EP0599815A1 - Alliage magnétique et procédé de fabrication - Google Patents

Alliage magnétique et procédé de fabrication Download PDF

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Publication number
EP0599815A1
EP0599815A1 EP94101456A EP94101456A EP0599815A1 EP 0599815 A1 EP0599815 A1 EP 0599815A1 EP 94101456 A EP94101456 A EP 94101456A EP 94101456 A EP94101456 A EP 94101456A EP 0599815 A1 EP0599815 A1 EP 0599815A1
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EP
European Patent Office
Prior art keywords
rare earth
magnetic alloy
iron
coercive force
atomic percent
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EP94101456A
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German (de)
English (en)
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EP0599815B1 (fr
Inventor
Osamu C/O Seiko Epson Corporation Kobayashi
Koji Osamu C/O Seiko Epson Corporation Akioka
Tatsuya Osamu Seiko Epson Corporation Shimoda
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Seiko Epson Corp
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Seiko Epson Corp
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Priority claimed from JP62104622A external-priority patent/JP2611221B2/ja
Application filed by Seiko Epson Corp filed Critical Seiko Epson Corp
Priority claimed from EP87308559A external-priority patent/EP0288637B1/fr
Publication of EP0599815A1 publication Critical patent/EP0599815A1/fr
Application granted granted Critical
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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
    • 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

