JP5235264B2 - Rare earth sintered magnet and manufacturing method thereof - Google Patents

Description

  The present invention relates to a rare earth sintered magnet and a manufacturing method thereof.

A rare earth-iron-boron rare earth sintered magnet typical as a high performance permanent magnet has a structure including a R ₂ Fe ₁₄ B type crystal phase (main phase) which is a tetragonal compound and a grain boundary phase, Exhibits excellent magnet properties. Here, R is at least one element selected from the group consisting of rare earth elements and yttrium, and mainly contains Nd and / or Pr. Fe is iron and B is boron, and some of these elements may be substituted by other elements. In the grain boundary phase, there are an R-rich phase having a relatively high concentration of the rare earth element R and a B-rich phase having a relatively high concentration of boron.

Hereinafter, a rare earth-iron-boron rare earth sintered magnet is referred to as an “RTB-based sintered magnet”. Here, “T” is a transition metal element mainly composed of iron. In an R-T-B based sintered magnet, the R ₂ T ₁₄ B phase (main phase) is a ferromagnetic phase that contributes to the magnetization action, and the R-rich phase present in the grain boundary phase is a low-melting nonmagnetic phase. is there.

  The RTB-based sintered magnet is formed by compressing a fine powder (average particle size: several μm) of an RTB-based sintered magnet alloy (mother alloy) with a press machine and then sintering the powder. Manufactured by. After sintering, an aging treatment is performed as necessary. The mother alloy used for the production of the RTB-based sintered magnet is suitably produced by using an ingot method by die casting or a strip casting method in which the molten alloy is rapidly cooled using a cooling roll.

  In order to produce an R—Fe—B sintered magnet having a high coercive force, a part of Nd and Pr widely used as the rare earth element R is replaced with Dy, Ho, and / or Tb, which are heavy rare earth elements. (For example, Patent Document 1). Since Dy, Tb, and Ho are rare earth elements having a high anisotropic magnetic field, the effect of increasing the coercive force is exhibited by substituting Nd at the site of the rare earth element R of the main phase.

  On the other hand, in order to develop a coercive force, a small amount of Al or Cu has been added from the beginning of the development of an RTB-based sintered magnet (eg, Patent Document 2). Al and Cu mixed in the raw material alloy as an inevitable impurity at the time when the R-T-B system sintered magnet was developed then realized the high coercive force of the R-T-B system sintered magnet. It has been found that this is an indispensable additive element. On the contrary, it is known that if Al and Cu are intentionally excluded, the coercive force of the RTB-based sintered magnet shows only a very low value and is not practically used.

  Patent Documents 3 to 5 disclose RTB-based sintered magnets to which various metal elements including Ni are added.

  Patent Document 3 discloses a permanent magnet containing 8 to 30% of Nd, 2 to 28% by weight of B, 4.5% or less of Ni as one of selective additive elements, and the balance being substantially Fe. ing.

  Patent Document 4 contains Nd of 8 to 30%, B of 2 to 28% by weight, 0 to 50% of Co, and Ni as a selective additive element of 8.0% or less, with the balance being substantially Fe. A permanent magnet having a high maximum energy product is disclosed.

In Patent Document 5, at least one of Nd and Pr is 14 to 18 atom%, B is 9 to 18 atom%, additive element A is 0.5 to 5 atom% in total, and the balance is substantially made of Fe. An anisotropic sintered magnet having a maximum energy product and coercivity is disclosed. As additive element A, Al 0.2-2.0 atomic%, Si 0.05-0.5 atomic%, Cu 0.03-0.6 atomic%, Cr 0.02-3.0 atomic%, Mn 0.05- 1.0 atomic% and Ni 0.02 to 1.0 atomic% are described.
JP-A-60-32306 JP-A-5-234733 JP 59-89401 A JP 59-132104 A Japanese Unexamined Patent Publication No. 1-2220803

  Dy, Tb, and Ho have the effect of increasing the coercive force as the amount added increases. However, since Dy, Tb, and Ho are rare elements, the practical application of electric vehicles will progress in the future. As demand for highly heat-resistant magnets used in electric vehicle motors and the like expands, there is a concern that raw material costs will increase as a result of tight Dy resources. For this reason, development of the Dy usage-amount reduction technology in a high coercive force magnet is strongly demanded. On the other hand, the addition of Al or Cu improves the coercive force, but has the problem of reducing the residual magnetic flux density.

