magnesium alloy

Abstract

To provide a magnesium alloy that has sufficient mechanical property in addition to flame retardancy.SOLUTION: The magnesium alloy of the present invention consists of 5.5-6.5 mass% of aluminum (Al) with respect to the whole, 0.2-0.5 mass% of calcium (Ca) with respect to the whole, 0.1-0.6 mass% of manganese (Mn) with respect to the whole, 0.5-1.5 mass% of misch metal (Mm) with respect to the whole, and the balance magnesium and unavoidable impurities.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a magnesium alloy having improved flame retardancy and mechanical properties. [Background technology]

[0002] BACKGROUND ART Various metal materials such as iron and aluminum are used to construct housings and various parts in a variety of equipment and devices, including electronic devices, precision instruments, transportation equipment such as automobiles and aircraft, and manufacturing machinery.

[0003] Electronic and precision instruments need to be lightweight for ease of use and portability. They also need to be lightweight yet durable and strong. From this perspective, lightweight metal materials are increasingly being used to construct the housings and various parts (components) of electronic and precision instruments.

[0004] Here, there is a particular need for weight reduction in transportation equipment to improve fuel efficiency and transportation performance. Lighter transportation equipment improves its running and flying performance. Furthermore, lighter transportation equipment reduces the amount of fuel required, improving fuel efficiency. In recent years, the electrification of transportation equipment, particularly automobiles and electric vehicles (EVs), has progressed rapidly, and there is an extremely high need for weight reduction in terms of battery weight, power consumption, and cruising range. Of course, there are many other benefits that come with weight reduction.

[0005] From this perspective, light metals such as aluminum and their alloys have come to be used as lightweight metallic materials. Among these light metal materials, there is a demand for light metal alloys that are suitable for molding processes such as die casting. Furthermore, structural members used in transportation equipment are required to have high mechanical properties such as strength in addition to light weight.

[0006] For example, reducing the weight of suspension components such as wheels for automobiles, including minicars and motorcycles, directly reduces unsprung weight, contributing to improved fuel economy and maneuverability. However, these components are subject to increased loads and operational stresses, as well as stresses from physical collisions. They must be strong enough to withstand these loads.

[0007] The same is true for manufacturing machinery. Many devices and equipment require ease of operation, ease of transport, fuel efficiency, and eco-friendliness, and lightweight construction is one of the criteria required to achieve these. To achieve this lightweight construction, light metal materials are being used or developed.

[0008] To reduce the weight of automobile wheels, iron-based metals were first used, followed by aluminum alloys, which are primarily composed of aluminum. Magnesium is a lighter element than aluminum. The density of magnesium at room temperature is 1.7 g / cm3, which is about 1 / 4 the density of iron and about 2 / 3 the density of aluminum.

[0009] For this reason, some vehicles use a magnesium alloy called AM60, which is an alloy containing approximately 6% aluminum by mass, 0.3% manganese by mass, and the remainder magnesium and unavoidable impurities. This AM60 alloy is die-cast to manufacture vehicle wheels.

[0010] However, AM60 alloy has the problem of being highly flammable due to its low ignition temperature. Because magnesium as an element has a low ignition temperature, magnesium alloys also have low ignition temperatures and are highly flammable. In other words, they have low flame retardancy. When molding AM60 magnesium alloys into structural components such as vehicle wheels, die casting is preferred, as this is suitable for reducing costs and increasing production volume.

[0011] During the molding process, such as die casting, heat is applied to the magnesium alloy. For this reason, low flame retardancy is undesirable, as it can have a negative impact on manufacturing precision and the manufacturing process. Furthermore, transportation equipment and electronic devices can become very hot depending on the conditions of use. In this case, low flame retardancy is also undesirable when magnesium alloys are used in structural components of transportation equipment and electronic devices.

[0012] As a result, the magnesium alloy known as AM60 had insufficient flame retardancy to be used as structural components in transportation equipment and electronic devices.

[0013] For this reason, a magnesium alloy technology for improving flame retardancy has been proposed (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Special Publication No. 2013-512338 Summary of the Invention [Problem to be solved by the invention]

[0015] Patent Document 1 discloses a magnesium alloy containing 1.0 to 7.0 wt% Al, 0.05 to 2.0 wt% Ca, 0.05 to 2.0 wt% Y, more than 0 to 6.0 wt% Zn, the balance being Mg and other unavoidable impurities, wherein the contents of Ca and Y are 0.1 to 2.5% relative to the total weight of the magnesium alloy.

