USRE38042E1 - Anisotropic magnetic powder and magnet thereof and method of producing same - Google Patents

Anisotropic magnetic powder and magnet thereof and method of producing same Download PDF

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USRE38042E1
USRE38042E1 US09/985,262 US98526201A USRE38042E US RE38042 E1 USRE38042 E1 US RE38042E1 US 98526201 A US98526201 A US 98526201A US RE38042 E USRE38042 E US RE38042E
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atomic
magnetically anisotropic
alloy
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Minoru Endoh
Yasuto Nozawa
Katsunori Iwasaki
Shigeho Tanigawa
Masaaki Tokunaga
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Proterial Ltd
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Hitachi Metals Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
    • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
    • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
    • H01F1/047—Alloys characterised by their composition
    • H01F1/053—Alloys characterised by their composition containing rare earth metals
    • H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
    • H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
    • H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
    • H01F1/0575—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
    • H01F1/0577—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together sintered
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B61—RAILWAYS
    • B61C—LOCOMOTIVES; MOTOR RAILCARS
    • B61C15/00—Maintaining or augmenting the starting or braking power by auxiliary devices and measures; Preventing wheel slippage; Controlling distribution of tractive effort between driving wheels
    • B61C15/08—Preventing wheel slippage
    • B61C15/10—Preventing wheel slippage by depositing sand or like friction increasing materials
    • B61C15/102—Preventing wheel slippage by depositing sand or like friction increasing materials with sanding equipment of mechanical or fluid type, e.g. by means of steam
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/04—Making non-ferrous alloys by powder metallurgy
    • C22C1/0433—Nickel- or cobalt-based alloys
    • C22C1/0441—Alloys based on intermetallic compounds of the type rare earth - Co, Ni
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
    • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
    • H01F1/047—Alloys characterised by their composition
    • H01F1/053—Alloys characterised by their composition containing rare earth metals
    • H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
    • H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
    • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
    • H01F1/047—Alloys characterised by their composition
    • H01F1/053—Alloys characterised by their composition containing rare earth metals
    • H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
    • H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
    • H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
    • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
    • H01F1/047—Alloys characterised by their composition
    • H01F1/053—Alloys characterised by their composition containing rare earth metals
    • H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
    • H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
    • H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
    • H01F1/0575—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
    • H01F1/0578—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together bonded together

Definitions

  • the present invention relates to a magnetically anisotropic magnetic powder composed of a rare earth element-iron-boron-gallium alloy powder, and a permanent magnet composed of such alloy powder dispersed in a resin, and more particularly to a resin-bonded permanent magnet having good thermal stability composed of a magnetically anisotropic rare earth element-iron-boron-gallium permanent magnet powder having fine crystal grains dispersed in a resin.
  • Typical conventional rare earth element permanent magnets are SmCo 5 permanent magnets, and Sm 2 Co 17 permanent magnets. These samarium cobalt magnets are prepared from ingots produced by melting samarium and cobalt in vacuum or in an inert gas atmosphere. These ingots are pulverized and the resulting powders are pressed in a magnetic field to form green bodies which are in turn sintered and heat-treated to provide permanent magnets.
  • the samarium.cobalt magnets are given magnetic anisotropy by pressing in a magnetic field as mentioned above.
  • the magnetic anisotropy greatly increases the magnetic properties of the magnets.
  • magnetically anisotropic, resin-bonded samarium.cobalt permanent magnets are obtained by injection-molding a mixture of samarium.cobalt magnet powder produced from the sintered magnet provided with anisotropy and a resin in a magnetic field, or by compression-molding the above mixture in a die.
  • resin-bonded samarium cobalt magnets can be obtained by preparing the sintered magnets having anisotropy, pulverizing them and then mixing them with resins as binders.
  • neodymium-iron-boron magnets have been proposed as new rare earth magnets surmounting the samarium.cobalt magnets containing samarium which is not only expensive but also unstable in its supply.
