Classifications

• • 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
  • 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

• This invention concerns alloy powder for rare earth resin bonded magnets and their manufacturing methods that are suitable for magnet rolls, speakers, various kinds of meters, magnets for focusing, motors, magnetic sensors.and actuators.
• the amorphous structure is specially heat treated to obtain alloy powder of fine crystalline clusters which consist of the boron compound phase, where its main components is Fe with the tetragonal Fe3P type crystalline structure, and the Nd2Fe14B type crystalline structure phase.
• the resultant powder is bonded by resin to obtain the residual magnetic flux density (Br) of more than 5kG, which hitherto unobtainable by any hard ferrite magnet.
• This invention concerns the manufacturing method of such Fe-B-R type isotropic resin bonded magnet.
• Permanent magnets that are used for electrostatic developing magnet rolls, electric apparatus motors, and actuators were limited mainly to hard ferrite magnets; but, it suffered from problems such as the low temperature demagnetizing characteristics at low temperature below iHc, and due to the nature of ceramic material, it had the low mechanical strength which is likely to result in cracking and chipping, and it is difficult to obtain a complex shape.
• Nd-Fe-B type resin bonded magnet satisfies the necessary magnetic characteristics, but it contains 10-15 at% of Nd, which requires many processes and a large scale production facility in separation, purification and reduction of the metal. It is not only very expensive in comparison to hard ferrite magnet, but also it requires nearly 20 kOe of the magnetizing magnetic field to magnetize 90% of the magnet, so that it is impossible to perform the complex multipolar magnetization necessary for a magnet for a magnet roll or other application such as stepping motors. At present, no one has discovered a magnet which can be economically manufactured in a large scale, has Br of 5 ⁇ 7 kG, and also has the excellent magnetizing properties.
• the Fe3B type Nd-Fe-B system magnet is made amorphous by the melt-quenching method using a revolving roll, and heat treating it to obtain the hard magnet material.
• the resultant iHc is low, and the heat treatment condition mentioned earlier is very severe; and the attempt to increase iHc resulted, for example, in lowering the magnetic energy product, and the reliable industrial production is not feasible. Therefore, it cannot economically replace the ferrite magnet as its substitute.
• this invention intends to provide the most suitable rare earth magnet alloy powder for resin bonded magnets and their production method.
• Inventors investigated various manufacturing methods that provide improved iHc and (BH)max of a Fe3B type Fe-B-R system magnet and its reliable industrial production.
• the amorphous structure was obtained by the melt-quenching method using a revolving roll.
• the amorphous structure can be obtained by a relatively slow circumferential velocity region (5 ⁇ 20m/sec.) of a revolving roll.
• This invention making essentially more than 90% into the amorphous structure from the Fe-Co-B-R-M molten alloy using the melt-quenching method; and after raising the temperature of resultant flakes and ribbons at the rare of 1 ⁇ 15°C and heat treating them for 5 minutes to 6 hours by keeping the temperature at 550 ⁇ 730°C, the fine crystalline cluster with the average crystalline diameter of 5nm ⁇ 100nm, which consists of the ferromagnetic phase with Nd2Fe14B type crystalline structures in addition to its predominant phase of the Fe3B type chemical compound phase.
• the relative abundance of these ferromagnetic phases increase while the alpha-Fe phase decreases.
• the effect of including at least one elements of Al, Si, Cu, Ga, Ag, and Au in Fe-Co-B-R alloy is that the magnetic characteristic of iHc ⁇ 3kOe, Br ⁇ 8kG, and (BH)max ⁇ 8MGOe is obtainable, by not lowering Br even with addition of Co and improving the squareness of the demagnetizing curve. Furthermore, by grinding the alloy and making it into the alloy powder for magnets, we obtained the alloy powder which is most suitable for the Fe-Co-BR-M system resin bonded magnet with the residual magnetic flux density (Br) with more than 5KG.
• the alloy powder is produced by the efficient gas atomizing method from the specific composition of the Fe-Co-B-R-M system molten alloy with a low concentration of rare earth elements, it is heat treated to obtain the metastable compound system which consists of the iron-rich Fe3B type compound phase, which is of the body centered tetragonal Fe3P type crystalline structure belonging to the space group l4, and the Nd2Fe14B type crystalline phase.
• the metastable compound system which consists of the iron-rich Fe3B type compound phase, which is of the body centered tetragonal Fe3P type crystalline structure belonging to the space group l4, and the Nd2Fe14B type crystalline phase.