[0016] The magnesium alloy of Patent Document 1 has improved flame retardancy and can be used as a structural member for equipment that is exposed to high-temperature environments, and can withstand high-temperature environments during manufacturing.

[0017] However, the magnesium alloy of Patent Document 1 contains added Y (yttrium). The addition of yttrium causes the problem of sludge formation during melting in alloy production. If sludge is formed or mixed in, it can lead to problems such as reduced corrosion resistance and mechanical properties when structural components are manufactured using the magnesium alloy as a material by die casting or the like.

[0018] Furthermore, a decrease in mechanical properties can lead to problems such as insufficient strength in the manufactured structural members. Here, tensile strength is important as an indicator of strength for structural members of transportation equipment, such as vehicle wheels. A certain degree of elongation and toughness is also required (to cope with loads during use). The magnesium alloy of Patent Document 1 has sufficient tensile strength, but has the problem of insufficient elongation and toughness. This problem poses a problem during manufacturing and results in insufficient required properties for the manufactured structural members.

[0019] In addition, structural components such as vehicle wheels must be highly resistant to impacts. Automobiles and other transportation vehicles inevitably travel over uneven surfaces. In such situations, tires are subjected to strong vibrations and shocks, which in turn applies shocks to vehicle wheels.

[0020] For this reason, magnesium alloys that can be used for vehicle wheels and the like are required to have high shock absorption properties.

[0021] In view of the above problems, an object of the present invention is to provide a magnesium alloy that has sufficient mechanical properties in addition to flame retardancy. [Means for solving the problem]

[0022] In view of the above problems, the magnesium alloy of the present invention comprises 5.5 mass % to 6.5 mass % of aluminum (Al) based on the total mass, 0.2% by mass to 0.5% by mass of calcium (Ca) based on the total, 0.1% by mass to 0.6% by mass of manganese (Mn) based on the total; 0.5% by mass to 1.5% by mass of misch metal (Mm) based on the total mass; The balance consists of magnesium and unavoidable impurities. [Effects of the Invention]

[0023] The magnesium alloy of the present invention is lighter than conventional aluminum alloys. Therefore, it can be used as a replacement material for structural components in fields where aluminum alloys have traditionally been used, such as vehicle wheels. Because it is lighter than conventional aluminum alloys, when it is used as a structural component for transportation equipment, for example, it can lead to improved fuel efficiency of the transportation equipment.

[0024] It also has excellent flame retardancy and can withstand high-temperature environments during manufacturing and use as a structural component, which results in improved ease of manufacturing and a wider range of applications for structural components.

[0025] In addition, because it has high tensile strength and a certain level of elongation, it can be used in fields where magnesium alloys were previously thought to be difficult to apply. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a flowchart of a manufacturing process of a magnesium alloy in accordance with a first embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing a melting step in an embodiment of the present invention. [Figure 3] 1 is a table showing the measurement results of three tensile strengths, elongations, and impact absorption energy. [Figure 4]This is a cross-table showing the tensile strength when the composition ranges of aluminum and misch metal are changed (calcium and manganese are constant at 0.3 mass%, and magnesium is the remainder). [Figure 5] This is a cross-table showing the elongation when the composition ranges of aluminum and misch metal are changed (calcium and manganese are constant at 0.3 mass%, magnesium is the remainder). [Figure 6] 1 is a cross-table showing the impact absorption energy when the composition ranges of aluminum and misch metal are changed (calcium and manganese are constant at 0.3 mass%, magnesium is the remainder). [Figure 7] 1 is a table showing the results of a combustion test of a magnesium alloy according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] The magnesium alloy according to the first aspect of the present invention comprises 5.5 mass % to 6.5 mass % of aluminum (Al) based on the total mass, 0.2% by mass to 0.5% by mass of calcium (Ca) based on the total, 0.1% by mass to 0.6% by mass of manganese (Mn) based on the total; 0.5% by mass to 1.5% by mass of misch metal (Mm) based on the total mass; The balance consists of magnesium and unavoidable impurities.

[0028] This structure provides a magnesium alloy that is excellent in tensile strength, elongation, and impact absorption, and is suitable for structural members that require lightweight construction.

[0029] In a magnesium alloy according to a second aspect of the present invention, in addition to the first aspect, the calcium content is 0.25 mass % to 0.35 mass % based on the total mass.

