JP4765747B2 - Method for producing R-Fe-B rare earth sintered magnet - Google Patents

Description

The present invention relates to a method for producing an R—Fe—B rare earth sintered magnet having R ₂ Fe ₁₄ B type compound crystal grains (R is a rare earth element) as a main phase, and in particular, light rare earth elements RL (of Nd and Pr). The present invention relates to a method for producing an R—Fe—B rare earth sintered magnet which contains at least one kind) as a main rare earth element R, and a part of the light rare earth element RL is substituted by Dy.

R-Fe-B rare earth sintered magnets with Nd ₂ Fe ₁₄ B type compound as the main phase are known as the most powerful magnets among permanent magnets, and are voice coil motors (VCM) for hard disk drives. In addition, it is used in various motors such as motors for mounting on hybrid vehicles, and home appliances. When R-Fe-B rare earth sintered magnets are used in various devices such as motors, they are required to have excellent heat resistance and high coercive force characteristics in order to cope with high temperature use environments.

As a means for improving the coercive force of an R—Fe—B rare earth sintered magnet, an alloy prepared by melting Dy as a raw material is used. According to this method, since the rare earth element R in the R ₂ Fe ₁₄ B phase containing the light rare earth element RL as the rare earth element R is substituted with Dy, the magnetocrystalline anisotropy (coercivity of the R ₂ Fe ₁₄ B phase) The essential physical quantity to be determined) is improved. However, the magnetic moment of the light rare earth element RL in the R ₂ Fe ₁₄ B phase is in the same direction as the magnetic moment of Fe, whereas the magnetic moment of Dy is opposite to the magnetic moment of Fe. As the light rare earth element RL is replaced with Dy, the residual magnetic flux density Br decreases.

  On the other hand, since Dy is a scarce resource, it is desired to reduce its usage. For these reasons, the method of replacing the entire light rare earth element RL with Dy is not preferable.

In order to develop a coercive force improving effect by adding a relatively small amount of Dy, an alloy / compound powder containing a large amount of Dy is added to the main phase mother alloy powder containing a large amount of light rare earth RL. It has been proposed to form and sinter. According to this method, since Dy is to distributed more in the grain boundary vicinity of the R ₂ Fe ₁₄ B phase, to improve efficiently the magnetocrystalline anisotropy of the R ₂ Fe ₁₄ B phase in the outer periphery of the main phase Is possible. Since the coercive force generation mechanism of the R—Fe—B rare earth sintered magnet is a nucleation type (nucleation type), a large amount of Dy is distributed in the outer shell portion (near the grain boundary) of the main phase. The magnetocrystalline anisotropy is increased, and the nucleation of reverse magnetic domains is hindered. As a result, the coercive force is improved. Moreover, since substitution by Dy does not occur in the center part of the crystal grains that do not contribute to the improvement of the coercive force, it is possible to suppress a decrease in the residual magnetic flux density Br.

  However, when this method is actually carried out, the diffusion rate of Dy increases in the sintering process (executed at 1000 ° C. to 1200 ° C. on an industrial scale), so that Dy also diffuses into the center of the crystal grains. As a result, it is not easy to obtain the expected organizational structure.

  Further, as another means for improving the coercive force of the R-Fe-B rare earth sintered magnet, after depositing a metal, alloy, compound, etc. containing Dy on the magnet surface at the stage of the sintered magnet, heat treatment and diffusion are performed. It has been studied to recover or improve the coercive force without significantly reducing the residual magnetic flux density (Patent Document 1, Patent Document 2, and Patent Document 3).

  Patent Document 1 contains 1.0 atomic% to 50.0 atomic% of at least one of Ti, W, Pt, Au, Cr, Ni, Cu, Co, Al, Ta, and Ag, and the balance R ′ ( R ′ discloses that an alloy thin film layer made of Ce, La, Nd, Pr, Dy, Ho, and Tb is formed on the ground surface of the sintered magnet body.