  • Japanese Patent Laid-Open Nos. 59-46008 and 59-64733 disclose permanent magnets obtained by forming ingots of neodymium-iron-boron alloys, pulverizing them to fine powders, pressing them in a magnetic field to provide green bodies which are sintered and then heat-treated, like the samarium.cobalt magnets. This production method is called a powder metallurgy method.
  • This method comprises melting a mixture of neodymium, iron and boron, rapidly quenching the melt by such a technique as melt spinning to provide fine flakes of the amorphous alloy, and heat-treating the flaky amorphous alloy to generate an Nd 2 Fe 14 B intermetallic compound.
  • the fine flakes of this rapidly-quenched alloy is solidified with a resin binder (Japanese Patent Laid-Open No. 59-211549).
  • Japanese Patent Laid-Open No. 60-100402 discloses a technique of hot-pressing this isotropic magnetic alloy, and then applying high temperatures and high pressure thereto so that plastic flow takes place partially in the alloy thereby imparting magnetic anisotropy thereto.
  • the conventional Nd-Fe-B permanent magnets have the following problems.
  • the resulting magnets essentially have low Curie temperatures, large crystal grain size and poor thermal stability. Accordingly, they cannot be suitably used for motors, etc. which are likely to be used in a high-temperature environment.
  • the magnetic properties are (BH)max of 3-5MGOe for those obtained by injection molding and (BH)max of 8-10MGOe for those obtained by compression molding, and further the magnetic properties vary widely depending upon the strength of a magnetic field for magnetizing the alloy.
  • the magnetic field should be 50 kOe or so, and it is difficult to magnetize the alloy after assembling for various applications.
  • the resulting alloy is isotopic isotropic so that it is disadvantageous just like the permanent magnet prepared by mixing rapidly-quenched alloy powder with a resin.
  • (BH)max of the resulting alloy is improved in proportion to the increase in the density, and it can reach 12MGOe or so. However, it is still impossible to magnetize it after assembling.
  • anisotropy can be achieved like the powder metallurgy method, providing (BH)max of 34-40MGOe, but annular magnets, for instance, magnet rings of 30 mm in outer diameter, 25 mm in inner diameter and 20 mm in thickness cannot easily be formed because die upsetting should be utilized to provide anisotropy.
  • magnets prepared by pulverizing ingots and solidifying them with wax powders used are so fine that they are likely to be burned, making it impossible to handle them in the atmosphere. Also since the magnets show a low squareness ratio in the magnetization curve, they cannot have high magnetic properties.
  • an object of the present invention is to solve the problems peculiar to the above conventional techniques, thereby providing an anisotropic resin-bonded magnet having good thermal stability and easily magnetizable after assembling, and magnetic powder usable therefor and a method of producing them.
  • the present invention comprises the following technical means.
  • the object of the present invention has been achieved first by forming magnetically anisotropic magnetic powder having an average crystal grain size of 0.01-0.5 ⁇ m from an R-Fe-B-Ga alloy, wherein R represents one or more rare earth elements including Y, Fe may be partially substituted by Co to include an R-Fe-Co-B-Ga alloy, and one or more additional elements (M) selected from Nb, W, V, Ta, Mo, Si, Al, Zr, Hf, P, C and Zn may be contained to include an R-Fe-B-Ga-M alloy and an R-Fe-Co-B-Ga-M alloy, second by forming a pressed powder magnet therefrom, and third by forming a resin-bonded magnet from powder of the above alloy having an average particle size of 1-1000 ⁇ m.
  • R represents one or more rare earth elements including Y
  • Fe may be partially substituted by Co to include an R-Fe-Co-B-Ga alloy
  • M additional elements selected from Nb, W, V, Ta
  • the present invention is based on our finding that a thermally stable, anisotropic resin-bonded magnet can be obtained from magnetic powder of an average particle size of 1-1000 ⁇ m prepared by pulverizing a magnetically anisotropic R-Fe-B-Ga alloy having an average crystal grain size of 0.01-0.5 ⁇ m. It has been found that gallium (Ga) is highly effective to improve the thermal stability of the magnet.
