Sm-fe-n-based sintered magnet and manufacturing method therefor

Abstract

An Sm-Fe-N-based sintered magnet comprising a sintered body of a magnetic material containing an Sm-Fe-N-based magnetic powder and a Zn-Al alloy powder, wherein the Al content of the Zn-Al alloy powder is 6-84 atom%, and the open porosity of the sintered magnet is not more than 15%.

Description

Sm-Fe-N sintered magnet and manufacturing method thereof

[0001] The present invention relates to an Sm—Fe—N sintered magnet and a method for producing the same.

[0002] Sm—Fe—N magnets are representative of rare earth-transition metal-nitrogen magnets, and have a high anisotropy field and remanent magnetization. Furthermore, Sm—Fe—N magnets have a relatively higher Curie temperature than other rare earth-transition metal-nitrogen magnets, giving them excellent heat resistance. For this reason, Sm—Fe—N magnetic powder has been used as one of the excellent materials for magnet powder.

[0003] Patent Document 1 discloses an Sm—Fe—N magnet using magnetic powder and a zinc-aluminum alloy containing 5 atomic percent aluminum. Patent Document 2 discloses an Sm—Fe—N magnet using magnetic powder and metallic zinc.

[0004] JP 2021-136347 A JP 2022-096382 A

[0005] The magnets of Patent Documents 1 and 2 show a large decrease in coercive force in high-temperature, high-humidity environments, which is thought to be due to the high open porosity of the magnets.

[0006] The present invention has been made in view of the above-mentioned problems, and aims to provide a sintered Sm—Fe—N based magnet in which the decrease in coercive force is suppressed even in high-temperature, high-humidity environments.

[0007] According to one aspect of the present invention, there is provided a sintered magnet comprising a sintered body of a magnetic material containing Sm-Fe-N magnetic powder and Zn-Al alloy powder, wherein the Al content of the Zn-Al alloy powder is 6 atomic % or more and 84 atomic % or less, and the open porosity of the sintered magnet is 15% or less.

[0008] According to another aspect of the present invention, there is provided a method for producing a Sm—Fe—N sintered magnet, comprising: mixing an Sm—Fe—N magnetic powder with a Zn—Al alloy powder having an Al content of 6 atomic % or more and 84 atomic % or less to obtain a magnetic material; and pressure-sintering the magnetic material at a temperature of 300° C. to 600° C. and a pressure of 0.5 GPa to 2.0 GPa.

[0009] According to the present invention, there is provided an Sm--Fe--N sintered magnet in which the decrease in coercive force is suppressed even in a high-temperature, high-humidity environment.

[0010] 1 is a flowchart showing an example of a method for producing a sintered magnet according to the present disclosure; 2 is a graph showing the relationship between the open porosity and the coercive force reduction rate of the sintered magnets produced in Examples and Comparative Examples;

[0011] Due to their manufacturing process, Sm-Fe-N sintered magnets tend to be porous, allowing air and moisture to easily penetrate from the outside into the magnet. Additionally, because their surface area tends to be large, sintered magnets are easily oxidized and hydroxylated. The oxides and hydroxides decompose the main phase, producing α-Fe. Therefore, their coercivity is particularly likely to decrease in high-temperature, high-humidity environments.

[0012] The Sm—Fe—N sintered magnet (hereinafter sometimes simply referred to as the magnet) of the present disclosure has an open porosity of 15% or less. This makes it difficult for air and moisture to penetrate from the outside, and the small surface area suppresses oxidation and hydroxylation. The coercivity of a magnet with a low open porosity is less likely to decrease even in high-temperature, high-humidity environments.

[0013] In addition, the Zn-Al alloy (zinc-aluminum alloy, hereinafter sometimes referred to as high-Al zinc alloy) powder used as a raw material with an Al content of 6 atomic % or more and 84 atomic % or less increases the initial coercive force and effectively suppresses the decrease in coercive force during use (especially in a high-temperature, high-humidity environment). The reason for this is not clear, but is thought to be as follows.

