Rare earth cobalt permanent magnets, methods and apparatuses for making same

Abstract

Provided are a rare-earth cobalt permanent magnet having excellent magnetic properties, a method of manufacturing such a rare-earth cobalt permanent magnet, and an apparatus. The rare-earth cobalt permanent magnet is composed of 23 to 27 mass% of R, 1.0 to 5.0 mass% of Cu, 18 to 25 mass% of Fe, 1.5 to 3.0 mass% of Zr, and Co as a balance, and inevitable impurities, R representing a rare-earth element including at least Sm, wherein the rare-earth cobalt permanent magnet includes a plurality of crystal grains and a grain boundary portion, and in the grain boundary portion, a concentration of Cu is at least twice a concentration of Zr.

Description

Technical Field

[0001] This disclosure relates to a rare-earth cobalt permanent magnet applicable to a variable magnetic field motor, a method for manufacturing such a rare-earth cobalt permanent magnet, and an apparatus. Background Technology

[0002] Variable field motors have attracted attention due to their ability to reduce the energy consumption of the motor. In a variable field motor, the magnetic flux varies according to the revolutions per unit time (e.g., RPM). Typically, for variable field motors, it is necessary to generate high magnetic flux when high torque is required at low speeds, while the magnetic flux decreases as the motor rotates at high speeds, so that the motor has high energy efficiency over a wide range of speeds from low to high.

[0003] Examples of methods for changing magnetic flux in a variable magnetic field motor include the variable magnetic force method, the magnetic field coil method, and the winding switching method. For example, Japanese Patent No. 4965924 discloses a method for generating a variable magnetic field by combining an NdFeB magnet with high magnetization and high coercivity with an AlNiCo magnet with high magnetization and low coercivity. However, there is a problem that the coercivity of the AlNiCo magnet is too low, making the magnet difficult to use.

[0004] Meanwhile, as a variable magnetic force method, a method using samarium cobalt magnets capable of changing magnetic flux has been studied.

[0005] For example, International Patent Publication No. WO2009 / 145229 proposes the use of samarium cobalt magnets as magnets for variable magnetic fields. However, in the technology disclosed in International Patent Publication No. WO2009 / 145229, the residual magnetization value is 80% or greater in a magnetic field of 10 kOe, therefore it is not considered that the motor can satisfactorily perform high torque operation in which strong magnetic flux is required. Summary of the Invention

[0006] To improve the efficiency of a variable field motor, it is desirable that when the permanent magnet is demagnetized and then remagnetized, the permanent magnet reaches saturation magnetization in a low magnetic field. Furthermore, a permanent magnet with a high rectangularity ratio is required. The rectangularity ratio is expressed as the ratio of the magnetic field (Hk) to the coercivity (Hcj) (Hk / Hcj).

[0007] This disclosure is made to address the aforementioned problems, and the purpose of this disclosure is to provide a rare-earth cobalt permanent magnet having high remanent flux density, low coercivity and high rectangularity ratio, and to provide a method for manufacturing such a rare-earth cobalt permanent magnet and an apparatus including such a rare-earth cobalt permanent magnet.

[0008] A first exemplary aspect is a rare-earth cobalt permanent magnet, said rare-earth cobalt permanent magnet comprising: 23% to 27% by mass of R, 1.0% to 5.0% by mass of Cu, 18% to 25% by mass of Fe, 1.5% to 3.0% by mass of Zr, and Co as the balance, as well as unavoidable impurities, wherein R represents a rare-earth element including at least Sm, wherein

[0009] The rare-earth cobalt permanent magnet comprises multiple grains and grain boundaries, and

[0010] In the grain boundary region, the concentration of Cu is at least twice the concentration of Zr.

[0011] In rare-earth cobalt permanent magnets, the size of the cell structure constituting the grains ranges from 50 nm to 200 nm.

[0012] On one hand, rare-earth cobalt permanent magnets have a saturation magnetization equal to or greater than 1.16T and an intrinsic coercivity Hcj of 120kA / m to 800kA / m.

[0013] On one hand, rare-earth cobalt permanent magnets have a saturation magnetization equal to or greater than 1.16T and an intrinsic coercivity Hcj of 240kA / m to 800kA / m.

[0014] In rare-earth cobalt permanent magnets, the rectangle ratio (Hk / Hcj) representing the ratio of the magnetic field Hk to the intrinsic coercivity Hcj when the remanent magnetization is 90% is equal to or higher than 60% in the demagnetization curve, and

[0015] When the rare-earth cobalt permanent magnet is remagnetized from a demagnetizing field that exceeds the inflection point in the demagnetizing curve, it obtains a magnetization intensity equal to or higher than 95% of the saturation magnetization intensity in a magnetic field that is equal to or weaker than five times the intrinsic coercivity Hcj.

[0016] In rare-earth cobalt permanent magnets, the rectangle ratio (Hk / Hcj) representing the ratio of the magnetic field Hk to the intrinsic coercivity Hcj when the remanent magnetization is 90% is equal to or greater than 60% in the demagnetization curve, and

[0017] When the rare-earth cobalt permanent magnet is remagnetized from a demagnetizing field that exceeds the inflection point in the demagnetizing curve, it obtains a magnetization intensity equal to or higher than 95% of the saturation magnetization intensity in a magnetic field that is equal to or weaker than three times the intrinsic coercivity Hcj.

[0018] In one aspect of rare-earth cobalt permanent magnets, when the diffraction intensity I(006) of the (006) plane and the diffraction intensity I(303) of the (303) plane are measured by powder X-ray diffraction, the diffraction intensity ratio I(006) / I(303) is 0.225 to 0.4.