  • the magnetically anisotropic magnetic powder according to the present invention has an average particle size of 1-1000 ⁇ m and is made from a magnetically anisotropic R-TM-B-Ga alloy having an average crystal grain size of 0.01-0.5 ⁇ m, wherein R represents one or more rare earth elements including Y, TM represents Fe which may be partially substituted by Co, B boron and Ga gallium.
  • the method of producing a magnetically anisotropic magnetic powder comprises the steps of rapidly quenching a melt of an R-TM-B-Ga alloy, wherein R represents one or more rare earth elements including Y, TM represents Fe which may be partially substituted by Co, B boron and Ga gallium, to form flakes made of an amorphous or partially crystallized R-TM-B-Ga alloy pressing these flakes to provide a pressed powder body with a higher density, subjecting it to plastic deformation while heating to form a magnetically anisotropic R-TM-B-Ga alloy having an average crystal grain size of 0.01-0.5 ⁇ m, heat-treating it to increase the coercive force thereof, and then pulverizing it.
  • R represents one or more rare earth elements including Y
  • TM represents Fe which may be partially substituted by Co, B boron and Ga gallium
  • the method of producing a magnetically anisotropic magnetic powder comprises the steps of rapidly quenching a melt of an R-TM-B-Ga alloy, wherein R represents one or more rare earth elements including Y, TM represents Fe which may be partially substituted by Co, B boron and Ga gallium, to form flakes of an amorphous or partially crystallized R-TM-B-Ga alloy, pressing the flakes to provide a pressed powder body with a higher density, subjecting it to plastic deformation while heating to provide a magnetically anisotropic R-TM-B-Ga alloy having an average crystal grain size of 0.01-0.5 ⁇ m, and then pulverizing it without heat treatment.
  • the magnetically anisotropic pressed powder magnet according to the present invention is made of magnetically anisotropic R-TM-B-Ga alloy having an average crystal grain size of 0.01-0.5 ⁇ m, wherein R represents one or more rare earth elements including Y, TM represents Fe which may be partially substituted by Co, B boron and Ga gallium, the magnetically anisotropic R-TM-B-Ga alloy having an axis of easy magnetization.
  • the magnetically anisotropic resin-bonded magnet according to the present invention is composed of 15-40 volume % of a resin binder and balance R-TM-B-Ga alloy powder having an average crystal grain size of 0.01-0.5 ⁇ m, wherein R represents one or more rare earth elements including Y, TM represents Fe which may be partially substituted by Co, B boron and Ga gallium, the magnetically anisotropic R-TM-B-Ga alloy having an axis of easy magnetization.
  • the magnetically anisotropic magnetic powder according to the present invention an average particle size of 1-1000 ⁇ m and is composed of an R-TM-B-Ga-M alloy powder having an average crystal grain size of 0.01-0.5 ⁇ m, wherein R represents one or more rare earth elements including Y, TM Fe which may be partially substituted by Co, B boron, Ga gallium and M one or more elements selected from the group consisting of Nb, W, V, Ta, Mo, Si, Al, Zr, Hf, P, C and Zn.
  • R represents one or more rare earth elements including Y, TM Fe which may be partially substituted by Co, B boron, Ga gallium and M one or more elements selected from the group consisting of Nb, W, V, Ta, Mo, Si, Al, Zr, Hf, P, C and Zn.
  • the method of producing a magnetically anisotropic magnetic powder comprises the steps of rapidly quenching a melt of an R-TM-B-Ga-M alloy, wherein R represents one or more rare earth elements including Y, TM represents Fe which may be partially substituted by Co, B boron, Ga gallium, and M one or more elements selected from the group consisting of Nb, W, V, Ta, Mo, Si, A;, Zr, Hf, P, C and Zn, to form flakes made of an amorphous or partially crystallized R-TM-B-Ga-M alloy, pressing these flakes to provide a pressed powder body with a higher density, subjecting it to plastic deformation while heating to form a magnetically anisotropic R-TM-B-Ga-M alloy having an average crystal grain size of 0.01-0.5 ⁇ m, heat-treating it to increase the coercive force thereof, and then pulverizing it.