  Patent Document 2 states that a metal element R (the R is a rare earth element selected from Y and Nd, Dy, Pr, Ho, and Tb) exceeds the depth corresponding to the radius of the crystal grains exposed on the outermost surface of the small magnet. 1 type or 2 types or more) is diffused, thereby modifying the damaged part of work-affected damage and improving (BH) max.

  Patent Document 3 discloses that a chemical vapor deposition film mainly composed of rare earth elements is formed on the surface of a magnet having a thickness of 2 mm or less to recover the magnet characteristics.

On the other hand, as another method for forming the Dy layer on the surface of the sintered magnet, a dipping (hot dip) method has been proposed. Patent Document 4 discloses that a magnet is immersed in a molten metal of Dy alloy such as Dy-Fe, and thereafter an aging treatment is performed.
JP-A-62-192566 JP 2004-304038 A JP 2005-285859 A JP 2005-209932 A

  The conventional techniques disclosed in Patent Document 1, Patent Document 2 and Patent Document 3 are all intended to recover the surface of a sintered magnet that has been deteriorated by processing. Is limited to the vicinity of the surface of the sintered magnet. For this reason, the effect of improving the coercive force is hardly obtained with a magnet having a thickness of 3 mm or more.

  In any of the methods of Patent Documents 1 to 3, a large amount of rare earth metal is also present in a portion other than the magnet inside the film forming apparatus (for example, the inner wall of the vacuum chamber) in the process of growing the Dy layer on the sintered magnet body. Since it accumulates, it is contrary to the resource saving of the heavy rare earth element which is a valuable resource.

  On the other hand, according to the method disclosed in Patent Document 4, the amount of Dy metal adhering to the device portion other than the magnet is small, and in principle, a high yield can be expected. However, in order to melt Dy, it is necessary to heat to a temperature equal to or higher than the melting point of Dy. When a rare earth sintered magnet is immersed in such a high temperature molten metal, the grain boundary phase of the rare earth sintered magnet is melted. As a result, the magnet characteristics deteriorate. In order to avoid such a problem, it is necessary to lower the temperature of the molten Dy. To that end, it is necessary to use a Dy alloy (for example, Dy-Fe) instead of Dy alone. However, when a rare earth sintered magnet is immersed in such a molten alloy, only an alloy layer containing a metal component (for example, Fe) other than Dy can be formed on the sintered magnet. When diffusion is performed from such an alloy layer into the sintered magnet, the diffusion efficiency of Dy is reduced due to the presence of metal components other than Dy.

  In addition, in the dipping method disclosed in Patent Document 4, it is difficult to control the thickness of the alloy layer formed on the surface of the rare earth magnet with high accuracy, and a film that is thicker than necessary is not uniform. Will be formed. For this reason, a surface grinding process for uniformly thinning the thick film alloy on the surface of the sintered magnet is required for the dipping method, which increases the manufacturing cost.

  The present invention has been made to solve the above-mentioned problems, and the object of the present invention is to efficiently diffuse and maintain a small amount of Dy inside the sintered magnet body without increasing the manufacturing cost. An object of the present invention is to provide a method for producing an R—Fe—B rare earth sintered magnet with improved magnetic force.

The method for producing an R—Fe—B rare earth sintered magnet according to the present invention mainly comprises R ₂ Fe ₁₄ B type compound crystal grains containing a light rare earth element RL (at least one of Nd and Pr) as a main rare earth element R. Step (A) of preparing at least one R—Fe—B rare earth sintered magnet body having a phase, and performing electroplating in a plating solution containing an organic solvent and Dy ions, A step (B) of depositing Dy on the surface of the rare earth sintered magnet body, and heating the R—Fe—B rare earth sintered magnet body on which the Dy is electrodeposited. And a step (C) of diffusing Dy inside the B-based rare earth sintered magnet body.

  In a preferred embodiment, in the step (B), electrolysis is performed without heating the plating solution.

  In a preferred embodiment, in the step (C), the heating temperature of the R—Fe—B rare earth sintered magnet body is set in the range of 700 ° C. or more and 1000 ° C. or less.

  In a preferred embodiment, in the step (C), heat treatment is performed in a state where the processing chamber is filled with a vacuum or an inert atmosphere.