[0019] A first method for manufacturing a rare-earth cobalt permanent magnet according to this disclosure includes:

[0020] Step (I) for preparing the alloy, the alloy being composed of the following components: 23 to 27% by mass of R, 1.0 to 5.0% by mass of Cu, 18 to 25% by mass of Fe, 1.5 to 3.0% by mass of Zr and Co as the balance and unavoidable impurities, where R represents a rare earth element including at least Sm.

[0021] The crushing step (II) involves pulverizing the alloy into powder;

[0022] The compression molding step (III) involves pressing powder into a molded body;

[0023] Step (IV) involves sintering the shaped body at 1200°C to 1250°C.

[0024] Step (V) of solution treatment on sintered molded body;

[0025] Step (VI) involves heat-treating the molded body that has undergone solution treatment at a temperature of 600°C to 850°C.

[0026] Step (VII) involves cooling the heat-treated molded body to 400°C or below at a rate of 0.2°C / min to 10°C / min.

[0027] Step (VIII) involves heat-treating the molded body at a temperature of 700°C to 900°C, which is higher than the temperature in step (VI); and

[0028] Step (IX) involves cooling the heat-treated molded body to 400°C or below at a rate of 0.1°C / min to 5°C / min.

[0029] A second method for manufacturing rare-earth cobalt permanent magnets according to this disclosure includes:

[0030] Step (I) for preparing the alloy, the alloy being composed of the following components: 23 to 27% by mass of R, 1.0 to 5.0% by mass of Cu, 18 to 25% by mass of Fe, 1.5 to 3.0% by mass of Zr and Co as the balance and unavoidable impurities, where R represents a rare earth element including at least Sm.

[0031] The crushing step (II) involves pulverizing the alloy into powder;

[0032] The compression molding step (III) involves pressing powder into a molded body;

[0033] Step (IV) involves sintering the shaped body at 1200°C to 1250°C.

[0034] Step (V) of solution treatment on sintered molded body;

[0035] Step (VI-a) involves heat-treating the molded body that has undergone solution treatment at 750°C to 850°C.

[0036] The step (VII-a) involves cooling the heat-treated molded body to 500°C to 600°C at a rate of 0.5°C / min to 10°C / min, followed by isothermal holding of the molded body.

[0037] The step of rapidly cooling the molded part that has been held at an isothermal temperature (VIII-a).

[0038] In addition, this disclosure also provides an apparatus including the aforementioned rare-earth cobalt permanent magnet.

[0039] According to this disclosure, a rare-earth cobalt permanent magnet having high remanent flux density, low coercivity and high rectangularity ratio can be provided, as well as a method for manufacturing such a rare-earth cobalt permanent magnet and an apparatus including such a rare-earth cobalt permanent magnet.

[0040] The above and other objects, features and advantages of this disclosure will be more fully understood from the detailed description and accompanying drawings given below, which are given by way of illustration only and are not intended to limit this disclosure. Attached Figure Description

[0041] Figure 1 This is a schematic diagram used to illustrate the structure of a permanent magnet;

[0042] Figure 2 It is a graph showing the first and second quadrants of the hysteresis curve of the permanent magnet according to Embodiment 1;

[0043] Figure 3 Dark-field scanning transmission electron microscopy (DF-STEM) images of the permanent magnet according to Example 1 are shown;

[0044] Figure 4 It is a graph showing the analytical results of the composition containing the permanent magnet grain boundary portion according to Example 1; and

[0045] Figure 5 The powder X-ray diffraction spectra of the permanent magnets according to Examples 3 and 4 and Reference Example 1 are shown. Detailed Implementation

[0046] The following will describe, in sequence, a rare-earth cobalt permanent magnet according to the present disclosure, a method for manufacturing a rare-earth cobalt permanent magnet, and an apparatus for manufacturing a rare-earth cobalt permanent magnet.

[0047] It should be noted that, unless otherwise specified, numerical ranges such as “nm” or “n to m” (i.e. “from n to m”) include both lower and upper limits.

[0048] Rare Earth Cobalt Permanent Magnets

[0049] The rare-earth cobalt permanent magnet according to this disclosure (hereinafter also referred to as the permanent magnet according to this disclosure, or simply as a permanent magnet) is composed of the following components: 23 to 27% by mass of rare-earth element R, 1.0 to 5.0% by mass of Cu, 18 to 25% by mass of Fe, 1.5 to 3.0% by mass of Zr, and Co as the balance, as well as unavoidable impurities, wherein the rare-earth element R includes at least Sm, wherein

[0050] The rare-earth cobalt permanent magnet comprises multiple grains and grain boundaries, and

[0051] In the grain boundary region, the concentration of Cu is at least twice the concentration of Zr.

[0052] It is generally believed that in the presence of Sm2CO 17 In rare earth cobalt permanent magnets with phase-type crystalline phases (hereinafter also referred to as "2-17 phase"), Cu increases the coercivity of the magnet, and Zr increases the amount of Fe solid solution, thereby indirectly increasing the remanent magnetic flux density Br of the magnet.

[0053] In the permanent magnet according to this disclosure, by using either of the two manufacturing methods described later, the concentration of Cu in the grain boundary portion is adjusted to at least two times, preferably at least three times, the concentration of Zr by controlling the diffusion of Cu and Zr. As a result, a permanent magnet with high remanent flux density, low coercivity, and high rectangularity can be obtained.

[0054] Since the permanent magnet according to this disclosure has magnetic characteristics suitable for a variable field motor as described above, it can be used to manufacture a highly efficient variable field motor over a wide range from low speed to high speed.

