JP7379935B2 - RFeB sintered magnet - Google Patents

Description

The present invention relates to an RFeB-based sintered magnet whose main constituent elements are rare earth elements (hereinafter referred to as "R"), iron (Fe), and boron (B).

RFeB-based sintered magnets were discovered in 1982 by Masato Sagawa et al., and have many magnetic properties such as residual magnetic flux density that are much higher than those of conventional permanent magnets. Therefore, RFeB sintered magnets are used in a variety of products, including motors for automobiles such as hybrid cars and electric cars, motors for industrial machinery, speakers, headphones, and permanent magnet magnetic resonance diagnostic equipment. .

Early RFeB-based sintered magnets had the drawback of relatively low coercive force iHc among various magnetic properties, but later, heavy rare earth elements R ^H such as Dy and Tb were added to the inside of RFeB-based sintered magnets. It has been revealed that the coercive force is improved by the presence of . Coercive force is the force that withstands the reversal of magnetization when a magnetic field in the opposite direction to the direction of magnetization is applied to a magnet, but the heavy rare earth element R ^H increases the coercive force by preventing this magnetization reversal. It is believed that it has the effect of However, it is not desirable to increase the content of heavy rare earth elements R ^H because the heavy rare earth elements R ^H are expensive and rare, and cause a decrease in residual magnetic flux density.

Patent Document 1 describes adding Ga (gallium) to improve the coercive force of an RFeB-based sintered magnet without adding the heavy rare earth element R ^H. In general, in RFeB sintered magnets, when a ferromagnetic material with high saturation magnetization exists in the grain boundaries, magnetic interaction occurs between adjacent crystal grains, and a reverse magnetic field (a magnetic field in the opposite direction to the magnetization) is applied. When magnetization is reversed in a certain crystal grain, the magnetization of adjacent crystal grains is also reversed due to the interaction, resulting in a decrease in coercive force. A typical example of a ferromagnetic material having a large saturation magnetization is one consisting of R and Fe that are not contained in crystal grains. On the other hand, when Ga (gallium) is added to RFeB-based sintered magnets, a ferromagnetic substance with relatively low saturation magnetization, represented by R ₆ Fe ₁₃ Ga, is generated at the grain boundaries, and the saturation magnetization is larger. Generation of ferromagnetic material is suppressed. As a result, even if the magnetization of a certain crystal grain is reversed when a reverse magnetic field is applied, the magnetic interaction that reverses the magnetization of adjacent crystal grains is weakened, so that the coercive force is improved.

Japanese Patent Application Publication No. 2014-132628 International publication WO2014/017249

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

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

The RFeB-based sintered magnet according to the present invention was made to solve the above problems,
28-33% by mass of rare earth element R, 0-2.5% by mass of Co (cobalt) (therefore, it may not contain Co), 0.3-0.7% by mass of Al (aluminum), 0.9-1.2% by mass of B. , contains less than 1500 ppm of O (oxygen), the balance being Fe,
An RFeAl phase with an R ₆ Fe _14-x Al _x type structure exists at the grain boundaries,
It is characterized by a coercive force of 16 kOe or more.

RFeAl phases with R ₆ Fe _14-x Al _x type structure have a tetragonal crystal structure, where the value of x can take values in the range 0.5 to 3.5. In addition, part of Fe in the RFeAl phase can be replaced by Co, and if the RFeB sintered magnet according to the present invention contains Cu as described later, part of the Al in the RFeAl phase can be replaced by Co. May be replaced. Furthermore, due to the occurrence of lattice defects, the ratio of the number of R atoms to the total number of atoms of Fe(Co) and Al(Cu) may deviate somewhat from 6:14.

As the rare earth element R, light rare earth elements such as Nd and Pr can be suitably used. Furthermore, it is not necessary to use a heavy rare earth element R ^H as the rare earth element R. However, in the present invention, it is not excluded that the heavy rare earth element R ^H is included as a part of the rare earth element R.

In addition to the above-mentioned elements, the RFeB-based sintered magnet of this embodiment may contain 0.2% by mass or less of Ga as an unavoidable impurity (not as an additive element). In addition, other unavoidable impurities include Cr (chromium) of 0.1% by mass or less, Mn (manganese) of 0.1% by mass or less, Ni (nickel) of 0.1% by mass or less, N (nitrogen) of 2000ppm or less, C (carbon ) may each contain up to 2000 ppm. It is desirable that the N content is 1000 ppm or less, and the C content is 1000 ppm or less.