  In a preferred embodiment, the electrolytic plating in the step (B) is pulse electrolytic plating.

  In a preferred embodiment, the plating solution is prepared by dissolving anhydrous Dy chloride in the organic solvent.

  In a preferred embodiment, in the step (B), a Dy layer having a thickness of 1 μm to 10 μm is formed on the surface of the R—Fe—B rare earth sintered magnet body.

  According to the present invention, after electroplating in a plating solution containing an organic solvent and Dy ions, Dy is electrodeposited on the surface of the R-Fe-B rare earth sintered magnet body, and then the sintered magnet body Dy is diffused inside For this reason, it is possible to diffuse the inside of the magnet body extremely efficiently without consuming Dy wastefully.

  Electroplating in an organic solvent does not need to be performed at such a high temperature that the grain boundary phase of the R—Fe—B rare earth sintered magnet body is melted, and can be suitably executed at room temperature, for example. Moreover, since it is easy to control the layer thickness of Dy deposited on the surface of the sintered magnet body, a polishing step for the Dy layer is not required after that. Further, the Dy layer formed on the surface of the sintered magnet body is not substantially alloyed and is mainly formed of Dy. For this reason, Dy can also be efficiently diffused into the sintered magnet body.

  Due to the diffusion of Dy, the light rare earth element RL can be replaced with Dy in the main phase outer shell in the rare earth sintered magnet body, so that the coercive force HcJ is increased while suppressing the decrease in the residual magnetic flux density Br. Is possible.

In the method for producing an R—Fe—B rare earth sintered magnet according to the present invention, first, an R—Fe—B rare earth sintered magnet body is prepared. This R—Fe—B rare earth sintered magnet body includes R ₂ Fe ₁₄ B type compound crystal grains (main phase) and rare earth-rich grain boundary phases. The R—Fe—B rare earth sintered magnet body at this stage contains a light rare earth element RL (at least one of Nd and Pr) as a main rare earth element R.

  Next, the R—Fe—B rare earth sintered magnet body is immersed in a plating solution containing an organic solvent and Dy ions, and electrolytic plating is performed in the plating solution. By this electrolytic plating, Dy ions in the organic solvent gather on the surface of the R—Fe—B rare earth sintered magnet body, and Dy is electrodeposited on the surface of the R—Fe—B rare earth sintered magnet body. After the R—Fe—B rare earth sintered magnet body with Dy electrodeposited on the surface is taken out of the plating solution, it is inserted into a heat treatment chamber such as a furnace. By performing the heat treatment on the R—Fe—B rare earth sintered magnet body in the heat treatment chamber, Dy is diffused from the surface to the inside of the R—Fe—B rare earth sintered magnet body.

  In the prior art, in the process of growing the Dy layer on the sintered magnet body, the Dy film-forming material supply source is consumed very inefficiently. For example, when a Dy layer is deposited on a sintered magnet body by a sputtering method, it is necessary to perform sputtering in a state where a Dy target is disposed at a position facing the sintered magnet body. At this time, Dy sputtered from the target collides with a portion where the sintered magnet body does not exist in the sputtering apparatus and accumulates there. The same thing occurs when using other thin film deposition techniques (such as vapor deposition) of Dy. That is, according to the conventional thin film deposition technique, there is a problem that much (for example, 80 to 90%) of Dy is wasted in the process of depositing the thin film on the sintered magnet body.

  On the other hand, in the present invention, Dy ions can be attracted to the surface of the R—Fe—B rare earth sintered magnet body by electrolytic plating in a plating solution. It becomes possible to use. Further, as compared with the conventional technique in which the R—Fe—B rare earth sintered magnet body is immersed in the molten Dy alloy, an advantageous effect that a Dy layer having a controlled thickness can be formed.