[0014] It is known that Al is easily oxidized and forms a passive oxide film. High-Al zinc alloys also oxidize preferentially over Sm-Fe-N magnetic powders, forming an oxide film in addition. It is believed that the sacrificial effect of such high-Al zinc alloys suppresses oxidation of Sm-Fe-N magnetic powders during the firing process and suppresses oxidation and hydroxylation of magnets in high-temperature, high-humidity environments. Furthermore, because the sacrificial effect of high-Al zinc alloys is exerted in small amounts, it is possible to maintain a high proportion of the main phase in the magnet and suppress a decrease in saturation magnetization.

[0015] The high-Al zinc alloy also serves to reduce the open porosity of the resulting magnet. Because the high-Al zinc alloy has a lower melting point than zinc metal, it easily spreads between the main phase grains during the sintering process. Furthermore, the spread high-Al zinc alloy tends to remain between the main phase grains. As a result, it is believed that a magnet with low open porosity can be obtained, with at least some of the open pores filled with the high-Al zinc alloy.

[0016] The reason why the high-Al zinc alloy tends to remain between the main phase grains is not clear, but it is thought to be because the high-Al zinc alloy can coexist as a solid phase and a liquid phase during the sintering process. The high-Al zinc alloy in the solid and liquid phases enters the gaps between the main phase grains (which can form open and closed pores) during the sintering process. The shape of these gaps is made complex by the solid phase. Once the liquid phase enters, it becomes difficult for it to escape from the gaps due to the anchor effect caused by the shape formed by the solid phase. In other words, it tends to remain in the gaps. As a result, the open pores are blocked, and the open porosity is reduced.

[0017] It is believed that zinc metal and zinc alloys with an Al content of less than 6 atomic percent (low-Al zinc alloys) are both liquid during the firing process. As a result, they tend to flow through the gaps in the mold, resulting in little effect in filling the gaps (open pores). Adding zinc metal or low-Al zinc alloys in an amount that allows them to remain in the gaps reduces the open porosity, but also reduces the magnetic properties (particularly the initial saturation magnetization).

[0018] To further enhance the effect of suppressing the decrease in coercive force in a high-temperature, high-humidity environment and to suppress the decrease in initial saturation magnetization, it is desirable to use a high-Al zinc alloy and adjust the open porosity to 15% or less.

[0019] Open porosity: Open pores are defined in JIS Z 8837:2018 as "pores that are not completely closed by walls, that are open on the particle surface directly or connected to other pores, and that allow fluid to penetrate." In this specification, open pores have the same meaning as in JIS Z 8837:2018, except that "particle" is read as "sintered magnet."

[0020] The open porosity (%) is the percentage of the volume of open pores in a sample, assuming that the external volume of the sample is 1. The open porosity (%) is expressed by the following formula: Open porosity (%) = 100 × open pore volume (cm ３ ) / apparent volume (cm ３ )

[0021] where open pore volume (cm ３ ) is the total volume of the open pores of the sample, and the apparent volume (cm ３ ) is the external volume including all internal pores, which can be calculated from the external dimensions of the sample.

[0022] Specifically, the open porosity (%) can be calculated from the volume of the sample excluding the open pore volume measured with a gas pycnometer (for example, Shimadzu Corporation's product name "Accupyc II1340") and the apparent volume: open porosity (%) = 100 × (apparent volume - volume measured with gas pycnometer) / apparent volume

[0023] When the sample volume is small, the open porosity can be measured in accordance with JIS Z 8837:2018, Appendix A. 1. Specifically, the open porosity can be determined by placing a calibrated steel ball or the like in a container together with the sample, and then subtracting the volume of the steel ball from the measurement result.

