JP2020077843A - RFeB system sintered magnet - Google Patents

Abstract

To provide a RFeB system sintered magnet with high coercive force without using rare-earth elements Rand Ga that are expensive additional elements as much as possible.SOLUTION: A RFeB system sintered magnet 15 contains a rare earth element R of 28 to 33 mass%, Co of 0 to 2.5 mass%, Al of 0.3 to 0.7 mass%, B of 0.9 to 1.2 mass%, O of less than 1500 ppm, and the balance is Fe, and an RFeAl phase having a RFeAltype structure exists at the grain boundary, and coercive force is 16 kOe or more.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an RFeB-based sintered magnet containing a rare earth element (hereinafter referred to as “R”), iron (Fe), and boron (B) as main constituent elements.

  The RFeB system sintered magnet was discovered by Masato Sagawa in 1982, and has many magnetic properties such as residual magnetic flux density, which are far higher than those of permanent magnets. Therefore, RFeB sintered magnets are used in various products such as motors for automobiles such as hybrid cars and electric cars, motors for industrial machinery, speakers, headphones, permanent magnet type magnetic resonance diagnostic devices, etc. ..

Although the initial RFeB system sintered magnet had the drawback that the coercive force iHc was relatively low among various magnetic properties, after that, the heavy rare earth element R ^H such as Dy and Tb was formed inside the RFeB system sintered magnet. It was clarified that the coercive force is improved by the presence of. The coercive force is a force that withstands the reversal of the magnetization when a magnetic field in the opposite direction to the direction of the magnetization is applied to the magnet, but the heavy rare earth element R ^H increases the coercive force by preventing this reversal of the magnetization It is believed to have the effect of causing. However, since the heavy rare earth element R ^H is expensive and rare and causes a reduction in the residual magnetic flux density, it is not desirable to increase the content of the heavy rare earth element R ^H.

Patent Document 1 describes that Ga (gallium) is added to improve the coercive force of the RFeB-based sintered magnet without adding the heavy rare earth element R ^H. Generally, in a RFeB sintered magnet, when a ferromagnetic material with a large saturation magnetization exists at a crystal grain boundary, a magnetic interaction occurs between adjacent crystal grains and a reverse magnetic field (a magnetic field in the opposite direction to the magnetization) is applied. If the magnetization of a certain crystal grain is reversed at this time, the coercive force is reduced because the magnetization of the adjacent crystal grain is also reversed by the interaction. As such a ferromagnet having a large saturation magnetization, a ferromagnet which is typically not contained in crystal grains and which is composed of R and Fe can be mentioned. On the other hand, when Ga (gallium) is added to the RFeB-based sintered magnet, a ferromagnetic material represented by R ₆ Fe ₁₃ Ga having a relatively small saturation magnetization is generated at the crystal grain boundary, and the saturation magnetization is larger. Generation of a ferromagnetic material is suppressed. As a result, even when the magnetization of a certain crystal grain is reversed when a reverse magnetic field is applied, the magnetic interaction that reverses the magnetization of the adjacent crystal grain is weakened, so that the coercive force is improved.

JP 2014-132628 JP International publication WO2014 / 017249

  However, since Ga is also expensive, adding Ga to the RFeB-based sintered magnet as described in Patent Document 1 causes a problem that the manufacturing cost increases.

The problem to be solved by the present invention is to provide an RFeB-based sintered magnet having a high coercive force without using the heavy rare earth elements R ^H and Ga which are expensive additive elements as much as possible.

RFeB system sintered magnet according to the present invention made to solve the above problems,
Rare earth element R 28-33% by mass, Co (cobalt) 0-2.5% by mass (so it may not contain Co), Al (aluminum) 0.3-0.7% by mass, B 0.9-1.2% by mass , O (oxygen) less than 1500ppm, the balance is Fe,
At the grain boundary, there is an RFeAl phase having a R ₆ Fe _14-x Al _x type structure,
The coercive force is 16 kOe or more.