  • R represents one or more rare earth elements including Y
  • TM represents Fe which may be partially
  • the method of producing a magnetically anisotropic magnetic powder comprises the steps of rapidly quenching a melt of an R-TM-B-Ga-M alloy, wherein R represents one or more rare earth elements including Y, TM Fe which may be partially substituted by Co, B boron, Ga gallium, and M one or more elements selected from the group consisting of Nb, W, V, Ta, Mo, Si, A;, Zr, Hf, P, C and Zn to form flakes made of an amorphous or partially crystallized R-TM-B-Ga-M alloy, pressing the flakes to provide a pressed powder body with a higher density, subjecting it to plastic deformation while heating to provide a magnetically anisotropic R-TM-B-Ga-M alloy having an average crystal grain size of 0.01-0.5 ⁇ m, and then pulverizing it without heat treatment.
  • R represents one or more rare earth elements including Y, TM Fe which may be partially substituted by Co, B boron, Ga gallium, and M
  • the magnetically anisotropic pressed powder magnet according to the present invention is made of magnetically anisotropic R-TM-B-Ga-M alloy having an average crystal grain size of 0.01-0.5 ⁇ m, wherein R represents one or more rare earth elements including Y, TM represents Fe which may be partially substituted by Co, B boron, Ga gallium, and M one or more elements selected from the group consisting of Nb, W, V, Ta, Mo, Si, Al, Zr, Hf, P, C and Zn, the magnetically anisotropic R-TM-B-Ga-M alloy having an axis of easy magnetization.
  • R represents one or more rare earth elements including Y
  • TM represents Fe which may be partially substituted by Co
  • B boron Ga gallium
  • M one or more elements selected from the group consisting of Nb, W, V, Ta, Mo, Si, Al, Zr, Hf, P, C and Zn
  • the magnetically anisotropic resin-bonded magnet according to the present invention is composed of 15-40 volume % of a resin binder and balance R-TM-B-Ga-M alloy powder having an average crystal grain size of 0.01-0.5 ⁇ m, wherein R represents one or more rare earth elements including Y, TM represents Fe which may be partially substituted by Co, B boron, Ga gallium, and M one or more elements selected from the group consisting of Nb, W, V, Ta, Mo, Si, Al, Zr, Hf, P, C and Zn, the magnetically anisotropic R-TM-B-Ga-M alloy having an axis of easy magnetization.
  • FIG. 1 is a graph showing the variation of irreversible loss of flux with heating temperature of the magnets (a), (b) and (c), wherein (a) denotes a magnet prepared by rapid quenching, heat treatment and resin impregnation, (b) a magnet prepared by rapid quenching, heat treatment and hot pressing, and (c) a magnet prepared by rapid quenching, HIP (“hot isostatic pressing”) and die upsetting; and
  • FIG. 2 is a graph showing the comparison in thermal stability of the anisotropic resin-bonded magnet (a) of Example 8, an anisotropic sintered magnet of Sm 2 Co 17 (b) and an anisotropic sintered magnet having the composition of Nd 13 DyFe 76.8 Co 2.2 B 6 Ga 0.9 Ta 0.1 (c).
  • the above alloy has preferably a composition of 11-18 atomic % of R, 5 atomic % or less of Ga, 4-11 atomic % of B, 30 atomic % or less of Co and balance Fe and inevitable impurities, and further preferably a composition of 11-18 atomic % of R, 0.01-3 atomic % of Ga, 4-11 atomic % of B, 30 atomic % or less of Co and balance Fe and inevitable impurities.
  • This alloy may contain one or more additional elements M selected from Nb, W, V, Ta, Mo, Si, Al, Zr, Hf, P, C and Zn.