[0024] (Sm—Fe—N sintered magnet) Sm—Fe—N sintered magnets are obtained by sintering (firing) a magnetic material containing Sm—Fe—N magnetic powder and a high-Al zinc alloy powder at a high temperature. In this disclosure, a sintered magnet refers to a magnet obtained by sintering a magnetic material at a high temperature.

[0025] The Sm—Fe—N magnetic powder forms the main phase grains of the magnet. The high-Al zinc alloy powder is arranged around the main phase grains through the sintering process, filling at least some of the gaps (open pores) between the main phase grains. The magnet of the present disclosure has low open porosity.

[0026] The open porosity (%) of the magnet is 15.0% or less. The open porosity (%) may be 12.0% or less, or may be 11.6% or less.

[0027] The magnet may contain no oxygen or may contain 1.5% by mass or less of oxygen. A magnet with an oxygen content of 1.5% by mass or less indicates that oxidation of the main phase grains is suppressed during the sintering process. Therefore, a higher coercive force can be expected. The oxygen content of the magnet may be 1.0% by mass or less, or may be 0.8% by mass or less.

[0028] The oxygen content can be measured by inert gas fusion-non-dispersive infrared absorption (NDIR).

[0029] The initial saturation magnetization Js of the magnet may be 0.90 T or more. The saturation magnetization Js of the magnet may be 0.95 T or more, or may be 1.00 T or more.

[0030] The initial coercive force Hcj of the magnet may be 800 kA / m or more, 850 kA / m or more, or 900 kA / m or more.

[0031] The rate of decrease in coercivity of a magnet after a high-temperature, high-humidity test may be 20% or less, 18% or less, 15% or less, or 13% or less. The rate of decrease (%) is calculated by 100 x (initial coercivity Hcj - coercivity after test Hcj) / (initial coercivity Hcj). The high-temperature, high-humidity test is performed for 24 hours at 125°C and 85% RH using Air-HAST (High Accelerated Stress Test). An apparatus such as the "EHS-411MD" manufactured by Espec Corporation is used.

[0032] The saturation magnetization Js and the coercive force Hcj can be measured under the condition of an externally applied magnetic field of 7 T using a vibrating sample magnetometer (VSM) (for example, VSM-5HSC1 manufactured by Toei Kogyo Co., Ltd.).

[0033] The magnet may contain other components (e.g., α-Fe) and trace elements that are inevitably mixed in. Examples of trace elements that are inevitably mixed in include carbon (C) and silicon (Si).

[0034] The magnet may include a sintered body of another magnetic powder. Examples of the other magnetic powder include a magnetic powder composed of a rare earth element other than Sm, Fe, and N, and a magnetic powder composed of a rare earth element including Sm, Fe, a transition metal element other than Fe, and N. Examples of rare earth elements other than Sm include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), and ytterbium (Yb). Examples of transition metal elements other than Fe include cobalt (Co), nickel (Ni), manganese (Mn), chromium (Cr), titanium (Ti), Zr (zirconia), niobium (Nb), tungsten (W), and vanadium (V).

[0035] Main Phase Grains The main phase grains form the main phase of the magnet. The main phase grains are crystal grains derived from the Sm—Fe—N magnetic powder (Sm—Fe—N crystal grains) and contain Sm, Fe, and N.

[0036] The main phase grains are at least partially composed of Th ２ Zn １７ Type, Th２ Ni １７ type or TbCu ７ The main phase has a crystal structure of the type SmFe ９ N １．５ Phase, Sm ２ Fe １７ N ３ The crystal structure of the main phase grains is not limited thereto and may be any crystal structure consisting of Sm, Fe, and N. A typical main phase is Sm ２ Fe １７ N ３ The crystal structure can be determined by X-ray diffraction.