[0055] Rare earth element R is a collective term for Sc, Y, and lanthanides. Furthermore, in the permanent magnet according to this disclosure, rare earth element R includes at least Sm. By containing rare earth elements in the aforementioned proportions, a permanent magnet with high magnetic anisotropy can be obtained. Rare earth element R may consist solely of Sm, or it may be a combination of Sm and other rare earth elements. Considering magnetic properties, other rare earth elements R are preferably at least one element selected from Nd, Pr, and Ce. Considering magnetic properties, based on all rare earth elements, rare earth element R preferably contains 70% by mass or more, more preferably 80% by mass or more, of Sm.

[0056] Rare-earth cobalt permanent magnets contain 1.0% to 5.0% Cu by mass. By adjusting the Cu content within this range, a high rectangularity ratio can be obtained while adjusting the coercivity within an appropriate range.

[0057] Rare-earth cobalt permanent magnets contain 18% to 25% Fe by mass. High remanent magnetic flux density can be easily achieved by adjusting the Fe content within this range. Furthermore, the saturation magnetization is increased by containing 18% or more Fe by mass. Moreover, the coercivity is adjusted to a suitable range by limiting the Fe content to 25% or less by mass.

[0058] Furthermore, the rare-earth cobalt permanent magnet contains 1.5% to 3.0% Zr by mass. By adjusting the Zr content within this range, the remanent magnetic flux density Br can be indirectly increased by increasing the amount of Fe solid solution. This also improves the maximum energy product (BH). 最大 The maximum magnetic energy product is the maximum static magnetic energy that a magnet can maintain.

[0059] In addition, the balance of the permanent magnet (i.e., 40% to 56.5% by mass) consists of Co and unavoidable impurities.

[0060] The presence of Co improves the thermal stability of the permanent magnet. However, when the Co content is too high, the Fe content relatively decreases, thereby increasing the likelihood of magnetization degradation. Based on these considerations, the Co content is preferably between 40% and 56.5% by mass.

[0061] Next, we will refer to Figure 1 Describe the structure of a permanent magnet. Figure 1 This is a schematic cross-sectional view showing a portion of the cross-section of a permanent magnet. (Example) Figure 1 The example shown illustrates that the permanent magnet 10 comprises a plurality of grains 1 (the region enclosed by solid lines in the figure) and grain boundary portions 2 between the grains 1 (solid lines in the figure). Each grain 1 has a unit cell phase 3 (the region enclosed only by dashed lines or by both dashed and solid lines in the figure) and a unit cell wall 4 (dashed lines in the figure), the unit cell phase 3 comprising Th2Zn 17 The crystalline phase with an RCo5-type structure (hereinafter also referred to as "phase 2-17"), wherein the cell wall 4 contains and surrounds the crystalline phase with an RCo5-type structure (hereinafter also referred to as "phase 1-5"). In this disclosure, the crystalline structure is a combination of a crystalline phase 3 and a cell wall 4 surrounding the crystalline phase, and it is the smallest unit constituting a grain.

[0062] As described above, permanent magnets have a cellular phase containing Th2Zn. 17 The Th₂Zn crystal phase is characterized by a morphological structure as the main phase. 17The R-3m type structure is a crystal structure with R-3m type space groups. In the permanent magnet according to this disclosure, the Th portion is occupied by rare earth elements and Zr, while the Zn portion is occupied by Co, Cu, Fe, and Zr. Furthermore, as described above, the permanent magnet has a cell wall containing a crystal phase with an RCo5 type structure. In the RCo5 type crystal phase, the R portion is rare earth elements and Zr, while the Co portion is Co, Cu, and Fe. In the permanent magnet 10, the size of the cell structure refers to the length of the cell wall 4 (the length of the RCo5 type crystal phase). In the permanent magnet according to this disclosure, the cell size is preferably 50 nm to 200 nm to obtain low coercivity.

[0063] Next, we will refer to Figure 2 The characteristics of the permanent magnet according to this disclosure are described. Figure 2 This is a graph showing the first and second quadrants (decay curves) of the hysteresis curve of the permanent magnet according to Embodiment 1 (described later). The vertical axis represents magnetization (magnetic polarization), and the horizontal axis represents the strength of the magnetic field. Positive values ​​on the horizontal axis represent the strength of the magnetic field applied in the direction in which the permanent magnet is magnetized, and negative values ​​represent the strength of the magnetic field applied in the direction in which the permanent magnet is demagnetized.

[0064] When a magnetic field is applied to a permanent magnet in the positive direction, it undergoes magnetic polarization according to the initial magnetization curve and eventually reaches saturation magnetization. Then, when a magnetic field is applied to the saturated permanent magnet in the negative direction, it rapidly demagnetizes and passes through an inflection point. The magnetic field strength at the point where the magnetic polarization becomes zero is the intrinsic coercivity (Hcj).

[0065] In this disclosure, the magnetic field at 90% remanent magnetization is denoted by Hk, and the ratio of the magnetic field Hk to the intrinsic coercivity Hci (Hk / Hcj) is defined as the rectangularity ratio. The permanent magnet according to this disclosure can have a rectangularity ratio of 60% or higher, preferably 70% or higher.

[0066] Furthermore, in the permanent magnet according to this disclosure, when it is remagnetized from a demagnetizing field (point A) beyond the inflection point in the demagnetizing curve, it obtains a magnetization intensity equal to or higher than 95% of the saturation magnetization intensity in a magnetic field equal to or weaker than five times the intrinsic coercivity Hcj (absolute value), preferably obtaining a magnetization intensity equal to or higher than 95% of the saturation magnetization intensity in a magnetic field equal to or weaker than three times the intrinsic coercivity Hcj (absolute value).

[0067] As described above, the permanent magnet according to this disclosure has excellent magnetization response properties to magnetic fields and can even be applied to variable field motors where the number of revolutions per unit time (e.g., RPM) changes frequently.