• the fine crystalline cluster of the average crystalline diameter of 5nm ⁇ 100nm in the predominant phase of the Fe3B type compound phase is obtained.
• the predominant Fe3B type compound phase and the Nd2Fe14B type crystalline phase are obtained, and these ferromagnetic phases coexist in each particle in the alloy powder for resin bonded magnets. Bonding the alloy powder by resin, it is possible to obtain the resin bonded magnet with the magnetic characteristics of iHc ⁇ 3kOe, Br ⁇ 5kG, and (BH)max ⁇ 4MGOe.
• the rare earth element, R is limited one or two elements of Pr or Nd with the specified concentration, high magnetic characteristics are observed.
• other rare earth elements for example, Ce and La are used, iHc does not exceed more than 2kOe.
• the medium weight rare earth elements after Sm and the heavy weight rare earth elements it induces degradation of the magnetic characteristic, and at the same time, resulted in the high cost magnet which is not desirable.
• Co is effective in improving the squareness of the demagnetizing curve, but when it exceeds 15at%, it remarkably decreases iHc to no more than 2kOe, so that the concentration is set at the range of 0.05 ⁇ 15at%.
• Al, Si, Cu, Ga, Ag, and Au improve the squareness of the demagnetizing curve by expanding the heat treatment temperature range, and increase (BH)max.
• at least 0.1at% of the additives is necessary. But when the concentration exceeds 3at%, it degrades the squareness and lower (BH)max. So, the concentration is set at the range of 0.1 ⁇ 3at%.
• the alloy powder which constitutes rare earth magnets of this invention is characterized by having the boron compound Fe3B type phase of highly saturated magnetization of 1.6T in which iron is the predominant element and which crystallization the body centered tetragonal Fe3P type crystalline structure, and having more than 70vol% of the Fe3B type compound phase.
• This boron compound is made by replacing a part of Fe with Co in Fe3B.
• This boron compound phase can coexist metastably under the certain range with the Nd2(Fe, Co)14B ferromagnetic phase which has the Nd2Fe14B type crystalline structure of the space group P4/mnm.
• the boron compound phase and the ferromagnetic phase coexist in order to have the high magnetic flux density and sufficient iHc.
• the thermal equilibrium Fe3B phase possessing the C16 type crystalline structure and the body centered cubical alpha-Fe phase rather than the metastable phases are grown.
• the high magnetization is obtained, but iHc degrades below 1kOe and cannot be used as a suitable magnet.
• a rare earth magnet consists of the alloy powder, which in turn is made with the coexisting boron compound phase, in which Fe3B type compound with the body centered tetragonal Fe3P type crystalline structure is the main component, and the Nd2Fe14B type crystalline phase coexists as another constituend phase.
• These phases are ferromagnetic, but the former phase by itself is magnetically soft; therefore, it must coexist with the latter phase to have the desirable iHc.
• the average crystalline particle diameter is not in the range of 5nm ⁇ 100nm, the square characteristic of the demagnetization curve will deteriorate and it cannot generate the sufficient magnetic flux at the activating point. Therefore, the average crystalline particle diameter must be set at 5nm ⁇ 100nm.
• the powder particle diameter with less than 0.1 micro meter requires a large amount of resin as a binder for its increased surface area, which results in lowering the packing density and is not desirable. Therefore, the powder particle diameter size is limited to 0.1-100 micro meter.
• the molten alloy with the above mentioned special composition is rapidly solidified either by the melt quenching method or atomizing method to transform the majority of it into the amorphous structure.
• the temperature was increased at the rate of 1 ⁇ 15°C/min specifically in the temperature range. beginning at 500°C or above, it is heat treated at 550 ⁇ 730°C for 5 minutes ⁇ 6 hours.
• the fine crystalline cluster It is important for the fine crystalline cluster to have the thermodynamically metastable Fe3B compound phase and with the average crystalline particle diameter of 5 ⁇ 100nm.
• the chilling method of the molten alloy there are the well known melt quenching method, the atomizing method, and a combination of the two methods. It is necessary to have essentially more than 90% amorphous in the rapidly solidified resultant alloy powder before the above mentioned beat treatment procedure.
• the roll surface rotational speed in the rage of 5 ⁇ 50m/sec. produces the desirable structure. That is to say, when the rotational speed is less than 5m/sec., it does not produce the amorphous structure but the amount of alpha-Fe phase precipitates increases. When the roll surface rotational speed exceeds 50m/sec., the chilled alloy does not form a continuous ribbon and alloy flakes scatter. It is not desirable since the alloy recovery yield and the yield efficiency decrease. If a minute amount of the alpha-Fe phase exists in the chilled ribbon, it is permissible since it does not noticeably lower the magnetic characteristic.