[0037] The average particle size of the main phase grains is not particularly limited. The average particle size of the main phase grains may be, for example, 0.5 μm or more and 3.0 μm or less. When the average particle size of the main phase grains is 0.5 μm or more, it is possible to effectively suppress the superparamagnetism of the Sm—Fe—N crystal grains. When the average particle size of the main phase grains is 3.0 μm or less, it is possible to improve the coercive force. The average particle size of the main phase grains may be 0.8 μm or more, or 1.0 μm or more. The average particle size of the main phase grains may be 2.5 μm or less, 2.0 μm or less, or 1.5 μm or less.

[0038] The method for calculating the average grain size of the main phase grains is as follows. First, a cross section of the magnet is photographed using a field emission scanning electron microscope (FE-SEM) so that a total of at least 50 grains are included. The main phase grains in the photographed image are identified using energy dispersive X-ray (EDX) analysis. Next, the total area A1 of the cross sections of the main phase grains in the photographed image and the number N1 of the main phase grains are determined. With A1 / N1 being the average cross-sectional area per main phase grain, the diameter of a circle (equivalent circle) having the same area as the average cross-sectional area is the average grain size of the main phase grains.

[0039] Sm—Fe—N based magnetic powder Sm—Fe—N based magnetic powder (hereinafter sometimes simply referred to as magnetic powder) contains samarium (Sm), iron (Fe), and nitrogen (N). The magnetic powder can have any composition consisting of Sm, Fe, and N. The magnetic powder is typically Sm ２ Fe １７ N ３ The composition may be, but is not limited to:

[0040] The average particle size of the magnetic powder is, for example, 0.5 μm or more and 3.0 μm or less. The average particle size of the magnetic powder may be 0.8 μm or more or 1.0 μm or more, in order to suppress superparamagnetism. The average particle size of the magnetic powder may be 2.5 μm or less, 2.0 μm or less, or 1.5 μm or less, in order to further increase the coercive force of the resulting magnet.

[0041] The "average particle size" of a powder (such as a magnetic powder) refers to the particle size (D50) at the point where the cumulative value reaches 50% on a cumulative curve obtained by calculating the particle size distribution on a volume basis and setting the total volume to 100%. The average particle size can be measured using a laser diffraction / scattering particle size / particle size distribution measuring device or an electron scanning microscope.

[0042] High-Al zinc alloy powder The Al content of the high-Al zinc alloy powder is 6 atomic % or more and 84 atomic % or less. From the viewpoint of coercivity, the Al content may be 11 atomic % or more, 15 atomic % or more, or 20 atomic % or more. The Al content may be 67 atomic % or less, or 50 atomic % or less. In one embodiment, the Al content of the high-Al zinc alloy powder is 15 atomic % or more and 50 atomic % or less.

[0043] The Al content can be measured, for example, by an inductively coupled plasma (ICP) emission spectrometer. The Al content may also be calculated from the ratio of raw materials used in preparing the alloy.

[0044] The average particle size of the high-Al zinc alloy powder is not particularly limited. The average particle size of the high-Al zinc alloy powder is, for example, 0.01 μm or more and 60 μm or less. The average particle size of the high-Al zinc alloy powder may be 50 μm or less, or may be 40 μm or less.

[0045] (Method for manufacturing Sm-Fe-N sintered magnet) The Sm-Fe-N sintered magnet is manufactured by a method comprising mixing an Sm-Fe-N magnetic powder with a high-Al zinc alloy powder to obtain a magnetic material, and pressure-sintering the magnetic material at a temperature of 300°C to 600°C and a pressure of 0.5 GPa to 2.0 GPa.

[0046] An example of a method for producing a sintered magnet will be described below: Fig. 1 is a flowchart showing an example of a method for producing a sintered magnet according to the present disclosure.

[0047] (1) Preparation of Sm—Fe—N based magnetic powder (S11) The Sm—Fe—N based magnetic powder may be a commercially available product. The Sm—Fe—N based magnetic powder may be prepared by nitriding an alloy powder containing Sm and Fe (Sm—Fe alloy).

