JP2007129106A - Rare-earth alloy system binderless magnet and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnet excellent in a dimensional accuracy and a degree of freedom of shape, and excellent in a heat resistance and magnetic characteristic than a bond magnet. <P>SOLUTION: A method for manufacturing a rare-earth alloy binderless magnet comprises the steps of preparing the rare-earth system quenching alloy magnetic powder (A), forming an compression molding having a volume percentage of not less than 70% nor more than 95% of the rare-earth system quenching alloy magnetic powder sharing to total by cool compression molding the rare-earth system quenching alloy magnetic powder without the use of a resin binder (B), heat treating the compression molding at the temperature of not less than 350°C nor more than 800°C after the step (B) and forming a magnetic body (C), and forming a vapor metal plating film on the surface of the magnet body (D). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rare earth alloy binderless magnet having excellent strength and a method for producing the same, and relates to a magnet produced by compression molding rare earth quenched alloy magnet powder under an ultrahigh pressure and having a vapor phase plating film formed on the surface. .

  Bond magnets in which a resin binder is added to powders of rare-earth quenched alloy magnets are excellent in dimensional accuracy and flexibility in shape, and are widely used in applications such as electronic equipment and electrical components. However, the heat resistance temperature of such a bonded magnet is limited by the heat resistance temperature of the resin binder used for bonding the magnet powder in addition to the magnetic heat resistance temperature of the magnet powder used. For example, in the case of a compression bonded magnet using a thermosetting epoxy resin, since the heat resistant temperature of the thermosetting epoxy resin is low, the upper limit temperature at which the magnet can be used regularly is as low as about 100 ° C. at the maximum. In addition, bond magnets using rare earth-based rapidly quenched alloy magnet powder contain iron and rare earths that are easily oxidized, so when used as they are without any surface treatment, magnetic properties are deteriorated and rust is generated due to oxidative corrosion. It may be necessary to perform some surface treatment because it may not meet the required characteristics, but a normal bonded magnet contains an insulating resin binder, so electroplating or metal deposition It is also difficult to perform surface treatment such as coating treatment.

  Furthermore, since a normal bonded magnet includes a resin binder, the volume ratio of the magnet powder cannot be increased to more than 83%. Since the resin binder does not contribute to the manifestation of magnet characteristics, the magnetic characteristics of the bonded magnet must be lower than that of the sintered magnet.

In the case of a compression bonded magnet having a relatively high volume ratio of magnet powder, the volume ratio of magnet powder is about 83%, but the maximum energy product is still limited to about 96 kJ / m ³ (12 MGOe).

  In recent years, for example, micro ring magnets having a diameter of 10 mm or less are used for small spindle motors, stepping motors, and various small sensors. In such applications, realization of permanent magnets having excellent moldability and improved magnetic properties is strongly desired, but the magnetic properties of bonded magnets are becoming insufficient.

  As a magnet having a volume ratio of magnet powder higher than that of a bond magnet, a full-density magnet is known. Patent Document 1 discloses a full-density magnet made from a nanocomposite quenched alloy. A full-density magnet is manufactured by compressing a rapidly cooled alloy magnet powder without using a resin binder and increasing the density.

  Patent Document 2 discloses compression molding by applying a pressure of 20 MPa or more and 80 MPa or less to a nanocomposite magnet powder at a temperature of 550 ° C. or more and 720 ° C. or less. The density of the full-density magnet thus produced achieves 92% or more of the true magnet density.

Patent Document 3 discloses a binderless magnet having a magnetic powder purity of 99% surrounded by a wrapping material, and Patent Document 4 discloses a powder magnetic core manufactured from nanocrystalline magnetic powder.
JP 2004-14906 A JP 2000-348919 A JP-A-10-270236 JP 2004-349585 A

  A fluence magnet as disclosed in Patent Document 1 is expected to have higher characteristics than a bonded magnet because of its high volume ratio of magnet powder, but a hot press technology such as hot pressing is used, so that the press cycle is long. Inferior to mass productivity. As a result, the production cost of the magnet is greatly increased, so that practical application is difficult.

  The magnet disclosed in Patent Document 2 is manufactured by compressing a magnet powder while heating it to a high temperature by a discharge plasma sintering method or the like. This technology also has a long press cycle and is inferior in mass productivity as in hot press.

  Patent Document 3 does not disclose a specific manufacturing method, and it is unclear how a high magnetic powder volume ratio is realized. Moreover, in the powder magnetic core disclosed in Patent Document 4, the magnet powder particles are bonded together by glass. The volume ratio of glass is considered to be approximately the same as the volume ratio of the resin binder in the conventional bonded magnet.

  As described above, the conventional technique of forming magnet powder without using a resin binder can achieve low mass productivity or only a magnetic powder volume ratio comparable to that of a bonded magnet.

  On the other hand, a high-temperature sintering process of 1000 to 1200 ° C. is indispensable in order to produce a sintered magnet in which magnetic powders are bonded substantially without gaps. In the sintering process, a liquid phase is formed, and a grain boundary phase including a rare earth-rich phase is generated. The grain boundary phase plays an important role for the development of coercive force, but since the green powder compact shrinks greatly in the sintering process, the shape change after the pressing process is large, resulting in dimensional accuracy and shape formation. Inferior to bonded magnets in terms of freedom.

  The present invention has been made to solve the above-mentioned problems, and its main purpose is to provide a magnet that is excellent in dimensional accuracy and freedom of shape, and that is superior in heat resistance and magnetic properties than a bonded magnet. It is in.

  The rare earth alloy binderless magnet of the present invention is a magnet having a magnet body in which particles of a rare earth quenching alloy magnet powder are bonded without a resin binder, and a vapor phase plating film provided on the surface of the magnet body. The volume ratio of the rare earth-based rapidly quenched alloy magnet powder in the entire magnet body is 70% or more and 95% or less.

  In a preferred embodiment, the quenched alloy magnet powder particles are bonded by precipitates from the quenched alloy magnet powder particles.