  The present invention has been made to solve the above-mentioned problems, and its main purpose is to exhibit a coercive force equivalent to the coercive force when Al or Cu is added, as compared with the case where Al or Cu is added. Another object is to provide a rare earth sintered magnet with improved residual magnetic flux density.

  The rare earth sintered magnet of the present invention is at least one element selected from the group consisting of 12.0 atomic% to 15.0 atomic% rare earth element (Nd, Pr, Gd, Tb, Dy, and Ho, Nd and / or Pr at least 50%), 5.5 atomic% to 8.5 atomic% boron (B), 0.005 atomic% to 0.40 atomic% nickel (Ni), and the balance Of iron (Fe) and inevitable impurities.

  In a preferred embodiment, the composition ratio of Ni is 0.005 atomic% to 0.20 atomic%.

  In a preferred embodiment, the inevitable impurities include Al, and the Al content is 0.4 atomic% or less.

  Another method of manufacturing a rare earth sintered magnet according to the present invention is at least one selected from the group consisting of 12.0 atomic% to 15.0 atomic% of rare earth elements (Nd, Pr, Gd, Tb, Dy, and Ho). Element containing Nd and / or Pr of 50% or more), 5.5 atomic% to 8.5 atomic% boron (B), 0.005 atomic% to 0.40 atomic% Ni, And a step of preparing an alloy containing the remaining iron (Fe) and inevitable impurities, a step of pulverizing the alloy to produce a powder, and a step of sintering the powder.

  The method for producing a rare earth sintered magnet according to the present invention comprises 12.0 atomic% to 15.0 atomic% of a rare earth element (at least one element selected from the group consisting of Nd, Pr, Gd, Tb, Dy, and Ho) An alloy containing Nd and / or Pr of 50% or more), 5.5 atomic% to 8.5 atomic% of boron (B), and the balance of iron (Fe) and inevitable impurities. A step of preparing, a step of pulverizing the alloy to prepare a powder, a step of adding 0.005 atomic% to 0.40 atomic% of nickel (Ni) to the powder, and preparing a Ni-added powder And a step of sintering the Ni-added powder.

  The rare earth sintered magnet of the present invention exhibits a coercive force equivalent to that of a conventional R—Fe—B based sintered magnet to which Cu or Al is added due to the action of Ni added in a small amount, and more than those magnets. A high residual magnetic flux density can be shown.

  Conventionally, attempts have been made to add various elements for the purpose of increasing the coercive force. However, the RTB-based sintered magnet to be compared contained Al and Cu as a matter of course along with inevitable impurities. This is because the coercive force obtained when these elements are not contained is too low.

  However, the present inventor added various amounts of various elements to the basic ternary composition of the Nd—Fe—B based sintered magnet in which no addition of Al or Cu was intentionally added. In this case, the present inventors have found that the effect of greatly improving the coercive force is exhibited without reducing the residual magnetic flux density, and the present invention has been completed.

  Conventionally, there has been no attempt to add Ni to an R-T-B sintered magnet. For example, Patent Documents 3 to 5 describe that Ni is added to an RTB-based sintered magnet, although the purpose of addition is different. However, since R and T-B sintered magnets to be added had naturally added Al or Cu (intentionally or unavoidably), the effect of increasing the coercive force by adding Ni is not limited to Al or Cu. Or it was buried in the coercive force increase effect by Dy etc. and was not observed. Moreover, as will be described in detail later, the Ni addition effect found by the inventors of the present application is obtained by suppressing the addition amount to an extremely low and narrow range, and is taught in Patent Documents 2 to 4 and the like. With the added amount, the Ni addition effect could not be properly obtained.

  As described above, the present invention was made on the basis of new knowledge that can be understood only by adding an extremely small amount of Ni using an RTB-based sintered magnet having a basic ternary composition as a comparative example. It is.