  As a result of intensive studies on a more efficient (higher RH yield) and higher coercivity process of the R—Fe—B rare earth sintered magnet, the present inventor has focused attention on electroplating as a high yield film forming method. However, since Dy has a low oxidation-reduction potential, when electroplating is performed in a general aqueous solution, water electrolysis occurs preferentially and Dy cannot be electrodeposited. The inventor has found that Dy can be deposited on the surface of the rare earth magnet by plating in an organic solvent containing Dy chloride. However, even in an organic solvent solution, a trace amount of water remains in the plating solution, and it is difficult to completely remove it. Further, Dy chloride is hardly dissolved in the organic solvent, and it is difficult to prepare a plating solution in which Dy ions are dissolved at a high concentration. As a result, the plating solution has a lower conductivity than that of a general aqueous plating solution. When a general constant current electrolysis is performed, the supply of Dy ions does not catch up near the surface of the rare earth magnet that is the cathode, and the reduction current is It was found that, due to the electrolysis of the remaining trace amount of water, the generated hydrogen caused the characteristics of the rare earth magnet to deteriorate, and eventually the Dy film was hardly formed on the surface of the rare earth magnet.

  Therefore, the present inventor has ensured the supply of Dy ions near the cathode by performing pulse electrolysis, and has a high yield and uniform Dy film on the magnet surface without causing deterioration of the characteristics of the rare earth magnet due to hydrogen gas generation. We succeeded in developing a high-performance rare earth magnet that combines high residual magnetic flux density and high coercive force by film formation and subsequent heat treatment.

The plating solution used in the present invention is prepared by dissolving Dy chloride (DyCl ₃ ) in an organic solvent. In order to prevent moisture from being contained in the plating solution as much as possible, it is preferable to use an anhydrous Dy chloride (DyCl ₃ ). Since anhydrous DyCl ₃ takes time to dissolve, it is preferable to stir and dissolve the inert gas such as dry Ar having a dew point of −50 ° C. or less while bubbling.

  As the organic solvent, polar solvents such as formamide and dimethylformamide are preferable in order to have high conductivity as much as possible and to dissolve Dy chloride uniformly.

  The Dy ion concentration in the plating solution is preferably 0.01 mol / l or more. If the concentration of Dy ions in the plating solution is less than 0.01 mol / l, the electrodeposition efficiency is low and impractical, and the supply of Dy ions does not catch up near the surface of the rare earth magnet that is the cathode. It is expended in the electrolysis of the remaining trace amount of water, hydrogen gas is likely to be generated, and there is a risk that the characteristics will deteriorate due to the magnet taking in hydrogen and embrittlement.

Pulse plating conditions are: maximum current (CD _max ) 1.0-5.0 A / dm ² , minimum current density (CD _min ) 0-1.0 A / dm ² , maximum current density value duration (T _on ) 1 It is preferable to use a pulse waveform current of ˜100 ms, minimum current density value duration (T _off ) of 1 to 100 ms, and a bath temperature of 5 to 50 ° C. By performing under such conditions, the film can be formed most efficiently without generating as much hydrogen gas as possible near the magnet surface.

  After forming the Dy layer on the surface of the R-Fe-B sintered magnet body in this way, heat treatment is performed to diffuse Dy from the surface to the inside.

  According to the present invention, since it is not necessary to sputter or evaporate the Dy supply source for film formation, it is possible to efficiently diffuse Dy dissolved in the organic solvent into the magnet body, which is valuable. This greatly contributes to resource saving of Dy, which is a resource.

By the diffusion treatment in the present invention, a part of the light rare earth element RL contained in the R ₂ Fe ₁₄ B main phase crystal grains is substituted with Dy that has penetrated from the sintered body surface by grain boundary diffusion, and R ₂ Fe ₁₄ A layer (thickness is, for example, 1 nm) in which Dy is relatively concentrated can be formed on the outer shell of the B main phase.