• the injection pressure is less than 10kgf/cm2
• the amorphous structure cannot be obtained.
• the alloy deposits on the surface of a recovery container without sufficiently being cooled, so that the powder beads into lumps resulting in low recovery yield of the alloy.
• the injection pressure exceeds 80kgf/cm2
• the volume fraction of powder is pulverized to the fine particle diameter of less than 0.1 micro meter increases, and not only lower the recovery yield and the recovery efficiency but also lower the pressing density, which is not desirable.
• the chilling method which combines the melt-quenching method and the gas atomization method is suitable for the mass production.
• the molten alloys is injected against the revolving roll in the form of spray using the gas-atomize technique. By selecting the roll surface rotational speed and the injection pressure, it is possible to obtain the desired amorphous particle diameter of alloy powder and flakes.
• the molten alloy of the above mentioned specific composition is rapidly solidified by the melt quenching method or the atomization method, converting the majority into the amorphous solid phase.
• the heat treatment that will produce the maximum magnetic characteristic, depends on the structural composition of alloy. But when the heat treatment temperature is less than 550°C, the amorphous phase remains and cannot obtain iHc of more than 2kOe; and when the temperature exceeds 730°C, the thermodynamically equilibrium phase, the alpha-Fe phase and the Fe2B or the Nd 1.1 Fe4B4 phase grow. Since the iHc generation will not take place in the equilibration phase mixture, the heat treatment temperature is limited to 550-730°C.
• the innert gas such as Ar gas is suitable as the heat treatment atmosphere.
• the heat treatment time can be short, but if it is less than 5 minutes the sufficient micro structure growth will not take place, and iHc and the squareness of the demagnetization curve deteriorate. Also, when it exceeds 6 hours, iHc with more than 2kOe cannot be obtained. Therefore, the heat treatment holding time is limited to 5 minutes-6 hours.
• the rate of the temperature increase from 500°C and above in the heat treatment process is the rate of the temperature increase from 500°C and above in the heat treatment process.
• the temperature increases at the rate less than 1°C /min. more than 2kOe of iHc cannot be obtained, since iHc deteriorates from the too large crystalline diameter of the Nd2Fe14B phase and the Fe3B phase.
• any rate of the temperature increase is acceptable including the rapid heating.
• the invented alloy powder for rare earth magnets which is obtained in such a way that the average crystalline particle diameter is 5nm ⁇ 100nm, is modified to fall in the average powder particle diameter of the alloy 0.1 ⁇ 500 micro meter range by, if nesessary, grinding when combination of gas atomized and melt spinning is used, the grinding process way not be necessary. Then the powder is mixed with well known resin to make a resin bonded magnet, which has the residual magnetic flux density (Br) exceeding 5kG.
• the resin bonded magnet obtained in this invention is an isotropic magnet, and it can be manufactured by any of the methods described below such as the compression molding, the injection molding, the extrusion molding, the roll molding, and the resin impregnation.
• thermosetting plastics,coupling agent, and lubricant are added to the magnet powder and mixed, it is compression molded and heated to cure the resin to obtain resin bonded magnets.
• the extrusion molding, and roll molding and after thermoplastic resin, coupling agent, lubricant are added to the magnet powder and mixed, it is molded by one of the molding methods such as the injection molding, the extrusion molding, and the roll molding.
• the magnet powder is compressed and heated if appropriate, it is impregnated by thermosetting plastics, and heated to cure the resin.
• resin bonded magnet is obtained by compress molding, heat treating it when appropriate (namely, when the rapidly solidified powder is directly compressed), and impregnating the magnet powder by thermoplastic resin.
• the weight proportion of the magnet powder in the resin bonded magnet which is different from the afore mentioned manufacturing method, is 70 ⁇ 99.5wt/% and the remainder is 0.5 ⁇ 30% of resin and others.
• the weight proportion of magnet powder is 95 ⁇ 99.5wt%; in the injection molding, the packing rate of magnet powder is 90 ⁇ 95wt%; in the impregnation molding, the weight proportion of magnet powder is 96 ⁇ 99.5%.
• Synthetic resin which is used as a binder can be thermosetting or thermoplastic, but thermally stable resin is preferred, and it can be appropriately selected from the polyamide, polyamide, phenol resin, fluoride resin, silicon resin and epoxy resin.