[0030] This configuration makes it possible to obtain a magnesium alloy with sufficient elongation.

[0031] In a magnesium alloy according to a third aspect of the present invention, in addition to the first or second aspect, the misch metal is contained in an amount of 0.5 mass % to 1.0 mass % of the total.

[0032] This configuration makes it possible to obtain a magnesium alloy with even greater elongation.

[0033] A fourth aspect of the present invention provides a magnesium alloy according to any one of the first to third aspects, wherein a test piece of the magnesium alloy has a tensile strength of 260 MPa or more.

[0034] This configuration allows application to structural members that require high durability against loads and stresses.

[0035] A magnesium alloy according to a fifth aspect of the present invention, in addition to any one of the first to fourth aspects, has an elongation of 15.0% or more in a test piece of the magnesium alloy.

[0036] This configuration allows the structure to be applied to structural members that require high safety by deforming without immediately breaking even when excessive load or stress is applied to the structural member.

[0037] A sixth aspect of the present invention provides a magnesium alloy according to any one of the first to fifth aspects, wherein a test piece of the magnesium alloy exhibits an impact absorption energy of 13 J or more in a Charpy impact test.

[0038] This structure makes it possible to obtain a magnesium alloy that, when applied to a structural member, has high shock absorption properties for the structural member.

[0039] A seventh aspect of the present invention provides a magnesium alloy according to the first to seventh aspects of the present invention, wherein the mischmetal is a combination of at least one of scandium (Sc), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0040] This structure makes it possible to obtain a magnesium alloy that is excellent in tensile strength, elongation, and shock absorption.

[0041] A cast structural member using a magnesium alloy according to an eighth aspect of the present invention uses any one of the first to seventh magnesium alloys.

[0042] This configuration allows for a cast structural member that has excellent resistance to loads, stresses, deformations, impacts, and the like.

[0043] A ninth aspect of the present invention provides a cast structural member using a magnesium alloy, in addition to the eighth aspect, wherein the cast structural member is used in any one of automobiles, motorcycles, aircraft, ships, and railway vehicles, This includes at least one of internal combustion engines and electric powertrains, traction motors, inverters, reducers, transmissions, pistons, shafts, connecting rods, covers, cylinders, cylinder blocks, arms, knuckles, pillars, wheels, compressor housings, steering, internal housings, engine mounts, oil pans, gears, gear cases, nuts, screws, bolts, heat sinks for LED lighting devices, pneumatic and electric tools, and the components and housings that make up these.

[0044] This configuration provides a member that is highly resistant to loads, stresses, deformations, impacts, and the like.

[0045] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0046] (Embodiment 1)

[0047] (magnesium alloy)

[0048] The magnesium alloy of the present invention has the following composition: 5.5% by mass to 6.5% by mass of aluminum (Al) based on the total, 0.2% by mass to 0.5% by mass of calcium (Ca) based on the total, 0.1% by mass to 0.6% by mass of manganese (Mn) based on the total; 0.5% by mass to 1.5% by mass of misch metal (Mm) based on the total mass; The balance consists of magnesium and unavoidable impurities.

[0049] Magnesium alloys contain magnesium, calcium, aluminum, manganese, and misch metal. However, this does not exclude the inclusion of unavoidable mixtures that are inevitably mixed in due to the origin of raw materials or the manufacturing process.

[0050] In addition, the present invention does not exclude the addition of components that do not impair the properties and characteristics of the magnesium alloy. Similarly, the present invention does not exclude the addition of components that do not impair the intent of the invention. For example, components other than those mentioned above may be added, but they do not impair the properties and characteristics of the magnesium alloy of the present invention.

[0051] The composition ratio of aluminum (hereinafter referred to as "Al" as needed) is 5.5 mass% to 6.5 mass% with respect to the total. The composition ratio of calcium (hereinafter referred to as "Ca" as needed) is 0.2 mass% to 0.5 mass% with respect to the total. The composition ratio of manganese (hereinafter referred to as "Mn" as needed) is 0.1 mass% to 0.6 mass%. The composition ratio of misch metal (hereinafter referred to as "Mm" as needed) is 0.5 mass% to 1.5 mass%.

[0052] The magnesium alloy of the present invention has such a composition ratio.

[0053] The magnesium alloy of the present invention is required to have tensile strength, elongation, and impact absorption properties. For example, the magnesium alloy of the present invention is used for structural members of transportation equipment and facility equipment. One example is its use in vehicle wheels.