The RFeAl phase having the R ₆ Fe _14-x Al _x type structure has a tetragonal crystal structure, and the value of x can take a value within the range of 0.5 to 3.5. Further, part of Fe in the RFeAl phase can be replaced with Co, and when the RFeB-based sintered magnet according to the present invention contains Cu as described later, part of Al in the RFeAl phase is replaced with Cu. Can be replaced. Further, due to the occurrence of lattice defects, the ratio of the number of R and the number of atoms of Fe (Co) and Al (Cu) combined can be slightly deviated from 6:14.

As the rare earth element R, a light rare earth element such as Nd or Pr can be preferably used. Further, it is not necessary to use the heavy rare earth element R ^H as the rare earth element R. However, in the present invention, inclusion of the heavy rare earth element R ^H as a part of the rare earth element R is not excluded.

  The RFeB sintered magnet of the present embodiment may contain 0.2 mass% or less of Ga as an unavoidable impurity (not as an additional element) in addition to the above-mentioned elements. As other inevitable impurities, Cr (chromium) is 0.1 mass% or less, Mn (manganese) is 0.1 mass% or less, Ni (nickel) is 0.1 mass% or less, N (nitrogen) is 2000ppm or less, C (carbon) ) Up to 2000 ppm, respectively. The N content is preferably 1000 ppm or less, and the C content is preferably 1000 ppm or less.

RFeB system sintered magnet according to the present invention,
Rare earth element R is 28 to 33 mass%, Co is 0 to 2.5 mass% (thus, Co may not be contained), Al is 0.3 to 0.7 mass%, B is 0.9 to 1.2 mass%, and the balance is A base material manufacturing step of manufacturing a base material made of an RFeB system sintered body by orienting a RFeB system magnet powder that is Fe in a magnetic field, and then sintering,
A first aging treatment step of heating the base material to a first aging temperature which is a temperature within a range of 700 to 900 ° C.,
Each step of heating the base material after the first aging treatment step to a second aging temperature which is a temperature within a range of 530 to 580 ° C. and a second aging treatment step is performed in a vacuum or an inert gas atmosphere. It is possible to manufacture by controlling the content of O to be less than 1500 ppm by carrying out in the inside.

  The second aging temperature is preferably in the range of 530 to 560 ° C.

  In the RFeB-based sintered magnet according to the present invention, after the RFeB-based magnet powder containing 0.3 to 0.7 mass% of Al is used to prepare a base material composed of the RFeB-based sintered body, the base material is subjected to the first aging treatment step. Is heated to a temperature in the range of 700 to 900 ° C., and further in the second aging treatment step to a temperature in the range of 530 to 580 ° C., preferably 530 to 560 ° C. RFeAl phase is generated. In addition, at the time when the first aging treatment step is completed, the RFeAl phase is not generated in the crystal grain boundaries. The RFeAl phase has a small saturation magnetization because some of the Fe atoms are replaced with Al atoms, which weakens the magnetic interaction between the Fe atoms.

  However, when a large amount of oxygen exists around the RFeB-based magnet powder in the base material manufacturing process, a large amount of rare earth oxide is formed in the RFeB-based magnet powder, and when the rare earth oxide is dissolved in the sintering process, the rare earth oxide is oxidized. A lot of Al is taken into the object. When a large amount of Al is taken into the rare earth oxide in this way, the RFeAl phase is not generated at the crystal grain boundaries. Therefore, in the present invention, the content of O as an impurity in the finally obtained RFeB-based sintered magnet is set to be less than 1500 ppm. The O content is preferably less than 1000 ppm.