  • the amount of the additional element M is 3 atomic % or less and more preferably 0.001-3 atomic %.
  • the addition of the additional element M and Ga in combination is effective to further improve the coercive force of the alloy. Of course, the addition of Ga only is effective in some cases.
  • the R-Fe-B alloy is an alloy containing R 2 Fe 14 B or R 2 (Fe,Co) 14 B as a main phase.
  • the composition range desirable for a permanent magnet is as follows:
  • R one or more rare earth elements including Y
  • R is less than 11 atomic %
  • sufficient iHc cannot be obtained, and when it exceeds 18 atomic %, the Br decreases.
  • the amount of R is 11-18 atomic %.
  • the amount of Co is 30 atomic % or less.
  • Ga is preferably 0.01-3 atomic %, and more preferably 0.05-2 atomic %.
  • M is effective to further increase the coercive force of the alloy, but when M exceeds 3 atomic %, undesirable decrease in 4 ⁇ Is and Tc take place.
  • the amount of M is 0.001-3 atomic %.
  • the alloy of the present invention may contain Al contained as an impurity in ferroboron, and further reducing materials and impurities mixed in the reduction of the rare earth element.
  • the average crystal grain size of the R-Fe-B-Ga alloy exceeds 0.5 ⁇ m, its iHc decreases, resulting in an irreversible loss of flux of 10% or more at 160° C. which in turn leads to an extreme decrease in thermal stability.
  • the average crystal grain size is less than 0.01 ⁇ m, the formed resin-bonded magnet has a low iHc so that the desired permanent magnet cannot be obtained. Therefore, the average crystal grain size is limited to 0.01-0 5 0.5 ⁇ m.
  • the ratio of the average dimension (c) of the crystal grains measured perpendicular to their C axes to the average size (a) thereof measured parallel to their C axes is preferably 2 or more.
  • the R-Fe-B-Ga alloy to be pulverized is required to have a residual magnetic flux density of 8 kG or more in a particular direction, namely in the direction of anisotropy.
  • the R-TM-B-Ga or R-TM-B-Ga-M alloy is given anisotropy by pressing or compacting flakes obtained by a rapid quenching method, by hot isostatic pressing (HIP) or hot pressing, and then subjecting the resulting pressed body to plastic deformation.
  • HIP hot isostatic pressing
  • One method for giving plastic deformation is die upsetting at high temperatures.
  • the magnetically anisotropic R-TM-B-Ga or R-TM-B-Ga-M alloy means herein an R-TM-B-Ga or R-TM-B-Ga-M alloy showing anisotropic magnetic properties in which the shape of a 4 ⁇ I-H curve thereof in the second quadrant varies depending upon the direction of magnetization.
  • a pressed powder body produced by the hot isostatic pressing of flakes usually has a residual magnetic flux density of 7.5 kG or less, while by using an R-TM-B-Ga or R-TM-B-Ga-M alloy having a residual magnetic flux density of 8 kG or more, the resulting resin-bonded magnets have higher magnetic properties such as residual magnetic flux density and energy product, than isotropic resin-bonded magnets.
  • the alloy flakes are pulverized to 100-200 ⁇ m or so.
  • the coarse powder produced by pulverization is molded at room temperature to obtain a green body.
  • the green body is subjected to hot isostatic pressing or hot pressing at 600°-750° C. to form a compacted block having a relatively small crystal grain size.
  • the block is then subjected to plastic working such as die upsetting at 600°-800° C. to provide an anisotropic flat plate.
  • the resulting flat plate product is called herein an anisotropic pressed powder magnet.
  • this may be used without further treatment or working. It may be heat-treated but the heat treatment can be omitted by adding Ga, because the addition of Ga increases iHc sufficiently enough in some cases.
  • the flat plate may be heat-treated at 600°-800° C. to improve iHc thereof. Pulverization of this flat plate can provide coarse powder for an anisotropic resin-bonded magnets.