[0054] Magnesium alloys for such applications are required to withstand loads and stresses when used as structural components such as vehicle wheels, and sufficient tensile strength is required to achieve this load and stress resistance.

[0055] At the same time, structural components such as vehicle wheels undergo deformation and strain depending on the load or stress applied. For this reason, magnesium alloys used in these components are required to have sufficient elongation. Furthermore, the elongation property makes them suitable for plastic processing.

[0056] Furthermore, structural components such as vehicle wheels are often subjected to impacts. Vehicle wheels are subject to impacts when the vehicle runs over a bump. Equipment may also be subject to impacts such as being dropped. Magnesium alloys are also required to have the ability to absorb such impacts.

[0057] The magnesium alloy of the present invention having the above-mentioned composition ratio has tensile strength, elongation, and impact absorption properties suitable for these applications, that is, it is a magnesium alloy suitable for the intended applications.

[0058] Also, Mischmetal is as follows:

[0059] Misch metal is a combination of at least one of scandium (Sc), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0060] The inclusion of misch metal improves strength and flame retardancy, as well as corrosion resistance.

[0061] (manufacturing process)

[0062] Magnesium alloys are produced with compositions that correspond to these composition ratios.

[0063] FIG. 1 is a flowchart of a manufacturing process of a magnesium alloy according to a first embodiment of the present invention.

[0064] As shown in the flowchart in Figure 1, magnesium alloys are manufactured through a weighing step ST1, a melting step ST2, a solidification step ST3, and a molding step ST4. Of course, Figure 1 shows the main steps in the manufacturing process, and there is no problem if other steps are added to manufacture magnesium alloys.

[0065] In the weighing step ST1, aluminum, calcium, misch metal, manganese, and magnesium are weighed so as to obtain the composition ratio described above. Inevitable mixtures may be contained depending on the purity of the raw material aluminum, etc., or may be contained due to mixing during the weighing step ST1, etc.

[0066] In the melting step ST2, the weighed raw materials are melted in a melting vessel. Fig. 2 is a schematic diagram showing the melting step in an embodiment of the present invention. The weighed raw materials, aluminum, calcium, manganese, misch metal, and magnesium, are charged into the melting vessel 100. These raw materials charged into the melting vessel 100 are melted by heating.

[0067] The molten metal obtained through the melting step ST2 is solidified by cooling, which is the solidification step ST3. By being solidified by cooling in the solidification step ST3, a solidified alloy is obtained.

[0068] Next, a molding step ST4 (which may be performed after the solidification step ST3 or in parallel with the solidification step ST3, for example) is performed as needed. Through this molding step ST4, a magnesium alloy in the shape of, for example, an ingot is produced.

[0069] Of course, additional steps may be performed after the molding step ST4.

[0070] The magnesium alloy produced in this manner is lighter than aluminum alloys containing aluminum as the main component because it is primarily composed of magnesium. Furthermore, this composition ratio makes the magnesium alloy suitable for structural components of transportation equipment and facility equipment, including vehicle wheels.

[0071] (Magnesium alloy properties)

[0072] The properties required for the magnesium alloy of the present invention are specified as follows.

[0073] (1) Tensile strength: The tensile strength of the magnesium alloy test piece is 260 MPa or more.

[0074] (2) Elongation: The elongation of the magnesium alloy test piece is 15.0% or more.

[0075] (3) Impact absorption (impact absorption energy): The impact absorption energy of a magnesium alloy test piece in a Charby impact test is 13 J or more.

[0076] The magnesium alloy of the present invention, which has the above-mentioned composition and composition ratio, has the properties (1) to (3). By having these properties, it can be suitably used as structural members for transportation equipment, such as the above-mentioned vehicle wheels, and structural members for facility equipment. By using magnesium as the main component, it is very lightweight, and sufficient quality can be achieved for molding and for the structural members used.

[0077] (Measurement method) The magnesium alloys defined by the above composition and composition range were measured for (1) tensile strength, (2) elongation, and (3) impact absorption energy. The measurement methods for each were as follows.

[0078] (1) Tensile strength Test pieces of several types of magnesium alloys were prepared by changing the composition ratio within the above-mentioned composition range. The tensile strength (3.10.1 "Tensile strength" in JIS Z 2241 (corresponding to ISO-6892-1) standard) of these test pieces was measured using a universal testing machine (INSTRON, Model 5982).

