JP4900085B2 - Rare earth magnet manufacturing method - Google Patents

Description

  The present invention relates to a method for producing a rare earth magnet.

  A rare earth magnet having a R-T-B (R is a rare earth element, T is a metal element including iron, etc.) system is a magnet having excellent magnetic properties, and many are aimed at further improving the magnetic properties. Is being studied. Generally, residual magnetic flux density (Br) and coercive force (HcJ) are used as an index representing the magnetic characteristics of a magnet. The larger these products (maximum energy product), the more excellent the magnetic characteristics are. be able to.

  In rare earth magnets, it is known that HcJ can be improved by using heavy rare earth elements such as Dy and Tb as part of the rare earth elements. However, since the composition containing these heavy metal elements has a smaller Br than a composition containing Nd, for example, if it is contained excessively, the maximum energy product of the magnet may be lowered.

  Thus, for example, Patent Document 1 below describes a rare earth magnet that is a sintered body obtained by adding an alloy such as Dy or Tb to an Nd—Fe—B alloy constituting the main phase of a rare earth magnet. . Such a rare earth magnet has a high concentration of Dy, Tb, etc. in the vicinity of the grain boundary, and has a non-uniform state in which almost no Dy, Tb, etc. are present in the center, so it is high with a small amount of heavy rare earth element added. It has been shown to have HcJ.

Patent Document 2 below describes a rare earth magnet made of a sintered body of an alloy having a composition of a normal rare earth magnet and a rare earth boron compound containing a heavy rare earth element. It has been shown that such a rare earth magnet can increase HcJ and suppress a decrease in Br.
JP-A-62-206802 JP-A 63-272006

  In recent years, rare earth magnets have a wide variety of uses, and there are increasing cases in which high magnetic properties are required compared to conventional magnets. Under such circumstances, a method for obtaining a rare earth magnet having a higher maximum energy product by increasing HcJ while further suppressing a decrease in Br is being sought.

  Therefore, the present invention has been made in view of such circumstances, and an object thereof is to provide a method for producing a rare earth magnet capable of improving HcJ while maintaining a good Br.

In order to achieve the above object, the method for producing a rare earth magnet of the present invention includes a forming step of forming a raw material powder composed of a plurality of raw material compounds to obtain a formed body, and a firing step of firing the formed body. As a raw material compound, at least one compound selected from a ^first raw material compound: R ¹ -T-B compound and R ¹ R ² -T-B compound (where R ¹ is a light rare earth element containing Y) , R ² is a heavy rare earth element, T is a metal element excluding the rare earth element and includes at least Fe.), Second raw material compound: R ¹ -T compound, R ¹ R ² -T compound and R ^At least one compound selected from ^2- T compounds and a third raw material compound: R ² -B compound or R ² -Al compound, and a compound having a melting point higher than those of the first and second raw material compounds Characterized by use .

  In the method for producing a rare earth magnet of the present invention, the raw material powder is composed of three kinds of raw material compounds, ie, first, second and third raw material compounds. When such a raw material powder is used, main phase particles are mainly formed from the first raw material compound, and a grain boundary phase is mainly formed from the second raw material compound in the firing step. At this time, the third raw material compound has a higher melting point than the first and second raw material compounds, and the reaction starts later than these, so that the inside of the main phase particle is not formed, and the outer shell portion thereof is formed. It is thought to form mainly. As a result, the obtained rare earth magnet has a high content ratio of heavy rare earth elements in the outer shell part (shell) of the main phase particles, and the core part (core) hardly contains heavy rare earth elements, so-called core-shell structure clearly. Can have.

  Therefore, the rare earth magnet obtained by the manufacturing method of the present invention has a high HcJ in the shell portion where the content ratio of heavy rare earth elements is large, and Br is well maintained by the core portion containing almost no heavy rare earth elements. Can be. Moreover, since HcJ can be improved by selectively containing heavy rare earth elements in the shell portion, the amount of rare heavy rare earth elements used can be reduced, and the manufacturing cost of rare earth magnets can be reduced. Is also possible.

In the method for producing a rare earth magnet of the present invention, the third raw material compound is preferably a boron compound containing R ² . By using such a boron compound as the third raw material compound, HcJ can be improved while further suppressing the decrease in Br, and the above-described core-shell structure can be formed more satisfactorily.

