EP2721618A1 - Neodymium/iron/boron-based permanent magnet - Google Patents

Neodymium/iron/boron-based permanent magnet

Info

Publication number
EP2721618A1
EP2721618A1 EP12800074.2A EP12800074A EP2721618A1 EP 2721618 A1 EP2721618 A1 EP 2721618A1 EP 12800074 A EP12800074 A EP 12800074A EP 2721618 A1 EP2721618 A1 EP 2721618A1
Authority
EP
European Patent Office
Prior art keywords
permanent magnet
component
boron
iron
combination
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP12800074.2A
Other languages
German (de)
French (fr)
Other versions
EP2721618A4 (en
Inventor
Renjie Chen
Aru YAN
Don Lee
Guanghui Yan
Youhao LIU
Alexandra Wilde
Peter Barth
Jiaqing Yu
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Ningbo Institute of Material Technology and Engineering of CAS
Robert Bosch GmbH
Original Assignee
Ningbo Institute of Material Technology and Engineering of CAS
Robert Bosch GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ningbo Institute of Material Technology and Engineering of CAS, Robert Bosch GmbH filed Critical Ningbo Institute of Material Technology and Engineering of CAS
Publication of EP2721618A1 publication Critical patent/EP2721618A1/en
Publication of EP2721618A4 publication Critical patent/EP2721618A4/en
Ceased legal-status Critical Current

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/02—Making ferrous alloys by powder metallurgy
    • C22C33/0257—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/10—Ferrous alloys, e.g. steel alloys containing cobalt
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
    • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
    • H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
    • H01F41/0273—Imparting anisotropy
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
    • B22F2998/10—Processes characterised by the sequence of their steps
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C2202/00—Physical properties
    • C22C2202/02—Magnetic

Definitions

  • the invention relates to a permanent magnet, more particularly to a sintered
  • the invention also relates to an electric motor, a generator and an integrated electromotor comprising the permanent magnet.
  • Electric motors with sintered neodymium/iron/boron-based permanent magnets are the vital components in electric vehicle and hybrid electric vehicle (EV/HEV). They show reduced copper losses, high power density, high efficiency, low rotor inertia, and other obvious advantages over induction motors.
  • the sintered neodymium/iron/boron-based permanent magnets in EV/HEV motors need to have high enough remanence, coercivty and thermal stability, provide high enough magnetic field to secure a stable motor performance within the whole working temperature range (normally from -40 to 180°C).
  • neodymium/iron/boron-based permanent magnets it is not so easy to retain high enough remanence and coercivity at a high temperature up to 180°C, although they have good magnetic properties at ambient temperature, the reason being that their remanence and coercivity will decay significantly as the temperature increases.
  • neodymium/iron/boron-based permanent magnets a main challenge for the neodymium/iron/boron-based permanent magnets is how to achieve high enough remanence and coercivity at a temperature up to 180°C (which is especially important for EV/HEV permanent magnet motors).
  • a conventional solution for this challenge is to add substantial quantities of heavy rare earth elements such as terbium (Tb) and dysprosium (Dy) to the permanent magnets.
  • Tb and Dy have a function to increase coercivity and thermal stability of the neodymium/iron/boron-based permanent magnets.
  • Coercivity is an important property of permanent magnets which measures the resistance of the magnets to becoming demagnetized, that is the magnitude of the applied demagnetizing field required to reduce the induction or magnetization of permanent magnets to zero after the magnets have been magnetized to saturation.
  • Intrinsic coercivity of the magnets is the permanent magnets' inherent ability to resist demagnetization.
  • a high intrinsic coercivity represents its great ability to withstand an external magnetic field.
  • Thermal stability is the ability of the permanent magnets to resist the change of coercivity and remanence against increasing temperature.
  • the remanence and coercivity of the current commercial magnets will decay at a respective rate of >0.12 /°C and >0.5 /°C as temperature increases from 20°C to 180°C.
  • the industries have attempted to introduce high contents of heavy rare earth elements Tb and Dy into the magnets to reduce the impact of the temperature on the remanence and coercivity of the permanent magnets .
  • US 2007/0137733 Al discloses a sytem of permanent magnet comprising rare earth material (>50wt.% Pr, 0-25wt.% Tb, 0-25wt.% Dy), Co and Ga with addition of Al, Cu, Cr, V, Nb and Zr.
  • rare earth material >50wt.% Pr, 0-25wt.% Tb, 0-25wt.% Dy
  • Co and Ga with addition of Al, Cu, Cr, V, Nb and Zr.