[0079] (2) Elongation Test pieces of several types of magnesium alloys were prepared by varying the composition ratio within the above-mentioned composition range. The elongation of these test pieces (3.3 (elongation) in JIS Z 2241 (corresponding to ISO-6892-1) standard) was measured using a universal testing machine (INSTRON, Model 5982).

[0080] (3) Impact energy absorption Test pieces were prepared from several types of magnesium alloys with different composition ratios within the above-mentioned composition range. The Charpy impact values ​​of these test pieces were measured using a Charpy impact tester (manufactured by Mori Testing Machinery Co., Ltd.) (JIS Z 2242 (corresponding to ISO148-1)).

[0081] The test temperature was 20±5° C., and the test piece temperature was 20±5° C. The absorbed energy when the test piece broke was calculated.

[0082] (Measurement results)

[0083] Figure 3 is a table showing the measurement results of three types of magnesium alloy specimens with different composition ratios: tensile strength, elongation, and impact absorption energy.

[0084] Here, for the various magnesium alloys, calcium was fixed at 0.3 mass% except for the top test piece in the table, which contained no calcium, and the second test piece, which had 0.6 mass% calcium, and manganese was also fixed at 0.3 mass%. Aluminum was varied in the range of 5.0 mass% to 7.5 mass%, and misch metal was varied from 0.0 mass% to 2.0 mass%.

[0085] The tensile strength, elongation, and impact absorption energy values ​​for each test specimen are shown in the table in Figure 3. Figures 4 to 6 show cross-tabulations of these three properties, with the vertical axis representing the change in the aluminum composition range and the horizontal axis representing the change in the misch metal composition range.

[0086] Figure 4 is a cross-tabulation showing the tensile strength when the composition ranges of aluminum and misch metal are varied (calcium and manganese are constant at 0.3 mass%, with magnesium being the remainder). The tensile strength values ​​with colored frames indicate test specimens with composition ratios that result in a tensile strength of 260 MPa or more, as specified. Test specimens with composition ratios that do not have colored frames do not meet the specified tensile strength of 260 MPa or more.

[0087] For example, a magnesium alloy with a composition ratio of 5.0 mass% aluminum, 0.5 mass% misch metal, 0.3 mass% each of calcium and manganese, and the remainder being magnesium, has a tensile strength of 258 MPa, which is below the specified 260 MPa.

[0088] Figure 5 is a cross-tabulation showing the elongation when the composition ranges of aluminum and misch metal are varied (calcium and manganese are constant at 0.3 mass%, with magnesium remaining). The elongation values ​​with colored frames indicate test specimens with a composition ratio of 15% or more, which is the specified elongation. Test specimens with composition ratios that are not colored in the frame do not meet the specified elongation of 15% or more.

[0089] For example, magnesium alloys containing 0.0 mass % or 2.0 mass % misch metal have elongation of 13.7% or 14.8%, which does not satisfy the specified requirement of 15% or more.

[0090] Figure 6 is a cross-tabulation showing the impact absorption energy when the composition ranges of aluminum and misch metal are changed (calcium and manganese are constant at 0.3 mass%, with magnesium being the remainder). The elongation values ​​with colored frames indicate test specimens with composition ratios that result in the specified impact absorption energy of 13 J or more. Test specimens with composition ratios that do not have colored frames do not meet the specified impact absorption energy of 13 J or more.

[0091] For example, the impact absorption energy of a magnesium alloy with an aluminum composition ratio of 7.0 mass % and a magnesium alloy with misch metal content of 2.0 mass % is 12.5 J and 12.0 J, respectively, which does not meet the specified requirement of 13 J or more.

[0092] In all of Figures 4 to 6, the magnesium alloy with the composition and composition ratio shown first satisfies the following target properties.

[0093] (1) Tensile strength: The tensile strength of the magnesium alloy test piece is 260 MPa or more. (2) Elongation: The elongation of the magnesium alloy test piece is 15.0% or more. (3) Impact absorption (impact absorption energy): The impact absorption energy of a magnesium alloy test piece in a Charby impact test is 13 J or more.

[0094] That is, as is clear from FIGS. 4 to 6, magnesium alloys that satisfy these characteristics (1) to (3) are those having the following composition ranges.

[0095] 5.5% by mass to 6.5% by mass of aluminum (Al) based on the total, 0.2% by mass to 0.5% by mass of calcium (Ca) based on the total, 0.1% by mass to 0.6% by mass of manganese (Mn) based on the total; 0.5% by mass to 1.5% by mass of misch metal (Mm) based on the total mass; The remainder of the magnesium alloy is magnesium and unavoidable impurities.