[0048] (2) Pulverization and Classification (S12) The Sm—Fe—N magnetic powder may be pulverized (or crushed) and classified. The pulverization (crushing) and classification are carried out under conditions such that the average particle size of the Sm—Fe—N magnetic powder is 0.5 μm or more and 3.0 μm or less. Fine powder is removed by classification.

[0049] Crushing or grinding can be carried out using, but is not limited to, an agate mortar, a jet mill (airflow grinding type, etc.), a ball mill, etc. Examples of airflow grinding type jet mills include, but are not limited to, the MC44 manufactured by Micromachinazione. Classification can be carried out using, but is not limited to, an airflow classifier, etc.

[0050] (3) Mixing of High Al Zinc Alloy Powder (S13) The Sm-Fe-N magnetic powder and the high Al zinc alloy powder are mixed to prepare a magnetic material.

[0051] As the proportion of high-Al zinc alloy powder increases, the open porosity decreases. When the proportion of high-Al zinc alloy powder is high and the main phase ratio is excessively reduced, the saturation magnetization decreases.

[0052] The mass of the high-Al zinc alloy powder in the magnetic material is, for example, 1.0 mass% or more and 30 mass% or less. When the mass of the high-Al zinc alloy powder is 1.0 mass% or more, the sacrificial effect is fully exhibited. When the mass of the Al zinc alloy powder is 30 mass% or less, the initial saturation magnetization becomes sufficiently large (for example, 0.90 T or more), and a magnet with excellent magnetic properties is obtained.

[0053] When the mass of the high-Al zinc alloy powder is 1.0 mass % or more and 30 mass % or less, the open porosity can be adjusted to 15% or less using only the high-Al zinc alloy.

[0054] The mass of the high Al zinc alloy powder may be 3.0 mass% or more, or 5.0 mass% or more, or 10.0 mass% or less, or 8.0 mass% or less.

[0055] In one embodiment, the mass of the high-Al zinc alloy powder in the magnetic material is 1.0 mass% or more and 10 mass% or less. When the mass of the high-Al zinc alloy powder is 1.0 mass% or more and 10 mass% or less, the open porosity can be adjusted to 15% or less and the saturation magnetization can be 0.95 T or more by using only the high-Al zinc alloy.

[0056] (4) Magnetic Field Compaction (S14) Before pressure sintering, the magnetic material may be compacted in a magnetic field. Magnetic field compaction is a process of compacting a magnetic material while applying a magnetic field. For magnetic field compaction, for example, a powder press equipped with a magnetic field generator is used. By compacting in a magnetic field, the easy magnetization axis of the Sm—Fe—N magnetic powder is aligned, resulting in higher magnetic properties.

[0057] The conditions for compaction in a magnetic field are not particularly limited. The magnetic field to be applied may be, for example, a static magnetic field of 1 T or more, or a pulsed magnetic field. Compaction in a magnetic field may be performed on a magnetic material filled in a mold used for pressure sintering.

[0058] All of the above steps may be carried out in an atmosphere with a low oxygen concentration of 10 ppm or less (particularly 2 ppm or less) on a volume basis. The above steps are carried out, for example, in a glove box purged with an inert gas (one or a mixture of two or more gases such as nitrogen, argon, and helium), preferably in a glove box connected to a gas circulation type oxygen and moisture purifier.

[0059] During the period from the preparation of the magnetic material until pressure sintering (or molding in a magnetic field), for the purpose of material handling, it is permissible to place the magnetic material in an air atmosphere while immersed in an organic solvent capable of preventing oxidation.

[0060] (5) Pressure Sintering (S15) The magnetic material filled in the mold is pressure sintered to obtain a Sm—Fe—N sintered magnet. The mold used may have any shape, such as, but not limited to, a cylindrical mold.

[0061] The pressure firing may be carried out under normal pressure in an inert gas atmosphere. The pressure firing may be carried out by any pressure firing method, including electric pressure firing. The pressure firing may be carried out, for example, by a hot press method or by electric sintering. The hot press method is a common sintering method, in which heating is performed while applying pressure in an inert atmosphere such as Ar. The electric sintering is a method in which a certain pressure is applied to a mold and an electric current is applied while maintaining this pressure.