In the RFeB system sintered magnet according to the present invention, an R-rich phase other than the RFeAl phase may exist in the crystal grain boundaries. The R-rich phase has a higher content of rare earth elements than R ₂ Fe ₁₄ B constituting the crystal grains of the RFeB system sintered magnet. Examples of the R-rich phase include a rare earth oxide (R ₂ O ₃ ) in which one or more of Fe, Co, Al, and Ga are solid-dissolved. Although Fe dissolved in the R-rich phase has ferromagnetism, in the RFeB system sintered magnet according to the present invention, Fe in the crystal grain boundary is incorporated into the RFeAl phase by forming the RFeAl phase in the crystal grain boundary. Therefore, the concentration of Fe that is solid-dissolved in the R-rich phase can be reduced, and thus the saturation magnetization of (the Fe that is solid-solved in) the R-rich phase can be reduced. As described above, the R-rich phase having a low Fe concentration diffuses throughout the grain boundaries by heating the base material at 530 to 580 ° C. in the second aging treatment step. In particular, the R-rich phase can be spread even in a small gap between two crystal grains.

As described above, in the RFeB-based sintered magnet according to the present invention, the saturation magnetization of the RFeAl phase (and the R-rich phase) is small at the grain boundaries, so that an inverse magnetic field was applied to the RFeB-based sintered magnet. Even if the magnetization of a certain crystal grain is reversed, the action of reversing the magnetization of the adjacent crystal grain via the grain boundary is weakened, so that a high coercive force of 16 kOe or more can be obtained. Moreover, the heavy rare earth elements R ^H and Ga are not used as much as possible, and Al that is cheaper than them may be used, so that the cost can be suppressed.

When the value of _x in R ₆ Fe _14-x Al _x of the RFeAl phase is less than 0.5, the saturation magnetization due to Fe in the RFeAl phase increases, and the magnetic interaction that reverses the magnetization of adjacent crystal grains is strong. turn into. On the other hand, when the value of x exceeds 3.5, the amount of Fe taken in by the RFeAl phase decreases, and the amount of Fe dissolved in the R-rich phase in the grain boundaries increases accordingly, resulting in saturation of the R-rich phase. Since the magnetization becomes large, the magnetic interaction for reversing the magnetization of the adjacent crystal grains becomes strong. Therefore, in the RFeB-based sintered magnet according to the present invention, it is desirable that the value of _x in R ₆ Fe _14-x Al _x of the RFeAl phase be within the range of 0.5 to 3.5.

  The RFeB-based sintered magnet according to the present invention further contains Cu (copper) in an amount of 0.1 to 0.5 mass%, the total content of Cu and Al exceeds 0.5 mass%, and the content of Al is the content of Cu. Is preferably larger than. Thereby, the wettability of the grain boundary phase is improved (optimized), and the grain boundary phase can be uniformly dispersed in the second aging treatment step, so that the coercive force is further improved.

The RFeB system sintered magnet according to the present invention preferably further contains Zr in an amount of 0.05 to 0.35% by mass. Thereby, the squareness ratio can be increased. Here, the squareness ratio is the reverse magnetic field Hk90 when the magnetization is 90% of the residual magnetic flux density B _r and the coercive force (the reverse magnetic field when the magnetization is 0) in the second quadrant (demagnetization curve) of the magnetization curve. ) IHc ratio is expressed as Hk90 / iHc. The higher the squareness ratio, the smaller the fluctuation of the magnetization due to the fluctuation of the magnetic field and the more stable the characteristics in the fluctuation magnetic field.

According to the present invention, it is possible to obtain an RFeB-based sintered magnet having a high coercive force without using heavy rare earth elements R ^H and Ga which are expensive additive elements as much as possible.

Schematic which shows an example of the method of manufacturing the RFeB system sintered magnet which concerns on this invention. The graph (a) which shows the result of the synchrotron radiation X-ray-diffraction measurement with respect to the sample of Examples 1, 2 and a comparative example, and its partial enlarged view (b). The RFeB-based sintered magnet of the present embodiment produced by using Alloy 3, comprising a first aging temperature (a), a heating time (b) in the first aging treatment step, a second aging temperature (c), and The graph which shows the result of having measured the coercive force about the several sample which the heating time (d) in a 2nd aging treatment process differs. 6 is a graph showing the results of measuring the coercive force of a plurality of samples, which are RFeB-based sintered magnets of the present embodiment produced using alloy 3, and which have different cooling rates after the second aging treatment step.

