R-Fe-B hot-work magnet for variable magnetic force motor, variable magnetic force motor, vehicle, and household electronic device

Abstract

This hot-worked R-Fe-B magnet for a variable-magnetic-force motor is an R2-Fe14-B-based hot-worked magnet (where R is at least one rare earth element selected from among Nd, La, Ce, and Y) comprising 12.2-14.5 at.% of R2(Nd1-xy-zLaxCeyYz) (0.0≤x≤0.2, 0.0≤y+z≤0.3), 5-6.5 at.% of B, 0.0-5.0 at.% of Co, and 0.0-1.0 at.% of Ga, with the balance being Fe and inevitable impurities.

Description

Technical Field

[0001] The present invention relates to an R-Fe-B hot-worked magnet for a variable magnetic force motor, a variable magnetic force motor, a vehicle, and a household electronic device. This application claims priority based on Japanese Patent Application No. 2021-201427 filed in Japan on December 13, 2021, and incorporates its content herein by reference.

Background Art

[0002] In conventional permanent magnet motors, high-performance Nd-Fe-B permanent magnets with large residual magnetization and large coercive force are used. For Nd-Fe-B permanent magnets, the composition is disclosed, for example, in Patent Document 1, and improvements suitable for motors for electric vehicles are proposed in Patent Documents 2 and 3. Nd-Fe-B permanent magnets are permanently magnetized in permanent magnet motors operating at various rotational speeds. A strong permanent magnet is required during acceleration of an automobile, but a large magnetic flux of the permanent magnet becomes unnecessary during medium- and high-speed motor rotation because high torque is not required.

[0003] The problem is that as the rotational speed of the motor increases, a current is required to weaken the magnetic flux in the coil, and thus an additional voltage is required. Since there is an upper limit to the supply voltage, there has been a problem that the operating speed is limited in conventional permanent magnet motors [Non-Patent Documents 1-2]. To solve this problem, a VMF (Variable-Magnetic-Force) motor has been demonstrated that controls the magnetization of a permanent magnet according to the rotational speed of the motor and can reduce the magnetic flux weakening current during medium- and high-speed operation of the motor. As a result, a high-output motor can be efficiently operated over a wide range of rotational speeds. Since the magnetization of the permanent magnet used in the VMF motor needs to be changed during operation according to the desired magnetic flux, the permanent magnet is required to have an appropriate coercive force of about 0.2 to 0.65 T so that the magnetization of the permanent magnet can be changed by a limited magnetic field generated from the coil [Non-Patent Documents 1-2]. Furthermore, magnetization changes sharply near the coercive force, and a flat minor magnetization curve is essentially desired. Moreover, these magnets are required to have a large residual magnetization.

[0004] There were two reasons why conventional Nd-Fe-B sintered magnets could not be used for VMF motor applications [Non-Patent Documents 1-2]. The first reason is that conventional Nd-Fe-B sintered magnets have a large coercive force that is not required for VMF motors. The second reason is that the minor magnetization curve of conventional Nd-Fe-B sintered magnets cannot maintain magnetization, and the magnetization of the magnet increases as the magnetic field increases. Therefore, the magnetic flux of the permanent magnet cannot be easily controlled, which is not beneficial for VMF motors. In recent years, sintered magnets using hydrogenated disproportionation desorption recombination (HDDR)-treated (Nd, Sm)Fe-B powder have a small coercive force of 0.2 T and can partially solve the shape of the minor loop. However, the residual magnetization of (Nd, Sm)-Fe-B sintered magnets is only 1.06 T, which limits the maximum magnetic flux of the magnet.

[0005] Another promising material for VFM motors is a hot-worked Nd-Fe-B permanent magnet. By adjusting the total Nd content while maintaining a large residual magnetization of 1.4 - 1.5 T, a small coercive force of 1.2 - 1.4 T can be achieved. The lower limit of the coercive force of anisotropic hot-worked neodymium magnets is reported to be about 0.9 - 1.0 T in alloys with slightly more Nd than the stoichiometric composition. When the Nd content in the alloy is further reduced, the Nd-rich grain boundary phase disappears, which is crucial for achieving the texture and large energy density of hot-worked magnets. Another way to reduce the coercive force while maintaining the Nd-rich phase of hot-worked neodymium magnets is to replace Nd with LRE, which is known to reduce the crystal anisotropy of the 2-14-1 parent phase.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] [Non-Patent Document 1] K. Sakai, K. Yuki, Y. Hashiba, N. Takahashi, and K. Yasui, in Proc. 2009 Int. Conf. Elect. Mach. Syst., (2009) 1-6. [Non-Patent Document 2] N. Limsuwan, et. al., “Design and evaluation of a variable-flux flux-intensifying interior permanent magnet machine,” IEEE Trans. Ind. Appl., 50 (2014) 1015-1024. [Non-Patent Document 3] Keiko Hizume, et al., “Performance Improvement of Hot-Worked Neodymium Magnets by Grain Boundary Diffusion Method,” Electric Steel, Vol. 92, pp. 11-18 (2021) [Non-Patent Document 4] Yasutaka Sasaki, Tadaatsu Okubo, Kazuhiro Takano, “Microstructure of Sintered Neodymium Magnets - Grain Boundary Phase and Interfacial Structure,” Transactions of the Japan Institute of Metals, Vol. 81, pp. 2-10 (2017) [Non-Patent Document 5] Kazuhiro Takano, Tadaatsu Okubo, H. Sepehri-Amin, “Microstructure Control Aimed at High Coercivity of Nd-Fe-B Magnets,” Transactions of the Japan Institute of Metals, Vol. 76, pp. 2-11 (2012) [Summary of the Invention] [Problems to be Solved by the Invention]