  • the intrinsic coercivity of the magnet is less than 18.9 KOe
  • Tb and no Dy the intrinsic coercivity is less than 2308KA/m
  • the intrinsic coercivity is less than
  • EP0680054B2 discloses a RE-Fe-B magnet comprising Dy (and no Tb), Co, C, O and Ag with addition of Al, Si, Sn, Zn, Nb, Mo, V, Cr, Zr, Hf, Ti and Mg, the magent having an intrinsic coercivity ranging from 748 to 1623KA/m.
  • EP1014392B2 discloses a rare earth/iron/boron-based permanent magnet comprising rare earth elements (Nd, Pr, Dy, Tb and Hf), Co, C, N, and O with addition of Al, Cu, Zr and Cr, the magnet having an intrinsic coercivity up to 159KA/m.
  • a neodymium/iron/boron- based permanent magnet comprising:
  • component R 2 to 13 wt.% of component R, wherein component R is selected from Pr, Ce, Gd, or Y, or any combination thereof,
  • component T 1.4 to 9 wt.% of component T, wherein component T is selected from Co, Cu, or Al, or any combination thereof,
  • component M 0.1 to 0.6 wt.% of component M, wherein component M is selected from Zr, Ti, or Mo, or any combination thereof,
  • the permanent magnet according to the invention has an intrinsic coercivity of 2040 to 2745KA/m at 20°C, and a temperature coefficient of intrinsic coercivity of 0.38 to 0.43%/°C.
  • neodymium/iron/boron-based permanent magnet comprising the steps of:
  • an alloy strip comprising 16 to 25 wt.% of Nd, 4 to 10 wt.% of Dy, 0 to 1.2 wt.% of Tb, 2 to 13 wt.% of component R, which is selected from Pr, Ce, Gd, or Y, or any combination thereof, 1.4 to 9 wt.% of component T, which is selected from Co, Cu, or Al, or any combination thereof, 0.1 to 0.6 wt.% of component M, which is selected from Zr, Ti, or Mo, or any combination thereof, 0.9 to 1.1 wt.% of B, and the balance of Fe;
  • an electric motor, a generator, an integrated starter-generator and/or other integrated electromotors comprising the permanent magnet.
  • Figure 1 schematically illustrates the flow chart of the method of manufacturing a neodymium/iron/boron-based permanent magnet according to the invention
  • Figure 2 schematically illustrates different shapes of the sintered
  • neodymium/iron/boron-based permanent magnet according to the invention.
  • the invention provides a novel sintered neodymium/iron/boron-based permanent magnet, consisting of Fe, B, a limited amount of heavy rare earth element Dy and very little or no Tb, light rare earth elements Nd and Pr, a combination of Co, Zr, Cu, Al, Y, Mo, Ti, Ce and/or Gd, and inevitable impurity such as O.
  • the magnet only contains a limited amount of Dy and very little or even no Tb, and yet has high coercivity and high thermal stability.
  • the magnet does not contain Ga, Nb, Cr and Ag. More specifically, the invention relates to a sintered neodymium/iron/boron-based permanent magnet, comprising:
  • component R 2 to 13 wt.% of component R, wherein component R is selected from Pr, Ce, Gd, or Y, or any combination thereof,
  • component T 1.4 to 9 wt.% of component T, wherein component T is selected from Co, Cu, or Al, or any combination thereof,
  • component M 0.1 to 0.6 wt.% of component M, wherein component M is selected from Zr, Ti, or Mo, or any combination thereof,
  • the permanent magnet according to the invention has an intrinsic coercivity of 2040 to 2745KA/m at 20°C, and a temperature coefficient of intrinsic coercivity of 0.38 to 0.43%/°C.
  • Dy may be present in an amount of 5 to 8 wt.%, and Tb may be present in an amount of 0 to 1 wt.%.
  • Component R is preferably Pr, Ce, or Y, or any combination thereof, and may be present in an amount of 4 to 6 wt.%.
  • Component T is preferably a combination of Co, Cu, and Al, and may be present in an amount of 1.5 to 4.0 wt.%.
  • Component M is preferably Zr, and may be present in an amount of 0.15 to 0.4 wt.%.
  • the components R, T, and M play an important role in improving the coercivity and thermal stability of the magnet.
  • the presence of these components refines the magnet grains and homogenize the micro structure of the magnet, thereby significantly improving the intrinsic coercivity (compared to the permanent magnet described in US 2007/0137733A1, the intrinsic coercivity at ambient temperature increases by about 64%).