  • the anisotropic R-Fe-B-Ga alloy has crystal grains flattened in the C direction.
  • the crystal grains desirably have the ratio of the average dimension (c) thereof in perpendicular to their c C axes to the average dimension (a) thereof in parallel to their C axes of 2 or more, so that the magnet has a residual magnetic flux density of 8 kG or more.
  • the average crystal grain size is defined herein as a value obtained by averaging the diameters of 30 or more crystal grains, which are converted to spheres having the same volume.
  • the heat treatment temperature is desirably 600°-900° C., because when it is less than 600° C., the coercive force cannot be increased, and when it is higher than 900° C., the coercive force decreases relative to the value than before the heat treatment.
  • the heat treatment is conducted for a period of time needed for keeping a sample at a uniform temperature. Taking productivity into consideration, it is 240 minutes or less.
  • the cooling rate should be 1° C./sec or more. When the cooling rate is less than 1° C./sec, the coercive force decreases compared to the value before the heat treatment.
  • the term “cooling rate” used herein means an average cooling rate from the heat treatment temperature (° C.) to (heat treatment temperature+room temperature)/2 (° C.).
  • the addition of Ga makes the heat treatment unnecessary in some cases, in which not only is the heat treatment step eliminated but also large magnets used for voice coil motors, etc. can be produced which suffer from substantially no cracking or oxidation.
  • the average particle size of the pulverized powder is 1-1000 ⁇ m for the following reasons: When it is less than 1 ⁇ m, the powder is easily burned, making it difficult to handle it in the air, and when it exceeds 1000 ⁇ m, a thin resin-bonded magnet of 1-2 mm in thickness cannot be produced, and also it is not suitable for injection molding.
  • the pulverization may be carried out by a usual method such as by a disc mill, a brown mill, an attritor, a ball mill, a vibration mill, a jet mill, etc.
  • the coarse powder can be blended with a thermosetting resin binder and compression-molded in a magnetic field and then thermally cured to provide an anisotropic resin-bonded magnet of a compression molding type. Further, the coarse powder can be blended with a thermoplastic resin binder and injection-molded in a magnetic field to provide an anisotropic resin-bonded magnet of an injection molding type.
  • thermosetting resins are easiest to use in the case of compression molding. Thermally stable polyamides, polyimides, polyesters, phenol resins, fluorine resins, silicone resins, epoxy resins, etc. may be used. And Al, Sn, Pb and various low-melting point solder alloys may also be used. In the case of injection molding, thermoplastic resins such as ethylene-vinyl acetate resins, nylons, etc. may be used.
  • Nd 15 Fe 77 B 7 Ga 1 alloy was prepared by arc melting, and this alloy was formed into thin flakes by rapid quenching via a single roll method in an argon atmosphere.
  • the peripheral speed of the roll was 30 m/sec., and the resulting flakes were in irregular shapes of about 30 ⁇ m in thickness.
  • X-ray diffraction measurement it was found that they were composed of a mixture of amorphous phases and crystal phases.
  • These thin flakes were pulverized to 32 mesh or finer and then compressed by a die at 6 tons/cm 2 without applying a magnetic field.
  • the resulting compressed product had a density of 5.8 g/cc.
  • the compressed product body was hot-pressed at 750° C.
  • the alloy after hot pressing had a density of 7.30 g/cc. Thus, a sufficiently high density was provided by hot pressing.
  • the upset sample was heated in an Ar atmosphere at 750° C. for 60 minutes, and then cooled by water at a cooling rate of 7° C./sec.
  • the magnetic properties before and after the heat treatment are shown in Table 1.
  • the heat-treated sample was pulverized to have a particle size range of 250-500 ⁇ m.
  • the resulting magnetic powder was mixed with 16 vol. % of an epoxy resin in a dry state, and the resulting powder was molded in a magnetic field of 10 kOe perpendicular to the direction of compression.
  • an anisotropic resin-bonded magnet was obtained.