[0068] Furthermore, the permanent magnets according to this disclosure may have magnetic properties including, for example, a saturation magnetization of 1.16T or greater than 1.16T and an intrinsic coercivity Hcj of 120kA / m to 800kA / m, preferably 200kA / m to 800kA / m, more preferably 240kA / m to 800kA / m.

[0069] <Manufacturing Method of Rare Earth Cobalt Permanent Magnets>

[0070] The rare-earth cobalt permanent magnet described above according to this disclosure can be manufactured using either of the two manufacturing methods shown below. These two manufacturing methods will be described.

[0071] (First Manufacturing Method)

[0072] A first method for manufacturing a rare-earth cobalt permanent magnet according to the present disclosure (hereinafter referred to as the first manufacturing method) includes:

[0073] Step (I) for preparing the alloy, the alloy being composed of the following components: 23% to 27% by mass of R, 1.0% to 5.0% by mass of Cu, 18% to 25% by mass of Fe, 1.5% to 3.0% by mass of Zr and Co as the balance and unavoidable impurities, where R represents a rare earth element including at least Sm.

[0074] The crushing step (II) involves pulverizing the alloy into powder;

[0075] The compression molding step (III) involves pressing powder into a molded body;

[0076] Step (IV) involves sintering the shaped body at 1200°C to 1250°C.

[0077] Step (V) of solution treatment on sintered molded body;

[0078] Step (VI) involves heat-treating the molded body that has undergone solution treatment at a temperature of 600°C to 850°C.

[0079] Step (VII) involves cooling the heat-treated molded body to 400°C or below at a rate of 0.2°C / min to 10°C / min.

[0080] Step (VIII) involves heat-treating the molded body at a temperature of 700°C to 900°C, which is higher than the temperature in step (VI); and

[0081] Step (IX) involves cooling the heat-treated molded body to 400°C or below at a rate of 0.1°C / min to 5°C / min.

[0082] According to the first manufacturing method described above, a rare-earth cobalt permanent magnet comprising multiple grains and grain boundary portions can be manufactured, wherein the concentration of Cu in the grain boundary portion is at least twice the concentration of Zr.

[0083] According to the first manufacturing method, rare earth cobalt permanent magnets with cell sizes of 50 nm to 200 nm can be appropriately manufactured.

[0084] According to the first manufacturing method, rare earth cobalt permanent magnets with a saturation magnetization of 1.16T or greater and an intrinsic coercivity Hcj of 240kA / m to 800kA / m can be appropriately manufactured.

[0085] According to the first manufacturing method, a rare-earth cobalt permanent magnet can be suitably manufactured, wherein the rectangular ratio of the ratio of the magnetic field Hk to the intrinsic coercivity Hcj (Hk / Hcj) when the remanent magnetization is 90% is equal to or greater than 60% in the demagnetization curve, and when the rare-earth cobalt permanent magnet is remagnetized from a demagnetization magnetic field exceeding the inflection point in the demagnetization curve, it obtains a magnetization equal to or greater than 95% of the saturation magnetization in a magnetic field equal to or weaker than three times the intrinsic coercivity Hcj.

[0086] Furthermore, according to the first manufacturing method, a rare earth cobalt permanent magnet can be suitably manufactured, wherein when the diffraction intensity I(006) of the (006) plane and the diffraction intensity I(303) of the (303) plane are measured by powder X-ray diffraction, the diffraction intensity ratio I(006) / I(303) is 0.225 to 0.4.

[0087] In the first manufacturing method, steps (I) to (IX) are typically performed in the order described above. Furthermore, the first manufacturing method may include other steps, provided that they do not impair the beneficial effects of this disclosure. Each step will be described below.

[0088] First, an alloy is prepared (step (I)) comprising: 23% to 27% by mass of R, 1.0% to 5.0% by mass of Cu, 18% to 25% by mass of Fe, 1.5% to 3.0% by mass of Zr, and Co and unavoidable impurities as the balance, wherein R represents a rare earth element including at least Sm. The method for preparing the alloy is not limited to any particular method. For example, the alloy can be prepared by obtaining a commercially available alloy with the desired composition or by mixing the above elements to obtain the desired composition.

[0089] Specific examples of element mixing will be described below, but the manufacturing method according to this disclosure is not limited to these examples.

[0090] First, the desired rare earth elements, each of Fe, Cu, and Co, and a base alloy are prepared as raw materials. It should be noted that an alloy with a low eutectic temperature is preferably selected as the base alloy, as this facilitates a more uniform composition in the resulting alloy. In this manufacturing method, FeZr or CuZr is preferably selected and used as the base alloy. As an example of FeZr, FeZr containing approximately 20% Fe and approximately 80% Zn is suitable. Furthermore, as an example of CuZr, CuZr containing approximately 50% Cu and 50% Zr is suitable.

[0091] A homogeneous alloy can be obtained by the following steps: mixing the above components to obtain the desired composition, placing the mixture in a crucible made of alumina, etc., and heating it in a 1×10⁻⁶ molten metal. -2 Torr or less than 1×10 -2 The mixture is melted in a vacuum or in an inert gas atmosphere using a high-frequency furnace. Furthermore, the manufacturing method according to this disclosure may include the step of casting the molten alloy using a mold to obtain an alloy ingot. Alternatively, as a different method, a sheet alloy with a thickness of approximately 1 mm can be manufactured by dripping the molten alloy onto a copper roller (belt casting). In this disclosure, a furnace melting method is preferred because permanent magnets with high remanent flux density and high rectangularity are readily obtained using this melting method.

[0092] When forming the alloy ingot by the above casting, the manufacturing method preferably includes a step of heat-treating the alloy ingot at a solution treatment temperature for not less than one hour and not more than 20 hours before step (II) (described later). This step can make the composition more homogeneous. It should be noted that the solution treatment temperature of the alloy ingot can be appropriately adjusted according to the composition of the alloy, etc.