  An embodiment of an RFeB-based sintered magnet according to the present invention will be described with reference to FIGS. 1 to 4.

(1) Composition The RFeB system sintered magnet of the present embodiment, as a whole composition, rare earth element R 28 ~ 33 mass%, Co 0 ~ 2.5 mass%, Al 0.3 ~ 0.7 mass%, B 0.9 ~. 1.2% by mass, containing less than 1500 ppm of O and Fe as the balance. Co may not be contained. As the rare earth element R, a light rare earth element such as Nd or Pr can be preferably used. Further, it is not necessary to use the heavy rare earth element R ^H as the rare earth element R. However, the RFeB system sintered magnet of the present embodiment may contain the heavy rare earth element R ^H as a part of the rare earth element R. Further, the RFeB system sintered magnet of the present embodiment may contain 0.1 to 0.5 mass% of Cu and / or 0.05 to 0.35 mass% of Zr in addition to these elements. When Cu is contained, it is preferable that the total content of Cu and Al exceeds 0.5 mass%, and the content of Al is larger than the content of Cu. In addition to these elements, the RFeB system sintered magnet of the present embodiment may also contain the above-mentioned unavoidable impurities.

The crystal grain boundary of the RFeB system sintered magnet of the present embodiment has an RFeAl phase, and an R-rich phase may be present. The composition of the RFeAl phase is represented by R ₆ Fe _14-x Al _x (0.5 ≦ x ≦ 3.5). A typical example of the R-rich phase is one in which one or more of Fe, Co, Al, and Ga are solid-dissolved in R ₂ O ₃ . Here, the concentration of Fe dissolved in the R-rich phase is lower than the concentration of Fe dissolved in the R-rich phase in the grain boundaries of the conventional RFeB-based sintered magnet because Fe is incorporated into the RFeAl phase. Become.

(2) Manufacturing Method The RFeB system sintered magnet of the present embodiment can be manufactured by the method described below. Each process described below is performed in a vacuum or an inert gas atmosphere.

  First, it contains the rare earth elements R, Co (which may not be contained), Al, B and Fe, and, if necessary, Cu and / or Zr, at the same content as the RFeB sintered magnet to be produced. The RFeB-based alloy ingot 11 is produced by, for example, a strip casting method. Next, this RFeB alloy ingot 11 is exposed to hydrogen gas to occlude hydrogen molecules (FIG. 1 (a)). As a result, the RFeB-based alloy ingot 11 becomes brittle. RFeB-based coarse powder 12 is produced by carrying out coarse crushing in which the thus embrittled RFeB-based alloy ingot 11 is mechanically crushed (FIG. 1 (b)). Further, the RFeB-based coarse powder 12 is finely pulverized by a jet mill so that the median particle diameter D50 has a particle size distribution of 3 μm or less, thereby producing an RFeB-based magnet powder 13 (FIG. 1 (c)). In the produced particles of the RFeB-based magnet powder 13, some of the hydrogen molecules stored in the RFeB-based alloy ingot 11 remain.

  Next, the RFeB-based magnet powder 13 is housed in a container 19 having a shape corresponding to the RFeB-based sintered magnet to be manufactured, and a magnetic field is applied to the RFeB-based magnet powder 13 in the container 19 to produce the RFeB-based magnet powder. The magnet powder 13 is oriented (FIG. 1 (d)). Then, the oriented RFeB-based magnet powder 13 is heated to a predetermined sintering temperature (a temperature in the range of 900 to 1050 ° C. is preferable) in a state of being housed in the container 19 (FIG. 1 (e)). Thus, the RFeB magnet powder 13 is sintered. As a result, the base material 14 made of the RFeB-based sintered body is obtained (FIG. 1 (f)). The operations up to this point correspond to the above-mentioned base material manufacturing step.

