al １１ RE ３ It is believed that if the proportion of this phase is high, extra energy is required for crack propagation, and the mechanical properties of the magnesium alloy member are improved.

[0063] As described above, it has been found that a magnesium alloy member containing the above-mentioned elements, with y / (x+y+z) being less than 0.25 and z / (x+y+z) being 0.02 or greater, exhibits excellent mechanical properties and high weather resistance. Specifically, the excellent mechanical properties are believed to be due to y / (x+y+z) being less than 0.25 and z / (x+y+z) being 0.02 or greater. Furthermore, the high weather resistance is believed to be due to the Al content being 10% by mass or greater and 15% by mass or less, which facilitates the formation of a protective film that improves weather resistance. While the above-described examples have been described using Ce and La as rare earth elements, similar effects are believed to be obtained when other rare earth elements are used. The other rare earth element is at least one rare earth element selected from the group consisting of elements of Group 3 of the periodic table, i.e., scandium (Sc), yttrium (Y), lanthanides, and actinides, and also includes misch metal (MM), an alloy containing multiple rare earth elements. Furthermore, the content of the rare earth element is not limited to the content of the above-mentioned examples, and is preferably 0.1 mass% or more and 1.0 mass% or less, as long as z / (x + y + z) is 0.02 or more. Furthermore, the above-mentioned Examples 1 to 3 were described as examples containing Zn and Ca. Even if the magnesium alloy member does not contain Zn or Ca, it is believed that excellent mechanical properties and weather resistance can be achieved by containing at least Al and a rare earth element, and satisfying y / (x + y + z) less than 0.25 and z / (x + y + z) being 0.02 or more.

[0064] The present disclosure allows various embodiments and modifications without departing from the broad spirit and scope of the present disclosure. Furthermore, the above-described embodiments are intended to illustrate the present disclosure and do not limit the scope of the present disclosure. That is, the scope of the present disclosure is defined by the claims, not the embodiments. Various modifications made within the scope of the claims and the meaning of the disclosure equivalent thereto are considered to be within the scope of the present disclosure.

[0065] This application is based on Japanese Patent Application No. 2024-024951, filed on February 21, 2024. The entire specification, claims, and drawings of Japanese Patent Application No. 2024-024951 are incorporated herein by reference.

Claims

1. A magnesium alloy containing 10% by mass or more and 15% by mass or less of Al, 0.1% by mass or more and 1.0% by mass or less of a rare earth element, the balance being Mg and unavoidable impurities, wherein the magnesium alloy comprises a magnesium phase, Mg １７ Al １２ phase, and Al １１ RE ３ phase, RE is a rare earth element, and magnesium phase, Mg １７ Al １２ phase, and Al １１ RE ３ The diffraction intensity of the magnesium phase is measured, and the sum of the maximum diffraction intensities of the magnesium phase is defined as x, Mg １７ Al １２ The sum of the maximum diffraction intensities of the phases is y, Al １１ RE ３ A magnesium alloy having a structure in which, when the sum of the maximum diffraction intensities of the phases is z, y / (x+y+z) is less than 0.25 and z / (x+y+z) is 0.02 or more.

2. The magnesium alloy according to claim 1, further containing one or more elements selected from the group consisting of 0.01% by mass or more and 2.0% by mass or less of Zn, 0.1% by mass or more and 1.0% by mass or less of Ca, and 0.1% by mass or more and 1.0% by mass or less of Mn.

3. A magnesium alloy member comprising the magnesium alloy according to claim 1 or 2.

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