[0096] Figure 4 is a cross-tabulation of tensile strength, and the range enclosed in a box in Figure 4 is the range where the tensile strength is 260 MPa or more. As can be seen from this range, the aluminum content is 5.5% to 6.5% by mass, and the misch metal content is 0.5% to 1.5% by mass.

[0097] Figure 5 is a cross-tabulation of elongation, and the range enclosed in a box in Figure 5 is the range where elongation is 15.0% or more. As can be seen from this range, aluminum is 5.5% to 6.5% by mass, and misch metal is 0.5% to 1.5% by mass.

[0098] Figure 6 is a cross-tabulation of impact absorption energy, and the range enclosed in a box in Figure 6 is the range where impact absorption energy is 13 J or more. As can be seen from this range, aluminum is 5.5 mass % to 6.5 mass %, and misch metal is 0.5 mass % to 1.5 mass %.

[0099] From these three test results in Figures 4 to 6 (test results corresponding to the property targets (1) to (3) above), it was confirmed that an aluminum content of 5.5 mass% to 6.5 mass% and a misch metal content of 0.5 mass% to 1.5 mass% were appropriate.

[0100] Furthermore, as shown in the second column of the table in Figure 3, when calcium is 0.6 mass%, the elongation is 14.7%. Therefore, when calcium is more than 0.5 mass%, the target properties cannot be achieved.

[0101] Fig. 7 is a table showing the results of a combustion test of magnesium alloys according to an embodiment of the present invention. In the combustion test shown in Fig. 7, alloys with each composition range were molten and held in the atmosphere. Those for which there were no problems with the molten metal are marked with "O", and those for which there were problems with the molten metal are marked with "X". When combustion was confirmed on the surface of the molten metal by visual inspection, it was determined that the alloy had low flame retardancy and was marked with "X".

[0102] The results in Figure 7 show that calcium burns when the content is 0% by mass or 0.1% by mass. In other words, this is not an appropriate addition range. At 0.6% by mass, there was no problem with flame retardancy, but as mentioned above regarding the results in Figure 3, the elongation was insufficient and this was inappropriate. Therefore, it was confirmed that the appropriate upper limit of calcium content is 0.5% by mass.

[0103] If the surface of the molten metal burns in a combustion test, it means that there is a possibility of ignition or combustion during the melting and casting processes in product manufacturing. In other words, it means that the flame retardancy is low when considering proper manufacturing and use. Such magnesium alloys are not recommended. Since calcium is an element that increases the flame retardancy of magnesium alloys, the amount of calcium added at 0.1 mass%, which was confirmed as "X" in the combustion test, is insufficient. On the other hand, at 0.2 mass%, it is "O" (Figure 7). This also confirmed that calcium of 0.2 mass% or more is necessary.

[0104] Therefore, from the above, it was confirmed that the appropriate calcium content is 0.2% by mass to 0.5% by mass.

[0105] 3 to 6, it was confirmed that the target properties (1) to (3) are satisfied when the manganese content is 0.3 mass%, provided that the other composition ranges are as described above. Since an excessive amount of manganese deteriorates the mechanical properties, it is appropriate that the manganese content be 0.1 mass% to 0.6 mass%.

[0106] Magnesium is the balance.

[0107] In the results corresponding to the properties (1) to (3) in Figures 4 to 6, the measurement results of each property in the range that satisfies the properties (the boxed area near the center of the table) are as follows. In the top of Figure 4, the test pieces of the nine compositions in this boxed area are numbered 1 to 9, and the results for each are shown below.

[0108] 1. A magnesium alloy containing 5.5% by mass of aluminum and 0.5% by mass of misch metal (calcium is fixed at 0.3% by mass and manganese at 0.3% by mass. Magnesium is the remainder, which is also true for items 2 and beyond below). Tensile strength: 260 MPa Growth: 23.1% Impact absorption energy: 15.8J

[0109] 2. A magnesium alloy containing 6.0% by mass of aluminum and 0.5% by mass of mischmetal (calcium is fixed at 0.3% by mass, manganese is fixed at 0.3% by mass, and magnesium is the balance). Tensile strength: 268.5 MPa Growth: 26.3% Impact absorption energy: 13.0J