  • a method of manufacturing the sintered neodymium/iron/boron-based permanent magnet according to the invention is illustrated as follows. Firstly, alloy strips having said composition are formed. Specifically, industrial pure raw materials (which all are metals or alloys) are smelted in the selected composition by vacuum- induction melting normally at 1380-1420°C (the vacuum degree being 5*10 ⁇ 2 to 7*10 ⁇ 2 Pa), and the raw materials can also be prealloys of master alloys made of the industrial pure raw materials. The smelter is then cast onto a spinning copper wheel which spins normally at 0.6- 3.5 m/s and cast into thin alloy strips having a thickness ranging from 0.1 to 1mm. The smelting process is performed under vacuum to avoid the oxidation of the metals and alloys.
  • the alloy strips are processed into fine powders.
  • the thin alloy strips are hydrogenated at 200KPa in a H 2 atmosphere, and then dehydogenated normally at 320°C and 580°C, then ground into fine powders by ball milling or jet milling in the protection of inert gas such as Ar and N 2 .
  • the rotation speed is about 4800Hz.
  • the formed fine powders have particle sizes ranging from ⁇ to ⁇ , with a mean particle size of about 3.5 ⁇ .
  • the fine powders are then aligned in a magnetic field with an intensity of 2T and compacted into a green body at a pressure of 40MPa in the protective N 2 gas.
  • particulate grains in the green body magnetically align to one direction, consequently the principal magnetic phase (RE) 2 Fei 4 B particles align along their easy axis.
  • the green body is further pressed and compacted into a higher density body by cold isostatic pressing at a pressure of about 300MPa for a duration of about 30s.
  • the higher density body is sintered at 900-1150°C for 1-10 hours to approximate its theoretical density.
  • the sintered body is then heat treated at
  • the sintering, heat treatment and aging processes are conducted under vacuum (the vacuum degree is, for example, 3*10 " Pa), and the subsequent cooling process is conducted in a protective inert gas atmosphere (for example, Ar).
  • a protective inert gas atmosphere for example, Ar
  • the sintered permanent magnet are then machined into different shapes (like the shapes as shown in Figure 2), applied with protective coatings and installed into an EV/HEV motor.
  • the obtained sintered permanent magnet is analysed and measured. Its chemical composition is analysed by inductive coupling plasma emission spectrograph (ICP). Its magnetic properties are measured by B-H tracer and physical property measurement system (PPMS), and the temperature coefficients of coercivity and remanence are then calculated.
  • ICP inductive coupling plasma emission spectrograph
  • PPMS physical property measurement system
  • the sintered neodymium/iron/boron-based permanent magnet according to the invention only contains a limited amount of Dy and very little or even no Tb, and yet has high coercivity and high thermal stability. It is a sintered neodymium/iron/boron-based permanent magnet having high coercivity, good thermal stability and a low production cost.
  • Example 1 A sintered neodymium/iron/boron-based permanent magnet comprising 10 wt.% of Dy and no Tb
  • Industrial pure raw materials (with a purity of 99%) were mixed in a ratio of 10wt.% Dy, 17.36wt.% Nd, 4.34wt.% Pr, 65.26wt.% Fe, 1.01 wt.% B, 1.0wt.% Co, 0.4wt.% Zr, 0.4wt.% Al and 0.23wt.% Cu, and introduced into a vacuum induction furnace (with a vacuum degree of 6*10 "2 Pa), and then smelted at 1420°C for 5 minutes. The smelter was cast onto a spinning copper wheel which spined at 1.7m/s and cast into thin alloy strips having a thickness of 0.5mm.
  • the purpose of vacuum smelting and casting was to avoid the oxidation of the metals and alloys. Then, the thin alloy strips were hydrogenated at 200KPa in a H 2 atmosphere, and then dehydrogenated at 320°C and 580°C. After dehydrogenation, the alloy strips were ground into fine powders having particle sizes ranging from ⁇ to ⁇ with a mean particle size of 3.5 ⁇ by jet milling at a rotation speed of 4800Hz in the protection of N 2 gas. The fine powders were aligned in a magnetic field with an intensity of 2T in the protective N 2 gas, and compacted into a green body at a pressure of 40MPa.
  • the principal magnetic phase (RE) 2 Fei 4 B particles aligned along their easy axis.
  • the green body was then further pressed and compacted into a higher density body by cold isostatic pressing at a pressure of 300MPa for a duration of 30s.