Since the coercive force generation mechanism of the R—Fe—B rare earth sintered magnet is a nucleation type, if the magnetocrystalline anisotropy in the outer shell of the main phase is increased, a reverse magnetic domain is formed in the vicinity of the grain boundary phase in the main phase. As a result, the coercive force HcJ of the entire main phase is effectively improved. In the present invention, since the heavy rare earth substitution layer can be formed in the outer shell portion of the main phase not only in the region close to the surface of the sintered magnet body but also in the region deep from the magnet surface, And the coercive force HcJ of the whole magnet is sufficiently improved. Therefore, according to the present invention, the amount of Dy consumed can be at least diffused and permeated into the sintered body, and by efficiently forming Dy ₂ Fe ₁₄ B in the main phase outer shell portion Thus, it is possible to improve the coercive force HcJ while suppressing a decrease in the residual magnetic flux density Br.

  As is clear from the above description, in the present invention, it is not necessary to add Dy in the raw material alloy stage. That is, a known R—Fe—B rare earth sintered magnet containing a light rare earth element RL (at least one of Nd and Pr) as a rare earth element R is prepared, and heavy rare earth elements are diffused from the surface into the magnet. . Even if the present invention is applied to an R—Fe—B based sintered magnet to which some Dy is added in the raw material alloy stage, the same effect can be obtained.

Dy electrodeposited on the surface diffuses in the grain boundary phase toward the inside of the magnet using the difference in Dy concentration at the magnet interface as a driving force. At this time, a part of the light rare earth element RL in the R ₂ Fe ₁₄ B phase is replaced by Dy that has diffused and penetrated from the magnet surface. As a result, a layer in which Dy is concentrated is formed in the outer shell of the R ₂ Fe ₁₄ B phase.

By forming such a Dy enriched layer, the magnetocrystalline anisotropy of the main phase outer shell is increased, and the coercive force HcJ is improved. That is, by using a small amount of Dy metal, Dy is diffused and penetrated deep inside the magnet, and only the main phase outer shell portion is efficiently converted to Dy ₂ Fe ₁₄ B. However, the coercive force HcJ can be improved over the entire magnet.

  According to the experiment, it was found that the light rare earth element RL diffuses from the inside of the sintered magnet body toward the surface as Dy diffuses and penetrates to form an RL concentrated layer on the surface of the magnet body. For this reason, the total amount of rare earth elements inside the sintered magnet body (volume ratio of the main phase) hardly changes, and a decrease in residual magnetic flux density is suppressed.

  As described above, since the R—Fe—B based sintered magnet has a coercive force generation mechanism by nucleation, the crystal magnetic anisotropy in the main phase outer shell is increased, so that the main phase Nucleation of reverse magnetic domains in the vicinity of the grain boundary phase is suppressed, and the coercive force HcJ is increased.

  Further, the content of Dy that diffuses is preferably set in a range of 0.1% to 1.5% by weight ratio of the whole magnet. If it exceeds 1.5%, the processing time required for diffusion may become too long, and if it is less than 0.1%, the effect of improving the coercive force HcJ is insufficient. A diffusion amount of 0.1% to 1.5% can be achieved by heat treatment in the above temperature range for 30 to 180 minutes.

  The surface state of the sintered magnet body is preferably closer to the metal state so that Dy can easily diffuse and penetrate, and it is better to perform an activation treatment such as acid washing or blasting before electrodeposition. The surface of the body may be in a state where oxidation has progressed after the cutting process is completed, for example.

  According to the present invention, it is possible to provide a high-performance magnet that increases both the residual magnetic flux density Br and the coercive force HcJ using a small amount of Dy, and does not deteriorate the magnetic characteristics even at high temperatures. Such a high-performance magnet greatly contributes to the realization of an ultra-small and high-power motor. The effect of the present invention using the grain boundary diffusion is particularly remarkable in a magnet having a thickness of 10 mm or less.

  Hereinafter, a preferred embodiment of a method for producing an R—Fe—B rare earth sintered magnet according to the present invention will be described.

[Raw material alloy]
First, an alloy containing a light rare earth element RL of 25% by mass or more and 40% by mass or less, B (boron) of 0.6% by mass to 1.6% by mass, the remainder Fe and inevitable impurities is prepared. . A part of B may be substituted by C (carbon), and a part of Fe (50 atomic% or less) may be substituted by another transition metal element (for example, Co or Ni). This alloy is suitable for a variety of purposes, including Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb, and About 0.01 to 1.0% by mass of at least one additive element M selected from the group consisting of Bi may be contained.