  In a preferred embodiment, the quenched alloy magnet powder particles are formed of an iron-based rare earth alloy containing boron, and the precipitate is at least one selected from the group consisting of iron, rare earth, and boron. It is composed of elements.

  In a preferred embodiment, cracks are formed in the particles of the quenched alloy magnet powder, and at least a part of the precipitation portion is present in the cracks.

  In a preferred embodiment, the vapor phase metal plating film is a metal composed of at least one element selected from the group consisting of Al, Zn, Sn, Ni, Ti, and Cu, or an alloy, oxide, or the like of the metal. It includes at least one layer made of nitride.

  In a preferred embodiment, the particles of the rare earth-based quenched alloy magnet powder contain one or more ferromagnetic crystal phases and have an average crystal grain size in the range of 10 nm to 300 nm.

  In a preferred embodiment, the particles of the rare earth rapidly quenched alloy magnet powder have a nanocomposite magnet structure containing a hard magnetic phase and a soft magnetic phase.

In a preferred embodiment, a density of ^{5.5g / cm 3 ~7.0g / cm 3} .

In a preferred embodiment, the composition formula T _100-xyz Q _x R _y M _z (T is a transition metal element including Fe or one or more elements selected from the group consisting of Co and Ni and Fe, Q is At least one element selected from the group consisting of B and C, R is at least one rare earth element substantially free of La and Ce, M is Ti, Al, Si, V, Cr, Mn, Cu Zn, Ga, Zr, Nb, Mo, Ag, Hf, Ta, W, Pt, Au, and at least one metal element selected from the group consisting of Pb) and a composition ratio x, y, and Each z has a composition satisfying 10 <x ≦ 35 atomic%, 2 ≦ y ≦ 10 atomic%, and 0 ≦ z ≦ 10 atomic%.

In a preferred embodiment, the composition formula T _100-xyz Q _x R _y M _z (T is a transition metal element including Fe or one or more elements selected from the group consisting of Co and Ni and Fe, Q is At least one element selected from the group consisting of B and C, R is at least one rare earth element substantially free of La and Ce, M is Ti, Al, Si, V, Cr, Mn, Cu Zn, Ga, Zr, Nb, Mo, Ag, Hf, Ta, W, Pt, Au, and at least one metal element selected from the group consisting of Pb) and a composition ratio x, y, and Each z has a composition satisfying 4 <x ≦ 10 atomic%, 6 ≦ y <12 atomic%, and 0 ≦ z ≦ 10 atomic%.

  The method of manufacturing a rare earth alloy binderless magnet according to the present invention includes a step (A) of preparing a rare earth quenching alloy magnet powder, and compressing the rare earth quenching alloy magnet powder cold without using a resin binder. By forming, a step (B) of forming a compression-molded body in which the volume ratio of the rare earth-based quenched alloy powder occupying the whole is 70% to 95%, and 350 ° C to 800 ° C after the step (B). It includes a step (C) of forming a magnet body by heat-treating the compression molded body at the following temperature, and a step (D) of forming a vapor phase metal plating film on the surface of the magnet body.

  In a preferred embodiment, the step (D) includes a step of inserting the magnet body into a film forming apparatus and performing film formation while moving the magnet body under reduced pressure.

  In a preferred embodiment, in the step (B), the quenched alloy magnet powder for a rare earth quenched magnet is compressed at a pressure of 500 MPa to 2500 MPa.

In a preferred embodiment, the heat treatment in the step (C) is performed in an inert gas atmosphere having a pressure of 1 × 10 ⁻² Pa or less.

  In a preferred embodiment, the heat treatment in the step (C) is performed in an inert gas atmosphere having a dew point of −40 ° C. or lower.

  According to the present invention, since no resin binder is used, the heat resistance temperature of the magnet is not limited to the heat resistance temperature of the resin binder, and excellent heat resistance can be exhibited. Moreover, since the process of mixing and kneading the magnet powder with the resin binder is not necessary, the manufacturing cost can be reduced.

  Furthermore, according to the present invention, since the volume ratio of the magnet powder is higher than that of the bonded magnet, the magnet characteristics are improved as compared with the bonded magnet. Therefore, even with a bonded magnet, it is difficult to obtain sufficient magnet characteristics, and even a small magnet having a diameter of 4 mm or less can exhibit excellent magnet characteristics according to the present invention.

  Moreover, since the binderless magnet of the present invention has a vapor-phase plating film on the surface of the magnet body, the strength and corrosion resistance of the magnet are improved.

  The rare earth alloy binderless magnet of the present invention is a magnet in which particles of a rare earth quenching alloy magnet powder are bonded without a resin binder, and the volume ratio of the rare earth quenching alloy magnet powder in the whole is 70% or more and 95. % Or less. The particles of the rare earth-based rapidly cooled alloy magnet powder are bonded not by ordinary high-temperature sintering or hot pressing but by cold pressing (cold compression) under ultra high pressure. In addition, the cold press in the present invention means that compression molding is performed without applying heat to the die or punch of the press device, and specifically, a temperature that cannot be hot forming (for example, 500). It shall mean that the powder is compression-molded at a temperature of ℃ or less, typically 100 ℃ or less.

  As described above, hot forming such as hot pressing and high-temperature sintering are conventionally required to firmly bond rare earth-based rapidly quenched alloy magnet powder particles without using a resin binder and to form them in bulk. Has been considered. In particular, when powder particles with extremely high hardness such as Nd—Fe—B type quenching magnets are targeted, the sintering process for forming a liquid phase is advanced by heating to a high temperature exceeding 800 ° C. during compression molding. However, there was technical common sense that molding was indispensable.