The RFeB-based sintered magnet according to the present invention is
Contains 28 to 33 mass% of the rare earth element R, 0 to 2.5 mass% of Co (therefore, it may not contain Co), 0.3 to 0.7 mass% of Al, 0.9 to 1.2 mass% of B, and the balance is A base material production step of producing a base material made of an RFeB-based sintered body by orienting RFeB-based magnet powder, which is Fe, in a magnetic field and then sintering it;
a first aging treatment step of heating the base material to a first aging temperature within a range of 700 to 900°C;
After performing the first aging treatment step, each step including the second aging treatment step of heating the base material to a second aging temperature within the range of 530 to 580°C is performed in a vacuum or an inert gas atmosphere. It can be manufactured by carrying out the process in such a way that the content of O is less than 1500 ppm.

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

In the RFeB-based sintered magnet according to the present invention, a base material made of an RFeB-based sintered body is prepared using RFeB-based magnet powder containing 0.3 to 0.7% by mass of Al, and then the base material is subjected to a first aging treatment step. By heating to a temperature in the range of 700 to 900°C, and further heating to a temperature in the range of 530 to 580°C, preferably 530 to 560°C in the second aging treatment step, grain boundaries are heated. RFeAl phase is generated. Note that, at the time when the first aging treatment step is completed, no RFeAl phase is generated at the 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, if a large amount of oxygen exists around the RFeB magnet powder during the base material manufacturing process, a large amount of rare earth oxides will be formed within the RFeB magnet powder, and when the rare earth oxides are dissolved in the sintering process, the rare earth oxides will be removed. A large amount of Al is incorporated into objects. If a large amount of Al is incorporated into the rare earth oxide in this way, no RFeAl phase is generated at the 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 content of O is desirably less than 1000 ppm.

In the RFeB-based sintered magnet according to the present invention, an R-rich phase other than the RFeAl phase may exist at the grain boundaries. The R-rich phase refers to a phase in which the content of rare earth elements is higher than that of R ₂ Fe ₁₄ B that constitutes the crystal grains of the RFeB-based sintered magnet. Examples of the R-rich phase include rare earth oxides (R ₂ O ₃ ) in which one or more of Fe, Co, Al, and Ga are dissolved in solid solution. Fe dissolved in the R-rich phase has ferromagnetism, but in the RFeB sintered magnet according to the present invention, Fe in the grain boundaries is incorporated into the RFeAl phase by forming an RFeAl phase at the grain boundaries. Therefore, the concentration of Fe dissolved in the R-rich phase can be lowered, thereby making it possible to reduce the saturation magnetization of the R-rich phase (Fe dissolved in the R-rich phase). The R-rich phase with such 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 where there is a small gap between two crystal grains.

As described above, in the RFeB-based sintered magnet according to the present invention, a reverse magnetic field is applied to the RFeB-based sintered magnet due to the presence of the RFeAl phase (and R-rich phase) with low saturation magnetization at the grain boundaries. Even if the magnetization of one crystal grain is reversed at the same time, the effect of reversing the magnetization of adjacent crystal grains via the grain boundary becomes weaker, so a high coercive force of 16 kOe or more can be obtained. Moreover, since it is sufficient to use Al, which is cheaper than the heavy rare earth elements R ^H and Ga, as much as possible, the cost can be kept down.

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, so the magnetic interaction that reverses the magnetization of adjacent crystal grains becomes 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, saturating the R-rich phase. As the magnetization increases, the magnetic interaction that reverses the magnetization of adjacent crystal grains becomes stronger. 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 is within the range of 0.5 to 3.5.

The RFeB sintered magnet according to the present invention further contains 0.1 to 0.5% by mass of Cu (copper), and the total content of Cu and Al exceeds 0.5% by mass, and the content of Al is the content of Cu. It is preferable that it is larger than . As a result, 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.