  • the higher density body was sintered at 1150°C for 2 hours, then heat treated at 900°C for 2 hours and aged at 650°C for 2 hours, to eventually form a sintered permanent magnet.
  • the sintering, heat treatment and aging processes were conducted under vacuum (the vacuum degree was 3*10 " Pa), and the subsequent cooling process was conducted in a protective Ar gas atmosphere.
  • the obtained sintered permanent magnet possesses the following good magnetic properties at 20°C: remanence (Br) of 1.12T, intrinsic coercivity (Hci) of 2745KA/m, energy product ((BH) max ) of 248KJ/m 3 ; at 180°C: remanence of 0.93T, intrinsic coercivity of 1050KA/m, energy product of 168KJ/m . Its temperature coefficients of remanence and intrinsic coercivty are respectively 0.11%/°C and 0.38%/°C within the temperature range of 20 to 180°C.
  • Example 2 A sintered neodymium/iron/boron-based permanent magnet comprising 5.8wt.% of Dy and 0.8 wt.% of Tb.
  • a sintered neodymium/iron/boron-based permanent magnet comprising 5.8wt.% Dy, 0.8wt.% Tb, 19.2 wt.% Nd, 4.8 wt.% Pr, 0.1 wt.% Ce, 0.2 wt.% Y, 65.52wt.% Fe, 0.98wt.% B, 2.0wt.% Co, 0.15wt.% Zr, 0.2wt.% Al and 0.25wt.% Cu was obtained.
  • Example 3 A sintered neodymium/iron/boron-based permanent magnet comprising 6.0wt.% of Dy and 0.8 wt.% of Tb.
  • a sintered neodymium/iron/boron-based permanent magnet comprising 6.0wt.% Dy, 0.8wt.% Tb, 19.2 wt.% Nd, 4.8 wt.% Pr, 0.2 wt.% Ce, 0.2 wt.% Y, 65.32wt.% Fe, 0.98wt.% B, 2.0wt.% Co, 0.15wt.% Zr, 0.2wt.% Al and 0.15 wt.% Cu was obtained.
  • Example 4 A sintered neodymium/iron/boron-based permanent magnet comprising 6.0wt.% of Dy and 0.7wt.% of Tb.
  • a sintered neodymium/iron/boron-based permanent magnet comprising 6.0wt.% Dy, 0.7wt.% Tb, 19.7 wt.% Nd, 4.92 wt.% Pr, 0.22 wt.% Ce, 0.2 wt.% Y, 63.26wt.% Fe, 0.97wt.% B, 3.0wt.% Co, 0.4wt.% Zr, 0.4wt.% Al and 0.23wt.% Cu was obtained.
  • Example 5 A sintered neodymium/iron/boron-based permanent magnet comprising 6.0wt.% of Dy and 0.7wt.% of Tb.
  • a sintered neodymium/iron/boron-based permanent magnet comprising 6.0wt.% Dy, 0.7wt.% Tb, 19.68 wt.% Nd, 4.92 wt.% Pr, 0.24 wt.% Ce, 0.2 wt.% Y, 65.14wt.% Fe, 0.97wt.% B, 1.0wt.% Co, 0.4wt.% Zr, 0.4wt.% Al and 0.35wt.% Cu was obtained.
  • the permanent magnet according to the invention only contains a limited amount of Dy and very little or even no Tb, and yet has a high remanence and coercivity at a temperature up to 180°C, and the remanence and coercivity decay less as the temperature increases.
  • the sintered neodymium/iron/boron-based permanent magnet according to the invention retains its good magnetic properties at a temperature up to 180°C, and therefore is capable of providing high enough magnetic field in the EV/HEV motors.
  • the permanent magnet of the invention has been described in great detail with respect to its application in electric motors, it would be easily appreciated by one of ordinary skilled in the art that the magnent can also be applied in generators, due to similar working principles to electric motors, in order to overcome some or all technical disadvantages as mentioned above. Likewise, the permanent magnet of the invention can also be applied in integrated starter-generators for electric vehicles and hybrid electric vehicles, as well as other integrated electromotors.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Power Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Hard Magnetic Materials (AREA)

Abstract

A sintered neodymium/iron/boron-based permanent magnet is provided. The permanent magnet comprises 16 to 25wt.% of Nd, 4 to 10 wt.% of Dy, 0 to 1.2 wt.% of Tb, 2 to 13 wt.% of component R, wherein component R is selected from Pr, Ce, Gd, or Y, or any combination thereof, 1.4 to 9 wt.% of component T, wherein component T is selected from Co, Cu, or Al, or any combination thereof, 0.1 to 0.6 wt.% of component M, wherein component M is selected from Zr, Ti, or Mo, or any combination thereof, 0.9 to 1.1 wt.% of B, and the balance of Fe. The permanent magnet only contains a limited amount of Dy and very little or even no Tb, and yet has high coercivity and high thermal stability. An electric motor, a generator and an integrated electromotor comprising the permanent magnet are also provided.