Definitions

  • This invention relates to magnetic alloys and methods of making the same.
  • Magnetic alloys, and especially permanent magnets made therefrom, are used in a wide field from household electric appliances to peripheral console units of large sized computers.
  • Typical permanent magnets now in use are alnico, hard ferrite magnets and rare earth element - transition metal magnets.
  • a R-Co (R represents a rare earth element) permanent magnet and a R-Fe-B permanent magnet, which are rare earth element-transition metal magnets can produce a high magnetic performance, so that much research has hitherto been conducted in relation to them.
  • Reference 1 Japanese Patent Laid-Open No. 46008/1984.
  • Reference 3 Japanese Patent Laid-Open No. 211549/1983.
  • Reference 5 Japanese Patent Laid-Open No. 100402/1985.
  • an alloy ingot is first made by melting and casting, and pulverised to obtain a metal powder having an appropriate particle size (several microns). Powder is needed with a binder of a moulding additive, and pressed in a magnetic field to obtain a moulded body.
  • the moulded body is sintered at approximately 1100 o C in an argon atmosphere for 1 hour and thereafter rapidly quenched to room temperature. After sintering, the sintered body is heat treated at approximately 600 o C to improve the coercive force.
  • a rapidly quenched thin fragment of an R-Fe-B alloy is first made using a melt spinning apparatus at an optimum substrate velocity.
  • the thus obtained ribbon-like thin fragment having a thickness of 30 ⁇ m microns) is an aggregate of crystals having a diameter of not more than 100 ⁇ m (1,000 Angstroms). It is brittle and easily broken. Since the crystal grains are distributed isotropically, the thin fragment is magnetically isotropic.
  • the thin fragment is pulverised to an appropriate particle size and kneaded with a resin. The mixture is then pressed.
  • Method (3) produces a dense R-Fe-B magnet having anisotropy by subjecting the rapidly quenched thin fragment obtained by method (2) to a so-called two-stage hot pressing process in vacuum or in an inert gas atmosphere.
  • uniaxial pressure is applied so as to align the easy magnetisation axis in parallel to the pressing direction and to make the magnet anisotropic.
  • the crystal grains of the thin fragment produced by the melt spinning apparatus have a smaller grain diameter than the grain diameter of the crystal grains which exhibit the largest coercive force so that the optimum grain diameter is obtained when the crystal grains are made coarser during the subsequent hot pressing process.
  • Method (1) necessitates the step of powdering an alloy. Since an R-Fe-B alloy is very active in oxygen, the step of powdering further accelerates oxidation, whereby the oxygen concentration of the sintered body is inconveniently raised. Furthermore, when the powder is moulded, a moulding additive such as zinc stearate must be used. The moulding additive is removed from the moulded body prior to the sintering step, but several percent thereof remains in the magnet in the form of carbon. This carbon unfavourably significantly lowers the magnetic performance of the R-Fe-B alloy.
  • the moulded body obtained by press moulding the alloy with the moulding additive added thereto is called a green body, which is very brittle and difficult to handle. It therefore disadvantageously requires much labour to insert the green bodies in a sintering oven in a neatly arranged form.
  • manufacture of an R-Fe-B permanent magnet generally not only requires expensive equipment, but also has low productivity, resulting in high manufacturing costs. It cannot, therefore, be said that method (1) is capable of making the best use of the merit of an R-Fe-B magnet which is comparatively inexpensive in material costs.
  • Both methods (2) and (3) use a vacuum melt spinning apparatus. This apparatus has very low productivity and is very expensive at present.
  • Method (2) adopting a resin bonding process produces a magnet having theoretical isotropy and, hence, a low energy product. Since the squareness of the hysteresis loop is not good, this magnet is disadvantageous both in the temperature characteristics and in use.
  • Method (3) is a unique method in that the hot pressing process is used in two stages. However, it cannot be denied that this method is very inefficient in actual mass production.
  • the crystal grains are remarkably coarse at a relatively high temperature of, for example, more than 800°C, which lowers the coercive force iHc to such a great extent that a practical permanent magnet is not obtainable.
  • a further method (4) of manufacturing a permanent magnet is disclosed in French patent publication no. 2 586 323.
  • a method is used, comprising melting an alloy, pouring the molten alloy into a mould casting it and either hot working before casting or applying a resin thereafter.
  • This method results in a permanent magnet which overcomes the problems of oxidation and the need to handle a green body.
  • the resultant permanent magnet also has slightly improved magnetic characteristics over method (1), (2) and (3) above.
  • the improvement is not significant and given the importance of such magnets greater magnetic characteristics are considered essential.
  • such a magnet still suffers from the disadvantage that the coercive force is unacceptably low since the crystal grains are relatively tiny.
  • the present invention seeks to eliminate the above described disadvantages of known methods and to provide a magnetic alloy and a method of making the same which can readily be used to manufacture a high performance low cost permanent magnet.
  • the known methods of making rare earth element-iron magnets have serious defects such as difficulty in handling pulverised powder and poor productivity.
  • the optimum composition of an R-Fe-B magnet is conventionally considered to be R15Fe77B8, as is described in Reference 2 above.
  • R and B are richer than in the composition R2Fe 82.4 B 5.9 , which is obtained by calculating the main phase R2Fe14B, compound in terms of percentage. This is because a non-magnetic phase such as an R-rich phase and B-rich phase as well as the main phase is necessary in order to obtain a coercive force.
  • the maximum value of the coercive force is obtained when the B content is lower than that of the main phase.
  • this composition range has not been taken into much consideration, because the coercive force is greatly reduced when a sintering process is used.
  • the coercive force is easy to obtain when the B content is lower than the stoichiometric composition, and difficult to obtain when the B content is higher.
  • the coercive force of a magnet of this type fundamentally conforms to a single magnetic domain model.
  • the magnet has a magnetic domain wall in the crystal grains, so that reverse magnetisation is easily caused by the movement of the magnetic wall, thereby reducing the coercive force.
  • the R2Fe14B phase has an appropriate grain diameter.
  • the appropriate grain diameter is about 10 ⁇ m (microns) and, in the case of a sintering type magnet, it is possible to determine the grain diameter by adjusting the grain size of the powder before sintering.
  • the composition has a great influence on the grain size, and if not less than 8 atm % of B is included, the R2Fe14B phase as cast is apt to have coarse grains, so that it is difficult to obtain a good coercive force unless the quenching rate is increased more than usual.
  • This region can be said from another point of view to be a phase richer in Fe than R2Fe14B phase, and Fe is first crystallised out as a primary crystal in the solidification step and subsequently the R2Fe14B phase appears by peritectic reaction.
  • the quenching rate is much higher than the equilibrium reaction, the R2Fe14B phase solidifies around the primary crystal Fe.
  • B is less, a phase richer in B such as an R15Fe77B8 phase, which is a typical composition of a sintering type magnet, is almost negligible.
  • the heat treatment is carried out in order to diffuse the primary crystal Fe so as to attain the equilibrium state, the coercive force largely depending on the diffusion of the Fe phase.
  • adoption of the columnar structure has two effects; one is that it enables the permanent magnet to possess plane anisotropy, and the other is that it enables the permanent magnet to obtain a high performance during hot working.
  • the intermetallic compound R2Fe14B which becomes the source of the magnetism of the R-Fe-B magnet, has the property of distributing the easy magnetisation axis C in a plane perpendicular to the columnar crystals when the columnar structures are grown.
  • the C axis is not in the direction of columnar crystal growth but is in a plane perpendicular thereto, namely, the permanent magnet has anisotropy in a plane.
  • This permanent magnet naturally and very advantageously has a higher performance than a permanent magnet which has a uniaxial macrostructure. Even if the columnar structure is adopted, the grain diameter must be fine in terms of the coercive force, and it is therefore desirable that the B content is low.
  • the adoption of a columnar structure further enhances the effect of hot working on bringing about anisotropy.
  • M.A. B X / ⁇ (Bx2 + By2 + Bz2) ⁇ x 100 (%) wherein Bx, By, Bz represent residual magnetic flux density in the directions x, y and z respectively, the degree of magnetic alignment in the isotropic magnet is about 60%, and in the plane anisotropic magnet, it is about 70%.
  • the effect of hot working on bringing about anisotropy exists irrespective of the degree of magnetic alignment of the material being processed, but the higher the degree of magnetic alignment of the original material, the higher the degree of magnetic alignment of the final processed material. Therefore, enhancing the degree of magnetic alignment of the original material by adopting a columnar structure is effective for finally obtaining a high performance anisotropic magnet.
  • rare earth element at least one selected from the group consisting of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu is used. Pr produces the highest magnetic performance.
  • Pr, Pr-Nd alloy, Ce-Pr-Nd alloy, etc. are used. Addition of a small amount of an element, e.g. heavy rare earth elements such as Dy and Tb, and Al, Mo, Si, etc. enhances the coercive force.
  • an element e.g. heavy rare earth elements such as Dy and Tb, and Al, Mo, Si, etc. enhances the coercive force.
  • the main phase of an R-Fe-B magnet is R2Fe14B. Therefore, if the R content is less than about 8 atm %, it is impossible to form the above described compound and the magnet has a cubic structure the same as that of an alpha-iron magnet, so that it is impossible to obtain high magnetic properties.
  • the R content is preferably 8 to 25 atm %.
  • the B is essential for forming an R2Fe14B phase, and if the B content is less than 2 atm %, a rhomobohedral R-Fe structure is formed, so that a high coercive force is not expected.
  • the B content exceeds 28 atm %, a non-magnetic B-rich phase increases, thereby greatly lowering the residual magnetic flux density.
  • the B content is preferably 2 to 8 atm %. If it exceeds 8 atm %, it is difficult to obtain a fine R2Fe14B phase, so that the coercive force is reduced.
  • Co is an effective element for increasing the Curie point of an R-Fe-B magnet.
  • the site of Fe is substituted by Co to form R2Co14B, but this compound has a small crystal magnetic anisotropy and with increase in amount, the coercive force of the magnet as a whole decreases. Therefore, in order to provide a coercive force of not smaller than 1 KOe, to use not more than 50 atm % Co is preferable.
  • Reference 6 shows the effect of Al on a sintered magnet, but the same effect is produced on a cast magnet.
  • Al is a non-magnetic element
  • the amount of Al to be added is increased, the residual magnetic flux density is lowered. If the amount exceeds 15 atm %, the residual magnetic flux density is lowered to not more than that of a hard ferrite and the roll of a rare earth magnet which has high performance is not attained. Therefore, the amount of Al to be added is not more than 15 atm %.
  • An alloy having the composition shown in Table 1 was first melted in an induction furnace, and cast into an iron mould to form a columnar structure.
  • the casting was annealed at 1000°C for 24 hours to be magnetically hardened.
  • the casting was cut and ground in this stage, thereby obtaining a magnet having plane anisotropy obtained by utilising the anisotropy of the columnar crystals.
  • the processing temperature was 1000°C.
  • Composition 1 Pr8Fe88B4 2 Pr14Fe82B4 3 Pr20Fe76B4 4 Pr25Fe71B4 5 Pr14Fe84B2 6 Pr14Fe80B6 7 Pr14Fe76B8 8 Pr14Fe72Co10B4 9 Pr14Fe57Co25B4 10 Pr14Fe42Co40B4 11 Pr13Dy2Fe81B4 12 Pr14Fe80B4Si2 13 Pr14Fe78Al4B4 14 Pr14Fe78Mo4B4 15 Nd14Fe82B4 16 Ce3Nd3P8Fe82B4 17 Nd14Fe76Al4B4 18 Pr14Fe80Ni2B4 19 Pr14Fe80Cu2B4 TABLE 2 No.

