JP4805998B2 - Permanent magnet and permanent magnet motor and generator using the same - Google Patents

Description

  The present invention relates to a permanent magnet, a permanent magnet motor and a generator using the permanent magnet.

  Sm—Co magnets, Nd—Fe—B magnets, and the like are known as high performance rare earth magnets, and are used in electric devices such as motors and generators. These magnets contain a large amount of iron (Fe) and cobalt (Co) and contribute to an increase in saturation magnetization. Furthermore, rare earth elements such as samarium (Sm) and neodymium (Nd) have a large magnetic anisotropy due to the behavior of 4f electrons in the crystal field. Since a large coercive force can be obtained by these, a high-performance permanent magnet is realized.

  There are increasing demands for reduction in size and weight and reduction in power consumption for various electric devices using permanent magnets, and in order to meet these demands, there is a demand for higher performance of permanent magnets. Specifically, there is a demand for a higher performance permanent magnet with an improved maximum magnetic energy product (BHmax). Furthermore, recently, when a permanent magnet is used for a motor of a hybrid vehicle (HEV), an electric vehicle (EV) or the like, it is required to increase the heat resistance of the permanent magnet.

  Nd-Fe-B magnets are mainly applied to HEV and EV motors. Since high heat resistance is required in such applications, (Nd, Dy) -Fe-B magnets in which a part of neodymium (Nd) is replaced with dysprosium (Dy) to increase coercivity are used. . Since Dy is one of rare elements, there is a strong demand for permanent magnets that do not use Dy when HEV and EV motors are widely used. On the other hand, it is known that Sm—Co magnets exhibit excellent heat resistance in a system that does not use Dy.

The Sm-Co permanent magnet has an SmCo ₅ type magnet based on a binary intermetallic compound of Sm and Co, and a two-phase separation structure of a Th ₂ Zn ₁₇ type crystal phase and a CaCu ₅ type crystal phase. In addition, Sm ₂ Co ₁₇ type magnets (see Patent Documents 1 to 3) that have obtained magnetic properties by a domain wall pinning type coercive force generation mechanism are known. The Sm ₂ Co ₁₇ type magnet is superior to the SmCo ₅ type magnet in magnetic properties such as coercive force and maximum magnetic energy product, and has excellent heat resistance due to a high Curie temperature. However, the Sm—Co based magnet is expensive because it contains a large amount of Co, and further has the disadvantage that the magnetization is smaller than that of the Nd—Fe—B based magnet.

In order to improve the magnetization of the Sm ₂ Co ₁₇ type magnet, it is effective to increase the content of Fe having a large saturation magnetization. Further, by increasing the Fe content, the cost of the Sm ₂ Co ₁₇ type magnet can be reduced. However, the increase in Fe content leads to instability of the TbCu ₇ type crystal phase (high temperature phase) that is a precursor of the Sm ₂ Co ₁₇ type magnet, and as a result, the Th ₂ Zn ₁₇ type crystal phase and the CaCu ₅ type crystal. A two-phase separated structure with the phase cannot be obtained. For this reason, a two-phase separation structure of a Th ₂ Zn ₁₇ type crystal phase and a CaCu ₅ type crystal phase obtained by stabilizing a TbCu ₇ type crystal phase with a composition having a high Fe concentration and subjecting it to an aging treatment. Increasing the Fe concentration is required to improve the magnetization and reduce the cost of the Sm ₂ Co ₁₇ type magnet.
JP 52-96923 A JP 52-115000 A Japanese Patent Laid-Open No. 53-137002

  The object of the present invention is to improve the magnetization and reduce the cost by increasing the Fe concentration of the Sm—Co magnet having excellent heat resistance while maintaining the crystal structure and the like that bring about the magnet characteristics. An object is to provide a magnet and a permanent magnet motor and a generator using the magnet.