  However, the present inventors have made various attempts to perform cold compression molding of rare-earth quenched alloy magnet powder without being bound by such technical common sense, and as a result, appropriately selected the mold material used for compression. If the processing accuracy is increased, it is possible to perform cold compression molding under an ultra-high pressure of 500 to 2500 MPa even with a rare earth-based rapidly cooled alloy magnet powder having a high hardness. It was found that sintering can proceed at a low temperature of 800 ° C. or lower, a binderless magnet can be formed, and that the formed binderless magnet exhibits excellent magnetic properties, and the present invention has been completed. This temperature range is the temperature required for solid-phase sintering of powdered compacts such as conventional ceramics (typically a high temperature of 1000 ° C. or higher) and liquid-phase sintering of conventional rare earth sintered magnets. It is much lower than the required temperature. By performing such low-temperature sintering, a binderless magnet can be formed while suppressing coarsening of crystal grains.

  The present inventors have investigated the reason why it has become possible to proceed with sintering at a low temperature that could not be achieved conventionally by cold compression molding under ultra-high pressure that could not be achieved conventionally. The components derived from the quenched alloy magnet powder are deposited between the individual particles of the quenched alloy magnet powder forming the binderless magnet, and the precipitates have found that the particles are bonded to each other. . It was also observed that cracks were generated in the quenched alloy magnet powder particles by cold compression molding under ultra-high pressure, and the cracks were recombined by similar precipitates.

  In the present invention, the surface and the inside of the quenched alloy magnet powder particles are cracked by cold compression under ultra-high pressure, whereby a very active new fracture surface appears on the surface and inside of the quenched alloy magnet powder particles. As it is, the mechanical strength is insufficient, but in the present invention, by performing heat treatment at a relatively low temperature after performing ultra-high pressure compression, components derived from the quenched alloy magnet powder can be removed from the newly broken surface. Precipitate. It is presumed that the precipitates thus formed are between the particles and greatly contribute to bonding. Such a precipitate component is considered to vary depending on the composition of the quenched alloy magnet, but according to the results of experiments by the inventors, it contains at least one of Fe, boron, and rare earth elements.

  Microscopic voids remain between particles bonded by such ultra-high pressure compression and heat treatment, and the volume ratio of such voids is 5% or more and 30% with respect to the total volume of the molded magnet. It is in the following range. After compression molding, a part of such voids may be filled with a resin or a low melting point metal (for example, zinc, tin, Al-Mn) for the purpose of sealing or the like, but such a resin is mainly used. The main bond between the particles of each of the quenched alloy magnet powders that does not function as a binder and forms the magnet of the present invention is made by the precipitates.

  In a conventional rare earth sintered magnet produced by high-temperature sintering, crystal grains (grains) functioning as a main phase are formed from an Nd—Fe—B compound having hard magnetism. On the other hand, since a grain boundary phase made of a nonmagnetic material exists between crystal grains, there are almost no voids in the rare earth sintered magnet. This rare earth sintered magnet is known to be extremely important for developing a high coercive force by having a nucleation type magnetic property development mechanism in which main phase crystal grains are partitioned by a grain boundary phase. .

  In contrast, in the rare earth alloy binderless magnet of the present invention, there is no alloy that functions as a grain boundary phase between the individual powder particles bonded to each other. The reason why high coercive force can still be exhibited is that the average crystal grain size of the fine metal structure constituting the magnet powder used in the binderless magnet is adjusted to be smaller than the “single domain crystal grain size”. It is. If the average crystal grain size is equal to or less than the single domain grain size, each crystal grain has a single domain structure and is inherent to a nucleation type that assumes a multi-domain structure as found in Nd-Fe-B rare earth sintered magnets. Instead of coercive force, each crystal grain in a single magnetic domain is linked by exchange interaction, and has a fine crystal type magnetic property expression mechanism that expresses intrinsic coercive force. Even if the sintering process is not performed at a temperature higher than the sintering temperature, a grain boundary phase formed by liquid phase sintering is not required, so that high intrinsic coercive force and excellent demagnetization curve squareness can be realized. .

  In the present invention, it is preferable to use a nanocomposite magnet powder having an average crystal grain size on the order of nanometers, or an amorphous quenched alloy magnet powder in which a fine crystal structure of nanometer order is formed by crystallization heat treatment. it can.

Magnet powder sold by MQI (so-called MQ powder) can also be used as the magnet powder of the present invention. However, since these contain a rare earth-rich phase, rare earth oxides are formed during sintering, and the magnet powder. There is a possibility that it is difficult to bond each other. For this reason, when these magnet powders are sintered, it is desirable to perform the sintering process in a vacuum of 10 ⁻² Pa or less.

  In contrast, a nanocomposite magnet containing a hard magnetic phase and a soft magnetic phase does not have a rare earth-rich phase. Therefore, after compression molding under cold and ultra-high pressure, oxidation of the rare earth proceeds in an inert atmosphere. The heat treatment step can be performed without causing the heat treatment. Although heat treatment after compression molding is not indispensable, by performing such heat treatment, it is possible to further increase the mechanical strength of the magnet body that is compression molded under cold and ultra high pressure. Therefore, for the rare earth binderless magnet of the present invention, it is preferable to use a nanocomposite magnet powder containing an iron-based boride in a soft magnetic phase with a low rare earth content.

As such a nanocomposite magnet powder, a rare earth nanocomposite magnet powder whose composition formula is represented by T _100-xyz Q _x R _y M _z can be suitably used. Here, T is a transition metal element containing Fe or one or more elements selected from the group consisting of Co and Ni and Fe, and Q is at least one element selected from the group consisting of B and C , R is at least one rare earth element substantially free of La and Ce, M is Ti, Al, Si, V, Cr, Mn, Cu, Zn, Ga, Zr, Nb, Mo, Ag, Hf, At least one metal element selected from the group consisting of Ta, W, Pt, Au, and Pb. The composition ratios x, y, and z satisfy 10 <x ≦ 35 atomic%, 2 ≦ y ≦ 10 atomic%, and 0 ≦ z ≦ 10 atomic%, respectively.

In the nanocomposite magnet powder having such a composition, the hard magnetic phase constituting the magnet is formed from crystal grains of R ₂ Fe ₁₄ B type compound, and the soft magnetic phase is formed from crystal grains of iron-based boride or α-Fe. Is done. The composite magnet powder is produced by rapidly solidifying a molten alloy having the above composition by a liquid quenching method.