[0093] Next, the alloy is pulverized into powder (step (II)). The method used to pulverize the alloy is not limited to any particular method and can be selected from known methods as appropriate. For example, the alloy ingot or sheet alloy is first coarsely pulverized to a size of about 100 μm to 500 μm using a known pulverizer, and then finely pulverized by a ball mill or air jet mill. Although the average particle size of the powder is not limited to any particular value, the alloy ingot or sheet alloy can be pulverized into powder with an average particle size of not less than 1 μm and not more than 10 μm, preferably about 6 μm, thereby shortening the sintering time of the sintering step (described later) and producing a uniform permanent magnet.

[0094] Next, the obtained powder is press-molded to obtain a molded body with the desired shape (step (III)). In the manufacturing method according to this disclosure, it is preferable to press-mold the obtained powder in a constant magnetic field to align the crystal orientation, thereby improving the magnetic properties. There are no particular limitations on the relationship between the direction of the magnetic field and the pressurization direction, and the relationship can be selected as appropriate based on the shape of the product, etc. For example, when manufacturing a toroidal magnet or a thin plate magnet, a parallel magnetic field can be used for pressurization, wherein the magnetic field is applied in a direction parallel to the pressurization direction. On the other hand, in order to obtain excellent magnetic properties, it is preferable to use a right-angle magnetic field for pressurization, wherein the magnetic field is applied at a right angle relative to the pressurization direction.

[0095] The magnitude of the magnetic field is not limited to any specific value, and depending on the application of the product, the magnetic field can be, for example, 15 kOe or weaker than 15 kOe, or 15 kOe or stronger than 15 kOe. However, to obtain excellent magnetic properties, it is preferable to perform pressure molding in a magnetic field of 15 kOe or stronger than 15 kOe. Furthermore, the pressure during pressure molding can be appropriately adjusted according to the size, shape, etc. of the product. For example, the pressure can be from 0.5 to 2.0 tons / cm². 2 That is, in the manufacturing method according to this disclosure, in order to achieve excellent magnetic properties, it is particularly preferable to apply a magnetic field perpendicular to the magnetic field of not less than 0.5 tons / cm². 2 And not higher than 2.0 tons / cm 2 The powder is pressed and shaped under pressure in a magnetic field of 15 kOe or stronger.

[0096] Next, the molded body is heated to obtain a sintered body (step (IV)). In this manufacturing method according to the present disclosure, the sintering conditions can be arbitrarily determined as long as the obtained sintered body is sufficiently densified. For example, known conditions can be used. In order to densify the sintered body, the sintering temperature is preferably between 1200°C and 1250°C. By adjusting the temperature to 1250°C or below, the volatilization of rare earth elements, especially Sm, is prevented, and thus a permanent magnet with excellent magnetic properties can be manufactured.

[0097] Regarding the temperature rise conditions during the sintering process, in order to remove adsorbed gases contained in the molded body, it is preferable to first begin evacuation at room temperature, and then preferably raise the temperature at a rate of 1°C / min to 10°C / min. During the above-mentioned temperature rise process, a hydrogen atmosphere can be used instead of evacuation. In this case, it is preferable to change the atmosphere to a vacuum atmosphere at a temperature equal to or below 1150°C.

[0098] The sintering time is preferably 20 to 240 minutes, more preferably 30 to 180 minutes, to ensure sufficient densification of the sintered body while preventing Sm volatilization. Furthermore, to prevent oxidation, a sintering time of 1 × 10⁻⁶ minutes is preferred. -2 Torr or less than 1×10-2 In a vacuum or inert gas atmosphere, more preferably in a 1×10⁻⁶ atmosphere. -4 Torr or less than 1×10 -4 The above sintering steps are carried out in a vacuum.

[0099] Next, the sintered body is gradually cooled at a cooling rate of 0.2°C / min to 5°C / min. Then, the gradually cooled sintered body undergoes a solution treatment (step (V)). The temperature of the solution treatment can be appropriately adjusted according to the sintered body and the desired magnetic properties; preferably, the solution treatment is performed at a temperature 20°C to 50°C lower than the sintering temperature. The duration of the solution treatment can be appropriately adjusted within, for example, a range of 2 hours to 20 hours.

[0100] After solution treatment, it is preferable to rapidly cool the sintered body to 400°C or below.

[0101] Next, the sintered body is heat-treated at 600°C to 850°C (step (VI)). The heat treatment time can be appropriately adjusted according to the desired magnetic properties, preferably, for example, 0.5 hours to 3 hours. The heat-treated body is cooled to 400°C or below at a rate of 0.2°C / min to 10°C / min (step (VII)). Next, the body is heat-treated at a temperature of 700°C to 900°C, which is higher than the temperature in step (VI) (step (VIII)). The heat treatment time can be, for example, 0.5 hours to 10 hours. Next, the heat-treated body is cooled to 400°C or below at a rate of 0.1°C / min to 5°C / min (step (IX)) to obtain the permanent magnet according to the present disclosure.

[0102] In the first manufacturing method, it is presumed that a cellular structure is formed in the grains during the isothermal residence in steps (VI and VIII). However, it is presumed that the Cu concentration in the grains is low at this stage, and Cu is enriched at the grain boundaries. Simultaneously, it is presumed that Zr is dissolved in the grains, thereby forming a 2-17 phase containing a large amount of Fe. In the first manufacturing method, a cellular structure with a cell wall of 50 nm to 200 nm is formed in the grains through two heat treatments (steps (VI) to (IX)), and Cu and Zr diffuse moderately. As a result, the Cu concentration in the grain boundary portions becomes at least twice, preferably at least three times, the Zr concentration.