  Here, hydrogen molecules contained in the particles of the RFeB-based magnet powder 13 are released to the outside by heating for sintering. At that time, carbon and hydrogen molecules existing as impurities in the RFeB magnet powder 13 react with each other to be gasified. As a result, carbon can be removed from the RFeB magnet powder 13. At that time, in order to make it difficult for hydrogen molecules to be detached from the particles of the RFeB-based magnet powder 13 before the hydrogen molecules react with carbon, up to a predetermined temperature (for example, 450 ° C.) during the temperature rising from room temperature to the sintering temperature. Is preferably an inert gas atmosphere and then heated to the sintering temperature in a vacuum atmosphere. The vacuum atmosphere is intended to remove the gas generated by the reaction between hydrogen molecules and carbon. The container 19 is made of a material having heat resistance at the above sintering temperature.

  When producing an RFeB-based sintered body, compression molding is generally performed (pressing method) while or after orienting the RFeB-based magnet powder in a magnetic field. On the other hand, in the present embodiment, the RFeB-based magnet powder 13 is sintered during the orientation of the RFeB-based magnet powder 13 and after the orientation without performing compression molding (PLP (press-less process) method). Since the PLP method does not require the use of a press machine for compression molding, the working space can be reduced. Therefore, it is easy to create an inert gas atmosphere or a vacuum atmosphere in the work space. Then, even if the particle size of the RFeB-based magnet powder 13 is reduced (the surface area of the particles is increased), the RFeB-based magnet powder 13 is less likely to be oxidized. As a result, the oxygen content of the produced base material can be reduced, so that rare earth oxides are less likely to be formed in the base material. As a result, it becomes difficult for Al to be taken into the rare earth oxide, so that the RFeAl phase can be generated at the grain boundaries. Further, by reducing the particle size of the RFeB-based magnet powder 13, when the average particle size of the RFeB-based magnet powder 13 becomes close to the average particle size of the crystal grains in the obtained RFeB-based sintered magnet, the RFeB-based magnet powder 13 The smaller the average particle size of, the smaller the average particle size of the crystal grains in the RFeB system sintered magnet, and thereby the coercive force of the RFeB system sintered magnet can be increased. The RFeB-based sintered magnet according to the present invention can be manufactured by using a pressing method, but as described above, it is preferable to use the PLP method in order to reduce the oxygen content of the base material. Is desirable.

  After the base material 14 is prepared as described above and once brought to room temperature, the base material 14 is heated to the first aging temperature which is a temperature within the range of 700 to 900 ° C. (FIG. 1 (g), first aging temperature). Processing step). Here, the time for maintaining the first aging temperature is not particularly limited. According to an experiment by the present inventor, even when the time for maintaining the second aging temperature is 0 minutes, that is, when the temperature is lowered at the moment when the first aging temperature is reached, the next second aging treatment step is performed. The coercive force of the resulting RFeB-based sintered magnet exceeds 16 kOe.

  Next, the base material 14 subjected to the first aging treatment step is heated to a second aging temperature which is a temperature within the range of 530 to 580 ° C, preferably within the range of 530 to 560 ° C (Fig. 1 (h), Second aging treatment step). Here, the time for maintaining the second aging temperature is not particularly limited. According to the experiments by the present inventor, even if the time for maintaining the second aging temperature is 0 minutes (when the temperature is lowered at the moment when the second aging temperature is reached), the obtained RFeB-based sintered magnet is Coercive force exceeds 16kOe. Then, the base material 14 is cooled to room temperature.

  By the above operation, the RFeB system sintered magnet 15 of this embodiment is obtained (FIG. 1 (i)).

(3) Example of RFeB-based sintered magnet of this embodiment Hereinafter, an example of manufacturing the RFeB-based sintered magnet of this embodiment will be described.