The permanent magnet according to an aspect of the present invention is:
Composition _{formula: R x (Fe p M q} Si r Cu s Co 1-p-q-r-s) 100-x
(Wherein R represents at least one element selected from rare earth elements including Y, M represents at least one element selected from Ti, Zr and Hf, and x satisfies 8 ≦ x ≦ 20 atomic%. The numbers, p, q, r, and s are atomic ratios of 0.3 ≦ p ≦ 0.6, 0.005 ≦ q ≦ 0.1, 0.005 ≦ r ≦ 0.1, and 0.005 ≦ s ≦, respectively. It is a number that satisfies 0.15)
And a structure mainly composed of a Th ₂ Zn ₁₇ type crystal phase and a CaCu ₅ type crystal phase.

  A permanent magnet motor according to another aspect of the present invention includes the permanent magnet according to the aspect of the present invention. The generator which concerns on the further another aspect of this invention comprises the permanent magnet which concerns on the aspect of this invention, It is characterized by the above-mentioned.

According to the permanent magnet according to the aspect of the present invention, a two-phase separated structure of a Th ₂ Zn ₁₇ type crystal phase and a CaCu ₅ type crystal phase can be stably obtained with a composition containing Fe at a high concentration. Therefore, it is possible to provide a permanent magnet having excellent magnetic properties and good heat resistance at low cost.

Hereinafter, modes for carrying out the present invention will be described. The permanent magnet of this embodiment is
Composition _{formula: R x (Fe p M q} Si r Cu s Co 1-p-q-r-s) 100-x ... (1)
(Wherein R represents at least one element selected from rare earth elements including Y, M represents at least one element selected from Ti, Zr and Hf, and x satisfies 8 ≦ x ≦ 20 atomic%. The numbers, p, q, r, and s are atomic ratios of 0.3 ≦ p ≦ 0.6, 0.005 ≦ q ≦ 0.1, 0.005 ≦ r ≦ 0.1, and 0.005 ≦ s ≦, respectively. It is a number that satisfies 0.15)
It has the composition represented by these.

The permanent magnet of this embodiment satisfies the composition of the formula (1) and has a structure mainly composed of a Th ₂ Zn ₁₇ type crystal phase and a CaCu ₅ type crystal phase. That is, the permanent magnet of this embodiment is based on R (mainly Sm) -Co system, and by blending Fe, element M (at least one selected from Ti, Zr and Hf), Cu and Si, A two-phase separation structure of a Th ₂ Zn ₁₇ type crystal phase and a CaCu ₅ type crystal phase is realized with a high Fe concentration composition.

Here, an R—Co permanent magnet having a two-phase separated structure of a Th ₂ Zn ₁₇ type crystal phase (hereinafter referred to as 2-17 phase) and a CaCu ₅ type crystal phase (hereinafter referred to as 1-5 phase). (R ₂ Co _17- type magnet) has a TbCu _7- type crystal phase (hereinafter referred to as 1-7 phase), which is a high-temperature phase as described above, as a precursor, and is subjected to an aging treatment to obtain a 2-17 phase. By separating the phase into 1-5 phases, magnet characteristics are obtained by a domain wall pinning type coercive force generation mechanism.

  In producing a permanent magnet by phase separation (2-17 phase and 1-5 phase) from the precursor (1-7 phase) as described above, in order to achieve a high Fe concentration, the stability of the precursor, That is, it is necessary to improve the stability of the 1-7 phase at a high Fe concentration. In contrast, in this embodiment, since the Si is further contained in the R- (Co, Fe, M, Cu) system in this embodiment, the 1-7 phase is stabilized with a higher Fe concentration composition than before. Can be made.

  Then, the 1-7 phase having a high Fe concentration is used as a starting material, and an aging heat treatment is applied thereto under appropriate conditions, so that the 2-17 phase and 1-5 have a higher Fe concentration composition than the conventional Sm—Co magnet. A two-phase separated structure with the phase can be obtained. Therefore, it is possible to improve the magnet characteristics (magnetization and the like) of the R—Co permanent magnet having excellent heat resistance and reduce the cost. The reason why the 1-7 phase having a high Fe concentration can be stabilized is that the electronegativity of Si is high and the atomic radius of Si is close to that of Fe.