[0008] As described above, the reasons why conventional Nd-Fe-B sintered magnets cannot be used for VMF motors are: (i) Nd-Fe-B sintered magnets with conventional compositions have a large coercive force that is not required for VMF motors, and (ii) the inclined minor loop makes it difficult to control the magnetic flux, which is not beneficial for VMF motors. Here, the minor loop refers to a loop curve where magnetism does not saturate, unlike the magnetic saturation curve. The present invention solves the above problems, and aims to provide an R-Fe-B hot-worked magnet for a variable magnetic force motor, a variable magnetic force motor, a vehicle, and a household electronic device, which has a small coercive force to the extent required for a VMF motor and can easily control the magnetic flux of a permanent magnet.

Means for Solving the Problems

[0009] In order to explore the possibility of applying (Nd, LRE)-Fe-B (LRE = Y, La, Ce) hot-worked magnets to VMF, the present inventor evaluated the magnetic properties and minor loop of (Nd 0.8 LRE 0.2 )2Fe 14 B hot-worked magnets, and thus arrived at the present invention. In addition, in order to explore the possibility of applying (Nd, Sm, LRE)-Fe-B (LRE = La, Ce) hot-worked magnets to VMF, the present inventor evaluated the magnetic properties and minor loop of (Nd 0.8 Sm 0.1 LRE 0.1 )2Fe 14 B hot-worked magnets, and thus arrived at the present invention.

[0010] [1] The R-Fe-B hot-worked magnet for a variable magnetic force motor of the present invention is, for example, as shown in Table 3, in an R2-Fe 14 -B (R is at least one rare earth element selected from Nd, La, Ce, and Y) hot-worked magnet, in atomic%, R2 is 12.2% or more and 14.5% or less of (Nd 1-x-y-z La x Ce y Y z )12.2% or more and 14.5% or less, and (0.0 ≦ x ≦ 0.2, 0.0 ≦ y + z ≦ 0.3), B is 5% or more and 6.5% or less, Co is 0.0% or more and 5.0 or less, Ga is 0.0% or more and 1.0 or less, and the balance is Fe and unavoidable impurities. [2] In the R-Fe-B hot-worked magnet [1] for a variable magnetic force motor of the present invention, preferably, the residual magnetic flux density μ0Mr is 1.3 T or more, and the coercive force μ0Hc is in the range of 0.1 T or more and 1.6 T or less.

[0011] [3] The R-Fe-B hot-worked magnet for a variable magnetic force motor of the present invention is, for example, as shown in Table 3, an R2-Fe 14 -B (R contains Nd and La, and further contains at least one rare earth element of Ce and Y) based hot-worked magnet, in atomic percentage, R2 is (Nd 1-x-y-z La x Ce y Y z ) 12.2% or more and 14.5% or less, and (0.05 ≦ x ≦ 0.4, 0.0 ≦ y + z ≦ 0.3), B is 5% or more and 6.5% or less, Co is 0.0% or more and 5.0 or less, Ga is 0.0% or more and 1.0 or less, and the balance is Fe and unavoidable impurities. [4] In the R-Fe-B hot-worked magnet [3] for a variable magnetic force motor of the present invention, preferably, the residual magnetic flux density μ0Mr is 1.0 T or more and 1.30 T or less, and the coercive force μ0Hc is in the range of 0.15 T or more and 1.2 T or less.

[0012] [5] The R-Fe-B hot-worked magnet for a variable magnetic force motor of the present invention is, for example, as shown in Table 3, an R2-Fe 14 -B (R contains Nd and La, and further contains at least one rare earth element of Ce and Y) based hot-worked magnet, in atomic percentage, R2 is (Nd 1-x-y-z La x Ce y Y z)It is above 12.2% and below 14.5%, (0.2 ≦ x ≦ 0.35, 0.1 ≦ y + z ≦ 0.4), B is 5% or more and 6.5% or less, Co is 0.0% or more and 5.0 or less, Ga is 0.0% or more and 1.0 or less, The balance may be Fe and unavoidable impurities. [6] In the R-Fe-B hot-worked magnet [5] for a variable magnetic force motor of the present invention, preferably, further, the residual magnetic flux density μ0Mr is 1.0 T or more and 1.25 T or less, and the coercive force μ0Hc is in the range of 0.15 T or more and 1.1 T or less.

[0013] [7] The R-Fe-B hot-worked magnet for a variable magnetic force motor of the present invention, for example, as shown in Table 5, R2-Fe 14 -B (R contains Nd and Sm, and further contains at least one rare earth element of Ce and La) based hot-worked magnet, in atomic percentage, R2 is (Nd 1-s-x-y Sm s La x Ce y ) It is above 12.2% and below 14.5%, (0.0 < s ≦ 0.2, 0.0 ≦ x + y ≦ 0.2), B is 5% or more and 6.5% or less, Co is 0.0% or more and 5.0 or less, Ga is 0.0% or more and 1.0 or less, The balance may be Fe and unavoidable impurities. [8] In the R-Fe-B hot-worked magnet [7] for a variable magnetic force motor of the present invention, preferably, further, the residual magnetic flux density μ0Mr is 1.0 T or more and 1.4 T or less, and the coercive force μ0Hc is in the range of 0.1 T or more and 0.7 T or less.