In the present invention, a nanocomposite magnet containing an α-Fe phase as a main soft magnetic phase or an R ₂ Fe ₁₄ B single-phase magnet with few rare earth-rich phases existing at grain boundaries can also be used. As such a nanocomposite magnet, a rare earth nanocomposite magnet powder whose composition formula is represented by T _100-xyz Q _x R _y M _z can be suitably used. Here, T is a transition metal element including Fe or one or more elements selected from the group consisting of Fe or Co and Ni and Fe, Q is at least one element selected from the group consisting of B and C, R is at least one rare earth element substantially free of La and Ce, M is Ti, Al, Si, V, Cr, Mn, Cu, Zn, Ga, Zr, Nb, Mo, Ag, Hf, Ta , W, Pt, Au, and Pb, and the composition ratios x, y, and z are 4 <x ≦ 10 atomic%, 6 ≦ y <, respectively. 12 atomic% and 0 ≦ z ≦ 10 atomic% are satisfied.

  In the binderless magnet according to the present invention, the volume ratio of the magnet powder is in the range of 70% to 95% of the whole, but in order to exhibit the permanent magnet characteristics superior to the conventional bonded magnet, It is preferable to set the lower limit to 75% or more. Since the magnet characteristics improve as the volume ratio of the magnet powder increases, the lower limit of the volume ratio is more preferably set to 85% or more. However, the upper limit of the volume ratio of the magnet powder is preferably 92% and more preferably 90% in consideration of the strength of the molded body, the durability of the mold, and mass productivity.

When a magnet powder containing an R ₂ Fe ₁₄ B type compound as a main phase is used, the density of the finally obtained binderless magnet is in the range of 5.5 g / cm ^{3 to} 7.0 g / cm ³ . A preferable range of the density of the binderless magnet is 6.3 g / cm ³ or more and 6.7 g / cm ³ or less, and a more preferable range is 6.5 g / cm ³ or more and 6.7 g / cm ³ or less. The compression bonded magnet using a conventional resin binder, the density of the entire magnet body is in the range of about ^{5.5g / cm 3 ~6.2g / cm 3} . As can be seen by comparing the two, the binderless magnet of the present invention has a relatively higher density, and as a result, the magnetic properties are also excellent.

  In the binderless magnet of the present invention, the average crystal grain size of the fine metal structure constituting the magnet powder used is preferably in the range of 10 nm to 300 nm. When the average crystal grain size is smaller than this range, the intrinsic coercive force is lowered. When the average grain size is larger than the upper limit of this range, the exchange interaction acting between the crystal grains is lowered. However, even if the above average crystal grain size exceeds the single domain crystal grain size, the average crystal grain size can be used in a specific usage environment (when the operating point of the magnet is high) if the average crystal grain size is 5 μm or less. Is possible.

  The binderless magnet of the present invention has a vapor plating film on the surface. The magnet body before the formation of the plating film has sufficient strength to withstand normal use, but it is inherently weaker in mechanical strength than conventional high-temperature sintered magnets, and does not crack or chip. Prone to occur. For this reason, if you attempt to use a magnet body that does not have a plating coating on the motor, etc., the magnet body will be destroyed when the motor is installed, or particles that have fallen off the surface of the magnet body when the motor is installed inside the part This may cause various problems such as splashing on the motor and affecting motor operation. Therefore, it can be suitably used for a motor or the like by supplementing the mechanical strength of the magnet body by having a coating film of a metal, its oxide or nitride on the surface.

(Production method)
Hereinafter, a preferred embodiment of a method for producing a rare earth alloy binderless magnet according to the present invention will be described.

  First, a rare earth-based rapidly cooled alloy magnet powder used for manufacturing the binderless magnet of the present invention is prepared. This powder is manufactured through a pulverization step after quenching a molten alloy having the above-described composition by a roll quenching method such as a melt spinning method or a strip casting method. Instead of using such a roll quenching method, the molten alloy can also be manufactured by quenching by an atomizing method. The average particle size of the rare earth quenched alloy magnet powder is preferably 300 μm or less. The average particle size of the powder is more preferably in the range of 30 μm to 250 μm, and still more preferably in the range of 50 μm to 200 μm. Moreover, it is preferable that a particle size distribution has two peaks from a viewpoint of reducing the space between the particles after compression molding and increasing the density of the magnet body.

  Next, the rare earth-based rapidly quenched alloy magnet powder thus obtained is molded by being compressed at an ultrahigh pressure in the cold. In a preferred embodiment of the present invention, since the cold compression molding is performed in a temperature environment of 500 ° C. or lower, typically 100 ° C. or lower, crystallization of the powder particles does not proceed during the compression molding. In the present invention, the powder particles before compression molding may be in a substantially crystallized state as a whole, or may have many amorphous parts. When the powder particles contain a lot of amorphous phase, it is preferable to perform heat treatment for crystallization after ultra-high pressure molding, but in the sintering process performed after ultra-high pressure molding, heat treatment for crystallization is performed. You may also serve.

  In order to reduce die damage during cold compression molding under ultra-high pressure, it is necessary to add and mix a lubricant such as calcium stearate to the rare-earth quenched alloy magnet powder before molding. preferable.

  FIG. 1 is a cross-sectional view showing a schematic configuration of an ultra-high pressure powder press apparatus that can be suitably used in the practice of the present invention. The apparatus of FIG. 1 is an apparatus capable of uniaxially pressing the powder material 2 filled in the cavity at high pressure, and defines a die 4 having an inner surface that defines the side surface of the cavity, and a bottom surface of the cavity. And a lower punch 6 having a lower pressure surface and an upper punch 8 having an upper pressure surface facing the lower pressure surface. The die 4, the lower punch 6 and / or the upper punch 8 are moved up and down by a driving device (not shown).