Six types of RFeB-based alloy ingots (hereinafter, referred to as alloys 1 to 7) having the compositions (measured values) described in Table 1 were produced by the strip casting method. In addition, "TRE" in Table 1 means the sum of the content rates of all rare earth elements (Total Rare-Earth), and here, Nd (neodymium), Pr (praseodymium), Dy (dysprosium), Tb (terbium) It is the sum of the content rates. In addition, rare earth elements other than these four kinds are not contained in alloys 1 to 7, except those contained as unavoidable impurities. The alloys 1 to 7 may contain inevitable impurities in addition to the elements listed in Table 1.

RFeB-based magnet powder 13 was produced by coarsely pulverizing and finely pulverizing each of these alloys 1 to 7 under the above-mentioned conditions. The RFeB-based magnet powder 13 was filled in a container 19 so that the packing density was 3.4 g / cm ³ , and then the RFeB-based magnet powder 13 was oriented in a magnetic field. Subsequently, the RFeB-based magnet powder 13 is heated from room temperature with the container 19 being filled in the container 19 to a sintering temperature between 985 ° C. and 995 ° C., maintained for 4 hours, and then cooled to room temperature. Was produced. During the sintering, an argon gas atmosphere was used from room temperature to 450 ° C., and then a vacuum atmosphere was used. Each of the base materials 14 obtained from each of the alloys 1 to 7 is heated at a first aging temperature of 800 ° C. for 30 minutes and then heated to a second aging temperature of 540 ° C. or 560 ° C. (listed in Table 1 for each alloy). The temperature was lowered, the temperature was maintained for 90 minutes, and then rapidly cooled to obtain an RFeB-based sintered magnet 15. The respective RFeB-based sintered magnets produced from the alloys 1 to 7 are referred to as the samples of Examples 1 to 7.

  In addition, as a comparative example, an alloy 1 (comparative example 1) and an alloy A (comparative examples 2 and 3) having the compositions shown in Table 1 were used to produce an RFeB sintered magnet by the same method as described above. The second aging temperature was 540 ° C. (sample using alloy 1) or 520 ° C. (sample using alloy A). Alloy A has an Al content of 0.16 mass% and is not included in the composition range of the RFeB system sintered magnet of the present invention. In Comparative Examples 1 and 3, the O content was set to be higher than in Examples 1 to 7 and Comparative Example 2. Here, the O content can be adjusted by controlling the manufacturing environment in the steps from crushing the RFeB-based alloy ingot 11 to filling the container 19 with the RFeB-based magnet powder 13.

Table 2 shows the results obtained by measuring the compositions of the manufactured samples of Examples 1 to 7 and Comparative Examples 1 to 3. Table 3 shows the coercive force iHc and the squareness ratio SQ of each of these samples, and the value of Hk90 measured for obtaining the squareness ratio SQ. Here, Hk90 is the value of the reverse magnetic field when the magnetization becomes 90% of the residual magnetic flux density B _r in the second quadrant (demagnetization curve) of the magnetization curve. The squareness ratio SQ is calculated by Hk90 / iHc.

  In each of the samples of Examples 1 to 7, the composition of each element listed in Table 2 satisfies the composition conditions for the RFeB system sintered magnet of the present invention. On the other hand, the samples of Comparative Examples 1 and 3 do not satisfy the requirement of the present invention (less than 1500 ppm) for the O content. Further, in the samples of Comparative Examples 2 and 3, the Al content does not satisfy the requirements (0.3 to 0.7 mass%) of the present invention. On the other hand, in the samples of Comparative Examples 2 and 3, the content rates of elements other than Al and O are almost the same as the content rates of those elements in the sample of Example 2.

  Comparing the coercive force iHc of the samples of Examples 1 to 6 not containing Dy and the samples of Comparative Examples among these Examples, it is 16.8 to 18.2 kOe which exceeds 16.0 kOe in all of the samples of Examples 1 to 6. On the other hand, in the samples of Comparative Examples 1 to 3, all are 14.5 to 15.7 kOe, which is lower than 16.0 kOe. In particular, the sample of Example 2 in which the contents of elements other than Al and O are almost the same as those in Comparative Examples 2 and 3 as described above is more remarkable than Comparative Examples 2 and 3 in which the coercive force iHc is 18.2 kOe. Has a high value.