[0103] Furthermore, according to the first manufacturing method, a rare earth cobalt permanent magnet can be suitably manufactured, wherein when the diffraction intensity I(006) of the (006) plane and the diffraction intensity I(303) of the (303) plane are measured by powder X-ray diffraction, the diffraction intensity ratio I(006) / I(303) is 0.225 to 0.4. Figure 5Powder X-ray diffraction spectra of permanent magnets according to Examples 3 and 4 and Reference Example 1 are shown. It is shown that in the permanent magnets obtained by the first manufacturing method, the peak intensity of the (006) plane, i.e., the easy magnetization axis (C-axis), becomes higher. As described above, according to the first manufacturing method, the orientation (i.e., alignment) of the C-axis is improved, resulting in improved magnetization properties.

[0104] (Second manufacturing method)

[0105] A second method for manufacturing a rare-earth cobalt permanent magnet according to the present disclosure (hereinafter referred to as the second manufacturing method) includes:

[0106] Step (I) for preparing the alloy, the alloy being composed of the following components: 23% to 27% by mass of R, 1.0% to 5.0% by mass of Cu, 18% to 25% by mass of Fe, 1.5% to 3.0% by mass of Zr and Co as the balance and unavoidable impurities, where R represents a rare earth element including at least Sm.

[0107] The crushing step (II) involves pulverizing the alloy into powder;

[0108] The compression molding step (III) involves pressing powder into a molded body;

[0109] Step (IV) involves sintering the shaped body at 1200°C to 1250°C.

[0110] Step (V) of solution treatment on sintered molded body;

[0111] Step (VI-a) involves heat-treating the molded body that has undergone solution treatment at 750°C to 850°C.

[0112] The step (VII-a) involves cooling the heat-treated molded body to 500°C to 600°C at a rate of 0.5°C / min to 10°C / min, followed by isothermal holding of the molded body.

[0113] The step of rapidly cooling the molded part that has been held at an isothermal temperature (VIII-a).

[0114] According to the second manufacturing method described above, a rare-earth cobalt permanent magnet comprising multiple grains and grain boundary portions can be manufactured, wherein the concentration of Cu in the grain boundary portions is at least twice the concentration of Zr.

[0115] According to the second manufacturing method, rare earth cobalt permanent magnets with cell sizes of 50 nm to 200 nm can be appropriately manufactured.

[0116] According to the second manufacturing method, rare earth cobalt permanent magnets with a saturation magnetization of 1.16T or greater and an intrinsic coercivity Hcj of 120kA / m to 800kA / m can be appropriately manufactured.

[0117] Furthermore, according to the second manufacturing method, a rare-earth cobalt permanent magnet can be suitably manufactured, wherein the rectangular ratio of the ratio of the magnetic field Hk to the intrinsic coercivity Hcj (Hk / Hcj) when the remanent magnetization is 90% is equal to or greater than 60% in the demagnetization curve, and when the rare-earth cobalt permanent magnet is remagnetized from a demagnetization magnetic field exceeding the inflection point in the demagnetization curve, it obtains a magnetization equal to or greater than 95% of the saturation magnetization in a magnetic field equal to or weaker than five times the intrinsic coercivity Hcj.

[0118] In the second manufacturing method, steps (I) to (VIII-a) are typically performed in the order described above. Furthermore, the second manufacturing method may include other steps, provided that the beneficial effects of this disclosure are not impaired.

[0119] It should be noted that in the second manufacturing method, steps (I) to (V) are similar to those in the first manufacturing method, and the preferred manufacturing conditions are also the same as those in the first manufacturing method; therefore, redundant descriptions are omitted.

[0120] After solution treatment (step (V)), it is preferable to rapidly cool the molded body to 400°C or below.

[0121] Next, the sintered body is heat-treated at 750°C to 850°C (step (VI-a)). The heat treatment time can be appropriately adjusted according to the desired magnetic properties, preferably, for example, 0.5 hours to 10 hours. Through this step, a cell structure with cell walls of 50 nm to 200 nm is formed in the grains, and Cu and Zr diffuse moderately. As a result, the concentration of Cu in the grain boundary regions becomes at least twice, preferably at least three times, the concentration of Zr.

[0122] The heat-treated molded body is cooled to 500°C to 600°C at a rate of 0.5°C / min to 10°C / min, and then isothermally held (i.e., isothermal resting) (step (VII-a)). The isothermal holding time can be appropriately adjusted within, for example, the range of 0.5 hours to 10 hours. By rapidly cooling the molded body that has undergone isothermal holding (step (VIII-a)), the permanent magnet according to the present disclosure is obtained.

[0123] In the second manufacturing method, it is presumed that a cellular structure forms within the grains during the isothermal dwell period in step (VI-a). However, it is presumed that the Cu concentration in the grains is low at this stage, and Cu is enriched at the grain boundaries. Simultaneously, it is presumed that Zr is dissolved in the grains, thereby forming a 2-17 phase containing a large amount of Fe. It is presumed that as the isothermal dwell period from step (VI-a) progresses to the gradual cooling process, Cu and Zr interdiffusion occurs, and Cu is enriched in the cell walls constituting the cellular structure within the grains, resulting in increased coercivity.

[0124] <device>

[0125] This disclosure also provides devices including the aforementioned permanent magnets. Examples of such devices include clocks (watches), electric motors, various instruments, communication equipment, computer terminals, speakers, DVDs, and sensors. As described above, the rare-earth cobalt permanent magnets according to this disclosure have high remanent magnetic flux density, low coercivity, and high rectangularity. Therefore, permanent magnets are particularly suitable for use in variable field motors, and thus, highly efficient variable field motors can be obtained over a wide range from low to high speeds.