[0062] In the case of electric current sintering, the interior of the pulse electric current sintering machine is maintained at a vacuum of, for example, 5 Pa or less. The pressure applied to the mold is, for example, 0.5 GPa or more and 2.0 GPa or less. The applied pressure may be 0.8 GPa or more, or 1.0 GPa or more. The applied pressure may be 1.8 GPa or less, or 1.6 GPa or less.

[0063] The pressure firing is performed at a temperature of 300° C. or higher and 600° C. or lower. The pressure firing temperature may be 350° C. or higher, or 400° C. or higher. The pressure firing temperature may be 580° C. or lower, or 550° C. or lower.

[0064] The open porosity can be easily adjusted to 15% or less by applying a pressure of 0.5 GPa to 2.0 GPa to the mold at a temperature of 300° C. to 600° C. The pressure and firing time is, for example, 30 seconds to 10 minutes.

[0065] The present disclosure is not limited to the above-described embodiments, and design modifications are possible within the scope of the gist of the present disclosure.

[0066] Hereinafter, the present disclosure will be described in more detail with reference to examples. However, the present disclosure is not limited to the following examples, and it is of course possible to make appropriate modifications within the scope applicable to the above and below-described aims, and all such modifications are included in the technical scope of the present disclosure.

[0067] Example 1 A sintered Sm-Fe-N magnet was produced by the following procedure: (i) Preparation of Sm-Fe-N magnetic powder. ２ Fe １７ N ３ An Sm--Fe--N magnetic powder having an average particle size of about 25 μm was prepared.

[0068] (ii) Pulverization and Classification The Sm—Fe—N magnetic powder was pulverized using an airflow pulverization jet mill at a pulverization pressure of 0.7 MPa. The pulverization was carried out in a glove box in a low-oxygen atmosphere of 2 ppm or less. After pulverization, an airflow classifier was used to remove fine powder (particles with a particle size of less than 0.04 μm). This adjusted the average particle size of the Sm—Fe—N magnetic powder to 1.6 μm.

[0069] The average particle size (D50) of the Sm-Fe-N magnetic powder was measured using a laser diffraction particle size distribution measuring device (manufactured by Sympatec, product name "HELOS").

[0070] (iii) Mixing of high Al-zinc alloy powder A magnetic material was prepared by mixing Sm-Fe-N magnetic powder with high Al-Zn alloy powder (Al: 21.22 atomic %, average particle size: 33 μm). The amount of high Al-Zn alloy powder added was 3.3 wt % of the magnetic material.

[0071] (iv) Magnetic Field Molding 0.2 g of the obtained magnetic material was immersed in heptane in a glove box under a low-oxygen atmosphere of 2 ppm or less to prepare a slurry. The obtained slurry was filled into a cemented carbide mold. The mold was removed from the glove box and placed in a powder press equipped with a magnetic field generator. While applying a static magnetic field of 1.5 T to the powder press, press molding was performed at a pressure of 1250 MPa in the direction perpendicular to the magnetic field.

[0072] (v) Pressure Sintering The mold was placed in a pulse current sintering machine equipped with a pressure mechanism using a servo-controlled press. Next, in the pulse current sintering machine, the pressure was maintained at 20 Pa in an Ar atmosphere. A pressure of 1.5 GPa was applied to the mold by the pressure mechanism, and current sintering was performed at 400°C for 1 minute while maintaining this pressure, to obtain a sintered magnet.

[0073] In Example 1, the above treatments (ii) to (iv) were carried out in a glove box (nitrogen substituted) connected to a gas circulation type oxygen and moisture purifier. The oxygen concentration in the glove box was set to 1 ppm or less. The sample was transferred between each device without being exposed to the atmosphere.