  The above-mentioned alloy can be suitably produced by rapidly cooling a molten raw material alloy by, for example, a strip casting method. Hereinafter, preparation of a rapidly solidified alloy by a strip casting method will be described.

  First, a raw material alloy having the above composition is melted by high frequency melting in an argon atmosphere to form a molten raw material alloy. Next, after holding this molten metal at about 1350 ° C., it is rapidly cooled by a single roll method to obtain, for example, a flake-shaped alloy ingot having a thickness of about 0.3 mm. The alloy slab thus produced is pulverized into flakes having a size of 1 to 10 mm, for example, before the next hydrogen pulverization. In addition, the manufacturing method of the raw material alloy by a strip cast method is disclosed by US Patent 5,383,978 specification, for example.

[Coarse grinding process]
The alloy slab coarsely crushed into flakes is accommodated in the hydrogen furnace. Next, a hydrogen embrittlement process (hereinafter sometimes referred to as “hydrogen pulverization process”) is performed inside the hydrogen furnace. When the coarsely pulverized alloy powder after hydrogen pulverization is taken out from the hydrogen furnace, it is preferable to perform the take-out operation in an inert atmosphere so that the coarsely pulverized powder does not come into contact with the atmosphere. This is because the coarsely pulverized powder is prevented from oxidizing and generating heat, and the magnetic properties of the magnet are improved.

  By the hydrogen pulverization, the rare earth alloy is pulverized to a size of about 0.1 mm to several mm, and the average particle size becomes 500 μm or less. After the hydrogen pulverization, the embrittled raw material alloy is preferably crushed more finely and cooled. In the case where the raw material is taken out in a relatively high temperature state, the cooling process time may be relatively long.

[Fine grinding process]
Next, the coarsely pulverized powder is finely pulverized using a jet mill pulverizer. A cyclone classifier is connected to the jet mill crusher used in the present embodiment. The jet mill pulverizer is supplied with the rare earth alloy (coarse pulverized powder) coarsely pulverized in the coarse pulverization step, and pulverizes in the pulverizer. The powder pulverized in the pulverizer is collected in a collection tank through a cyclone classifier. Thus, a fine powder of about 0.1 to 20 μm (typically 3 to 5 μm) can be obtained. The pulverizer used for such fine pulverization is not limited to a jet mill, and may be an attritor or a ball mill. In grinding, a lubricant such as zinc stearate may be used as a grinding aid.

[Press molding]
In this embodiment, for example, 0.3 wt% of a lubricant is added to and mixed with the magnetic powder produced by the above method in a rocking mixer, and the surface of the alloy powder particles is coated with the lubricant. Next, the magnetic powder produced by the above-described method is molded in an orientation magnetic field using a known press machine. The intensity of the applied magnetic field is, for example, 1.5 to 1.7 Tesla (T). The molding pressure is set so that the green density of the molded body is, for example, about 4 to 4.5 g / cm ³ .

[Sintering process]
With respect to said powder molded object, the process hold | maintained for 10 to 240 minutes at the temperature within the range of 650-1000 degreeC, and sintering further by the temperature (for example, 1000-1200 degreeC) higher than said holding temperature after that. It is preferable to sequentially perform the proceeding steps. During sintering, particularly when a liquid phase is generated (when the temperature is in the range of 650 to 1000 ° C.), the R-rich phase in the grain boundary phase begins to melt and a liquid phase is formed. Then, sintering progresses and a sintered magnet body is formed. After sintering, an aging treatment (500 to 1000 ° C.) is performed as necessary.

[Dy electrodeposition process]
Next, electrolytic plating is performed in a plating solution in which Dy ions are dissolved in an organic solvent to efficiently form Dy on the surface of the sintered magnet body.

  In order to diffuse an appropriate amount of Dy into the magnet body, the thickness of the Dy layer deposited on the surface is preferably set in the range of 1 to 10 μm. For this purpose, it is preferable to perform a plating treatment for 0.5 to 5 hours by pulse electrolysis.