  In the state shown in FIG. 1A, the upper part of the cavity is opened, and the magnet powder 2 is filled in the cavity. Thereafter, as shown in FIG. 1B, the upper punch 8 is lowered or the die 4 and the lower punch 6 are relatively raised, whereby the magnet powder 2 in the cavity is compression-molded.

  The die 4 and the upper and lower punches 6 and 8 are made of, for example, cemented carbide or powder high speed. The die 4 and the upper and lower punches 6 and 8 are not limited to those described above, and high strength materials such as SKS, SKD, and SKH can also be used.

  These high-strength materials are hard, but have brittle properties, and therefore easily break when the pressing direction is slightly shifted. Therefore, in order to enable the ultra-high pressure forming as in the present invention, it is necessary to set the accuracy of the deviation and inclination of the central axis of the die 4 and the upper and lower punches 6 and 8 to 0.01 mm or less. If this axial deviation or axial inclination is large, the upper and lower punches 6 and 8 are buckled and damaged when an ultrahigh pressure is applied. This problem occurs remarkably because the shaft diameters of the upper and lower punches 6 and 8 become smaller as the size of the compact becomes smaller.

  The ultra-high pressure powder press apparatus used in the present embodiment is provided with the configuration shown in FIG. 2 in order to prevent damage to the upper and lower punches 6 and 8 and to stably carry out an ultra-high pressure press that has been difficult in the past. Is desirable. Hereinafter, the configuration of the high-pressure powder press apparatus shown in FIG. 2 will be described.

  In the apparatus of FIG. 2, the fixed die plate 14 fixes the die 4, and the lower punch 6 is inserted into the through hole of the die 4. The lower punch 6 moves up and down by the lower ram 16, while the upper punch 8 is reinforced by the upper punch outer diameter reinforcing guide 28 and moves up and down by the upper ram 18. After the upper ram 18 is lowered and the lower end of the outer diameter reinforcing guide 28 comes into contact with the upper surface of the die 4, the lowering of the upper punch reinforcing guide 28 is stopped, but the upper punch 8 is further lowered and the through hole of the die 4 is lowered. Intrude inside. By providing the upper punch outer diameter reinforcing guide 28, the durability of the upper punch 8 under an ultrahigh pressure can be improved.

  This press apparatus includes a pair of linear guide rails 30a and 30b arranged symmetrically with the center of the fixed die plate 14 as a reference axis. The upper ram 18 and the lower ram 16 communicate with each other by linear guide rails 30a and 30b and slide up and down. Further, in the press apparatus shown in FIG. 2, the thickness (H) of the feeder cup 32 can be reduced because the linear (strong vibration) type feeder is employed. As a result, the gap between the upper punch 8 and the die 4 when the upper punch 8 is retracted upward can be reduced. The narrower the gap is, the lower the amount of vertical movement of the upper punch 8 is, so that it is possible to reduce the axis deviation and the axis inclination that tend to occur with the vertical movement.

  In the conventional powder press apparatus, the vertical sliding shaft of the upper ram and the vertical sliding shaft of the lower ram are separated from each other, so that an axis deviation or an inclination of the shaft is likely to occur, and the accuracy is about 0.04. On the other hand, in the ultra-high pressure powder press apparatus having the configuration shown in FIG. 2, the vertical movement of the upper ram 18 and the lower ram 16 is restricted by the linear guide rails 30a and 30b. .01 mm or less.

  According to the experiments of the present inventors, it is preferable that the compression molding for the magnet powder 2 is performed by applying a pressure of 500 MPa to 2500 MPa. From the viewpoint of increasing the volume ratio of the magnet powder in the binderless magnet and improving the magnetic properties, the pressure is preferably 1300 MPa or more, more preferably 1500 MPa or more, and further preferably 1700 MPa or more. In consideration of mass productivity, it is desirable to set the pressure to 2000 MPa or less. When the pressure is lower than the above lower limit value, the bonding strength between the powder particles is reduced, so that the mechanical strength after molding becomes insufficient, and a magnet may be cracked or chipped during handling. On the other hand, if the pressure at the time of compression molding exceeds the above upper limit value, the load on the mold becomes too large, making it difficult to adopt as a mass production technique.

  The compression molded body 10 thus obtained is subjected to heat treatment after molding. By this heat treatment, a component derived from the quenched alloy magnet powder is deposited on the surface of the magnet powder particles and on the internal cracks, and the particles are bonded by the precipitate. When the heat treatment temperature is lower than 350 ° C., a component derived from the quenched alloy magnet powder is precipitated, and the effect of bonding the particles by this precipitate cannot be obtained. There is a possibility that crystal grains in the magnet powder forming the compact are coarsened and the magnetic properties are deteriorated. For this reason, the heat treatment temperature is preferably set in a range of 350 ° C. or higher and 800 ° C. or lower, and more preferably set in a range of 400 ° C. or higher and 600 ° C. or lower. The heat treatment time depends on the heat treatment temperature, but can be set within a range of 5 minutes to 6 hours.

  In addition, when the particles of the magnet powder have an amorphous phase at the time of compression molding, crystallization can be advanced by the above heat treatment. It is also possible to advance the sintering even at a low temperature by utilizing the heat generated by crystallization.

In order to prevent the molded body 10 from being oxidized during the heat treatment, the heat treatment is preferably performed in an inert gas atmosphere. However, if the inert gas contains a small amount of oxygen or water vapor, it is inevitable to oxidize the molded body. Therefore, it is preferable to reduce the partial pressure of oxygen or water vapor as much as possible. For this reason, it is desirable to reduce the pressure of the heat treatment atmosphere gas to 1 × 10 ⁻² Pa or less, and it is more desirable to use a dry gas having a dew point of −40 ° C. or less.