  Moreover, the samples of Examples 3 to 5 contain 0.08 to 0.11% by mass of Zr, and the squareness ratio SQ is higher than that of the other samples (Examples 1 and 2 and Comparative Examples 1 to 3). (94.6-95.4%). The sample of Example 7 contains 2.50% by mass of Dy and has a higher coercive force iHc value than the other samples.

Next, FIG. 2 shows the results of X-ray diffraction measurement performed on the samples of Examples 1 and 2 and Comparative Example. In this measurement, the synchrotron radiation X-ray diffraction measurement of the Aichi Synchroton Light Center (Science and Technology Exchange Center) was used, and the synchrotron radiation with a wavelength of 0.09 nm was used. 2 (a) shows the measurement results of each sample in the range of 2θ of 10 to 70 °, and FIG. 2 (b) partially shows the horizontal axis (2θ) and the vertical axis (intensity). Enlarged and overlayed data for three samples. At the location indicated by the arrow in FIG. 2B, there are three peaks that appear in Examples 1 and 2 but not in Comparative Example. These three peaks are Nd ₆ Fe ₁₁ Al ₃ (R ₆ Fe _14- contained in the powder diffraction database “PDF” (Powder Diffraction File) operated by the International Center for Diffraction Data (ICDD). _x Al _x is in good agreement with the X-ray diffraction pattern (PDF # 01-078-9291) of R = Nd, x = 3). This data means that the samples of Examples 1 and 2 contain a phase having the same crystal structure as R ₆ Fe _14-x Al _x , that is, the RFeAl phase.

Next, with respect to the sample of Example 2, using wavelength-dispersive X-ray spectroscopy (WDX), it was arbitrarily selected in the grain boundaries, and at the measurement points containing all three elements of R, Fe and Al. The composition ratios of these three kinds and Co and Cu were obtained. The results are shown in Table 4.

  At these six measurement points, the ratio of the composition ratio of R atoms and the sum of the composition ratios of four atoms of Fe, Co, Al and Cu is close to 6:14, and the RFeAl phase is It is considered to have been formed.

  By thus forming the RFeAl phase at the crystal grain boundary, the amount of Fe dissolved in the R-rich phase is reduced. And, since the saturation magnetization of the RFeAl phase is small, and the amount of Fe dissolved in the R-rich phase is small, the magnetic interaction between the crystal grains becomes small, so the RFeB-based sintered magnet of the present embodiment is High coercive force.

  Next, for the base material 14 produced using the RFeB-based magnet powder obtained from the alloy 3, samples were prepared under a plurality of conditions in which the temperature and the heating time in the first aging treatment step and the second aging treatment step were different. It was produced and the coercive force was measured. The results will be described below.

  Fig. 3 (a) shows the coercive force after the first aging treatment step (before the second aging treatment step) of the samples prepared under the three different conditions of the first aging temperature of 700 ° C, 800 ° C, and 900 ° C. And the coercive force of the obtained RFeB-based sintered magnet (after the second aging treatment step). For these three samples, the heating time in the first aging treatment step was 30 minutes, the second aging temperature was 560 ° C., and the heating time in the second aging treatment step was 30 minutes. As a result of this experiment, the coercive force of each of the obtained RFeB-based sintered magnets exceeded 16 kOe, and the first aging temperature was almost the same regardless of the value within the above range.

  In FIG. 3 (b), the coercive force after the first aging treatment step of the samples prepared under the six conditions different in the heating time in the first aging treatment step within the range of 0 to 540 minutes was obtained. The coercive force of the RFeB system sintered magnet is shown. For these six samples, the first aging temperature was 800 ° C, the second aging temperature was 560 ° C, and the heating time in the second aging treatment step was 30 minutes. The coercive force of each of the obtained RFeB-based sintered magnets exceeded 16 kOe, and the heating time in the first aging treatment step was almost the same regardless of the value within the above range.