  The R—Co permanent magnet of this embodiment has a composition represented by the formula (1). In the formula (1), at least one element selected from rare earth elements including Y is used as the element R. Any of the R elements brings about a large magnetic anisotropy to the magnet material, and is added in a range of 8 to 20 atomic% in order to impart a high coercive force. When the blending amount of the element R is less than 8 atomic%, a large amount of α-Fe phase is precipitated and a large coercive force cannot be obtained. When the compounding amount of the element R exceeds 20 atomic%, the saturation magnetization is remarkably lowered. The compounding amount of the element R is more preferably in the range of 10 to 15 atomic%, further preferably in the range of 10.5 to 12.5 atomic%.

  As the element R, it is preferable to use at least one element selected from samarium (Sm), neodymium (Nd) and praseodymium (Pr), and it is particularly preferable to use Sm. Sm is effective in enhancing the performance of the magnet material, particularly the coercive force. From such a point, it is preferable that 50 atomic% or more of the total amount of the element R is Sm, and more preferably 70 atomic% or more of the total amount of the element R is Sm.

  As the element M, at least one element selected from titanium (Ti), zirconium (Zr), and hafnium (Hf) is used. By blending the element M, a large coercive force can be expressed with a high Fe concentration composition. The compounding amount of the element M is in the range of 0.005 ≦ q ≦ 0.1 as the q value of the formula (1), that is, in the range of 0.5 to 10 atomic% of the total amount of Fe, Co, Cu, elements M and Si. To do.

  When the amount of element M exceeds 10 atomic% of the total amount of Fe, Co, Cu, element M and Si, the magnetization is remarkably lowered, and when it is less than 0.5 atomic%, the effect of increasing the Fe concentration is sufficiently obtained. Can't get. The blending amount of the element M is preferably in the range of 0.01 ≦ q ≦ 0.06, more preferably in the range of 0.02 ≦ q ≦ 0.04. Furthermore, the coercive force can be further increased by setting Zr to 50 atomic% or more of the total amount of M elements. Of the elements M, Hf is more expensive than Ti and Zr. Therefore, even when Hf is used, it is desirable to make it less than 20 atomic% of the total amount of the elements M.

  As described above, silicon (Si) contributes to the stabilization of the 1-7 phase in a high Fe concentration composition, and this makes it possible to improve the magnetization and reduce the cost. The compounding amount of Si is in the range of 0.005 ≦ r ≦ 0.1 as the r value in the formula (1), that is, in the range of 0.5 to 10 atomic% of the total amount of Fe, Co, Cu, element M and Si. . If a larger amount of Si is added than this, the magnetization is remarkably lowered, and if it is less than this, the effect of increasing the Fe concentration cannot be obtained sufficiently. The amount of Si is more preferably 0.01 ≦ r ≦ 0.05, and still more preferably 0.01 ≦ r ≦ 0.03.

  A part of Si may be substituted with at least one element X selected from Ge and Sn. Thereby, magnet characteristics such as coercive force can be enhanced. However, if the substitution amount of Si by the element X becomes excessive, the stabilizing effect of the 1-7 phase at a high Fe concentration composition may be lowered. For this reason, the substitution amount by the element X is preferably 20 atomic% or less of the Si amount.

  Copper (Cu) is an essential element for developing a high coercive force in the R—Co permanent magnet. The compounding amount of Cu is in the range of 0.005 ≦ s ≦ 0.15 as the s value of the formula (1), that is, in the range of 0.5 to 15 atomic% of the total amount of Fe, Co, Cu, element M and Si. . When the amount of Cu exceeds 15 atomic% of the total amount of Fe, Co, Cu, element M and Si, the magnetization is remarkably lowered, and when it is less than 0.5 atomic%, it is difficult to obtain a high coercive force. Become. As for s value which shows the compounding quantity of Cu, it is more preferable to set it as the range of 0.02 <= r <= 0.1, More preferably, it is the range of 0.03 <= s <= 0.08.