[0014] [9] A variable magnetic force motor using the R-Fe-B hot-worked magnet [1] to [8] for a variable magnetic force motor.

[10] A vehicle using the R-Fe-B hot-worked magnet [1] to [6] for a variable magnetic force motor. The vehicle can be, for example, an automobile or a motorcycle. The vehicle using the above variable magnetic force motor.

[11] Household electronic appliances using the R-Fe-B hot-worked magnet for a variable magnetic force motor [1] to [6]. The household electronic appliance may be any one of, for example, a washing machine, a refrigerator, a freezer, and a vacuum cleaner. A household electronic appliance using the variable magnetic force motor.

Effect of the Invention

[0015] According to the R-Fe-B hot-worked magnet for a variable magnetic force motor of the present invention, an R-Fe-B hot-worked magnet for a variable magnetic force motor having a small coercive force required for a VMF motor and capable of easily controlling the magnetic flux of a permanent magnet can be obtained.

Brief Description of the Drawings

[0016]

Figure 1

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Embodiments for Carrying Out the Invention

[0017] In this specification, in principle, the boundary values between the upper limit and the lower limit are also included. Therefore, for the symbol '~' indicating a numerical range, it means 'above' and 'below'. However, when the boundary values between the upper limit and the lower limit are not included, it shall be expressed as 'less than' or 'exceed'.

[0018] <Manufacturing process of hot-worked magnet> (Nd 0.8 LRE 0.2 ) 14.0 Fe 75.7 Co 4.52 Ga 0.54 B 5.24 An alloy ingot having a composition of at% (LRE = Y, La, Ce) (hereinafter referred to as Nd 0.8 LRE 0.2 ) was prepared by induction melting of high-purity elements and cast into a low-carbon steel mold. This ingot was rapidly quenched with a Cu wheel at 30 m / s to obtain an isotropic nanocrystalline ribbon. The quenched ribbon was hot-pressed at 650 °C in a vacuum at 380 MPa to form, and further hot-pressed at 780 °C to 75% of its height in an argon atmosphere. <Manufacturing process of Nd-Fe-B sintered magnet> Nd 14.0 Fe 75.7 Co 4.52 Ga 0.54 B 5.24 An ingot of at% alloy was prepared by induction melting. Strip cast flakes were created from the ingot by the strip casting method. The strip casting method refers to a casting method in which the metal to be used as a material is melted and the molten metal is poured onto a copper roll for rapid solidification. Strip cast flakes are rapidly solidified thin flakes of RE-Fe-B-based alloys for sintered magnets. The wheel speed is 1 to 5 m / s. The strip cast flakes were subjected to hydrogen reduction at a temperature of 150 to 220 °C for 1 to 5 hours. Thereafter, jet mill powder with an average particle size of 1 to 5 μm was prepared from the hydrogen-reduced powder. This jet mill powder was aligned in a magnetic field to produce a green compact. Sintering was performed at a temperature of 900 to 1150 °C for 2 to 9 hours under vacuum. Annealing after sintering was performed at 500 to 680 °C for 1 to 5 hours.

[0019] <Measurement of Magnetic Properties> The magnetic properties at room temperature were measured using a BH tracer, and the temperature-dependent coercivity and minor loop were obtained using a superconducting quantum interference device vibrating sample magnetometer (SQUID-VSM) under a maximum applied magnetic field of 7 T. The microstructure was examined by SEM using a CrossBeam 1540 EsB manufactured by Carl Zeiss. The anisotropy magnetic field of the anisotropic magnet was measured using a Dynacool physical property measurement system (PPMS) under a maximum applied magnetic field of 14 T. In addition, an optical magneto-optical Kerr effect (MOKE) microscope was used to examine magnetic domain propagation. The sample was cut into a size of 2.5 mm × 0.6 mm × 3 mm (c-axis) and pre-magnetized at a maximum magnetic field of 5 T using a pulse magnetization device. The contrast of a pure magnetic domain was obtained by subtracting background information after saturating the magnet again at a maximum magnetic field of 1.3 T using a MOKE microscope.

[0020] Figure 1 is an explanatory diagram of the flat minor magnetization curve and flatness factor for the hot-worked magnet of the present invention. The horizontal axis represents the coercivity μ0Hc, and the vertical axis represents the residual magnetic flux density μ0Mr. Using the saturation magnetic flux density Js and the coercivity μ0Hc in the J-H demagnetization curve, the following flatness factor is defined. The J-H demagnetization curve shows how the magnetization magnitude of the magnet changes with an external magnetic field. Here, F f is the flatness factor, 0.5Js is half of the saturation magnetic flux density Js, H 0.5Js is the value of the magnetic field corresponding to 50% of the saturation magnetic flux density Js, which is the value of the coercivity μ0Hc when the residual magnetic flux density μ0Mr is zero, H c J-H mag is the coercivity or coercivity value Hc of the saturation J-H curve when the residual magnetic flux density μ0Mr is zero.