Description

NEODYMIUM/IRON/BORON-BASED PERMANENT MAGNET
Field of the Invention
The invention relates to a permanent magnet, more particularly to a sintered
neodymium/iron/boron-based permanent magnet with high coercivity and high thermal stability. The invention also relates to an electric motor, a generator and an integrated electromotor comprising the permanent magnet.
Background of the Invention
Electric motors with sintered neodymium/iron/boron-based permanent magnets are the vital components in electric vehicle and hybrid electric vehicle (EV/HEV). They show reduced copper losses, high power density, high efficiency, low rotor inertia, and other obvious advantages over induction motors.
The sintered neodymium/iron/boron-based permanent magnets in EV/HEV motors need to have high enough remanence, coercivty and thermal stability, provide high enough magnetic field to secure a stable motor performance within the whole working temperature range (normally from -40 to 180°C).
However, for the neodymium/iron/boron-based permanent magnets, it is not so easy to retain high enough remanence and coercivity at a high temperature up to 180°C, although they have good magnetic properties at ambient temperature, the reason being that their remanence and coercivity will decay significantly as the temperature increases.
Thus, a main challenge for the neodymium/iron/boron-based permanent magnets is how to achieve high enough remanence and coercivity at a temperature up to 180°C (which is especially important for EV/HEV permanent magnet motors). A conventional solution for this challenge is to add substantial quantities of heavy rare earth elements such as terbium (Tb) and dysprosium (Dy) to the permanent magnets. Tb and Dy have a function to increase coercivity and thermal stability of the neodymium/iron/boron-based permanent magnets.
Coercivity is an important property of permanent magnets which measures the resistance of the magnets to becoming demagnetized, that is the magnitude of the applied demagnetizing field required to reduce the induction or magnetization of permanent magnets to zero after the magnets have been magnetized to saturation. Generally, the larger the coercivity is, the greater the thermal stability of the magnets in a high temperature
environment is and the less they are affected by an external magnetic field. Intrinsic coercivity of the magnets is the permanent magnets' inherent ability to resist demagnetization. For a permanent magnetic material, a high intrinsic coercivity represents its great ability to withstand an external magnetic field.
Thermal stability is the ability of the permanent magnets to resist the change of coercivity and remanence against increasing temperature. The remanence and coercivity of the current commercial magnets will decay at a respective rate of >0.12 /°C and >0.5 /°C as temperature increases from 20°C to 180°C. In order to improve the thermal stability of the permanent magnets, the industries have attempted to introduce high contents of heavy rare earth elements Tb and Dy into the magnets to reduce the impact of the temperature on the remanence and coercivity of the permanent magnets .
However, as market demands for Tb and Dy continuously increase, the market prices of Tb and Dy are rocketing, which significantly increases the production cost of the permanent magnets. How to reduce the production cost is another challenge for the permanent magnets.
US 2007/0137733 Al discloses a sytem of permanent magnet comprising rare earth material (>50wt.% Pr, 0-25wt.% Tb, 0-25wt.% Dy), Co and Ga with addition of Al, Cu, Cr, V, Nb and Zr. In case of comprising Dy and no Tb, the intrinsic coercivity of the magnet is less than 18.9 KOe; in case of comprising Tb and no Dy, the intrinsic coercivity is less than 2308KA/m; in case of comprising both Tb and Dy, the intrinsic coercivity is less than
1592KA/m.
EP0680054B2 discloses a RE-Fe-B magnet comprising Dy (and no Tb), Co, C, O and Ag with addition of Al, Si, Sn, Zn, Nb, Mo, V, Cr, Zr, Hf, Ti and Mg, the magent having an intrinsic coercivity ranging from 748 to 1623KA/m.
EP1014392B2 discloses a rare earth/iron/boron-based permanent magnet comprising rare earth elements (Nd, Pr, Dy, Tb and Hf), Co, C, N, and O with addition of Al, Cu, Zr and Cr, the magnet having an intrinsic coercivity up to 159KA/m.