  According to this embodiment, since film formation can be performed on the magnet surface with good yield without sputtering or evaporating Dy, a high-performance rare earth magnet having a high coercive force can be obtained with a small amount of Dy. Further, there is no need for a grinding process after the treatment as in Patent Document 4.

[Diffusion process]
Next, Dy is diffused and penetrated from the surface of the sintered magnet body to improve the coercive force HcJ. Specifically, a sintered magnet body having Dy deposited on the surface is disposed in the processing chamber, and Dy is diffused from the surface of the sintered magnet body to the inside by heating.

  The heat treatment for diffusion may be performed by heating the entire atmosphere of the processing chamber in a state where the R-Fe-B rare earth sintered magnet body is left in the processing chamber, or by high-frequency induction heating or the like, You may carry out by heating a sintered magnet body directly.

  The heating temperature in the treatment chamber is preferably 700 ° C to 1000 ° C, and more preferably 850 ° C to 950 ° C. In this temperature region, Dy diffuses efficiently through the grain boundary phase of the sintered magnet body. When diffusion is performed in the above temperature range, the diffusion can be performed by heat treatment for about 30 to 180 minutes so that Dy is contained at a ratio of 0.1% to 1% with respect to the weight of the sintered magnet body.

  In addition, the “processing chamber” in this specification includes a space that can include a sintered magnet body, and may mean a processing chamber of a heat treatment furnace, or may be a process accommodated in such a processing chamber. It may also mean a container.

  The inside of the treatment chamber during the heat treatment is preferably an inert atmosphere. The “inert atmosphere” in this specification includes a state filled with a vacuum or an inert gas. The “inert gas” is a rare gas such as argon (Ar), for example, but may be included in the “inert gas” as long as it does not chemically react with the sintered magnet body.

  The diffusion process in this embodiment is not sensitive to the surface condition of the sintered magnet body, and a film made of Zn, Sn, or the like may be formed on the surface of the sintered magnet body before the diffusion process. This is because Zn and Sn are low melting point metals, and if they are in a small amount, they do not deteriorate the magnetic properties and do not hinder the diffusion described above.

  First, an ingot of an alloy blended so as to have a composition of Nd: 31.8, B: 0.97, Co: 0.92, Cu: 0.1, Al: 0.24, and the balance: Fe (% by mass) Was melted by a strip casting apparatus and solidified by cooling. Thus, alloy flakes having a thickness of 0.2 to 0.3 mm were produced.

  Next, this alloy flake was filled in a container and accommodated in a hydrogen treatment apparatus. Then, the hydrogen treatment apparatus was filled with a hydrogen gas atmosphere at a pressure of 500 kPa, so that hydrogen was occluded in the alloy flakes at room temperature and then released. By performing such a hydrogen treatment, the alloy flakes were embrittled to produce an amorphous powder having a size of about 0.15 to 0.2 mm.

  After adding 0.05 wt% zinc stearate as a grinding aid to the coarsely pulverized powder produced by the hydrogen treatment described above and mixing, a pulverization step using a jet mill device is performed, so that the powder particle size is about 3 μm. Powder was produced.

  The fine powder thus produced was molded by a press apparatus to produce a powder compact. Specifically, the powder particles were compressed in a magnetic field-oriented state in an applied magnetic field and pressed. Thereafter, the molded body was extracted from the press apparatus and subjected to a sintering process at 1020 ° C. for 4 hours in a vacuum furnace. Thus, after producing a sintered body block having a 15 mm square cube shape, the sintered body block is mechanically processed to obtain a sintered magnet having a thickness (magnetization direction size) of 1 mm × length of 10 mm × width of 10 mm. Several bodies were made.

  Next, Dy plating was performed on the sintered magnet body under the conditions shown in Table 1 below.

While bubbling 50 ml of an organic solvent (formamide or dimethylformamide) with Ar 300 ml / min dried at a dew point of −60 ° C. or lower, a predetermined amount of DyCl ₃ was slowly added to the organic solvent. The organic solvent was stirred for about 3 days until all of the DyCl ₃ was dissolved.