Equation

[0021] <Nd 0.8 LRE 0.2 <Measurement of Magnetic Properties of Hot-Worked Magnets (LRE = Ce, La, Y)> Figure 2(a) shows Nd 0.8 LRE0.2 It is the room temperature demagnetization curve of a hot-worked magnet (LRE = Ce, La, Y). For the LRE-free magnet, a coercivity of 1.40 T and a remanent magnetization (μ0Mr) of 1.38 T were obtained. On the other hand, for 0.8 Y 0.2 -Fe-B, the coercivity was 1.22 T and the remanent magnetization was 1.32 T, which were lower than those of the LRE-free magnet. Fig. 2(b) shows the 0.8 LRE 0.2 temperature dependence of the coercivity and the coercivity coefficient (β) of the hot-worked magnet from 300 K to 500 K. For the LRE-free sample, the value of β was measured to be -0.424% / K. Nd 0.8 Ce 0.2 In the sample, the β value decreased to -0.454% / K. However, for the 0.8 Y 0.2 sample, β = -0.423% / K, and the thermal stability of the coercivity did not decrease compared to the sample without LRE. For the 0.8 LRE 0.2 -Fe-B sample, the magnet with Ce substitution showed the largest room temperature coercivity, but the sample with Y addition had high thermal stability of the coercivity, medium room temperature coercivity, and at high temperature (>420 K), the 0.8 Y 0.2 sample had a larger coercivity than the 0.8 Ce 0.2 sample.

[0022] Fig. 3 is a backscattered electron (BSE) SEM image obtained from a magnet without LRE and a hot-worked magnet with LRE addition. In all samples, 2:14:1 crystallites showing gray contrast are surrounded by thin RE-rich grain boundary phases (appearing bright). The platelet-like 2-14-1 grains were oriented with their c-axes parallel to the loading direction after hot working. The average crystal grain size of the samples was calculated based on the BSE-SEM images and summarized in Table 1. Table 1 shows the 0.8 LRE 0.2 average crystal grain sizes Dc, Dab, the anisotropy field Ha, and the saturation magnetization μ0Ms of the hot-worked samples.

[0023]

Table 1

[0024] The particle size varies depending on the type of LRE used in the alloy composition. The largest average crystal grain size was obtained for the sample without LRE (about 421 nm (Dc) along the c-plane and about 110 nm (Dab) in the direction perpendicular to the c-plane). The smallest average particle size was for Nd 0.8 La 0.2 sample, where the width (Dc) was about 186 nm and the height (Dab) was about 59 nm, and the volume fraction of grain boundaries increased. Also, the area ratio of RE-rich triple points with bright contrast decreased significantly from 10.3% of the LRE-free sample to 4.6% of the Nd 0.8 La 0.2 sample. As a result, in Fig. 3(d), the grain boundaries appear thin and dark.

[0025] Fig. 4(a) shows the FORC of a commercially available N50-type sintered Nd-Fe-B magnet with the composition of Nd 11.73 Pr 2.87 Fe 77.69 Co 1.04 Cu0.09Al0.49B6.09 (at.%). After reducing the external magnetic field from 7.0 T to different values in the second quadrant and then saturating it again to 7 T, the FORC of the magnet could be evaluated. As seen in Fig. 4(a), the magnetization value of the sintered magnet changes easily with the increase of the magnetic field in the second quadrant. This means that the magnetic flux of the Nd-Fe-B sintered magnet cannot be easily controlled, so it is not suitable for use in VMF motors. In contrast, the FORCs of the hot-worked Nd-Fe-B and (Nd )-Fe-B magnets shown in Fig. 4(b-d) are much flatter compared to the case of the sintered magnet. This is thought to be due to the fact that, regardless of the dopants (Ce, Y, La), the magnetization value of the minor loop of the hot-worked Nd-Fe-B magnet is stronger against the change of the external magnetic field, which is caused by the ultra-fine crystal grains of the hot-worked Nd-Fe-B magnet. (Nd 0.8 LRE 0.2 )-Fe-B magnets shown in Fig. 4(b-d) are much flatter compared to the case of the sintered magnet. This is thought to be due to the fact that, regardless of the dopants (Ce, Y, La), the magnetization value of the minor loop of the hot-worked Nd-Fe-B magnet is stronger against the change of the external magnetic field, which is caused by the ultra-fine crystal grains of the hot-worked Nd-Fe-B magnet. (Nd 0.8 La 0.2)-Fe-B hot-worked magnets not only exhibit flat FORCs, but also note that they have a moderate coercivity of 0.5 T and a sharp magnetization transition around the coercivity value. The coercivity value measured by SQUID-VSM is slightly smaller than that of the B-H tracer. The reason is that, unlike the B-H tracer sample, only a small amount of sample is required for SQUID-VSM measurement, and the coercivity decreases slightly when the surface of the magnet is polished.

[0026] Here, we will explain how to control the shape of FORC based on magnetic domain propagation using a MOKE microscope. As shown in Fig. 5, after saturating the magnetization of the sample, the magnetic field was decreased to observe reverse magnetic domains. Then, to understand how the propagation of magnetic walls occurs, the magnetic field was increased again towards the saturation magnetization. The experimental plan of the applied magnetic field mimics the FORC shown in Fig. 4. In the MOKE image shown in Fig. 5(a), the area ratio of the reverse magnetic domain with black contrast was determined to be 73% at -0.86 T. A distinct multi-domain structure appears, and at 0.2 T, the area ratio of the reversed magnetic domains decreases to 59%. When the magnetic field is further increased to 0.47 T, the magnetic walls of the multi-domain structure are easily displaced, resulting in a significant decrease in the area ratio of the reverse magnetic domains to 33%. This is consistent with what is observed by X-ray magnetic circular dichroism (XMCD).