Furthermore, the method for producing a rare earth magnet of the present invention has a pulverization step of obtaining a raw material powder by pulverizing and mixing a plurality of raw material compounds before the molding step, from the pulverization step to the firing step. It is more preferable to perform the step in an atmosphere having an oxygen concentration of 100 ppm or less. By performing the pulverization to firing process in an environment with a low oxygen concentration in this way, it becomes possible to suppress the oxidation of R ¹ and R ² and further form a core-shell structure. As a result, a rare earth magnet having high Br and high HcJ is more easily obtained.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the manufacturing method of the rare earth magnet which can improve HcJ, maintaining Br favorable.

  Hereinafter, preferred embodiments of the present invention will be described.

In the method for producing a rare earth magnet according to a preferred embodiment, first, first, second and third raw material compounds are prepared. The first raw material compound is at least one compound selected from R ¹ -T-B compounds and R ¹ R ² -T-B compounds, and the second raw material compounds are R ¹ -T compounds, R ¹ at least one compound selected from the R 2 ^-T compound and R ² -T compound, the third raw material compound comprises R ^2, is a high melting point compound than the first and second starting compound .

Here, R ¹ in each raw material compound described above is a light rare earth element including Y, and specifically, at least one selected from the group consisting of Y, La, Ce, Pr, Nd, Sm, and Eu. Elements. R ² is a heavy rare earth element, and specifically includes at least one element selected from the group consisting of Gd, Tb, Dy, Ho, Er, Yb, and Lu. Further, T is a metal element excluding rare earth elements and contains at least Fe. Examples of T include Fe, Co, Ni, Mn, Al, Cu, Nb, Zr, Ti, W, Mo, V, Ga, Zn, and Si. Note that R ¹ , R ^2, T, and the like contained in the first to third raw material compounds may be the same or different.

Specifically, the R ¹ -T-B compound or R ¹ R ² -T-B compound that is the first raw material compound is R ¹ ₂ T ₁₄ B or (R ¹ R ² ) ₂ T _{14, respectively.} Examples thereof include compounds having a composition represented by B. As R ¹ in the first raw material compound, Nd is preferable. R ² is preferably Dy or Tb, and Dy is more preferable from the viewpoint of reducing raw material costs. Furthermore, as T, when Co is included in addition to Fe, the Curie temperature of the rare earth magnet is improved and the corrosion resistance tends to be improved. Further, as T, it is more preferable to include Al and / or Cu in addition to Fe and Co because excellent HcJ, corrosion resistance, and temperature characteristics tend to be obtained.

Further, ^R 1 -T compound is a second raw material ^compound, as R ^{1 R} 2 -T compounds or ^R 2 -T compounds, _{^{respectively, R 1 2 T 17, (}} R 1 R 2) 2 T 17, R Examples thereof include compounds having a composition represented by ² ₂ T ₁₇ , R ² ₁ T ₃ or the like. R ¹ in these second raw material compounds is preferably Nd, and R ² is preferably Dy or Tb, more preferably Dy. Further, T preferably contains Al and / or Cu in addition to Fe which is an essential element.

Furthermore, as a compound containing R ² which is the third raw material compound and having a higher melting point than the first and second raw material compounds, a compound in which R ² and B or Al are combined, that is, an R ² -B compound. or ^R 2 -Al compounds are exemplified, ^{specifically,} a compound having a composition represented by R 2 _{B 2} or ^R 2 _{B 4} or ^R ₂ 2 Al or ^R 2 Al are preferred. As R ² in the third raw material compound, Dy or Tb is preferable, and Dy is more preferable. The third raw material compound preferably has a higher melting point of 10 ° C. or higher and more preferably has a higher melting point of 30 ° C. or higher than the compound having the higher melting point of the first and second raw material compounds.

  Each raw material compound, for example, is produced by performing a cast casting method using raw materials of these constituent metals (metal simple substance, alloy, etc.) to produce each bulk raw material compound (raw material alloy) having a desired composition. Can be obtained. Examples of the raw material include rare earth metals or rare earth alloys, pure iron, ferroboron, and alloys thereof.

  In the production of the rare earth magnet, each of the raw material compounds prepared above is then pulverized into particles and mixed to obtain a raw material powder (pulverization step). The raw material compound is preferably pulverized in two steps, a coarse pulverization step and a fine pulverization step. The coarse pulverization step can be performed in an inert gas atmosphere using, for example, a stamp mill, a jaw crusher, a brown mill, or the like. Further, from the viewpoint of obtaining good magnetic properties by reducing the oxygen concentration in the obtained rare earth magnet, it is possible to store hydrogen in the raw material compound and perform hydrogen storage pulverization by using crack generation due to volume expansion. preferable. In the coarse pulverization step, pulverization is performed until the particle size of each raw material compound is about several hundred μm.