  A plurality of sintered magnet bodies were immersed in an organic solvent in a state of being fixed to a jig, and plated by pulse electrolysis under the conditions shown in Table 1.

  A Dy layer was formed on the surface of the sintered magnet body after the plating treatment. After removing the sintered magnet body from the plating solution, the sintered magnet body was washed with ethanol.

Next, the obtained sample was heat-treated in a vacuum heat treatment furnace under the conditions of 900 ° C., 60 min, and 1.0 × 10 ⁻² Pa, and then subjected to aging treatment under the conditions of 500 ° C., 60 min, and 2 Pa.

  Next, magnet characteristics (residual magnetic flux density: Br, coercive force: HcJ) were measured using a B-H tracer. Moreover, the electrodeposition state and diffusion state of Dy were evaluated by EPMA (EPM-810, manufactured by Shimadzu Corporation).

  Table 2 and FIG. 1 show the magnet characteristics. As can be seen from these results, the coercive force was improved by the method of this example. Here, the “Comparative Example” is a sintered magnet body manufactured in the same manner as Samples 1 to 4, but differs from Samples 1 to 4 in that the formation of the Dy layer and Dy diffusion were not performed. As can be seen from these results, the coercive force is improved according to the method of this example.

  FIG. 2 is a photograph showing the results of surface EPMA analysis after Dy plating of Sample 2. FIG. 2 shows that Dy has diffused into the grain boundary phase inside the sintered magnet body.

  According to the present invention, Dy can be efficiently diffused inside the sintered magnet body without wasting Dy, and Dy can be concentrated in the outer shell portion of the main phase crystal grains. A high-performance magnet having a high coercive force can be provided.

It is a graph which shows the magnet characteristic acquired about the Example of this invention, (a) is a graph which shows the residual magnetic flux density Br, (b) is a graph which shows the coercive force HcJ. It is a photograph which shows the surface EPMA analysis result obtained about the Example (sample 2) of this invention.

Claims (6)

At least one R—Fe—B rare earth sintered magnet body having R ₂ Fe ₁₄ B type compound crystal grains containing a light rare earth element RL (at least one of Nd and Pr) as a main rare earth element R as a main phase. Step (A) to be prepared,
A step (B) of depositing Dy on the surface of the R—Fe—B rare earth sintered magnet body by performing electroplating in a plating solution containing an organic solvent and Dy ions;
A step (C) of diffusing Dy inside the R-Fe-B rare earth sintered magnet body by heating the R-Fe-B rare earth sintered magnet body on which the Dy is electrodeposited;
It encompasses,
The electrolytic plating in the step (B) is pulse electrolytic plating,
In the pulse electrolytic plating, the maximum current density is 1.0 to 5.0 A / dm ² , the minimum current density is 0 to 1.0 A / dm ² , the duration of the maximum current density value is 1 to 100 ms, and the duration of the minimum current density value is A method for producing an R—Fe—B rare earth sintered magnet, wherein a current of a pulse waveform of 1 to 100 ms is used and a bath temperature is 5 to 50 ° C.   The method for producing an R—Fe—B rare earth sintered magnet according to claim 1, wherein in the step (B), electrolysis is performed without heating the plating solution.   2. The R—Fe—B rare earth sintered body according to claim 1, wherein in the step (C), the heating temperature of the R—Fe—B rare earth sintered magnet body is set within a range of 700 ° C. or higher and 1000 ° C. or lower. Magnet manufacturing method.   2. The method for producing an R—Fe—B rare earth sintered magnet according to claim 1, wherein in the step (C), heat treatment is performed in a state where the processing chamber is filled with a vacuum or an inert atmosphere.   The said plating solution is a manufacturing method of the R-Fe-B type sintered magnet of Claim 1 adjusted by melt | dissolving anhydrous Dy chloride in the said organic solvent.   2. The R—Fe—B based sintering according to claim 1, wherein in the step (B), a Dy layer having a thickness of 1 μm to 10 μm is formed on a surface of the R—Fe—B based rare earth sintered magnet body. Magnet manufacturing method.