[0110] 3. A magnesium alloy containing 6.5% by mass of aluminum and 0.5% by mass of mischmetal (calcium is fixed at 0.3% by mass, manganese is fixed at 0.3% by mass, and magnesium is the balance). Tensile strength: 273.5 MPa Growth: 25.4% Impact absorption energy: 15.4J

[0111] 4. A magnesium alloy containing 5.5% by mass of aluminum and 1.0% by mass of mischmetal (calcium is fixed at 0.3% by mass, manganese is fixed at 0.3% by mass, and magnesium is the balance). Tensile strength: 277.5 MPa Elongation: 16.0% Impact absorption energy: 20.3J

[0112] 5. A magnesium alloy containing 6.0% by mass of aluminum and 1.0% by mass of mischmetal (calcium is fixed at 0.3% by mass, manganese is fixed at 0.3% by mass, and magnesium is the balance). Tensile strength: 269.0 MPa Growth: 16.4% Impact absorption energy: 18.4J

[0113] 6. A magnesium alloy containing 6.5% by mass of aluminum and 1.0% by mass of mischmetal (calcium is fixed at 0.3% by mass, manganese is fixed at 0.3% by mass, and magnesium is the balance). Tensile strength: 267.0 MPa Elongation: 16.5% Impact absorption energy: 14.4J

[0114] 7. A magnesium alloy containing 5.5% by mass of aluminum and 1.5% by mass of mischmetal (calcium is fixed at 0.3% by mass, manganese is fixed at 0.3% by mass, and magnesium is the balance). Tensile strength: 278.0 MPa Elongation: 15.0% Impact absorption energy: 15.1J

[0115] 8. A magnesium alloy containing 6.0% by mass of aluminum and 1.5% by mass of mischmetal (calcium is fixed at 0.3% by mass, manganese is fixed at 0.3% by mass, and magnesium is the balance). Tensile strength: 272.5 MPa Elongation: 16.5% Impact absorption energy: 17.5J

[0116] 9. A magnesium alloy containing 6.5% by mass of aluminum and 1.5% by mass of mischmetal (calcium is fixed at 0.3% by mass, manganese is fixed at 0.3% by mass, and magnesium is the balance). Tensile strength: 277.0 MPa Growth: 18.2% Impact absorption energy: 14.7J

[0117] That is, it was confirmed that the range enclosed by the boxes in Figures 4 to 6 is the composition range that satisfies the properties (1) to (3), as described above. 5.5% by mass to 6.5% by mass of aluminum (Al) based on the total, 0.2% by mass to 0.5% by mass of calcium (Ca) based on the total, 0.1% by mass to 0.6% by mass of manganese (Mn) based on the total; 0.5% by mass to 1.5% by mass of misch metal (Mm) based on the total mass; A magnesium alloy consisting of the remainder being magnesium and unavoidable impurities. This magnesium alloy satisfies the characteristics (1) to (3) and is composed primarily of lightweight magnesium, making it lightweight yet suitable for use in structural components such as vehicle wheels. This was confirmed by the test results shown in Figures 3 to 7.

[0118] (Variations with a more narrow composition range)

[0119] (Calcium composition range) It is also preferable that the calcium content is 0.25% by mass to 0.35% by mass based on the total mass.

[0120] The narrower calcium composition range can further improve elongation properties.

[0121] Here, the composition of Ca can be determined as follows.

[0122] The Ca content must be 0.2% by mass or more for the following reason: When casting a magnesium alloy, Ca can form a strong protective film on the surface of the molten metal, and this protective film improves flame retardancy. If the Ca content is less than 0.2% by mass, the formation of this protective film will be insufficient, and the effect of improving flame retardancy will also be insufficient.

[0123] Adding a large amount of Ca tends to reduce elongation, and this tendency becomes particularly pronounced when the amount exceeds 0.5 mass%. Also, too much Ca increases the wettability of the molten metal, increasing its affinity with the furnace wall and making it more susceptible to ignition.

[0124] The manganese (Mn) composition may also be determined as follows.

[0125] The Mn content must be 0.1% by mass or more, and preferably 0.25% by mass or more, for the following reason: Mn is effective in removing iron from the molten metal during casting, but if it is less than 0.1% by mass, this removal effect is insufficient, and iron remains in the magnesium alloy, reducing corrosion resistance.

[0126] On the other hand, the Mn content must be 0.6% by mass or less, and preferably 0.35% by mass or less, for the following reason: If there is too much Mn, intermetallic compounds with Al or Mn itself tends to precipitate, and if the content exceeds 0.6% by mass, this problem cannot be ignored.