Further, it is preferable that the RFeB-based sintered magnet according to the present invention further contains 0.05 to 0.35% by mass of Zr. Thereby, the squareness ratio can be increased. Here, the squareness ratio is the reverse magnetic field Hk90 when the magnetization becomes 90% of the residual magnetic flux density B _r and the coercive force (the reverse magnetic field when the magnetization becomes 0) in the second quadrant (demagnetization curve) of the magnetization curve. ) is expressed as the ratio of iHc, Hk90/iHc. The higher the squareness ratio, the smaller the fluctuation in magnetization due to fluctuations in the magnetic field, meaning that the material has stable characteristics in a fluctuating magnetic field.

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

FIG. 2 is a schematic diagram showing an example of a method for manufacturing an RFeB-based sintered magnet according to the present invention. Graph (a) showing the results of synchrotron radiation X-ray diffraction measurements on samples of Examples 1 and 2 and Comparative Example, and its partially enlarged view (b). The RFeB-based sintered magnet of this embodiment manufactured using Alloy 3 has a first aging temperature (a), a heating time in the first aging treatment step (b), a second aging temperature (c), and a second aging temperature (c). 2 is a graph showing the results of coercive force measurements of multiple samples with different heating times (d) in the aging process. 3 is a graph showing the results of measuring coercive force of a plurality of samples of the RFeB sintered magnet of the present embodiment manufactured using Alloy 3 and having different cooling rates after the second aging treatment step.

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

(1) Composition The RFeB sintered magnet of this embodiment has a total composition of 28 to 33 mass% of rare earth element R, 0 to 2.5 mass% of Co, 0.3 to 0.7 mass% of Al, and 0.9 to 0.9 mass% of B. Contains 1.2% by mass, less than 1500ppm of O, and the balance contains Fe. Co may not be contained. As the rare earth element R, light rare earth elements such as Nd and Pr can be suitably used. Furthermore, it is not necessary to use a heavy rare earth element R ^H as the rare earth element R. However, the RFeB-based sintered magnet of this embodiment may include a heavy rare earth element R ^H as a part of the rare earth element R. In addition to these elements, the RFeB-based 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. When containing Cu, it is preferable that the total content of Cu and Al exceeds 0.5% by mass, and the content of Al is higher than the content of Cu. In addition to these elements, the RFeB-based sintered magnet of this embodiment may also contain the above-mentioned inevitable impurities.

The grain boundaries of the RFeB-based sintered magnet of this embodiment have an RFeAl phase, and may further include an R-rich phase. The composition of the RFeAl phase is expressed as 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 dissolved in R ₂ O ₃ as a solid solution. 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 conventional RFeB-based sintered magnets because Fe is incorporated into the RFeAl phase. Become.

(2) Manufacturing method The RFeB-based sintered magnet of this embodiment can be manufactured by the method described below. Each step described below is performed in vacuum or in an inert gas atmosphere.

First, contain rare earth elements R, Co (does not need to be contained), Al, B, and Fe, and Cu and/or Zr if necessary, at the same content rate as the RFeB sintered magnet to be manufactured. The RFeB 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)). This causes the RFeB alloy ingot 11 to become brittle. The RFeB-based alloy ingot 11 thus embrittled is mechanically pulverized to produce RFeB-based coarse powder 12 (FIG. 1(b)). Furthermore, RFeB-based magnet powder 13 is produced by pulverizing the RFeB-based coarse powder 12 using a jet mill so that the particle size distribution has a median particle size D50 of 3 μm or less (FIG. 1(c)). A part of the hydrogen molecules occluded in the RFeB alloy lump 11 remain in the particles of the produced RFeB magnet powder 13.

Next, the RFeB-based magnet powder 13 is placed 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. The magnet powder 13 is oriented (FIG. 1(d)). Subsequently, the oriented RFeB-based magnet powder 13 is heated to a predetermined sintering temperature (preferably within the range of 900 to 1050°C) while still housed in the container 19 (FIG. 1(e)). As a result, the RFeB magnet powder 13 is sintered. As a result, a base material 14 made of an RFeB-based sintered body is obtained (FIG. 1(f)). The operations up to this point correspond to the above-mentioned base material production process.