[0027] Based on the contrast of the magnetic domains in the MOKE data, the magnetization values normalized at each magnetic field were plotted. The FORC constructed from the MOKE data was plotted in Fig. 4(e) and compared with the FORC from SQUID-VSM measurement. The FORC from the MOKE data shows the same trend as the FORC from the SQUID-VSM data. That is, the magnetization gradually increases as the external magnetic field of the sintered magnet increases. On the other hand, from the MOKE results shown in Fig. 5(b), it can be seen that in (Nd 0.8 La 0.2 )-Fe-B hot-worked magnets, the magnetic domains do not easily propagate even when the magnetic field is increased from -0.52 T to 0.24 T in the second quadrant of the magnetization curve. (Nd 0.8 La 0.2)-Fe-B hot-worked magnet's normalized magnetization curve obtained from the MOKE image is shown in Fig. 4(f). The reason for controlling the magnetization value of FORC in the MOKE image clearly explains that it is the pinning effect at the grain boundary phase of the (Nd 0.8 La 0.2 )-Fe-B hot-worked magnet.

[0028] Table 2 shows the magnetic properties of the Nd-Fe-B sintered magnet and the Nd-Fe-B hot-worked magnet as comparative examples, and the (Nd 0.6 La 0.3 Ce 0.1 )-Fe-B hot-worked magnet which is an embodiment of the present invention. As the magnetic properties, the coercive force μ0H c , the remanent magnetic flux density μ0M r and the squareness factor F f are shown.

[0029]

Table 2

[0030] <Parentheses: Nd 0.8 LRE 0.2 Magnetic properties of hot-worked magnet (LRE = Ce, La, Y)> From the above results, it was found that Ce can replace Nd to obtain a high room temperature coercive force, Y can improve the thermal stability of the coercive force, and La has an adverse effect on the external characteristics compared with Ce and Y. The temperature-dependent coercive force reported in the present invention indicates that in the Nd 0.8 LRE 0.2 -Fe-B (LRE = Ce, Y) hot-worked magnet, a coercive force of 0.8 T or more can be maintained at temperatures below 360 K, indicating the possibility of application at medium temperatures (90 °C) such as in wind turbines. Furthermore, in order to expand the applications of the LRE-substituted magnet, the possibility of applying the Nd 0.8 LRE 0.2 -Fe-B hot-worked magnet to a VMF (variable magnetic force) motor to improve the motor efficiency at a wide range of rotational speeds is also being studied. To meet the requirements of the permanent magnet for VMF applications, a moderate coercive force of 0.2 to 0.65 T, high remanent magnetization, and a flat FORC are desirable. The Nd-Fe-B sintered magnet cannot be selected for this application because its coercivity is relatively large. Furthermore, in the VMF motor, there is a large variation in the shape of the FORC of magnetization, so the magnetization value cannot be accurately adjusted.

[0031] In the present invention, as shown in FIGS. 4 and 5, it is shown that in order to control the shape of the FORC of magnetization, it is necessary to better control the propagation of magnetic walls. When the particle size is reduced, the multi-domain structure commonly seen in conventional Nd-Fe-B sintered magnets changes to a single-domain structure in hot-worked magnets. Also, in ultrafine-grained magnets, the volume fraction of grain boundaries increases, which acts as pinning sites for the propagation of magnetic walls during the remagnetization process. As a result, a flat FORC required for VFM applications can be obtained. Therefore, ultrafine-grained hot-worked magnets are an attractive option for use in VMF applications. The inventors demonstrated that by substituting 20% of Nd with La, not only can the cost of the magnet be reduced, but the coercivity of the magnet can also be reduced to μ0Hc = 0.48T, which is suitable for the use in VMF motors. This appropriate coercivity is due to controlling the inherent magnetic properties of the matrix (Nd, La)2Fe 14 B phase. Also, the large remanent magnetization of 1.2T in the (Nd 0.8 La 0.2 )Fe-B hot-worked magnet is also an advantage leading to higher output power in VFM motors.

[0032] In conclusion, the possibility of applying (Nd 0.8 LRE 0.2 )2Fe 14 B high-temperature processed magnets to VMF (variable magnetic force) motors was explored. The (Nd 0.8 Ce 0.2 )2Fe 14 B magnet shows a high coercivity of 1.41T and a low remanent magnetization of 1.30T compared to LRE-free magnets. The (Nd 0.8 Y 0.2 )2Fe 14 B magnet shows no decrease in the thermal stability of coercivity (β = -0.423% / K) and shows an appropriate coercivity of 1.22T and a remanent magnetization of 1.32T. When 20% of Nd was replaced by La, the coercive force was 0.48 T and the residual magnetization was 1.2 T, which were adjusted to values suitable for application to a VMF motor. The remarkable result of the present invention is that (Nd 0.8 La 0.2 )2Fe 14 the shape of the FORC of the magnet is flat, which is derived from the large volume fraction of the grain boundaries of the ultrafine hot-worked magnet revealed by the MOKE microscope. Also, the FORC is flattened by the pinning effect. The present invention shows that a low-cost (Nd 0.8 La 0.2 )2Fe 14 B hot-worked magnet can be an excellent candidate for application to a VMF motor.