  • anisotropic resin-bonded magnet of the present invention has better magnetization and higher magnetic properties than the comparable isotropic resin-bonded magnet.
  • Example 1 With respect to composition and conditions of rapid quenching, hot pressing, molding in a magnetic field in perpendicular to the direction of compression, heat treatment and curing, this Example was the same as Example 1.
  • the results are shown in Table 3.
  • the magnetic properties shown in Table 3 are values obtained at a magnetization intensity of 25 kOe.
  • the increase of the compression ratio serves to increase the magnetic properties of the resulting anisotropic resin-bonded magnet.
  • Magnetic powder was prepared from an Nd 14 Fe 79 B 6 Ga 1 alloy in the same manner as in Example 1.
  • the magnetic powder was blended with 33 volume % of EVA to form pellets.
  • the pellets were injection-molded at 150° C.
  • a test piece produced by the injection molding was in a circular shape of 20 mm in diameter and 10 mm in thickness, and the magnetic field applied during the injection molding was 8 kOe.
  • the magnetic properties of the test piece was Br of nearly 7.1 KG, bHc of nearly 5.8 kOe, iHc of nearly 18.5 kOe and (BH)max of nearly 10.5 MGOe when measured at a magnetization intensity of 25 kOe.
  • Anisotropic resin-bonded magnets having the compositions as shown using Table 4 were prepared in the same compression molding method as in Example 1. The magnetic properties measured are shown in Table 4.
  • Sample Nos. 1-5 show the influence of Nd
  • Sample Nos. 6-10 show the influence of B
  • Sample Nos. 11-19 show the influence of Ga
  • Sample Nos. 20-23, 24-27, 28-31, 32-35, 36-39, 40-43, 44-47, 48-51, 52-55, 56-59, 60-63 and 64-67 respectively show the effects of Ga plus additional elements, W, V, Ta, Mo, Si, Al, Zr, Hf, P, C, Zn and Nb.
  • Nd is preferably 11-18 atomic %, boron 4-11 atomic %, Ga 5 atomic % or less and each additional element 3 atomic % or less.
  • An alloy having the composition of Nd 14.1 Fe 73.0 Co 3.4 B 6.9 Ga 1.7 W 0.9 was prepared by arc melting and then rapidly quenched by a single roll method.
  • the resulting flaky sample was compressed by HIP and upset by a die to provide a flatten flattened product.
  • the resulting bulky sample was pulverized to 80 ⁇ m or less, impregnated with an epoxy resin and then molded in an a magnetic field.
  • Example 2 An Nd 15 Fe 72.7 Co 3.2 B 7 Ga 1.8 Nb 0.3 alloy was treated in the same manner as in Example 1 to produce magnetic powder.
  • This magnetic powder was blended with an EVA binder to form pellets which were then injection-molded to produce a magnet of 12 mm in inner diameter, 16 mm in outer diameter and 25 mm in height.
  • An anisotropic resin-bonded magnet of a compression molding type having the composition of Nd 13 DyFe 76.8 Co 2.2 B 6 Ga 0.9 Ta 0.1 was prepared in the same manner as in Example 1.
  • the magnetic properties of the magnet were Br of nearly 6.6 kG, bHc of nearly 6.2 kOe, iHc of nearly 21.0 kOe and (BH)max of nearly 10.2MGOe.
  • the magnet had a crystal grain size of 0.11 ⁇ m.
  • the magnet was worked to 10 mm in diameter ⁇ 7 mm thick and tested with respect to thermal stability. The results are shown in FIG. 2 as curve a.
  • an anisotropic sintered Sm 2 Co 17 magnet (curve b) and an anisotropic R-Fe-B sintered magnet (curve a) of the same composition were tested.
  • anisotropic resin-bonded magnet of the present invention had better thermal stability than the comparable anisotropic sintered magnet of the same composition tested as a comparative material.
  • Example 1 was repeated except for changing the particle size of magnetic powder to prepare an anisotropic resin-bonded magnet of Nd 14 Fe 79 B 6 Ga 1 .