[0074] Examples 2 to 5 Sintered magnets were obtained in the same manner as in Example 1, except that the amount of high Al—Zn alloy powder added was changed as shown in Tables 1 and 2.

[0075] Comparative Example 1 A sintered magnet was obtained in the same manner as in Example 1, except that no high Al-Zn alloy powder was added.

[0076] Comparative Examples 2 and 3 Sintered magnets were obtained in the same manner as in Example 1, except that Zn powder (average particle size: 4 μm) was added as shown in Table 2 instead of the high Al—Zn alloy powder.

[0077] Comparative Example 4 A sintered magnet was obtained in the same manner as in Example 1, except that a low Al-Zn alloy powder (Al: 5 atomic %, average particle size: 25 μm) was added instead of the high Al-Zn alloy powder, as shown in Table 2.

[0078] [Evaluation] (Average grain size of main phase grains) The cross section of the magnet was observed with an FE-SEM, and the average grain size of the main phase grains was calculated as described above.

[0079] (Open Porosity) The open porosity of the magnet was measured using a gas pycnometer (Shimadzu Corporation, product name "Accupyc II 1340").

[0080] (Initial Magnetic Properties) The saturation magnetization Js and coercive force of the magnet were measured using a vibrating sample magnetometer (VSM). Table 1 shows the measurement results for saturation magnetization Js, and Table 2 shows the measurement results for coercive force.

[0081] (Magnetic properties after high temperature and high humidity test) An Air-HAST test was carried out at 125°C and 85% RH for 24 hours using an EHS-411MD magnet manufactured by Espec Corp. After that, the coercive force of the magnet was measured using a vibrating sample magnetometer (VSM).

[0082] (Density) The mass of the magnet is divided by the apparent volume to determine the volume density (g / cm ３) was sought.

[0083] (Oxygen Content) The oxygen content of the magnet was measured by inert gas fusion-non-dispersive infrared absorption method (NDIR method).

[0084]

[0085]

[0086] 2 is a graph showing the relationship between open porosity and coercive force reduction rate for the sintered magnets produced in Examples 1 to 3 and 5 and Comparative Examples 1 to 4. The graph shows that there is a correlation between open porosity and coercive force reduction rate, and there is also a correlation between the amount of high Al-Zn alloy powder added and open porosity.

[0087] It can be seen from the approximation curves of Comparative Example 1 and Examples 1 to 3 and 5 that when the amount of high Al-Zn alloy powder added is less than 50%, the open porosity decreases and the coercive force loss rate decreases as the amount added increases. With regard to Example 5, since the amount of high Al-Zn alloy powder added was as high as 50%, it is thought that a phenomenon different from that in Examples 1 to 3 occurred during sintering, but the open porosity was 15% or less, and the effect of suppressing the coercive force loss rate was obtained.

[0088] From the approximation curves of Comparative Examples 1 to 4, it can be seen that although there is a correlation between the open porosity and the coercive force reduction rate, the coercive force reduction rate shows a high value overall. For example, the open porosity and coercive force reduction rate differed greatly between Example 2 and Comparative Example 4, which had the same addition amount. This shows that even with the same open porosity, using a high Al-Zn alloy powder is more effective in suppressing coercive force reduction than using a low Al-Zn alloy powder or Zn powder. This is thought to be because the high Al-Zn alloy powder contains a large amount of Al.