  According to the study of the present inventor, the added Ni is considered to exist mainly in the grain boundary phase of the sintered magnet. In RTB-based sintered magnets, it is known that the grain boundary phase plays an important role in the expression of the coercive force, and a small amount of added Ni increases the coercive force in the grain boundary phase. Presumed to have some effect. However, the details of the coercivity increasing mechanism due to the addition of Ni are currently unknown, and the inventor of the present application is eagerly trying to elucidate.

  Hereinafter, preferred embodiments of the rare earth sintered magnet of the present invention will be described.

(Embodiment 1)
[Raw material alloy]
First, 12.0 atomic% to 15.0 atomic% of rare earth element R, 5.5 atomic% to 8.5 atomic% of B, 0.005 atomic% to 0.40 atomic% of Ni, and the balance A raw material alloy containing Fe and inevitable impurities is prepared. Here, R is at least one element selected from the group consisting of Nd, Pr, Gd, Tb, Dy, and Ho, and includes 50% or more of Nd and / or Pr.

  If the composition ratio of R, B, and Fe is out of the above range, the basic structure of the RTB-based sintered magnet cannot be obtained, and desired magnet characteristics cannot be exhibited. In the present invention, by adding an extremely small amount of Ni of 0.005 atomic% to 0.40 atomic%, the saturation magnetic flux density is almost reduced as compared with an R—Fe—B rare earth magnet having a basic ternary composition. In addition, the coercive force can be increased more than twice. When the composition ratio of Ni to be added is less than 0.005 atomic%, the effect of increasing the coercive force cannot be obtained. Conversely, when the composition ratio exceeds 0.40 atomic%, the coercive force decreases. For this reason, the composition ratio of Ni is set in the range of 0.005 atomic% or more and 0.40 atomic% or less. A preferable range of the composition ratio of Ni is 0.005 atomic% or more and 0.20 atomic% or less.

  The timing of adding Ni is arbitrary as long as it is before the sintering step. You may add at the time of melt | dissolution of a raw material alloy, you may prepare the mother alloy which does not contain Ni element, and may add as a fine powder before grind | pulverizing by a jet mill, or after grind | pulverizing. The fine Ni powder may be produced by pulverizing Ni metal, or may be a Ni oxide powder. The average particle diameter of the Ni metal or Ni compound in the powder state can be set to 0.5 μm to 50 μm, for example. This is because, within such a particle size range, an appropriate sintered body can be obtained by mixing with other alloy powders.

  The sintered magnet of the present invention may contain Al and Cu as inevitable impurities. However, when the Al content increases, the residual magnetic flux density decreases, so the Al content is 0.4. It is preferable to adjust to atomic% or less. Further, 50 atomic% or less of Ni to be added may be replaced with another metal element. For example, 50 atomic% or less of Ni may be substituted with at least one element selected from the group consisting of Ag, Pd, Pt, Cu, Au, Ga, and In.

  In order to produce a mother alloy used for manufacturing a sintered magnet according to the present invention, for example, an ingot casting method or a rapid cooling method (such as a strip casting method or a centrifugal casting method) can be used. Hereinafter, a method for producing a raw material alloy will be described by taking as an example the case of using a strip casting method.

  First, an alloy having the above composition is melted by high frequency melting in an argon atmosphere to form a molten alloy. Next, after this molten alloy is maintained at 1350 ° C., the molten alloy is rapidly cooled by a single roll method to obtain, for example, a flaky alloy ingot having a thickness of about 0.3 mm. The rapid cooling conditions at this time are, for example, a roll peripheral speed of about 1 m / second, a cooling speed of 500 ° C./second, and supercooling of 200 ° C. The quenched alloy slab thus produced is pulverized into flakes having a size of 1 to 10 mm 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.

  In such a raw material alloy stage, Ni may already be added, or may be added after the pulverization step described below.

[Coarse grinding process]
The raw material alloy slab coarsely crushed into flakes is inserted into 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 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, it is preferable that the embrittled raw material alloy is further crushed and cooled by a cooling device such as a rotary cooler. When the raw material is taken out in a relatively high temperature state, the time for the cooling process by a rotary cooler or the like may be made 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 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.

[Press molding]
In the present 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 Tesla (T).

[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, 1000-1100 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. Thereafter, sintering proceeds and a sintered magnet is formed. After sintering, an aging treatment is performed as necessary.