  Next, in the fine pulverization step, the pulverized product obtained in the coarse pulverization step is further finely pulverized until the average particle size becomes 3 to 5 μm. The fine pulverization can be performed using, for example, a jet mill.

  Then, raw material powder is obtained by mixing the powder of each obtained raw material compound, for example in nitrogen atmosphere. The mixing ratio of the powders of the first to third raw material mixtures is adjusted so that the desired composition of the rare earth magnet is obtained.

Then, the raw material powder mentioned above is shape | molded and a molded object is obtained (molding process). The molding can be performed, for example, by filling the raw material powder in a mold disposed in an electromagnet and then pressing the raw material powder while applying a magnetic field by the electromagnet to orient the crystal axis of the raw material powder. . The molding in the magnetic field can be performed, for example, in a magnetic field of 12.0 to 17.0 kOe at a pressure of about 0.7 t / cm ^{2 to} 1.5 t / cm ² .

  Next, the obtained molded body is fired in a vacuum or an inert gas atmosphere to obtain a sintered body (firing step). Firing is preferably set as appropriate according to conditions such as composition, pulverization method, and particle size, but may be performed at 1000 to 1100 ° C. for 1 to 5 hours, for example. In addition, from the viewpoint of satisfactorily forming a core-shell structure as will be described later, for example, the firing conditions such as the firing time may be appropriately changed.

In the rare earth magnet manufacturing method of the present embodiment, the series of steps from the pulverization step to the firing step described above is performed in an atmosphere in which the oxygen concentration is preferably 100 ppm or less, more preferably 50 ppm or less, and even more preferably 30 ppm or less. It is preferable. Examples of such an atmosphere include a vacuum or an inert gas atmosphere having an oxygen concentration of 100 ppm or less. By doing so, it becomes possible to greatly reduce the content of oxygen inevitably contained in the obtained rare earth magnet, the oxidation of R ¹ and R ² contained in the rare earth magnet is suppressed, and R contributing to HcJ The amount of rich phase can be increased. Further, a core-shell structure as will be described later is formed more satisfactorily.

  After the firing step, the obtained sintered body is subjected to an aging treatment as necessary. The aging treatment is a heat treatment for the sintered body and can further improve the HcJ of the rare earth magnet. The aging treatment can be performed, for example, in two stages. In this case, it is preferable to perform the aging treatment under two temperature conditions of around 800 ° C. and around 600 ° C. When aging treatment is performed under such conditions, particularly excellent HcJ tends to be obtained. On the other hand, when the aging treatment is performed in one stage, the temperature is preferably around 600 ° C.

  Then, after such an aging treatment, a rare earth magnet can be obtained by processing the sintered body into a desired shape as necessary.

  According to the manufacturing method of the present embodiment described above, for example, a rare earth magnet having the following structure is obtained. FIG. 1 is a schematic diagram showing an enlarged cross-sectional configuration of a rare earth magnet obtained by a manufacturing method according to a preferred embodiment. As shown in FIG. 1, the rare earth magnet 1 of this embodiment is composed of main phase particles 2 and grain boundary phases 4. The main phase particle 2 includes a core portion 12 that forms the central portion of the particle 2 and a shell portion 14 that forms an outer shell portion of the main phase particle 2 so as to cover the core portion 12.

The main phase particle 2 is a phase having a tetragonal crystal structure in which the compositions represented by R ¹ ₂ T ₁₄ B, R ² ₂ T ₁₄ B, and (R ¹ R ² ) ₂ T ₁₄ B are combined. is there. The main phase particle 2 mainly has a core portion 12 and a shell portion 14 having different R ² content ratios. That is, the shell portion 14 has a higher content ratio of R ² than the core portion 12.

On the other hand, the grain boundary phase 4 is a phase mainly interposed between the main phase particles 2 constituting the rare earth magnet 1, and is a phase having a composition different from that of the main phase particles 2. Such a grain boundary phase 4 includes, for example, an R-rich phase in which the content ratio of the rare earth element R (R ¹ and R ² ) is larger than that of the main phase particle 2, a B-rich phase in which the B content ratio is large (see FIG. Not shown).

  The rare earth magnet 1 having such a configuration includes, for example, the content ratio of each constituent element in the following ratio.