  • an anisotropic sintered magnet of Nd 13 Dy 2 Fe 78 B 7 was used to investigate the variation of coercive force with particle size. The results are shown in Table 6. It is shown that a sintered body has a coercive force decreased by pulverization, unable to be used as a starting a material for resin-bonded magnets, while the hot pressed and die upset magnet of the present invention undergoes substantially no decrease in coercive force by pulverization.
  • Example 1 was repeated except for changing crystal grain size by changing the upsetting temperature to prepare an anisotropic resin-bonded magnet.
  • the results are shown in Table 7 . It is shown showed that with an average crystal grain size of 0.01 ⁇ m to 0.5 ⁇ m, good magnetic properties can be achieved.
  • Example 1 was repeated except for changing the heat treatment time to prepare an upset sample of R-Fe-B-Ga. The results are shown in Table 8 7 . It is shown that magnetic properties do not change as long as the heating time at 750° C. is within 240 minutes.
  • Example 1 was repeated except for changing the heat treatment temperature with the heating time of 10 minutes to prepare an upset sample of R-Fe-B-Ga.
  • the results are shown in Table 9 8 . It is shown that with heat treatment temperature of 600°-900° C., good magnetic properties can be obtained.
  • Example 1 was repeated except for changing the cooling method with a constant heating tim time of 10 minutes to prepare an upset sample of Nd-Fe-B-Ga.
  • the results are shown in Table 10 9 . It is shown that with the cooling rate of 1° C./sec or more, good results are obtained.
  • Cooling Rate Coercive Force Cooling Method [° C./sec] (° C./sec) [kOe](kOe) Water Cooling 370 23.1 Oil Cooling 180 23.3 Rapid Cooling with Ar 61 23.0 Slow Cooling with Ar 18 22.5 Spontaneous Cooling in Vacuum 4 20.2 Cooling in Furnace 0.3 20.4 Before Heat Treatment — 21.1
  • the magnetic powder for anisotropic resin-bonded magnets containing Ga according to the present invention has excellent magnetizability and small irreversible loss of flux even in a relatively high temperature environment, and is useful for anisotropic resin-bonded magnets which can be magnetized after assembling.

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US20040025974A1 (en) * 2002-05-24 2004-02-12 Don Lee Nanocrystalline and nanocomposite rare earth permanent magnet materials and method of making the same
US20050081960A1 (en) * 2002-04-29 2005-04-21 Shiqiang Liu Method of improving toughness of sintered RE-Fe-B-type, rare earth permanent magnets
US20060005898A1 (en) * 2004-06-30 2006-01-12 Shiqiang Liu Anisotropic nanocomposite rare earth permanent magnets and method of making
US20060054245A1 (en) * 2003-12-31 2006-03-16 Shiqiang Liu Nanocomposite permanent magnets
US20110050382A1 (en) * 2009-08-25 2011-03-03 Access Business Group International Llc Flux concentrator and method of making a magnetic flux concentrator

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Publication number Priority date Publication date Assignee Title
US20050081960A1 (en) * 2002-04-29 2005-04-21 Shiqiang Liu Method of improving toughness of sintered RE-Fe-B-type, rare earth permanent magnets
US20040025974A1 (en) * 2002-05-24 2004-02-12 Don Lee Nanocrystalline and nanocomposite rare earth permanent magnet materials and method of making the same
US20060054245A1 (en) * 2003-12-31 2006-03-16 Shiqiang Liu Nanocomposite permanent magnets
US20060005898A1 (en) * 2004-06-30 2006-01-12 Shiqiang Liu Anisotropic nanocomposite rare earth permanent magnets and method of making
US20110050382A1 (en) * 2009-08-25 2011-03-03 Access Business Group International Llc Flux concentrator and method of making a magnetic flux concentrator
US8692639B2 (en) 2009-08-25 2014-04-08 Access Business Group International Llc Flux concentrator and method of making a magnetic flux concentrator

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