  Iron (Fe) is mainly responsible for the magnetization of the magnet material. By increasing the amount of Fe, the saturation magnetization of the magnet material can be increased. However, if the amount of Fe is excessive, the α-Fe phase is precipitated, or it is difficult to obtain a two-phase separated structure of 2-17 phase and 1-5 phase, which may reduce the coercive force. . The blending amount of Fe is in the range of 0.3 ≦ p ≦ 0.6 as the p value of the formula (1), that is, in the range of 30 to 60 atomic% of the total amount of Fe, Co, Cu, element M and Si. The p value indicating the blending amount of Fe is more preferably in the range of 0.3 ≦ p ≦ 0.5, and further preferably in the range of 0.35 ≦ p ≦ 0.45.

  Cobalt (Co) plays an important role in magnetizing the magnetic material and is an important element for developing a high coercive force. Further, when a large amount of Co is blended, the Curie temperature is improved, and the thermal stability of the magnet characteristics can be enhanced. If the amount of Co is small, these effects are reduced. However, when Co is blended excessively, the blending amount of Fe is relatively decreased, and the effect of improving magnetization based on the increase in Fe concentration is lowered. The blending amount of Co is set so that the blending amount of each element with respect to the total amount of Fe, Co, Cu, elements M and Si, particularly the blending amount of Fe is in the range of 30 to 60 atomic%.

  A part of Co may be substituted with at least one element Z selected from Ni, V, Cr, Mn, Al, Ga, Nb, Ta and W. Thereby, magnet characteristics such as coercive force can be enhanced. However, if the amount of substitution of Co by the element Z becomes excessive, there is a risk of lowering the magnetization. Therefore, the amount of substitution by the element Z is preferably 20 atomic% or less of the amount of Co.

The R—Co permanent magnet having the above-described composition has a microstructure in which a Cu-rich CaCu ₅ phase (1-5 phase) and a Fe-rich Th ₂ Zn ₁₇ type crystal phase (2-17 phase) are separated into two phases. And exhibits magnet characteristics based on such a two-phase separated structure. In this embodiment, since the Fe concentration of the Th ₂ Zn ₁₇ type crystal phase (2-17 phase) is mainly increased, the magnetization of the R—Co permanent magnet can be improved and the cost can be further reduced. Become.

  The permanent magnet of this embodiment is produced as follows, for example. First, an alloy powder containing a predetermined amount of each element is prepared. The alloy powder is prepared by pulverizing a cast alloy ingot after arc melting or high frequency melting of the alloy raw material. The alloy powder may be prepared by pulverizing and preparing a flake-like alloy ribbon by a strip casting method or the like. Other methods for preparing the alloy powder include mechanical alloying method, mechanical grinding method, gas atomization method, reduction diffusion method and the like. The alloy powder or the alloy before pulverization may be homogenized by performing a heat treatment as necessary. The alloy is pulverized using a jet mill, a ball mill, or the like. The pulverization is preferably performed in an inert gas atmosphere in order to prevent oxidation of the powder.

  Next, a powder compact in which the crystal axis of the alloy powder is oriented is manufactured by filling the alloy powder in a mold placed in a magnetic field by an electromagnet or the like and applying pressure while applying the magnetic field. By sintering such a green compact at a temperature in the range of 1200 ° C. to 1300 ° C. for 0.5 to 15 hours, a dense sintered body can be obtained. Sintering is usually performed in a vacuum or in an inert gas atmosphere such as argon gas in order to prevent oxidation or the like.

  When the sintering temperature is less than 1200 ° C., the density of the sintered body is lowered, and when it exceeds 1300 ° C., Sm in the powder evaporates and good magnetic properties cannot be obtained. The sintering temperature is more preferably in the range of 1150 to 1250 ° C. When the sintering time is less than 0.5 hours, the density of the sintered body becomes non-uniform, and when it exceeds 15 hours, Sm and the like in the powder evaporate and good magnetic properties cannot be obtained. The sintering time is more preferably in the range of 1 to 5 hours.