• melt quenched ribbon was of the amorphous structure by the powder X ray diffraction method using the characteristic X ray of Cu-K-alpha.
• the measurement of samples indicated that the predominant phase is a Fe3B phase, of the tetragonal Fe3P type structure crystalline structures, and also indicated the multi phase structure including the Nd2Fe14B phase and alpha-Fe phase coexist.
• the average crystalline diameter for these crystals is less than 0.1 micro meter.
• Co in these phases replace a part of Fe, but for Ag, Al, Si, Cu and Ga, it was difficult to analyze since they are minute additives and of ultra fine crystalline structures.
• melt-quenched ribbons that are made under the same condition as in Example 1, of compositions No.2 and No.7 of Example 1 are rapidly heated to 500°C in the Ar gas atmosphere, the temperature was raised at the rate of 11°C /min. above 500°C, and heat treated at 620°C for 10 min. After the ribbons are cooled, samples are prepared under the same condition (Comparison, No.14, No.18) as in Example 1, and the magnetic characteristic was measured using the VSM. Table 2 shows their results.
• melt-quenched ribbons that are made under the same conditions as Example 1, of compositions No.2 and No.7 of Example 1 were rapidly heated to 500°C in the Ar gas atmosphere, the temperature was kept at 500°C for 10 minutes for the heat treatment for the comparisons No. 15 and No. 19; and for the comparisons No. 16 and No.20, the temperature was raised at 4°C /min. and it was kept at 750°C for 10 minutes for the heat treatment. After a respective ribbon was cooled, the sample was prepared in the same manner as in Example 1, and the magnetic characteristic was measured using the VSM. Table 2 shows their result.
• Example 1 Melt-quenched ribbons obtained in Example 1, whose compositions are No.4 and No.9 of Table 1, after they were heat treated as in Table 1, the ribbons were ground to less than 150 micro meter in the average particle diameter.
• the magnet powder was mixed with epoxy resin as a binder with the proportion of 3wt%, and a resin bonded magnet of a density of 5.8g/cm3 with a dimension of 15mm X 15mm X 7mm was made.
• the structure of the alloy powder thus obtained was confirmed to be amorphous by means of the characteristic X ray of Cu-K-alpha.
• the result of measurement indicates that the multi-phase exists with the Fe3B phase as the predominant phase, of the tetragonal Fe3P structures, mixed with the Nd2Fe14B phase and the alpha-Fe phase coexists.
• the average crystalline particle diameter was less than 0.1 micro meter in all phases.
• Co replaces a part of Fe in each phase; but as far as Al, Si, Cu, Ga, Ag, and Au are concerned, since these are minute additives and of ultra fine crystalline structures, they were not detectable.
• the sample structure was multi phaseed where the predominant Fe3B type phase, the Nd2Fe14B type phase, and the alpha-Fe phase coexist with the average crystalline diameter of less than 0.1 micro meter. Moreover, Co replaces a part of Fe in each phase.
• the density of this resin bonded magnet is 5.6g/cm3, and Table 6 shows its magnetic characteristics.
• the comparison sample No.44 showed the amorphous structure, while No.45 showed the multi phase structure of the Fe2B phase and the alpha-Fe phase coexisting.
• Table 5 Composion(at%) Heating rate Heat treatment temperature Keeping time R Fe Co B M (°C/min.) min.
• This invention concerns rapidly solidifying the Fe-Co-B-R-M type molten alloy with the specific composition by the melt-quenching method or by the atomizing method or a combination of these two methods, transforming the bulk of it into the amorphous structure powder with the average particle diameter of 0.1-100 micro meter; after heat treating the amorphous alloy powder; magnet alloy powder of fine crystalline clusters with the average crystalline diameter of 5 ⁇ 100nm is obtained.
• the resin bonded magnet obtained by this invented method has a small quantity of rare earth and the manufacturing method is simple, it is suitable for a large scale manufacturing. It has more than 5kG of the residual magnetic flux density (Br), and possesses magnetic characteristic that exceeds that of hard ferrite magnet. By utilizing the unit molding of magnetic parts and magnets, it is possible to shorten the manufacturing processes.
• This invention can provide resin bonded magnets that exceeds sintered hard ferrite magnets in the performance to cost ratio.

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• 1992
  • 1992-11-10 CN CN92114394A patent/CN1053988C/zh not_active Expired - Lifetime
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