  By the above heat treatment, a process similar to the sintering process proceeds between the powder particles. However, unlike the rare-earth sintered magnet, liquid phase does not occur, and there are continuous gaps between the particles. In addition, according to the heat treatment performed after compression molding as described above, the degree of bonding between the powder particles is increased, and the mechanical strength of the compression molded body is improved. When the heat treatment temperature is a high temperature close to 800 ° C., the same process as the sintering process proceeds between the powder particles, but liquid phase does not occur like rare earth sintered magnets, and gaps continue between the particles. Exist. From the viewpoint of enhancing the magnet characteristics, the above heat treatment is not indispensable, but in order to increase the mechanical strength of the binderless magnet to a practical level, it is preferable to perform the heat treatment after compression molding. Thus, unlike the heat treatment performed with compression molding in the hot press process, the heat treatment performed after compression molding can be performed on a large number of compression molded bodies. In the conventional hot press, since it is necessary to execute a temperature rising / falling cycle for each compression molding process, it takes a long time (for example, 10 to 60 minutes) to obtain individual compression molded bodies. In the present invention, the time required for the compression molding process can be shortened to a short time of 0.01 to 0.1 minutes, for example. This means that the production quantity per minute reaches 10 to 100 pieces. For this reason, even if a heat treatment step is added, the time required for manufacturing the binderless magnet per unit amount hardly increases, and high mass productivity can be realized.

  A low melting point metal powder may be added to and mixed with the rare earth quenched alloy magnet powder before compression molding. In this case, it is preferable that the powder particle diameter of the low melting point metal to be added is in the range of about 10 μm to about 50 μm. The low melting point metal powder melts between the magnet powder particles during low-temperature sintering, and further strengthens the bonding between the powders during solid-phase sintering in which the substances precipitated from the magnet powder alloy are bonded to each other. Or it brings about the effect which enters into the space | gap between the powder particles of a rare earth quenching alloy magnet, and seals. Further, when the low melting point metal powder contained in the compression molded body is melted by the heat treatment, it plays a role of bonding between the magnet powder particles, so that the effect of improving the mechanical strength of the binderless magnet is also obtained. The mixing ratio of the low melting point metal powder is preferably adjusted to a range of 10 wt% or more and 26 wt% or less. If the ratio of the low melting point metal powder is less than the lower limit of this range, the effect of adding the low melting point metal powder does not appear sufficiently, and if it exceeds the upper limit of the above range, the binding force between the magnet particles can be reduced. There is sex.

  The binderless magnet of the present invention is preferably formed into a thin magnet or thin ring magnet having a thickness of 0.5 to 3 mm, or a small magnet (including a ring magnet) having a diameter of φ2 to φ5 mm. If the magnet has such a shape and size, the density can be made uniform inside the compression-molded body, so that it is easy to suppress the fluctuation of the magnetic characteristics depending on the portion of the binderless magnet.

  According to the production method of the present invention, a new fracture surface is generated on the surface and inside of the magnet powder particles by compression molding under ultra-high pressure. When heat treatment is performed after compression molding, even when the temperature is 800 ° C. or lower, components derived from the quenched alloy magnet powder are precipitated from the newly fractured surface, and each particle is bonded by this precipitate. Since such low-temperature solid-phase sintering is possible, it is possible to avoid shrinkage and hot plastic deformation due to high-temperature sintering, and net shape molding with excellent shape freedom and dimensional accuracy similar to bond magnets Is possible. Moreover, integral molding with a yoke, a shaft, etc. is also possible.

  In the binderless magnet of the present invention, a vapor phase plating film is formed on the surface of the magnet body. As this vapor phase plating film, a metal film made of Al, Zn, Sn, Ni, Ti, Cu and alloys thereof can be used. An oxide or nitride film containing these metal elements is also preferably used.

  Of the above coatings, the Al coating has a strong effect of increasing the mechanical strength and corrosion resistance of the magnet body, and can improve the adhesion durability of the magnet. On the other hand, the Ni coating has the effect of improving the cleanliness of the surface of the magnet body in addition to the corrosion resistance. The coating may be a single layer or a multilayer. In order to take advantage of the characteristics of a binderless magnet that has excellent characteristics even with a small size and excellent dimensional accuracy, the total thickness of the coating should be set in the range of 1 to 10 μm, preferably in the range of 3 to 7 μm. Is desirable.

  As a film forming method, a known vacuum deposition method, ion plating method, sputtering method or the like can be employed. Compared to conventional high-temperature sintered magnets, the magnet body before film formation is inherently weak in mechanical strength and tends to crack or chip. For this reason, it is preferable to prevent collision between magnets or between a magnet and a processing vessel as much as possible during the film forming process. For example, the magnet body is agitated by placing a plurality of magnet bodies on a holding member having a dish shape and rotating or swinging the holding member. In this state, it is preferable to deposit the atoms and ions of the film forming material from the target arranged above the magnet body. Such a deposition method is referred to as an upper target (down deposit) type film forming method. According to this method, since almost no load or impact force is applied to the magnet body, it is difficult for the magnet body to crack or chip during film formation.

  Examples of the upper target type film forming method include an arc ion plating method, a sputtering method, and an ion plating method described in JP-A-2000-336473.

  When forming a film of Al, Sn, Zn, or an alloy thereof, it is preferable to heat the magnet body to 200 to 300 ° C. during film formation. Thereby, the density of the coating is improved and the adhesion between the magnet powder and the coating on the surface of the magnet body is improved, so that the mechanical strength and the corrosion resistance of the magnet are further improved.

  In applications where high cleanliness is required on the magnet surface, such as a spindle motor for an HDD drive, it is preferable to form a Ni coating. The Ni coating can be suitably formed by an ion plating method. Instead of forming a metal film, an oxide or nitride film may be formed. The oxide or nitride film can be suitably formed by a reactive vapor deposition method, a reactive ion plating method, or the like.

First, a rare earth iron boron based isotropic nanocomposite magnetic powder (SPRAX-XB, -XC, -XD) manufactured by NEOMAX Co., Ltd. and a single phase of Nd ₂ Fe ₁₄ B phase are used as magnet powder. In addition to powder (N1) and hard magnetic Nd ₂ Fe ₁₄ B, rare earth iron boron-based isotropic nanocomposite magnet powder (N2, N3) in which α-Fe is arranged in the soft magnetic phase was prepared. Table 1 shows the alloy compositions of these six types of magnet powders, and Table 2 shows the magnet properties and average powder particle sizes of the magnet powders themselves.