There remains a need for a neodymium/iron/boron-based permanent magnet with high coercivity and high thermal stability, and having a low production cost. Summary of the Invention
According to one aspect of the invention, there is provided a neodymium/iron/boron- based permanent magnet, comprising:
16 to 25 wt.% of Nd,
4 to 10 wt.% of Dy,
O to 1.2 wt.% of Tb,
2 to 13 wt.% of component R, wherein component R is selected from Pr, Ce, Gd, or Y, or any combination thereof,
1.4 to 9 wt.% of component T, wherein component T is selected from Co, Cu, or Al, or any combination thereof,
0.1 to 0.6 wt.% of component M, wherein component M is selected from Zr, Ti, or Mo, or any combination thereof,
0.9 to 1.1 wt.% of B, and
the balance of Fe.
The permanent magnet according to the invention has an intrinsic coercivity of 2040 to 2745KA/m at 20°C, and a temperature coefficient of intrinsic coercivity of 0.38 to 0.43%/°C.
According to another aspect of the invention, there is provided a method of
manufacturing a neodymium/iron/boron-based permanent magnet, comprising the steps of:
(1) forming an alloy strip, the alloy comprising 16 to 25 wt.% of Nd, 4 to 10 wt.% of Dy, 0 to 1.2 wt.% of Tb, 2 to 13 wt.% of component R, which is selected from Pr, Ce, Gd, or Y, or any combination thereof, 1.4 to 9 wt.% of component T, which is selected from Co, Cu, or Al, or any combination thereof, 0.1 to 0.6 wt.% of component M, which is selected from Zr, Ti, or Mo, or any combination thereof, 0.9 to 1.1 wt.% of B, and the balance of Fe;
(2) forming fine powders from the alloy strip;
(3) aligning the fine powders in a magnetic field, and compacting into a green body;
(4) further pressing and compacting the green body into a higher density body by cold isostatic pressing; and
(5) sintering the higher density body, followed by heat treatment and aging. According to yet another aspect of the invention, there is provided an electric motor, a generator, an integrated starter-generator and/or other integrated electromotors comprising the permanent magnet.
Brief Description of the Drawings
The invention will be described in greater detail with reference to the accompanying drawings in which:
Figure 1 schematically illustrates the flow chart of the method of manufacturing a neodymium/iron/boron-based permanent magnet according to the invention;
Figure 2 schematically illustrates different shapes of the sintered
neodymium/iron/boron-based permanent magnet according to the invention.
Detailed Description of the Invention
Unless otherwise stated, all patents, patent applications, articles and any other publications cited herein are hereby incorporated by reference in their entireties.
Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art. In the case of conflict, the definitions given in the present description will control.
It is also noted that a list of upper preferable values and lower preferable values of an amount, concentration or other value or paramenter specifically discloses all ranges formed from any pair of an upper preferred value and a lower preferred value, regardless of whether additional ranges are separately disclosed. Unless otherwise stated, the value ranges listed herein are intended to include end points, and all integers and fractions within the ranges.
The invention provides a novel sintered neodymium/iron/boron-based permanent magnet, consisting of Fe, B, a limited amount of heavy rare earth element Dy and very little or no Tb, light rare earth elements Nd and Pr, a combination of Co, Zr, Cu, Al, Y, Mo, Ti, Ce and/or Gd, and inevitable impurity such as O. The magnet only contains a limited amount of Dy and very little or even no Tb, and yet has high coercivity and high thermal stability.The magnet does not contain Ga, Nb, Cr and Ag. More specifically, the invention relates to a sintered neodymium/iron/boron-based permanent magnet, comprising:
16 to 25 wt.% of Nd,
4 to 10 wt.% of Dy,
O to 1.2 wt.% of Tb,
2 to 13 wt.% of component R, wherein component R is selected from Pr, Ce, Gd, or Y, or any combination thereof,
1.4 to 9 wt.% of component T, wherein component T is selected from Co, Cu, or Al, or any combination thereof,
0.1 to 0.6 wt.% of component M, wherein component M is selected from Zr, Ti, or Mo, or any combination thereof,
0.9 to 1.1 wt.% of B, and
the balance of Fe.
The permanent magnet according to the invention has an intrinsic coercivity of 2040 to 2745KA/m at 20°C, and a temperature coefficient of intrinsic coercivity of 0.38 to 0.43%/°C.