  Next, the crystal structure is controlled by subjecting the sintered body to solution heat treatment and aging heat treatment. The solution heat treatment is preferably held at a temperature in the range of 1130 to 1230 ° C. for 0.5 to 8 hours in order to obtain the precursor 1-7 phase. Aging heat treatment is carried out at a temperature in the range of 700 to 900 ° C. for 0.5 to 20 hours and then to 400 ° C. in order to separate the precursor 1-7 phase into 2-17 and 1-5 phases. It is preferable to carry out by slowly cooling and subsequently cooling to room temperature. The slow cooling after the aging heat treatment is preferably performed at a cooling rate in the range of 0.5 to 5 ° C./min. Control of the crystal structure is important for controlling the coercive force.

  When the solution heat treatment temperature is lower than 1130 ° C., the ratio of the 1-7 phase cannot be sufficiently increased, and good magnetic properties cannot be obtained. Even when the solution heat treatment temperature exceeds 1230 ° C., the ratio of the 1-7 phase decreases, and good magnetic properties cannot be obtained. The solution heat treatment temperature is more preferably in the range of 1150 to 1210 ° C. When the solution heat treatment time is less than 0.5 hours, the constituent phases become non-uniform, and when it exceeds 8 hours, Sm and the like in the sintered body evaporate and good magnetic properties cannot be obtained. The solution heat treatment time is more preferably in the range of 1 to 4 hours. The solution heat treatment is performed in vacuum or in an inert gas atmosphere such as argon gas in order to prevent oxidation.

  When the aging heat treatment temperature is less than 700 ° C. or exceeds 900 ° C., a homogeneous mixed phase of 2-17 phase and 1-5 phase cannot be obtained. The aging heat treatment temperature is more preferably in the range of 750 to 900 ° C. If the aging heat treatment time is less than 0.5 hours, phase separation from the 1-7 phase to the 2-17 phase and the 1-5 phase cannot be completed, and if it exceeds 20 hours, the crystal grains become coarse There is a risk that the magnetic properties may be deteriorated due to the above. The aging heat treatment time is more preferably in the range of 1 to 10 hours. Aging heat treatment is usually performed in an inert gas atmosphere such as vacuum or argon gas in order to prevent oxidation.

  By applying the manufacturing method as described above, a permanent magnet, specifically a sintered magnet, having a two-phase separated structure of 2-17 phase and 1-5 phase at a high Fe concentration can be obtained. The permanent magnet of this embodiment is not limited to a sintered magnet but may be a bonded magnet. The bonded magnet is produced, for example, by mixing a magnet material (alloy powder) having a controlled crystal structure and the like with a binder component such as a resin binder or a metal binder, and compression-molding the mixture into a desired magnet shape.

  The permanent magnet of this embodiment is mainly used for a permanent magnet motor or a generator. Permanent magnet motors (generators) are more efficient than conventional induction motors (generators) and have advantages such as downsizing and noise reduction. Therefore, railway vehicles, hybrid vehicles (HEV), electric vehicles ( EV) and the like are becoming widespread as drive motors and generators. According to the permanent magnet motor and the generator having the permanent magnet of this embodiment, that is, the permanent magnet motor and the generator according to the embodiment of the present invention, it is possible to realize high efficiency, downsizing, cost reduction, and the like. It becomes. Furthermore, since R-Co permanent magnets are excellent in heat resistance, they are suitable for drive motors and generators such as railway vehicles, HEVs, and EVs. Various known configurations are applied to the permanent magnet motor and the generator.

  Furthermore, the permanent magnet of this embodiment is also effective as a variable magnet or a fixed magnet in a variable magnetic flux drive system as disclosed in, for example, Japanese Patent Application Laid-Open Nos. 2008-29148 and 2008-43172. By applying the permanent magnet of the embodiment to at least one of the variable magnet and the fixed magnet, the variable magnetic flux drive system can be improved in efficiency, size, cost, and the like.