  Fig. 3 (c) shows the coercive force after the first aging treatment and the obtained RFeB-based sintered magnets of the samples prepared under the six different conditions in the second aging temperature range of 530 to 580 ° C. Shows the coercive force of. For these six samples, the first aging temperature was 800 ° C., the heating time in the first aging treatment step was 30 minutes, and the heating time in the second aging treatment step was 30 minutes. As a result of this experiment, the coercive force of each of the obtained RFeB system sintered magnets exceeded 16 kOe, and the coercive force increased as the temperature increased in the second aging temperature range.

  In FIG. 3 (d), the coercive force after the first aging treatment step of the samples prepared under the six conditions different in the heating time in the second aging treatment step within the range of 0 to 540 minutes was obtained. The coercive force of the RFeB system sintered magnet is shown. For these six samples, the first aging temperature was 800 ° C, the heating time in the first aging treatment step was 30 minutes, and the second aging temperature was 560 ° C. The coercive force of each of the obtained RFeB system sintered magnets exceeded 16 kOe, and the heating time in the second aging treatment step was almost the same regardless of the value within the above range.

  As described above, from the experimental results shown in FIG. 3, the magnitude of the coercive force in the RFeB system sintered magnet of the present embodiment shows that the heating time in the first aging treatment step and the second aging treatment step at the time of production, and the first aging treatment. It can be seen that the temperature has almost no effect and that the coercive force can be further improved by adjusting the second aging temperature.

  Next, for the base material 14 produced using the RFeB-based magnet powder obtained from the alloy 3, the first aging temperature is 800 ° C., the heating time of the first aging treatment step is 30 minutes, and the second aging temperature is Aging temperature is 540 ° C and the heating time of the second aging treatment step (time kept at 540 ° C) is 30 minutes, then the aging treatment is performed and then the cooling rate when cooling from the second aging temperature to 100 ° C is different. A sample of RFeB system sintered magnet was prepared. At the same time, as a comparative example, the case where the second aging treatment step is performed without performing the first aging treatment step on the base material 14 manufactured using the RFeB-based magnet powder obtained from the alloy 3 Similarly, a plurality of RFeB system sintered magnet samples with different cooling rates were prepared. FIG. 4 shows the results of measuring the coercive force of these RFeB system sintered magnet samples. As a result, the coercive force of each of the samples of the comparative examples was below 16 kOe, whereas the coercive force of each of the samples of this example in which both the first aging treatment step and the second aging treatment step were performed was 16 kOe. Exceeded. Among the samples of this example, the sample having the slowest cooling rate from the second aging temperature to 100 ° C. (3 ° C./min) had a coercive force slightly higher than that of the other samples having the cooling rate of 5 ° C./min or more. Became lower. That is, the cooling rate from the second aging temperature to 100 ° C. is preferably 5 ° C./minute or more.

11 ... RFeB-based alloy ingot 12 ... RFeB-based coarse powder 13 ... RFeB-based magnet powder 14 ... Base material 15 ... RFeB-based sintered magnet 19 ... Container

Claims (3)

The rare earth element R is 28 to 33 mass%, Co is 0 to 2.5 mass%, Al is 0.3 to 0.7 mass%, B is 0.9 to 1.2 mass%, O is contained at less than 1500 ppm, and the balance is Fe.
At the grain boundary, there is an RFeAl phase having a R ₆ Fe _14-x Al _x type structure,
An RFeB-based sintered magnet having a coercive force of 16 kOe or more.   Furthermore, 0.1-0.5 mass% of Cu is contained, the total of the content rates of Cu and Al exceeds 0.5 mass%, and the content rate of Al is larger than the content rate of Cu. RFeB system sintered magnet.   The RFeB system sintered magnet according to claim 1 or 2, further containing 0.05 to 0.35 mass% of Zr.

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