In the permanent magnet according to the invention, Dy may be present in an amount of 5 to 8 wt.%, and Tb may be present in an amount of 0 to 1 wt.%. Component R is preferably Pr, Ce, or Y, or any combination thereof, and may be present in an amount of 4 to 6 wt.%. Component T is preferably a combination of Co, Cu, and Al, and may be present in an amount of 1.5 to 4.0 wt.%. Component M is preferably Zr, and may be present in an amount of 0.15 to 0.4 wt.%.
In the permanent magent comprising limited amount of Dy and very little or even no Tb according to the invention, the components R, T, and M play an important role in improving the coercivity and thermal stability of the magnet. The presence of these components refines the magnet grains and homogenize the micro structure of the magnet, thereby significantly improving the intrinsic coercivity (compared to the permanent magnet described in US 2007/0137733A1, the intrinsic coercivity at ambient temperature increases by about 64%).
A method of manufacturing the sintered neodymium/iron/boron-based permanent magnet according to the invention is illustrated as follows. Firstly, alloy strips having said composition are formed. Specifically, industrial pure raw materials (which all are metals or alloys) are smelted in the selected composition by vacuum- induction melting normally at 1380-1420°C (the vacuum degree being 5*10~2 to 7*10~2 Pa), and the raw materials can also be prealloys of master alloys made of the industrial pure raw materials. The smelter is then cast onto a spinning copper wheel which spins normally at 0.6- 3.5 m/s and cast into thin alloy strips having a thickness ranging from 0.1 to 1mm. The smelting process is performed under vacuum to avoid the oxidation of the metals and alloys.
Then, the alloy strips are processed into fine powders. Specifically, the thin alloy strips are hydrogenated at 200KPa in a H2 atmosphere, and then dehydogenated normally at 320°C and 580°C, then ground into fine powders by ball milling or jet milling in the protection of inert gas such as Ar and N2. In case of jet milling, the rotation speed is about 4800Hz. The formed fine powders have particle sizes ranging from Ιμιη to ΙΟμιη, with a mean particle size of about 3.5μιη.
The fine powders are then aligned in a magnetic field with an intensity of 2T and compacted into a green body at a pressure of 40MPa in the protective N2 gas. In this process, particulate grains in the green body magnetically align to one direction, consequently the principal magnetic phase (RE)2Fei4B particles align along their easy axis.
The green body is further pressed and compacted into a higher density body by cold isostatic pressing at a pressure of about 300MPa for a duration of about 30s.
After the above processes, the higher density body is sintered at 900-1150°C for 1-10 hours to approximate its theoretical density. The sintered body is then heat treated at
800~900°C for 1-3 hours and aged at 400~650°C for 1-3 hours, to eventually form a sintered permanent magnet. The sintering, heat treatment and aging processes are conducted under vacuum (the vacuum degree is, for example, 3*10" Pa), and the subsequent cooling process is conducted in a protective inert gas atmosphere (for example, Ar).
The sintered permanent magnet are then machined into different shapes (like the shapes as shown in Figure 2), applied with protective coatings and installed into an EV/HEV motor.
The obtained sintered permanent magnet is analysed and measured. Its chemical composition is analysed by inductive coupling plasma emission spectrograph (ICP). Its magnetic properties are measured by B-H tracer and physical property measurement system (PPMS), and the temperature coefficients of coercivity and remanence are then calculated.
The sintered neodymium/iron/boron-based permanent magnet according to the invention only contains a limited amount of Dy and very little or even no Tb, and yet has high coercivity and high thermal stability. It is a sintered neodymium/iron/boron-based permanent magnet having high coercivity, good thermal stability and a low production cost.
The following examples are given to illustrate the sintered neodymium/iron/boron-based permanent magnet according to the invention, but are not to be construed as limiting the scope of the invention in any way.