Here, hydrogen molecules contained in the particles of the RFeB magnet powder 13 are released to the outside by heating for sintering. At this time, carbon present as an impurity in the RFeB magnet powder 13 reacts with hydrogen molecules to gasify. Thereby, carbon can be removed from the RFeB magnet powder 13. At that time, in order to make it difficult for the hydrogen molecules to detach from the particles of the RFeB magnet powder 13 before the hydrogen molecules and carbon react, the temperature is increased to a predetermined temperature (for example, 450°C) between room temperature and the sintering temperature. It is preferable to use an inert gas atmosphere and then raise the temperature to the sintering temperature in a vacuum atmosphere. The purpose of creating a vacuum atmosphere here is to remove gas generated by the reaction between hydrogen molecules and carbon. The container 19 is made of a material that is heat resistant at the above sintering temperature.

When producing an RFeB-based sintered body, it is common to perform compression molding (pressing method) while or after orienting the RFeB-based magnet powder in a magnetic field. In contrast, in this embodiment, the RFeB magnet powder 13 is sintered without compression molding during or after the orientation of the RFeB magnet powder 13 (PLP (press-less process) method). Since the PLP method does not require the use of a press machine for compression molding, the work 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 made smaller (the surface area of the particles is increased), the RFeB-based magnet powder 13 becomes difficult to oxidize. As a result, the oxygen content of the base material to be produced can be reduced, making it difficult for rare earth oxides to be formed within the base material. This makes it difficult for Al to be incorporated into the rare earth oxide, allowing RFeAl phase to be generated at grain boundaries. Furthermore, by reducing the particle size of the RFeB-based magnet powder 13, the average particle size of the RFeB-based magnet powder 13 approaches the average grain size of the crystal grains in the obtained RFeB-based sintered magnet. The smaller the average grain size of the RFeB-based sintered magnet, the smaller the average grain size of the crystal grains in the RFeB-based sintered magnet, thereby increasing the coercive force of the RFeB-based sintered magnet. Note that the RFeB sintered magnet according to the present invention can be manufactured using a pressing method, but as described above, it is also possible to manufacture the RFeB-based sintered magnet using the PLP method in order to reduce the oxygen content of the base material. is desirable.

The base material 14 is produced as described above, and after once brought to room temperature, the base material 14 is heated to a first aging temperature within the range of 700 to 900°C (FIG. 1(g), first aging temperature). processing process). Here, the time period for maintaining the first aging temperature is not particularly limited. According to the inventor's experiments, even if the time to maintain the second aging temperature is 0 minutes, that is, the temperature is lowered at the moment the first aging temperature is reached, the next second aging treatment step is not performed. The RFeB sintered magnet obtained through this process has a coercive force of over 16kOe.

Next, the base material 14 that has been subjected to the first aging treatment step is heated to a second aging temperature that is within the range of 530 to 580°C, preferably within the range of 530 to 560°C (Fig. 1 (h), 2nd aging treatment step). Here, the time period for maintaining the second aging temperature is not particularly limited. According to the inventor's experiments, even if the time to maintain the second aging temperature is 0 minutes (when the temperature is lowered the moment the second aging temperature is reached), the resulting RFeB-based sintered magnet Coercive force exceeds 16kOe. Thereafter, the base material 14 is cooled to room temperature.

Through the above operations, the RFeB-based sintered magnet 15 of this embodiment is obtained (FIG. 1(i)).

(3) Examples of RFeB-based sintered magnets of the present embodiment Below, examples will be shown in which the RFeB-based sintered magnets of the present embodiment were manufactured.

Six types of RFeB alloy ingots (hereinafter referred to as Alloys 1 to 7) having the compositions (actually measured values) listed in Table 1 were each produced by a strip casting method. In addition, "TRE" in Table 1 refers to the sum of the content rates of all rare earth elements (Total Rare-Earth); It is the sum of the content rates. Note that rare earth elements other than these four types are not contained in Alloys 1 to 7, except for those contained as unavoidable impurities. Note that Alloys 1 to 7 may contain unavoidable impurities in addition to the elements listed in Table 1.