  Next, 0.5 out wt% calcium stearate was added to these magnet powders and mixed. Then, the said magnet powder was shape | molded and the molded object was produced from each magnet powder. The dimensions of the molded body are an inner diameter of 7.7 mm, an outer diameter of 12.8 mm, and a height of 4.8 mm. Table 3 below shows the molding conditions of Examples 1 to 7 and Comparative Examples 1 to 4.

  The moldings of Examples 1 to 7 were performed in the same apparatus and method in the cold without heating the molding apparatus except that the pressure during compression molding was different. For the molded body of each example, after the molding step, in a nitrogen atmosphere with a dew point of −40 ° C., Examples 1-3, 5, 6, and 7 were at a temperature of 500 ° C., and Example 4 was 800 A heat treatment was performed at a temperature of 10 ° C. for 10 minutes.

(Comparative Example 1)
After preparing SPRAX-XD magnet powder, a kneader process (stirring process) was performed on 98 wt% magnet powder and 2 wt% epoxy resin to obtain a mixture of magnet powder and epoxy resin. A 0.5 mwt% calcium stearate was added to this mixture, followed by compression molding at a pressure of 900 MPa to produce a molded body.

  Next, the molded body thus obtained was subjected to a heat treatment for 30 minutes at a temperature of 180 ° C. in a nitrogen atmosphere furnace having a dew point of −40 ° C.

(Comparative Example 2)
In Comparative Example 1, 98 wt% magnet powder and 2 wt% epoxy resin were mixed. In Comparative Example 2, 97 wt% magnet powder and 3 wt% epoxy resin were mixed. In other respects, there is no difference in manufacturing method between Comparative Example 1 and Comparative Example 2.

(Comparative Example 3)
After preparing SPRAX-XD magnet powder, 90 wt% magnet powder and 10 wt% PPS (polyphenylene sulfide) were extruded using a biaxial extruder. Then, the pellet raw material of (phi) 3 mm x 4 mm was produced by cutting to suitable length. Using this pellet, injection molding was performed under the conditions of a resin temperature of 340 ° C., a mold temperature of 180 ° C., and an injection pressure of 220 MPa, and a molded body of Comparative Example 3 was produced.

(Comparative Example 4)
After preparing SPRAX-XB magnet powder, 95 wt% magnet powder and 5 wt% polyamide (PA12) were extruded using a biaxial extruder. Then, the pellet raw material of (phi) 3 mm x 4 mm was produced by cutting to suitable length. Using this pellet, injection molding was performed under the conditions of a resin temperature of 290 ° C., a mold temperature of 120 ° C., and an injection pressure of 210 MPa, and a molded body of Comparative Example 4 was produced.

  About the Example and comparative example which heat-processed as needed, the volume ratio and compact density of the magnet powder were measured. The measurement results are shown in Table 4 below.

  Next, the magnet characteristics and heat resistance of each molded body were evaluated. The evaluation results are shown in Table 5 below. Evaluation of heat resistance was performed based on the presence or absence of a shape change when each molded body was left in the atmosphere at 150 ° C. for 24 hours.

  As can be seen from the above results, the volume ratio of the magnet powder in Example 1 and Examples 4, 5, 6, and 7 subjected to compression molding at the highest pressure is the highest, and Example 1 and Examples 4, 5, 6 and 7 exhibited the most excellent magnetic properties. In addition, all of the examples had sufficiently high mechanical strength and exhibited excellent magnet characteristics despite the absence of a binder.

  With respect to the magnet of Example 4, the sintered state was observed. 3 and 4 show SEM photographs of cracks inside the magnetic powder and between magnet powder particles. As shown in FIG. 3, cracks are formed inside the powder particles, and a large number of precipitation parts (parts having high brightness in the figure) are formed in the cracks. Also, precipitates are observed between the powder particles as shown in FIG. According to the component analysis by EDS (Energy dispersive X-ray spectroscopy), this precipitate was mainly composed of Fe.

  Next, a vapor phase film was formed on the surface of the magnet bodies of Examples 1 to 4 described above. Specifically, magnet bodies corresponding to Examples 1 to 4 were prepared and loaded into an oblique rotating disk in a vacuum chamber of a multi-arc PVD apparatus (M350A manufactured by Nissin Electric). After filling the vacuum chamber with an argon (Ar) atmosphere whose pressure is reduced to 1 Pa, arc discharge at a current of 100 A is performed for 60 minutes by an arc type ion plating method using Al as an evaporation source, and an Al film having a thickness of about 5 μm is formed. Formed. When forming the Al film, a bias voltage of −50 V was applied to the magnet body.

  Thus, the corrosion resistance and mechanical strength of the magnet on which the Al film was formed were measured. The results are shown in Table 6. For the mechanical strength, the crushing strength of the magnet was measured with a tensile and compression tester (SL-2001 manufactured by Imada Seisakusho).

  In Table 6, the samples which did not heat the magnet body during the formation of the Al film are designated as Examples 8 to 11, and the samples heated at 300 ° C. are designated as Examples 12 to 15. Since tests were also conducted on the magnet bodies of Examples 1 to 4 in which no Al film was formed on the surface, the results are shown in Table 6 for reference. In addition, about magnets (Comparative Examples 1 to 4) in which magnet powder is bonded with resin, when placed in a vacuum atmosphere in a vacuum chamber, gas is released from the resin component contained in the magnet, so a dense Al film can be formed. There wasn't.

  As is apparent from Table 6, the binderless magnet of the present invention has a dense vapor-phase plating film on the surface of the magnet body, so that not only corrosion resistance but also mechanical strength is improved.