[0127] (Mischmetal composition range) It is also preferable that the misch metal content is 0.5 mass % to 1.0 mass % of the total mass. With the misch metal content in this range, the elongation of the magnesium alloy is further increased.

[0128] As shown in FIG. 5, when the misch metal content is 0.5 mass % to 1.0 mass %, the elongation becomes 16% or more, which is higher.

[0129] As described above, the magnesium alloy in the first embodiment has tensile strength, elongation, and shock absorption properties suitable for structural members such as vehicle wheels.

[0130] (Embodiment 2)

[0131] Next, a second embodiment will be described. In the second embodiment, a use mode of the magnesium alloy described in the first embodiment will be described. The magnesium alloy described in the first embodiment is applied to a cast structural member. That is, in the second embodiment, a cast structural member using the magnesium alloy of the first embodiment will be described.

[0132] The magnesium alloy obtained in the first embodiment is cast and subjected to necessary forming processing to obtain a cast structural member.

[0133] Here, the cast structural members may include the following:

[0134] At least one of the following: internal combustion engines and electric powertrains, traction motors, inverters, reducers, transmissions, pistons, shafts, connecting rods, covers, cylinders, cylinder blocks, arms, knuckles, pillars, wheels, compressor housings, steering wheels, internal housings, engine mounts, oil pans, gears, gear cases, nuts, screws, bolts, heat sinks for LED lighting devices, pneumatic and electric tools, and the components and housings that make up these, in automobiles, motorcycles, aircraft, ships, and railway vehicles.

[0135] Such fields are used as:

[0136] Magnesium alloys are extremely lightweight, and their use in the structural components listed above can reduce the weight of the structural components. Furthermore, their suitable tensile strength, elongation, and shock absorption properties make them more suitable for the molding and use of structural components.

[0137] Furthermore, by using the magnesium alloy of the present invention for these cast structural members, the cast structural members can have sufficient strength to withstand the stresses that occur when the cast structural members are fixed, and can also withstand vibrations and impacts.

[0138] When applied to a vehicle wheel, it can withstand the stress, vibration and shock of the wheel fastening portion.

[0139] The magnesium alloy described in the first embodiment is an example for explaining the gist of the present invention, and includes modifications and alterations within the scope of the present invention. [Explanation of symbols]

[0140] 100 melting vessel

Claims

1. 5.5% by mass to 6.5% by mass of aluminum (Al) based on the total mass; 0.2% by mass to 0.5% by mass of calcium (Ca) based on the total mass; 0.1% by mass to 0.6% by mass of manganese (Mn) based on the total mass; 0.5% by mass to 1.5% by mass of misch metal (Mm) based on the total mass; The remainder of the magnesium alloy is magnesium and unavoidable impurities.

2. 2. The magnesium alloy according to claim 1, wherein the calcium content is 0.25% by mass to 0.35% by mass based on the total.

3. 3. The magnesium alloy according to claim 1, wherein the misch metal is contained in an amount of 0.5 to 1.0 mass% of the total.

4. 4. The magnesium alloy according to claim 1, wherein a test piece of the magnesium alloy has a tensile strength of 260 MPa or more.

5. 5. The magnesium alloy according to claim 1, wherein a test piece of the magnesium alloy has an elongation of 15.0% or more.

6. 6. The magnesium alloy according to claim 1, wherein a test piece of the magnesium alloy has an impact absorption energy of 13 J or more in a Charpy impact test when the test temperature is 20±5°C and the test piece temperature is 20±5°C.

7. 7. The magnesium alloy according to claim 1, wherein the mischmetal is a combination of at least one of scandium (Sc), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

8. A cast structural member made of the magnesium alloy according to any one of claims 1 to 7.

9. The cast structural member is for use in any one of an automobile, a motorcycle, an aircraft, a ship, and a railway vehicle. Cast structural members using the magnesium alloy according to claim 8, including at least one of internal combustion engines and electric power trains, traction motors, inverters, reducers, transmissions, pistons, shafts, connecting rods, covers, cylinders, cylinder blocks, arms, knuckles, pillars, wheels, compressor housings, steering wheels, internal housings, engine mounts, oil pans, gears, gear cases, nuts, screws, bolts, heat sinks for LED lighting devices, pneumatic and electric tools, and components and housings that constitute these.

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