[0089] <1> A sintered magnet including a sintered body of a magnetic material containing Sm—Fe—N magnetic powder and Zn—Al alloy powder, wherein the Zn—Al alloy powder has an Al content of 6 atomic % or more and 84 atomic % or less, and the sintered magnet has an open porosity of 15% or less. <2> The Sm—Fe—N sintered magnet according to <1>, wherein the Zn—Al alloy powder has an Al content of 15 atomic % or more and 50 atomic % or less. <3> The Sm—Fe—N sintered magnet according to <1> or <2>, which does not contain oxygen or contains oxygen in an amount of 1.5 mass % or less. <4> The Sm—Fe—N sintered magnet according to any one of <1> to <3>, wherein the sintered body contains main phase grains that are crystals containing Sm, Fe, and N derived from the Sm—Fe—N magnetic powder, and the average grain size of the main phase grains is 0.5 μm or more and 3 μm or less. <5> The Sm—Fe—N sintered magnet of any one of <1> to <4>, having a saturation magnetization of 0.9 T or more. <6> A method for producing an Sm—Fe—N sintered magnet, comprising: mixing an Sm—Fe—N magnetic powder with a Zn—Al alloy powder having an Al content of 6 atomic % or more and 84 atomic % or less to obtain a magnetic material; and pressure-sintering the magnetic material at a temperature of 300°C to 600°C and a pressure of 0.5 GPa to 2.0 GPa. <7> A method for producing an Sm—Fe—N sintered magnet according to <6>, in which the Zn—Al alloy powder accounts for 1 mass % to 30 mass % of the magnetic material. <8> A method for producing an Sm—Fe—N sintered magnet according to <6> or <7>, in which the Zn—Al alloy powder accounts for 1 mass % to 10 mass % of the magnetic material. <9> The method for producing a Sm—Fe—N sintered magnet according to any one of <6> to <8>, wherein the pressure sintering is carried out in an atmosphere with a low oxygen concentration, where the volumetric oxygen concentration is 2 ppm or less.

[0090] The sintered magnet and magnet powder of the present invention can be used in a wide range of applications in the field of various motors, such as in-vehicle accessory motors and main motors for EVs and HEVs, and more specifically, in oil pump motors, electric power steering motors, and EV / HEV drive motors.

[0091] This application claims priority based on Japanese Patent Application No. 2024-111644, filed on July 11, 2024, the entire contents of which are incorporated herein by reference.

Claims

1. A sintered magnet comprising a sintered body of a magnetic material containing Sm-Fe-N magnetic powder and Zn-Al alloy powder, wherein the Al content of the Zn-Al alloy powder is 6 atomic % or more and 84 atomic % or less, and the open porosity of the sintered magnet is 15% or less.

2. The Sm-Fe-N sintered magnet according to claim 1, wherein the Al content of the Zn-Al alloy powder is 15 atomic % or more and 50 atomic % or less.

3. A Sm-Fe-N sintered magnet according to claim 1 or 2, which contains no oxygen or not more than 1.5 mass % of oxygen.

4. The Sm-Fe-N sintered magnet according to any one of claims 1 to 3, wherein the sintered body contains main phase grains that are crystals containing Sm, Fe, and N derived from the Sm-Fe-N magnetic powder, and the average grain size of the main phase grains is 0.5 μm or more and 3 μm or less.

5. The Sm-Fe-N sintered magnet according to any one of claims 1 to 4, having a saturation magnetization of 0.9 T or more.

6. A method for producing a Sm-Fe-N sintered magnet, comprising: mixing an Sm-Fe-N magnetic powder with a Zn-Al alloy powder having an Al content of 6 atomic % or more and 84 atomic % or less to obtain a magnetic material; and pressure-sintering the magnetic material at a temperature of 300°C to 600°C and a pressure of 0.5 GPa to 2.0 GPa.

7. The method for producing a Sm-Fe-N sintered magnet according to claim 6, wherein the Zn-Al alloy powder accounts for 1% by mass or more and 30% by mass or less of the magnetic material.

8. A method for producing a Sm-Fe-N sintered magnet according to claim 6 or 7, wherein the Zn-Al alloy powder accounts for 1% by mass or more and 10% by mass or less of the magnetic material.

9. A method for producing a Sm—Fe—N sintered magnet according to any one of claims 6 to 8, wherein the pressure sintering is carried out in an atmosphere with a low oxygen concentration, where the volumetric oxygen concentration is 2 ppm or less.

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