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  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Hard Magnetic Materials (AREA)
EP94101456A 1987-04-30 1987-09-28 Alliage magnétique et procédé de fabrication Expired - Lifetime EP0599815B1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
JP62104622A JP2611221B2 (ja) 1986-05-01 1987-04-30 永久磁石の製造方法
JP104622/87 1987-04-30
EP87308559A EP0288637B1 (fr) 1987-04-30 1987-09-28 Aimant permanent et son procédé de fabrication

Related Parent Applications (3)

Application Number Title Priority Date Filing Date
EP87308559.1 Division 1987-09-28
EP87308559A Division EP0288637B1 (fr) 1987-04-30 1987-09-28 Aimant permanent et son procédé de fabrication
EP87308559A Division-Into EP0288637B1 (fr) 1987-04-30 1987-09-28 Aimant permanent et son procédé de fabrication

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EP0599815A1 true EP0599815A1 (fr) 1994-06-01
EP0599815B1 EP0599815B1 (fr) 1998-01-07

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2586323A1 (fr) * 1985-08-13 1987-02-20 Seiko Epson Corp Aimant permanent a base de terres rares-fer
JPS62198103A (ja) * 1986-02-26 1987-09-01 Seiko Epson Corp 希土類−鉄系永久磁石

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2586323A1 (fr) * 1985-08-13 1987-02-20 Seiko Epson Corp Aimant permanent a base de terres rares-fer
JPS62198103A (ja) * 1986-02-26 1987-09-01 Seiko Epson Corp 希土類−鉄系永久磁石

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 12, no. 49 (E - 582)<2896> 13 February 1988 (1988-02-13) *
T.MIZOGUCHI ET AL, APPLIED PHYSICS LETTERS, vol. 48, no. 19, 12 May 1986 (1986-05-12), NEW YORK US, pages 1309 - 1310 *

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