That is, first, the content ratio of the rare earth element R in which R ¹ and R ² are combined is preferably 25 to 35% by mass, more preferably 28 to 33% by mass, and 29 to 32% by mass. Further preferred. If the R content is less than 25% by mass, the R ₂ T ₁₄ B phase, which is the main phase, is difficult to form, and an α-Fe phase having soft magnetism is easily formed, resulting in a decrease in HcJ. There is a case. On the other hand, if it exceeds 35% by mass, the volume ratio of the R ₂ T ₁₄ B phase is decreased, and Br may be decreased. In addition, the reaction between R and oxygen results in an excessive increase in the oxygen content, and as a result, the R-rich phase contributing to HcJ decreases, and HcJ may also decrease.

  Moreover, it is preferable in the content rate of B (boron) being 0.5-4.5 mass%. When the content ratio of B is less than 0.5% by mass, HcJ may be reduced, and when it exceeds 4.5% by mass, Br tends to be insufficient. From these viewpoints, the content ratio of B is preferably 0.5 to 1.5% by mass, and more preferably 0.8 to 1.2% by mass.

  The rare earth magnet 1 of the present embodiment includes at least Fe (iron) as an element represented by T. The content ratio of Fe is not limited to the essential constituent elements described above, but the remainder excluding any additional elements described later. Become. Further, in the rare earth magnet 1, a part of T may be Co (cobalt). By containing Co, the Curie temperature of the rare earth magnet 1 tends to be improved or the corrosion resistance tends to be improved. The content ratio of Co is preferably 4% by mass or less (not including 0% by mass), more preferably 0.1 to 2.0% by mass, and further preferably 0.3 to 1.0% by mass. preferable.

  Furthermore, the rare earth magnet 1 preferably contains 0.2 to 0.6 mass% of Al (aluminum) and / or Cu (copper) in total. By containing Al or Cu within this range, the HcJ, corrosion resistance, and temperature characteristics of the rare earth magnet 1 can be improved. Further, the rare earth magnet 1 preferably contains Zr (zirconium) in an amount of 0.03 to 0.25% by mass, more preferably 0.05 to 0.2% by mass, and still more preferably 0.1 to 0.15% by mass. May be. Zr can suppress abnormal growth of crystal grains during the manufacturing process of the rare earth magnet 1, and contributes to improvement of magnetic properties by making the structure of the obtained sintered body (rare earth magnet 1) uniform and fine.

  Furthermore, the rare earth magnet 1 may contain O (oxygen) derived from atmospheric oxygen or the like, but the oxygen content of the rare earth magnet 1 is preferably 2000 ppm or less, and more preferably 1500 ppm or less. More preferably, it is 1000 ppm or less. Thus, when the amount of oxygen is small, precipitation of the oxide phase, which is a nonmagnetic component, is suppressed, and more excellent magnetic properties can be obtained.

  The rare earth magnet 1 of the present embodiment has inevitable impurities such as Mn, Ca, Ni, Si, Cl, S, and F that are inevitably included in the manufacturing process in addition to the above-described constituent elements, for example, About 0.001-0.5 mass% may be contained.

  The preferred embodiment has been described above, but the method for producing a rare earth magnet of the present invention and the rare earth magnet obtained by such a production method are not necessarily limited to the above-described embodiment, and can be appropriately changed without departing from the scope of the invention. It is.

  For example, in the manufacturing method of the above-described embodiment, only the first to third raw material compounds are used as the raw material compound. However, the present invention is not limited to this, and for example, another raw material compound for containing an additive element or the like is further used. May be. Further, in the rare earth magnet 1 obtained by the preferred embodiment, the main phase particle 2 has the core portion 12 and the shell portion 14 as shown in FIG. 1, but these are clearly distinguished for convenience. In practice, the boundary may not be clearly distinguished in this way.

EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to these Examples.
[Preparation of rare earth magnets]

(Examples 1-2 and Comparative Examples 1-3)
First, alloys a1 to a6, alloy b and alloys c1 to c2 shown in Table 1 below were prepared as first to third raw material compounds, respectively. These were prepared by preparing raw materials for each alloy, and using these, alloy a and alloy b were cast by the strip casting method, and alloy c was cast by arc melting. In the table, “Bal.” Means the balance excluding the content of other constituent elements.