[0033] <Nd 0.8 LRE 0.2 Measurement of magnetic properties of hot-worked magnets (LRE = Ce, La, Y) FIG. 6 is a diagram for explaining the magnetic properties of various anisotropic hot-worked magnets of the present invention. The horizontal axis is the coercive force μ0Hc (T), and the vertical axis is the residual magnetic flux density μ0Mr (T).

[0034] Table 3 is a table for explaining the element composition of the measurement points where the magnetic properties of the various anisotropic hot-worked magnets shown in FIG. 6 are plotted.

[0035]

Table 3

[0036] Table 4 is an explanation of the composition range having desirable magnetic properties for the R-Fe-B anisotropic hot-worked magnet for a variable magnetic force motor of the present invention. (Nd 1-x-y-z La x Ce y Y z ) 12.2-14.5 -Fe bal -Co 0.0-5.0 -Ga 0.0-1.0 -B 5-6.5 (at.%) of La x Ce y Yz is used as a parameter in the composition range. As a preferable first range of magnetic properties, the remanent magnetic flux density μ0Mr is 1.3 T or more, and the coercive force μ0Hc is in the range of 0.1 T or more and 1.6 T or less. Such a composition range is for La x Ce y Y z (0.0 ≦ x ≦ 0.2, 0.0 ≦ y + z ≦ 0.3). As a preferable second range of magnetic properties, the remanent magnetic flux density μ0Mr is 1.1 T or more and 1.3 T or less, and the coercive force μ0Hc is in the range of 0.15 T or more and 1.1 T or less. Such a composition range is for La x Ce y Y z (0.05 ≦ x ≦ 0.4, 0.0 ≦ y + z ≦ 0.3). As an optimal range of magnetic properties, the remanent magnetic flux density μ0Mr is 1.0 T or more and 1.25 T or less, and the coercive force μ0Hc is in the range of 0.15 T or more and 0.7 T or less. Such a composition range is for La x Ce y Y z (0.2 ≦ x ≦ 0.35, 0.1 ≦ y + z ≦ 0.4).

[0037]

Table 4

[0038] <Nd 0.8 Sm 0.1 LRE 0.1 Manufacturing process of hot-worked magnet (LRE = Ce, La)> (Nd 0.8 Sm 0.1 LRE 0.1 ) 12.9 Fe 76.31 Co 4.47 Ga 0.50 B 5.82 (at%) alloy ingot having a composition of (LRE = La, Ce) (hereinafter, Nd 0.8 Sm 0.1 LRE 0.1(indicated as such) was produced by induction melting of high-purity elements and cast into a low-carbon steel mold. This ingot was rapidly solidified by a Cu wheel at a speed of 30 m / s to obtain an isotropic nanocrystalline ribbon. The rapidly solidified ribbon was hot-pressed at 630 °C in a vacuum of 380 MPa to form, and then hot-pressed to 75% of its height at 750 °C in an argon atmosphere. The Nd thus obtained 0.8 Sm 0.1 LRE 0.1 Regarding the hot-worked magnet (LRE = Ce, La), in the example where the grain boundary diffusion method was further applied, this Nd 0.8 Sm 0.1 LRE 0.1 The hot-worked magnet (LRE = Ce, La) was coated with an alloy of 4 wt% (based on the weight of the hot-worked magnet) of Nd 80 Cu 20 and then heat-treated at 650 °C for 3 hours. Nd 80 Cu 20 The alloy was used as a diffusion material to perform the grain boundary diffusion method on Nd 0.8 Sm 0.1 LRE 0.1 In the hot-worked magnet (LRE = Ce, La), Cu can be detected at the grain boundary. The detection of Cu at the grain boundary can be performed by EDS analysis with a scanning transmission electron microscope. As an example of the diffusion material used in the grain boundary diffusion method, RE-M (RE: Pr, Nd, Tb, Dy, M: Ga, Cu, Al) can be exemplified. Whether the hot-worked magnet has been subjected to the grain boundary diffusion method can be determined by investigating whether the constituent elements of the diffusion material are contained in the grain boundary.

[0039] <Nd 0.8 Sm 0.1 LRE 0.1 Measurement of magnetic properties of hot-worked magnet (LRE = Ce, La) Figure 7 shows the FORC of the Nd 0.8 Sm 0.1 LRE 0.1 hot-worked magnet (LRE = Ce, La), where (a) is when LRE = Ce, that is, (Nd 0.8 Sm 0.1 Ce 0.1) - FORC of the (Nd 0.8 Sm 0.1 La 0.1 ) - Fe - B hot - worked magnet. (Nd 0.8 Sm 0.1 Ce 0.1 ) - Fe - B hot - worked magnets and the flatness factors F 0.8 Sm 0.1 La 0.1 ) - Fe - B hot - worked magnets were 0.83 and 0.87 respectively. These flatness factors F f were superior to the flatness factor F f shown in Table 1 for the (Nd 0.6 La 0.3 Ce 0.1 ) - Fe - B hot - worked magnet (= 0.75). f (= 0.75). Also, the coercive force μ0H 0.8 Sm 0.1 Ce 0.1 ) - Fe - B hot - worked magnet and the residual magnetic flux density μ0M c were 0.16 T and 1.29 T respectively, and the coercive force μ0H r and the residual magnetic flux density μ0M 0.8 Sm 0.1 La 0.1 ) - Fe - B hot - worked magnet were 0.26 T and 1.35 T respectively. c and the residual magnetic flux density μ0M r were 0.26 T and 1.35 T respectively.