[0126] [Example]

[0127] The present disclosure will be described in detail below with reference to embodiments and comparative examples. It should be noted that the present disclosure is not limited to the description of the following embodiments.

[0128] <Example 1: Second Manufacturing Method>

[0129] By using a high-frequency furnace, at 1×10 -2 Torr or less than 1×10 -2 A base alloy containing 20% ​​by mass Fe and 80% by mass Zr, along with a composition containing various elements, was melted in a vacuum to obtain an alloy ingot with a composition of 25.0% by mass Sm, 4.0% by mass Cu, 21.0% by mass Fe, 2.2% by mass Zr, and Co as the balance.

[0130] Next, the obtained alloy ingot was heat-treated at 1170°C for 15 hours, then coarsely pulverized, and then finely pulverized into powder with an average diameter of about 6 μm using an air jet mill in an inert gas atmosphere. Next, it was further pulverized in a magnetic field of 15 kOe at a speed of 1.0 t / cm². 2 The powder is pressed under pressure and molded into a shape with a length of 100mm, a width of 50mm, and a height of 50mm using a mold.

[0131] The molded body obtained at 1200℃ is subjected to 1×10 -2 Torr or less than 1×10 -2Sintering was carried out in a vacuum. Next, the sintered body was cooled to 1170°C at a rate of 1°C / min, held for 4 hours, and subjected to solution treatment. Immediately afterwards, the sintered body was rapidly cooled at a rate of 100°C / min.

[0132] The sintered body, which had been rapidly cooled, was subjected to isothermal aging treatment by heating it in an inert gas atmosphere and holding it at 800°C for 1 hour. Then, the sintered body was continuously and gradually cooled to 550°C or below at a cooling rate of 2°C / min, held at 550°C for five hours, and then rapidly cooled to obtain the permanent magnet according to Example 1.

[0133] <Example 2: Second Manufacturing Method>

[0134] Except for changing the heating and holding time at 800°C in the isothermal aging process to 5 hours, the permanent magnet according to Example 2 was obtained in the same manner as in Example 1.

[0135] <Comparative Example 1>

[0136] The permanent magnet according to Comparative Example 1 was obtained in the same manner as in Example 1, except that the heating and holding time at 850°C in the isothermal aging process was changed to 10 hours, and the temperature was reduced to 350°C or below in the subsequent continuous and gradual cooling at a cooling rate of 0.25°C / min.

[0137] [Evaluate]

[0138] As measurement samples, permanent magnet sheets were obtained by processing (e.g., cutting) the permanent magnets according to Examples 1 and 2 and Comparative Example 1 into sheets with a shape of 10×10×7mm. The direction of the 7mm thickness is the orientation direction of the magnetic field (C-axis orientation) (i.e., alignment).

[0139] Reference Figure 2 The hysteresis curve of Example 1 is described. This hysteresis curve is measured by inserting the sample into the poles of an electromagnet called a DC (direct current) magnetization analyzer. Furthermore, although no correction is needed for the demagnetizing field, the apparent magnetization decreases in magnetic fields exceeding 10 kOe in the first quadrant due to the so-called mirror effect. However, in reality, the magnetization curve becomes the curve that magnetizes the permanent magnet to saturation magnetization. Figure 2As shown, it can be understood that in Example 1, the initial magnetization curve rises steeply and reaches saturation magnetization in a low magnetic field of approximately 10 kOe. Measurements of the small hysteresis loop are also shown (indicated by dashed lines). In Example 1, the magnetization curve is shown to coincide with the initial magnetization curve in the range of 8 kOe to 10 kOe. Furthermore, when comparing their magnetic susceptibility at 10 kOe, they are almost identical. Similar measurements were performed for Example 2 and Comparative Example 1. Table 1 shows the measurement results.

[0140] In addition, Table 1 also shows the measurement results of the residual magnetic flux density.

[0141] Next, Figure 3 The image shown is a DF-STEM (dark-field scanning transmission electron microscope) image from Example 1. Figure 3 In the image, the left image is a DF-STEM image, and the right image is an image of the Cu composition extracted from it. It can be seen that through Sm2Co... 17 The heat treatment of the alloy produces a characteristic cellular structure. The interior of the cellular unit consists of 2-17 crystalline phases composed of ferromagnetic phases, while the cell walls between cells are composed of 1-5 crystalline phases containing non-magnetic Cu. Therefore, the cell size can be measured from the Cu composition image. It can be seen that the cellular size of the alloy measured by the above method ranges from 50 nm to 200 nm.

[0142] also, Figure 4 The results of the compositional analysis are shown, in which grain boundary phases were observed between the grains. Figure 4 The “position” in the diagram indicates the distance from the top of line LG4 to… Figure 4 The distances between measurement points in the DF-STEM image shown on the left are illustrated, with the upper end defined as zero (i.e., as the origin). Figure 4 As shown, Cu and Zr are enriched in the grain boundary phase. Table 1 shows the ratio of Cu to Zr. It can be seen that in Example 1, the proportion of Cu is higher than that of Zr.

[0143] Table 1

[0144]

[0145] <Example 3: First Manufacturing Method>

[0146] Except for the amount of added raw materials, the shaped body of the alloy ingot was obtained in the same manner as in Example 1, with a composition of 21.55% by mass Fe, 25.65% by mass Sm, 4.5% by mass Cu, 2.20% by mass Zr and Co as the balance.