  Next, the raw material compounds obtained above were each pulverized and then mixed. In this step, first, hydrogen was occluded in each raw material compound, and then hydrogen pulverization treatment was performed in which dehydrogenation was performed in an Ar atmosphere at 600 ° C. for 1 hour. Subsequently, 0.15 wt% of oleic acid amide was added to the powder after hydrogen pulverization as a pulverization aid, mixed for 5 to 30 minutes using a nauter mixer, and then finely pulverized using a jet mill. It was set as the powder whose particle size is 3 micrometers.

And the fine powder obtained from each raw material compound is mixed so that it may become the combination and mixing | blending ratio of the raw material compound shown in Table 2, and the raw material powder corresponding to the rare earth magnets of Examples 1-2 and Comparative Examples 1-3 Were prepared respectively. The unit of the numerical values in the table is% by weight. In this example, each step from the pulverization step to the firing step was performed in an atmosphere having an oxygen concentration of less than 100 ppm.

Then, each raw material powder was filled in a mold disposed in an electromagnet, and then subjected to molding in a magnetic field in which a pressure of 1.2 t / cm ² was applied while applying a magnetic field of 15 kOe to obtain a molded body. . Thereafter, the compact was fired in vacuum at 1030 ° C. for 4 hours, and then rapidly cooled to obtain a sintered body. Then, the obtained sintered bodies were subjected to two-stage aging treatment of 850 ° C. for 1 hour and 540 ° C. for 2 hours (both in an Ar atmosphere), whereby Examples 1-2 and Comparative Example 1 were performed. ~ 3 rare earth magnets were obtained respectively.

These rare earth magnets are all Nd: 25.3 wt%, Dy: 5 wt%, Al: 0.2 wt%, Cu: 0.07 wt%, Co: 0.5 wt%, B: 1.0 wt%, It is obtained by adjusting the mixing ratio of the raw material compounds so that the composition of Zr: 0.2 wt% and Fe: balance is obtained.
[Characteristic evaluation]

About each of the obtained rare earth magnets of Examples 1-2 and Comparative Examples 1-3, Br (residual magnetic flux density, unit: kG) and HcJ (coercive force, unit: kOe) were measured using a BH tracer. did. The results obtained are summarized in Table 3 and FIG. FIG. 2 is a plot of Br values versus HcJ obtained with a rare earth magnet. The results shown in Table 3 and FIG. 2 are values obtained by averaging three samples prepared for the rare earth magnets of the examples and comparative examples. Also, the solid line drawn in FIG. 2 is a straight line showing the change in magnetic characteristics obtained when the amount of substitution of Dy with respect to Nd is changed, and shows a standard for the technically similar magnetic characteristic potential. ing.

  From Table 3 and FIG. 2, the rare earth magnets of Examples 1 and 2 in which the first, second, and third raw material compounds are combined as the raw material compound are Comparative Example 1, in which the first and second raw material compounds are combined. Compared to Comparative Example 2 in which the first and third raw material compounds are combined, and Comparative Example 3 in which two types of the first raw material compound and the third raw material compound are combined, excellent HcJ while maintaining a high Br It was confirmed that

It is a schematic diagram which expands and shows the cross-sectional structure of the rare earth magnet obtained by the manufacturing method of suitable embodiment. It is the figure which plotted the value of Br with respect to HcJ obtained by each rare earth magnet of Examples 1-2 and Comparative Examples 1-3.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Rare earth magnet, 2 ... Main phase particle, 4 ... Grain boundary phase, 12 ... Core part, 14 ... Shell part.

Claims (3)

A molding step of molding a raw material powder composed of a plurality of raw material compounds to obtain a molded body;
A firing step of firing the molded body,
As the raw material compound,
First raw material compound: at least one compound selected from R ¹ -TB compound and R ¹ R ² -TB compound (where R ¹ is a light rare earth element including Y, and R ² is a heavy rare earth element) , T is a metal element excluding rare earth elements and an element containing at least Fe).
Second raw material compound: at least one compound selected from R ¹ -T compound, R ¹ R ² -T compound and R ² -T compound, and
Third raw material compound: R ² -B compound or R ² -Al compound, which has a higher melting point than the first and second raw material compounds,
A method for producing a rare earth magnet. ^2. The rare earth magnet according to claim 1, wherein the third raw material compound is a compound having a composition represented by R ² B _2, R ² B _4, R ² ₂ Al, or R ² Al . Production method. Before the molding step, it has a pulverization step of obtaining the raw material powder by pulverizing and mixing a plurality of the raw material compounds respectively,
The method for producing a rare earth magnet according to claim 1 or 2, wherein the steps from the crushing step to the firing step are performed in an atmosphere having an oxygen concentration of 100 ppm or less.

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