[0040] Figures 8(a) and (b) are the BSE - SEM images of the (Nd 0.8 Sm 0.1 Ce 0.1 ) - Fe - B hot - worked magnet and the (Nd 0.8 Sm 0.1 La 0.1 ) - Fe - B hot - worked magnet respectively. The left side is at low magnification (scale bar is 5 μm), and the right side is at high magnification (scale bar is 500 nm). (Nd 0.8 Sm 0.1 Ce 0.1In the interface region of the original flakes of the (Nd)-Fe-B hot-worked magnet, a gray-contrast (Sm,Ce)Fe2 phase is observed. This is 0.8 Sm 0.1 La 0.1 )-In the (Nd)-Fe-B hot-worked magnet, the formation of the (Sm,Ce)Fe2 phase is suppressed by replacing Ce with La. As a result, the area fraction of the RE-rich triple points increases inside the ribbons of the (Nd 0.8 Sm 0.1 La 0.1 )-Fe-B hot-worked magnet. This can explain the enhanced coercivity and the flatness of the FORC (First-order Reversal Curve) achieved in the (Nd 0.8 Sm 0.1 La 0.1 )-Fe-B hot-worked magnet.

[0041] For improving the flatness of the FORC, a grain boundary diffusion treatment was performed on the (Nd 0.8 Sm 0.1 La 0.1 )-Fe-B hot-worked magnet. Fig. 9(a) is the hysteresis curve, and Fig. 9(b) is the temperature dependence of the coercivity. Fig. 9(a) shows the room-temperature characteristics of the (Nd 0.8 Sm 0.1 La 0.1 )-Fe-B hot-worked magnet itself and the (Nd 0.8 Sm 0.1 La 0.1 )-Fe-B hot-worked magnet subjected to a 4 wt% Nd-Cu diffusion process. After the Nd-Cu diffusion process, the coercivity μ0H c is improved to 0.56 T, and the residual magnetic flux density μ0M r decreases to 1.29 T. Thanks to the improved coercivity at room temperature, a coercivity of 0.15 T at the application temperature (460 K) could be achieved. This coercivity is a desirable value for practical applications. In other words, the Nd-Cu diffusion-treated (Nd 0.8 Sm 0.1 La 0.1 )-Fe-B hot-worked magnet can have a desirable coercivity for use over the entire operating temperature range (300 - 460 K).

[0042] Figures 10(a) and (b) are BSE-SEM images of the as-hot-worked (Nd 0.8 Sm 0.1 La 0.1 )-Fe-B magnet itself, and Figures 10(c) and (d) are BSE-SEM images of the Nd-Cu diffusion-treated (Nd 0.8 Sm 0.1 La 0.1 )-Fe-B hot-worked magnet. The upper side is at a low magnification (scale bar is 5 μm) and the lower side is at a high magnification (scale bar is 500 nm) respectively.

[0043] As can be seen from Figure 10, after the grain boundary diffusion process, the area fraction of the RE-rich triple point region inside the ribbon increases, and the thin grain boundary phase becomes more visible in the hot-worked magnet. Thus, as shown in Figure 11(a), the enhanced coercivity achieved in the Nd-Cu diffusion-treated (Nd 0.8 Sm 0.1 La 0.1 )-Fe-B hot-worked magnet and the better flatness of the FORC can be explained.

[0044] Figure 11 shows the FORC of the Nd-Cu diffusion-treated (Nd 0.8 Sm 0.1 La 0.1 )-Fe-B hot-worked magnet, where (a) is at room temperature and (b) is at 460 K.

[0045] After the Nd-Cu grain boundary diffusion process, the flatness factor improved from 0.87 to 0.95. This value is the maximum value of the flatness factor reported so far for VMF motor applications and maintains a flatness factor of 0.94 even at high temperature (460 K).

[0046] Table 5 summarizes the magnetic properties of the Nd 0.8 Sm 0.1 LRE 0.1 hot-worked magnets (LRE = Ce, La).

[0047]

Table 5

[0048] For Samples 1 to 18, those having preferable magnetic properties as the R-Fe-B anisotropic hot-worked magnet for a variable magnetic force motor are classified. (Nd 1-x-y-z La x Ce y Y z ) 12.2-14.5 -Fe bal -Co 0.0-5.0 -Ga 0.0-1.0 -B 5-6.5 (at.%) of La x Ce y Y z 、and, (Nd 1-s-x-y Sm s La x Ce y ) 12.2-14.5 -Fe bal -Co 0.0-5.0 -Ga 0.0-1.0 -B 5-6.5 (at.%) of Sm s La x Ce y are used as the parameters of the composition range.