Examples of the present invention will be described below.
Example 1
An alloy consisting of Nd: 14.1 atomic%, B: 6.1 atomic%, Ni: 0.05 to 0.6 atomic%, Al: 0.05 atomic%, and the balance Fe is prepared. A sintered magnet was produced by the production method (Example 1). On the other hand, Comparative Example 1 was produced in the same manner as in Example 1 except that a mother alloy having the same composition as in Example 1 was used except that Ni was not added.

  The average particle size of the powder before press molding was 4.4 to 4.6 μm. Molding was performed in a 1.0 T magnetic field. After molding, a sintering process at 1000 to 1100 ° C. for 4 hours and an aging treatment at 580 to 660 ° C. for 2 hours were performed. The obtained sintered body had a rectangular parallelepiped shape of 11 mm × 10 mm × 18 mm.

FIG. 1 is a graph showing the relationship between the amount of added Ni and the magnet characteristics. The left vertical axis of the graph is the coercive force H _cJ (kA / m), and the right vertical axis is the residual magnetic flux density B _r (T). Measurement of coercivity are indicated by "○", the measured value of the residual magnetic flux density B _r is shown by "◆".

As can be seen from FIG. 1, by adding only 0.05 atomic% of Ni, the value (about approx. 2 times) compared to the coercive force H _cJ (about 340 kA / m) of Comparative Example 1 (without Ni addition) It can be seen that it increases to about 800 kA / m). In the example of FIG. 1, the coercive force H _cJ shows a peak value when the Ni addition amount is about 0.05 atomic%. When the amount of added Ni exceeds 0.4 atomic%, the effect of adding Ni gradually decreases. On the other hand, the residual magnetic flux density B _r is, Ni amount is equal to or less than 0.4 atomic%, hardly changes.

  According to a further detailed experiment, it has been found that the effect of Ni addition is manifested when the Ni addition amount is 0.005 atomic% or more. From the above, in the present invention, the amount of Ni added is set in the range of 0.005 atomic% to 0.4 atomic%.

(Example 2)
An alloy composed of Nd: 14.1 atomic%, B: 6.1 atomic% and the balance Fe was prepared, and sintered magnets were manufactured by the manufacturing method of the above-described embodiment (Example 2 and Comparative Example 2). In this example, 0.02 to 0.5 atomic% of Ni powder was mixed with the powder of the alloy before the press molding step, and in Comparative Example 2, Ni powder was not mixed. Ni was mixed with the alloy powder in two forms, Ni metal powder or NiO powder.

  The average particle size of the powder before press molding was 4.6 μm. The press molding was performed in a 1.0 T magnetic field. After the press molding, a sintering process at 1000 to 1100 ° C. for 4 hours and an aging treatment at 580 to 620 ° C. for 2 hours were performed. The obtained sintered body had a rectangular parallelepiped shape of 11 mm × 10 mm × 18 mm.

FIG. 2 is a graph showing the relationship between the Ni addition amount and the coercive force H _cJ . In FIG. 2, the measurement result when the Ni metal powder is added is indicated by “◯”, and the measurement result when the NiO powder is added is indicated by “x”.

  As can be seen by comparing FIG. 1 and FIG. 2, the effect of adding a small amount of Ni does not depend on the timing of addition. It may be added from the alloy stage before Ni grinding, or may be added after powdering. As is clear from FIG. 2, Ni may be added in the form of a Ni compound such as an oxide or in the form of Ni metal.

(Example 3)
An alloy having the composition shown in Table 1 below was prepared, and sintered magnets (Example 3 and Comparative Example 3) were prepared by the manufacturing method of the above-described embodiment.

  The average particle size of the powder before press molding was 4.5 μm. Molding was performed in a 1.0 T magnetic field. After molding, a sintering process at 1000 to 1100 ° C. for 4 hours and an aging treatment at 500 to 620 ° C. for 2 hours were performed. The obtained sintered body had a rectangular parallelepiped shape of 11 mm × 10 mm × 18 mm.

  The composition and magnetic properties of Example 3 and Comparative Example 3 are shown in Table 1 below.