RFeB magnet powder 13 was produced by coarsely pulverizing and finely pulverizing each of these alloys 1 to 7 under the conditions described above. This 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. Next, the RFeB magnet powder 13 is heated from room temperature to a sintering temperature between 985°C and 995°C while being filled in the container 19, maintained for 4 hours, and then cooled to room temperature. was created. During sintering, an argon gas atmosphere was used from room temperature until the temperature reached 450°C, and then a vacuum atmosphere was used. The base material 14 obtained from each alloy 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 RFeB-based sintered magnet 15 was obtained by lowering the temperature, maintaining it for 90 minutes, and then rapidly cooling it. The RFeB-based sintered magnets produced from Alloys 1 to 7 are referred to as samples of Examples 1 to 7.

In addition, as a comparative example, RFeB-based sintered magnets were produced in the same manner as above using Alloy 1 (Comparative Example 1) and Alloy A (Comparative Examples 2 and 3) having the compositions listed in Table 1. 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% by mass, and is not included in the composition range of the RFeB-based sintered magnet of the present invention. In Comparative Examples 1 and 3, the O content was made higher than in Examples 1 to 7 and Comparative Example 2. Here, the content of O can be adjusted by controlling the manufacturing environment in the process from pulverizing the RFeB-based alloy ingot 11 to filling the container 19 with the RFeB-based magnet powder 13.

Table 2 shows the results of measuring the compositions of the prepared samples of Examples 1 to 7 and Comparative Examples 1 to 3. Furthermore, Table 3 shows the coercive force iHc and squareness ratio SQ of each of these samples, as well as the Hk90 values measured to determine 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 determined by Hk90/iHc.

In all of the samples of Examples 1 to 7, the composition of each element listed in Table 2 satisfies the composition conditions for the RFeB-based sintered magnet of the present invention. On the other hand, in the samples of Comparative Examples 1 and 3, the O content did not meet the requirements of the present invention (less than 1500 ppm). In addition, the samples of Comparative Examples 2 and 3 do not have Al content that satisfies the requirements of the present invention (0.3 to 0.7% by mass). On the other hand, in the samples of Comparative Examples 2 and 3, the content of elements other than Al and O is approximately the same as the content of these elements in the sample of Example 2.

Comparing the coercive force iHc of the samples of Examples 1 to 6, which do not contain Dy, and the sample of the comparative example, the samples of Examples 1 to 6 all have a value of 16.8 to 18.2 kOe, which exceeds 16.0 kOe. In contrast, the samples of Comparative Examples 1 to 3 all had values of 14.5 to 15.7 kOe, which are lower than 16.0 kOe. In particular, as mentioned above, the sample of Example 2, in which the content of elements other than Al and O is approximately the same as Comparative Examples 2 and 3, has a coercive force iHc of 18.2 kOe, which is more remarkable than that of Comparative Examples 2 and 3. has a high value.

In addition, the samples of Examples 3 to 5 contain 0.08 to 0.11% by mass of Zr, and have higher squareness ratio SQ values than 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 measurements performed on the samples of Examples 1 and 2 and Comparative Example. In this measurement, we used synchrotron radiation X-ray diffraction measurement at the Aichi Synchroton Light Center (Science and Technology Exchange Center, a public interest incorporated foundation), and measured using synchrotron radiation with a wavelength of 0.09 nm. Figure 2(a) shows the measurement results for each sample in the 2θ range of 10 to 70°, and Figure 2(b) shows the horizontal axis (2θ) and vertical axis (intensity) partially. It is enlarged and the data of three samples are shown superimposed. At the locations indicated by arrows in FIG. 2(b), there are three peaks that appear in Examples 1 and 2 but do not appear in the comparative example. These three peaks are Nd ₆ Fe ₁₁ Al ₃ (R ₆ Fe _14- It matches well with the X-ray diffraction pattern (PDF#01-078-9291) of _R =Nd, x=3 at _x Al 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 , ie, RFeAl phase.

Next, using the wavelength dispersive X-ray spectroscopy (WDX) for the sample of Example 2, arbitrarily selected measurement points within the grain boundaries containing all three elements of R, Fe, and Al were measured. The composition ratios of these three species and Co and Cu were determined. The results are shown in Table 4.

At these six measurement points, the ratio of the composition ratio of R atoms to the sum of the composition ratios of four types of atoms, Fe, Co, Al, and Cu, is close to 6:14, indicating that the RFeAl phase is It is thought that it is formed.

By forming the RFeAl phase at the grain boundaries in this way, the amount of Fe dissolved in the R-rich phase decreases. The RFeB-based sintered magnet of this embodiment is Coercive force increases.