  Next, specific examples of the present invention will be described.

(Examples 1-4)
First, high-purity raw materials were prepared at the ratios shown in Table 1, and these were arc-melted in an Ar gas atmosphere to produce an alloy ingot. Subsequently, these alloy ingots were coarsely pulverized in a mortar, and then finely pulverized using a ball mill so that the average particle diameter was about several μm. Each of these fine powders was press-molded in a magnetic field to form a green compact, and then sintered in an Ar gas atmosphere under conditions of 1250 ° C. × 1 hour, thereby producing sintered bodies.

Next, the crystal structure of the sintered body was controlled by subjecting these sintered bodies to vacuum heat treatment under conditions of 1180 ° C. × 1 hour. As a result of performing X-ray diffraction of each sintered body, it was confirmed that all the sintered bodies after the heat treatment exhibited a TbCu ₇ type structure and the crystal c-axis was oriented in the magnetic field direction. These sintered bodies are heat-treated in vacuum at 850 ° C. for 10 hours, then gradually cooled to 400 ° C. at a cooling rate of 1 ° C./minute, held at 400 ° C. for 1 hour, and then cooled to room temperature. As a result, intended sintered magnets were obtained.

  When the structure of the sintered magnet thus produced (the formed phase after aging heat treatment) was observed with a TEM, it was confirmed that both had a two-phase separated structure of 2-17 phase and 1-5 phase. It was done. Such a sintered magnet was subjected to the characteristic evaluation described later.

(Comparative Examples 1 and 2)
Sintered bodies were produced in the same manner as in Example 1 using raw material powders prepared by preparing high-purity raw materials at the ratios shown in Table 1. When the obtained sintered body was subjected to X-ray diffraction, a diffraction peak indicating the formation of a 2-17 phase was observed. A magnet made of such a sintered body was subjected to the characteristic evaluation described later.

  Next, for each of the sintered magnets of Examples 1 to 4 and Comparative Examples 1 to 2, residual magnetization, coercive force, and BHmax were measured with a BH tracer. These measurement results are shown in Table 1. As is clear from Table 1, the coercive force of 200 kA / m or more was obtained in the sintered magnets of Examples 1 to 4 in which Si was blended. Further, it was confirmed that the remanent magnetization was as high as 1.0 T or more. In contrast, the sintered magnets of Comparative Examples 1 and 2 had a low coercive force of less than 200 kA / m.

Claims (7)

Composition _{formula: R x (Fe p M q} Si r Cu s Co 1-p-q-r-s) 100-x
(Wherein R represents at least one element selected from rare earth elements including Y, M represents at least one element selected from Ti, Zr and Hf, and x satisfies 8 ≦ x ≦ 20 atomic%. The numbers, p, q, r, and s are atomic ratios of 0.3 ≦ p ≦ 0.6, 0.005 ≦ q ≦ 0.1, 0.005 ≦ r ≦ 0.1, and 0.005 ≦ s ≦, respectively. It is a number that satisfies 0.15)
And a structure mainly composed of a Th ₂ Zn ₁₇ type crystal phase and a CaCu ₅ type crystal phase. The permanent magnet according to claim 1,
50% or more of the total amount of the element R is Sm. The permanent magnet according to claim 1 or 2,
50% or more of the total amount of the element M is Zr. The permanent magnet according to any one of claims 1 to 3,
A permanent magnet, wherein a part of Co is substituted with at least one selected from Ni, V, Cr, Mn, Al, Ga, Nb, Ta and W within a range of 20 atomic% or less. The permanent magnet according to any one of claims 1 to 4,
A permanent magnet, wherein a part of the Si is substituted with at least one selected from Ge and Sn in a range of 20 atomic% or less.   A permanent magnet motor comprising the permanent magnet according to any one of claims 1 to 5.   A generator comprising the permanent magnet according to any one of claims 1 to 5.