As can be seen from Table 1, be added Cu or Ag besides Ni, it is possible to obtain a high residual magnetic flux density B _r and coercivity H _cJ. However, in the case where the total amount of Ni and Cu was 0.6 atomic%, which was larger than 0.4 atomic%, the coercive force H _cJ was lowered even when Ni was added.

Example 4
The above-described embodiment is prepared by preparing an alloy including Nd: 14.1 atomic%, B: 6.1 atomic%, Ni: 0.05 atomic%, Al: 0.05 to 0.5 atomic%, and the balance Fe. Sintered magnets were produced by the manufacturing method (Example 4 and Comparative Example 4).

  The average particle size of the powder before press molding was 4.5 to 4.7 μm. Molding was performed in a 1.0 T magnetic field. After the molding, a sintering process for 4 hours at 1000 to 1060 ° C. and an aging treatment for 2 hours at 600 to 620 ° C. were performed. The obtained sintered body had a rectangular parallelepiped shape of 11 mm × 10 mm × 18 mm.

FIG. 3 is a graph showing the relationship between the residual magnetic flux density _Br and the Al addition amount. It can be seen that when the Al addition amount exceeds 0.40 atomic%, the saturation magnetic flux density is lowered, and the effect of adding a small amount of Ni may be impaired.

(Example 5)
An alloy consisting of Nd: 11.4 atomic%, Pr: 2.8 atomic%, B: 6.1 atomic%, Ni: 0.05 atomic%, and the balance Fe is prepared. Example 5 was produced. Measurement of the magnetic properties for Example 5, the coercive force H _cJ is 855kA / m, residual flux density B _r was 1.39T. It was confirmed that the effects of the present invention can be achieved even when a rare earth element such as Pr is added in addition to Nd.

  The rare earth sintered magnet of the present invention exhibits a coercive force equivalent to that of a conventional R—Fe—B rare earth sintered magnet to which Cu or Al is added, and exhibits a higher residual magnetic flux density than those magnets. For this reason, the rare earth sintered magnet of the present invention is suitably used for various applications in which both coercive force and residual magnetic flux density are required to have high values.

It is a graph which shows the relationship between Ni addition amount and a magnet characteristic. The left vertical axis of the graph is the coercive force H _cJ (kA / m), and the right vertical axis is the residual magnetic flux density B _r (T). Measurement of coercive force indicated by "○", the measured value of the residual magnetic flux density B _r is shown by "◆". It is a graph which shows the relationship between Ni addition amount and coercive force _HcJ . In FIG. 2, the measurement result when the Ni metal powder is added is indicated by “◯”, and the measurement result when the NiO powder is added is indicated by “x”. It is a graph which shows the relationship between residual magnetic flux density _Br and Al addition amount.

Claims (3)

12.0 atomic% to 15.0 atomic% of a rare earth element (Nd and / or Pr),
5.5 atomic percent to 8.5 atomic percent boron (B),
0.02 atomic% to 0.1 atomic% nickel (Ni ) ,
The balance iron (Fe) and inevitable impurities;
Containing
A rare earth sintered magnet in which the content of Al contained as an inevitable impurity is 0.4 atomic% or less. 12.0 atomic% to 15.0 atomic% rare earth element (Nd and / or Pr), 5.5 atomic% to 8.5 atomic% boron (B), 0.02 atomic% to 0.1 Preparing an alloy containing atomic% nickel (Ni ) , the remaining iron (Fe) and unavoidable impurities, and the content of Al contained as unavoidable impurities is 0.4 atomic% or less; ,
Crushing the alloy to produce a powder;
Sintering the powder;
A method for producing a rare earth sintered magnet comprising: 12.0 atomic% to 15.0 atomic% of rare earth elements (Nd and / or Pr), 5.5 atomic% to 8.5 atomic% of boron (B), the balance iron (Fe) and inevitable A step of preparing an alloy containing impurities and having an Al content of 0.4 atomic% or less contained as unavoidable impurities;
Crushing the alloy to produce a powder;
Adding 0.02 atomic% to 0.1 atomic% of nickel (Ni ) to the powder to produce a Ni-added powder;
Sintering the Ni-added powder;
A method for producing a rare earth sintered magnet comprising:

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