Next, samples were subjected to a plurality of conditions with different temperatures and heating times in the first aging treatment step and the second aging treatment step for the base material 14 made using the RFeB magnet powder obtained from Alloy 3. It was manufactured and its coercive force was measured. The results are described below.

Figure 3(a) shows the coercive force after the first aging treatment process (before the second aging treatment process) of the samples prepared under three conditions with different first aging temperatures 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 the obtained RFeB-based sintered magnets was all above 16 kOe, and the coercive force was almost the same regardless of the first aging temperature within the above range.

Figure 3(b) shows the coercive force after the first aging process and the obtained The coercive force of RFeB sintered magnets 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 process was 30 minutes. The coercive forces of the obtained RFeB-based sintered magnets were all over 16 kOe, and were almost the same regardless of the heating time in the first aging treatment step within the above range.

Figure 3(c) shows the coercive force after the first aging treatment process of samples prepared under six conditions with different second aging temperatures in the range of 530 to 580°C, and the obtained RFeB-based sintered magnets. shows the coercive force of For these six samples, the first aging temperature was 800°C, the heating time in the first aging process was 30 minutes, and the heating time in the second aging process was 30 minutes. As a result of this experiment, the coercive force of the obtained RFeB-based sintered magnets all exceeded 16 kOe, and when the second aging temperature was within the above range, the higher the temperature, the greater the coercive force.

Figure 3(d) shows the coercive force after the first aging treatment process and the obtained The coercive force of RFeB sintered magnets 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 the obtained RFeB-based sintered magnets was all over 16 kOe, and the coercive force was almost the same regardless of the value as long as the heating time in the second aging treatment step was within the above range.

As mentioned above, from the experimental results shown in FIG. 3, the magnitude of the coercive force in the RFeB sintered magnet of this embodiment depends on the heating time in the first aging treatment step and the second aging treatment step during manufacturing, and the heating time in the first aging treatment step and the first aging treatment step. It can be seen that temperature has almost no effect, and that coercive force can be further improved by adjusting the second aging temperature.

Next, for the base material 14 made using the RFeB magnet powder obtained from Alloy 3, the first aging temperature was set to 800°C, the heating time of the first aging treatment step was 30 minutes, and the second aging temperature was set to 800°C. Regarding multiple examples in which the aging treatment is performed with the temperature at 540°C and the heating time (time maintained at 540°C) in the second aging treatment step for 30 minutes, and then the cooling rate is different when cooling from the second aging temperature to 100°C. A sample of RFeB-based sintered magnet was fabricated. In addition, as a comparative example, the second aging treatment step was performed on the base material 14 made using the RFeB magnet powder obtained from Alloy 3 without performing the first aging treatment step. Similarly, multiple samples of RFeB-based sintered magnets with different cooling rates were fabricated. Figure 4 shows the results of measuring the coercive force of these RFeB sintered magnet samples. As a result, the coercive force of all samples of the comparative example was less than 16 kOe, whereas the coercive force of the samples of this example, which had undergone both the first aging treatment process and the second aging treatment process, was 16 kOe. exceeded. Among the samples in this example, the sample with the slowest cooling rate from the second aging temperature to 100°C (3°C/min) has a slightly higher coercive force than the other samples whose cooling rate is 5°C/min or more. has become lower. That is, the cooling rate from the second aging temperature to 100°C is preferably 5°C/min or more.

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

Claims (3)

Contains 28 to 33 mass% of rare earth elements R, 0 to 2.5 mass% of Co, 0.3 to 0.7 mass% of Al , 0.1 to 0.5 mass% of Cu , 0.96 to 1.2 mass% of B, less than 1500 ppm of O, and the balance is Fe,
The total content of Cu and Al exceeds 0.5% by mass,
The Al content is higher than the Cu content,
An RFeAl phase with an R ₆ Fe _14-x Al _x type structure exists at the grain boundaries,
An RFeB-based sintered magnet characterized by a coercive force of 16 kOe or more. The RFeB-based sintered magnet according to claim 1, characterized in that it contains neither Dy nor Tb, which are heavy rare earth elements. The RFeB-based sintered magnet according to claim 1 or 2, further comprising 0.05 to 0.35% by mass of Zr.

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