[0049] (1) Samples 11, 12, 19, and 20 are listed as those having a remanence density μ0Mr of 1.1 T or more and a coercive force μ0Hc in the range of 0.2 T or more and 0.65 T or less. Based on these samples, preferable composition ranges include La x Ce y Y z (0.2 ≤ x ≤ 0.4, 0.0 < y + z ≤ 0.3), Sm s La x Ce y (0.0 < s ≤ 0.2, 0.0 < x + y ≤ 0.2). More preferable composition ranges include La x Ce y Y z (0.15 ≤ x ≤ 0.35, 0.05 ≤ y + z ≤ 0.25), Sm s La x Ce y (0.05 ≤ s ≤ 0.15, 0.05 ≤ x + y ≤ 0.15).

[0050] (2) Samples 6, 10, 11, 12, 19, and 20 are listed as those having a remanent magnetic flux density μ0Mr of 1.1 T or more and a coercive force μ0Hc in the range of 0.2 T or more and 0.8 T or less. Based on these samples, the preferred composition ranges include La x Ce y Y z (0.1 ≤ x ≤ 0.4, 0.0 ≤ y + z ≤ 0.3), Sm s La x Ce y (0.0 < s ≤ 0.2, 0.0 < x + y ≤ 0.2) can be mentioned. The more preferred composition ranges include La x Ce y Y z (0.15 ≤ x ≤ 0.35, 0.0 ≤ y + z ≤ 0.25), Sm s La x Ce y (0.05 < s ≤ 0.15, 0.05 ≤ x + y ≤ 0.15) can be mentioned.

[0051] (3) Samples 5, 6, 9, 10, 11, 12, 15, 19, and 20 are listed as those having a remanent magnetic flux density μ0Mr of 1.1 T or more and a coercive force μ0Hc in the range of 0.2 T or more and 0.9 T or less. Based on these samples, the preferred composition ranges include La x Ce y Y z (0.0 ≤ x ≤ 0.4, 0.0 ≤ y + z ≤ 0.4), Sm s La x Ce y (0.0 < s ≤ 0.2, 0.0 < x + y ≤ 0.2) can be mentioned. The more preferred composition ranges include La x Ce y Y z (0.0 ≤ x ≤ 0.35, 0.15 ≤ y + z ≤ 0.35), Sm s La x Ce y (0.05 < s ≤ 0.15, 0.05 ≤ x + y ≤ 0.15) can be mentioned.

[0052] (4) The samples 11, 19, and 20 are cited as those in which the residual magnetic flux density μ0Mr is 1.1 T or more, the coercive force μ0Hc is in the range of 0.2 T or more and 0.65 T or less, and the flatness factor Ff is 0.7 or more. Based on these samples, as a preferable composition range, La x Ce y Y z (0.2 ≦ x ≦ 0.4, 0.0 < y + z ≦ 0.2), Sm s La x Ce y (0.0 < s ≦ 0.2, 0.0 < x + y ≦ 0.2) can be cited. As a more preferable composition range, La x Ce y Y z (0.25 ≦ x ≦ 0.35, 0.05 ≦ y + z ≦ 0.15), Sm s La x Ce y (0.05 < s ≦ 0.15, 0.05 ≦ x + y ≦ 0.15) can be cited.

[0053] FIG. 12 is a main part configuration diagram showing an example of a variable magnetic force motor in which the hot-worked magnet of the present invention is used. The variable magnetic force motor is composed of a wound stator and a permanent magnet rotor in a low magnetic force mode and a high magnetic force mode. The wound rotor is a rotating part, also called a rotor, and is provided with windings. The wound rotor is attached to a shaft serving as an output shaft via a bearing (not shown). The permanent magnet stator is a part that generates a force for rotating the rotor and is provided with permanent magnets. The permanent magnet is a source of a magnetic field and is important as a material constituting the motor. The bracket (not shown) is a part that supports the bearing and integrally covers the wound stator.

Industrial Applicability

[0054] According to the R-Fe-B hot-worked magnet for a variable magnetic force motor of the present invention, an R-Fe-B hot-worked magnet for a variable magnetic force motor can be obtained that has a small coercive force to the extent required for a VMF motor and can easily control the magnetic flux of the permanent magnet.

Claims

1. R ２ -Fe １４ -B (wherein R contains Nd and Sm and further contains at least one rare earth element of La and Ce) in the hot-worked magnet of the system, in atomic percent, R ２ is (Nd １－ｓ－ｘ－ｙ Sm ｓ La ｘ Ce ｙ ) 12.2% or more and 14.5% or less, and (0.0 < s ≤ 0.2, 0.0 ≤ x + y ≤ 0.2), B is 5% or more and 6.5% or less, Co is 0.0% or more and 5.0 or less, Ga is 0.0% or more and 1.0 or less, An R-Fe-B hot-worked magnet for a variable magnetic force motor, with the balance being Fe and unavoidable impurities.

2. Furthermore, Residual magnetic flux density μ ０ Mr is 1.0 T or more and 1.4 T or less, Coercive force μ ０ Hc is in the range of 0.1 T or more and 0.7 T or less The R-Fe-B hot-worked magnet for a variable magnetic force motor according to Claim 1.

3. A variable magnetic force motor using the R-Fe-B hot-worked magnet for a variable magnetic force motor according to any one of Claims 1 to 2.

4. A vehicle using the variable magnetic force motor according to Claim 3.

5. A household electronic device using the variable magnetic force motor according to Claim 3.

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