  The binderless magnet of the present invention does not contain a resin binder, is excellent in heat resistance, and can achieve a high magnetic powder volume ratio compared to a bonded magnet. Therefore, it is widely used in various fields as an alternative to conventional bonded magnets. It is done.

  Further, since the binderless magnet of the present invention does not contain a resin, it is easy to perform surface treatment such as plating, and a magnet having excellent corrosion resistance can be obtained. Furthermore, since it contains almost no non-magnetic material such as resin, it is easy to extract only magnetic powder from waste or defective products, and it is also highly recyclable.

It is a figure which shows the structural example of the compression molding apparatus used suitably for manufacture of the binderless magnet by this invention. It is a figure which shows the structural example of the ultra-high pressure powder press apparatus used suitably by embodiment of this invention. It is a cross-sectional SEM photograph which shows the inside of the powder particle in Example 4 of this invention. It is a cross-sectional SEM photograph which shows between the powder particles in Example 4 of this invention.

Explanation of symbols

2 Magnet powder (rare earth quenching alloy magnet powder)
4 Die 6 Lower punch 8 Upper punch 10 Molded body (compression molded body)
14 Fixed die plate 16 Lower ram 18 Upper ram 28 Upper punch outer diameter reinforcement guide 30a Linear guide rail 30b Linear guide rail 32 Feeder cup

Claims (15)

A magnet having particles of rare-earth quenched alloy magnet powder bonded without a resin binder, and a vapor-phase plating film provided on the surface of the magnet,
A rare earth alloy binderless magnet, wherein a volume ratio of the rare earth quenching alloy magnet powder in the entire magnet body is 70% or more and 95% or less.   2. The rare earth alloy binderless magnet according to claim 1, wherein the particles of the quenched alloy magnet powder are bonded together by precipitates from the quenched alloy magnet powder particles.   The particles of the quenched alloy magnet powder are formed from an iron-based rare earth alloy containing boron, and the precipitate is composed of at least one element selected from the group consisting of iron, rare earth, and boron. The rare earth alloy binderless magnet according to claim 2.   The rare earth alloy binderless magnet according to claim 2 or 3, wherein cracks are formed in the particles of the rapidly cooled alloy magnet powder, and at least a part of the precipitation portion exists in the crack.   The vapor phase metal plating film is at least a metal composed of at least one element selected from the group consisting of Al, Zn, Sn, Ni, Ti, Cu, or an alloy, oxide, or nitride of the metal. The rare earth alloy binderless magnet according to claim 1, comprising one layer.   6. The rare earth according to claim 1, wherein the particles of the rare earth-based quenched alloy magnet powder contain one or more types of ferromagnetic crystal phases and have an average crystal grain size in the range of 10 nm to 300 nm. Alloy binderless magnet.   The rare earth alloy binderless magnet according to any one of claims 1 to 6, wherein the particles of the rare earth rapidly quenched alloy magnet powder have a nanocomposite magnet structure containing a hard magnetic phase and a soft magnetic phase. Rare earth alloy based binderless magnet according to any one of claims 1 to 7, a density of ^{5.5g / cm 3 ~7.0g / cm 3} . Composition formula T _100-xyz Q _x R _y M _z (T is a transition metal element including Fe or one or more elements selected from the group consisting of Co and Ni and Fe, Q is composed of B and C At least one element selected from the group, R is at least one rare earth element substantially free of La and Ce, M is Ti, Al, Si, V, Cr, Mn, Cu, Zn, Ga, At least one metal element selected from the group consisting of Zr, Nb, Mo, Ag, Hf, Ta, W, Pt, Au, and Pb), and the composition ratios x, y, and z are respectively
10 <x ≦ 35 atomic%,
2 ≦ y ≦ 10 atomic%, and 0 ≦ z ≦ 10 atomic%
The rare earth alloy binderless magnet according to any one of claims 1 to 8, having a composition satisfying Composition formula T _100-xyz Q _x R _y M _z (T is a transition metal element including Fe or one or more elements selected from the group consisting of Co and Ni and Fe, Q is composed of B and C At least one element selected from the group, R is at least one rare earth element substantially free of La and Ce, M is Ti, Al, Si, V, Cr, Mn, Cu, Zn, Ga, At least one metal element selected from the group consisting of Zr, Nb, Mo, Ag, Hf, Ta, W, Pt, Au, and Pb), and the composition ratios x, y, and z are respectively
4 <x ≦ 10 atomic%,
6 ≦ y <12 atomic%, and 0 ≦ z ≦ 10 atomic%
The rare earth alloy binderless magnet according to any one of claims 1 to 8, having a composition satisfying Preparing a rare earth quenched alloy magnet powder (A);
A compression-molded body in which the rare earth-based rapidly quenched alloy magnet powder is compacted by cold compression without using a resin binder, and the volume ratio of the rare-earth-based quenched alloy magnet powder in the whole is 70% to 95%. Forming a step (B),
A step (C) of performing a heat treatment on the compression molded body at a temperature of 350 ° C. or higher and 800 ° C. or lower after the step (B) to form a magnet body;
Forming a vapor phase metal plating film on the surface of the magnet body (D);
For producing rare earth alloy binderless magnets.   The rare earth alloy binderless magnet manufacturing method according to claim 11, wherein the step (D) includes a step of performing film formation while inserting the magnet body into a film formation apparatus and moving the magnet body under reduced pressure. Method.   The method for producing a rare earth alloy binderless magnet according to claim 11 or 12, wherein in the step (B), the quenched alloy magnet powder for a rare earth quenched magnet is compressed at a pressure of 500 MPa to 2500 MPa. The method for producing a rare earth alloy binderless magnet according to any one of claims 11 to 13, wherein the heat treatment in the step (C) is performed in an inert gas atmosphere having a pressure of 1 × 10 ^-2 Pa or less.   The method for producing a rare earth alloy binderless magnet according to any one of claims 11 to 14, wherein the heat treatment in the step (C) is performed in an inert gas atmosphere having a dew point of -40 ° C or lower.