[0147] The molded body obtained at 1210℃ was subjected to 1×10 -2Torr or less than 1×10 -2 The sintered body was sintered in a vacuum for one hour. Next, it was subjected to a solution treatment at 1155°C for 15 hours, and then immediately cooled at a cooling rate of 100°C / min. The rapidly cooled sintered body was then subjected to isothermal aging by heating it in an inert gas atmosphere and holding it at 750°C for two hours. The sintered body was then gradually cooled to 400°C at a cooling rate of 2°C / min. Furthermore, it was subjected to isothermal aging by heating the sintered body in an inert gas atmosphere and holding it at 765°C for 5.5 hours. The sintered body was then continuously and gradually cooled to 700°C at a cooling rate of 0.5°C / min, to 500°C at a cooling rate of 0.25°C / min, and to 400°C or below at a cooling rate of 0.5°C / min, thereby obtaining the permanent magnet according to Example 3.

[0148] <Example 4: Second Manufacturing Method>

[0149] The ingot was shaped in the same manner as in Example 3, and the shaped body was sintered, subjected to solution treatment, and rapidly cooled. The rapidly cooled sintered body was subjected to isothermal aging treatment by heating in an inert gas atmosphere and holding at 815°C for 5.5 hours. Then, the sintered body was continuously and gradually cooled to 550°C at a cooling rate of 2°C / min, held at 550°C for five hours, and then rapidly cooled to obtain the permanent magnet according to Example 4.

[0150] <Reference Example 1>

[0151] The permanent magnet according to Reference Example 1 was obtained in the same manner as in Example 3, except that the aging treatment step at 750°C and subsequent steps were not performed.

[0152] [Evaluate]

[0153] Examples 3 and 4 were evaluated in the same manner as in Examples 1 and 2. Table 2 shows the results.

[0154] also, Figure 5 The spectra of permanent magnets according to Examples 3 and 4 and Reference Example 1, measured by powder X-ray diffraction, are shown. It should be noted that, compared with Sm2Co of Reference Example 1... 17The relevant peaks have been marked. In Reference Example 1, the diffraction intensity ratio I(006) / I(303) between the diffraction intensity I(006) of the (006) plane and the diffraction intensity I(303) of the (303) plane is 0.138; in Example 3, I(006) / I(303) is 0.270; and in Example 4, I(006) / I(303) is 0.197. This indicates that in the permanent magnet obtained by the first manufacturing method, such as the permanent magnet obtained in Example 3, the peak intensity of the (006) plane, i.e., the easy magnetization axis (C-axis), becomes higher. As described above, according to the first manufacturing method, the orientation (i.e., alignment) of the C-axis is improved, resulting in improved magnetization properties.

[0155] Table 2

[0156]

[0157] *Magnetic susceptibility: Measured in an applied magnetic field of 10 kOe.

[0158] As described above, it has been found that the rare earth cobalt permanent magnet according to this disclosure is composed of the following components: 23% to 27% by mass of rare earth element R, 1.0% to 5.0% by mass of Cu, 18% to 25% by mass of Fe, 1.5% to 3.0% by mass of Zr, and Co as the balance, as well as unavoidable impurities. The rare earth cobalt permanent magnet contains multiple grains and grain boundary portions, and in the grain boundary portions, the concentration of Cu is at least twice the concentration of Zr. It also has high remanent magnetic flux density, low coercivity, high rectangularity ratio, and magnetic properties suitable for variable magnetic field motors.

[0159] It is apparent in the description of this disclosure that embodiments of this disclosure can be varied in many ways. Such variations are not considered to depart from the spirit and scope of this disclosure, and all such modifications, which will be apparent to those skilled in the art, are intended to include those equal to or less than the scope of the appended claims.

Claims

1. A rare-earth cobalt permanent magnet, comprising the following components: 23 to 27% by mass of R, 1.0 to 5.0% by mass of Cu, 18 to 21.55% by mass of Fe, 1.5 to 2.2% by mass of Zr, and Co as the balance, as well as unavoidable impurities, where R indicates the presence of rare earth elements including at least Sm. The rare-earth cobalt permanent magnet comprises multiple grains and grain boundaries. In the grain boundary region, the concentration of Cu is at least three times the concentration of Zr. The intrinsic coercivity Hcj ranges from 240 kA / m to 4.1 × 10⁻⁶. 3 / 4πkA / m, and The rectangle ratio (Hk / Hcj) representing the ratio of the magnetic field Hk to the intrinsic coercivity Hcj when the remanent magnetization is 90% is equal to or greater than 60% in the demagnetization curve, and When the rare-earth cobalt permanent magnet is remagnetized from a demagnetizing magnetic field exceeding the inflection point of the demagnetizing curve, it obtains a magnetization equal to or higher than 95% of the saturation magnetization in a magnetic field equal to or weaker than five times the intrinsic coercivity Hcj. The size of the unit cell structure that makes up the grain ranges from 50 nm to 200 nm.

2. The rare-earth cobalt permanent magnet according to claim 1, wherein the saturation magnetization is equal to or greater than 1.16T.

3. The rare-earth cobalt permanent magnet according to claim 1 or 2, wherein the rectangle ratio (Hk / Hcj) representing the ratio of the magnetic field Hk to the intrinsic coercivity Hcj when the remanent magnetization is 90% is equal to or greater than 60% in the demagnetization curve, and When the rare-earth cobalt permanent magnet is remagnetized from a demagnetizing field that exceeds the inflection point in the demagnetizing curve, it obtains a magnetization intensity equal to or higher than 95% of the saturation magnetization intensity in a magnetic field that is equal to or weaker than three times the intrinsic coercivity Hcj.

4. The rare earth cobalt permanent magnet according to claim 1 or 2, wherein when the diffraction intensity I(006) of the (006) plane and the diffraction intensity I(303) of the (303) plane are measured by powder X-ray diffraction, the diffraction intensity ratio I(006) / I(303) is 0.225 to 0.

4.

5. An apparatus comprising a rare-earth cobalt permanent magnet according to any one of claims 1 to 4.

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