Example 1: A sintered neodymium/iron/boron-based permanent magnet comprising 10 wt.% of Dy and no Tb
Industrial pure raw materials (with a purity of 99%) were mixed in a ratio of 10wt.% Dy, 17.36wt.% Nd, 4.34wt.% Pr, 65.26wt.% Fe, 1.01 wt.% B, 1.0wt.% Co, 0.4wt.% Zr, 0.4wt.% Al and 0.23wt.% Cu, and introduced into a vacuum induction furnace (with a vacuum degree of 6*10"2 Pa), and then smelted at 1420°C for 5 minutes. The smelter was cast onto a spinning copper wheel which spined at 1.7m/s and cast into thin alloy strips having a thickness of 0.5mm. The purpose of vacuum smelting and casting was to avoid the oxidation of the metals and alloys. Then, the thin alloy strips were hydrogenated at 200KPa in a H2 atmosphere, and then dehydrogenated at 320°C and 580°C. After dehydrogenation, the alloy strips were ground into fine powders having particle sizes ranging from Ιμιη to ΙΟμιη with a mean particle size of 3.5μιη by jet milling at a rotation speed of 4800Hz in the protection of N2 gas. The fine powders were aligned in a magnetic field with an intensity of 2T in the protective N2 gas, and compacted into a green body at a pressure of 40MPa. In this aligning moulding process, the principal magnetic phase (RE)2Fei4B particles aligned along their easy axis. The green body was then further pressed and compacted into a higher density body by cold isostatic pressing at a pressure of 300MPa for a duration of 30s. After the above processes, the higher density body was sintered at 1150°C for 2 hours, then heat treated at 900°C for 2 hours and aged at 650°C for 2 hours, to eventually form a sintered permanent magnet. The sintering, heat treatment and aging processes were conducted under vacuum (the vacuum degree was 3*10" Pa), and the subsequent cooling process was conducted in a protective Ar gas atmosphere. The obtained sintered permanent magnet possesses the following good magnetic properties at 20°C: remanence (Br) of 1.12T, intrinsic coercivity (Hci) of 2745KA/m, energy product ((BH)max) of 248KJ/m3; at 180°C: remanence of 0.93T, intrinsic coercivity of 1050KA/m, energy product of 168KJ/m . Its temperature coefficients of remanence and intrinsic coercivty are respectively 0.11%/°C and 0.38%/°C within the temperature range of 20 to 180°C.
Example 2: A sintered neodymium/iron/boron-based permanent magnet comprising 5.8wt.% of Dy and 0.8 wt.% of Tb.
By using a process similar to Example 1, a sintered neodymium/iron/boron-based permanent magnet comprising 5.8wt.% Dy, 0.8wt.% Tb, 19.2 wt.% Nd, 4.8 wt.% Pr, 0.1 wt.% Ce, 0.2 wt.% Y, 65.52wt.% Fe, 0.98wt.% B, 2.0wt.% Co, 0.15wt.% Zr, 0.2wt.% Al and 0.25wt.% Cu was obtained.
It possesses the following magnetic properties at 20°C: remanence of 1.18T, intrinsic coercivity of 2052KA/m, energy product of 270KJ/m3; at 180°C: remanence of 0.94T, intrinsic coercivity of 646KA/m, energy product of 170KJ/m . Its temperature coefficients of remanence and intrinsic coercivty are respectively 0.13%/°C and 0.43%/°C within the temperature range of 20 to 180°C.
Example 3: A sintered neodymium/iron/boron-based permanent magnet comprising 6.0wt.% of Dy and 0.8 wt.% of Tb.
By using a process similar to Example 1, a sintered neodymium/iron/boron-based permanent magnet comprising 6.0wt.% Dy, 0.8wt.% Tb, 19.2 wt.% Nd, 4.8 wt.% Pr, 0.2 wt.% Ce, 0.2 wt.% Y, 65.32wt.% Fe, 0.98wt.% B, 2.0wt.% Co, 0.15wt.% Zr, 0.2wt.% Al and 0.15 wt.% Cu was obtained.
It possesses the following magnetic properties at 20°C: remanence of 1.20T, intrinsic coercivity of 2324KA/m, energy product of 283KJ/m3; at 180°C: remanence of 0.96T, intrinsic coercivity of 823KA/m, energy product of 180KJ/m . Its temperature coefficients of remanence and intrinsic coercivty are respectively 0.13%/°C and 0.40%/°C within the temperature range of 20 to 180°C. Example 4: A sintered neodymium/iron/boron-based permanent magnet comprising 6.0wt.% of Dy and 0.7wt.% of Tb.
By using a process similar to Example 1, a sintered neodymium/iron/boron-based permanent magnet comprising 6.0wt.% Dy, 0.7wt.% Tb, 19.7 wt.% Nd, 4.92 wt.% Pr, 0.22 wt.% Ce, 0.2 wt.% Y, 63.26wt.% Fe, 0.97wt.% B, 3.0wt.% Co, 0.4wt.% Zr, 0.4wt.% Al and 0.23wt.% Cu was obtained.
It possesses the following magnetic properties at 20°C: remanence of 1.19T, intrinsic coercivity of 2068KA/m, energy product of 279KJ/m3; at 180°C: remanence of 0.96T, intrinsic coercivity of 657KA/m, energy product of 177KJ/m . Its temperature coefficients of remanence and intrinsic coercivty are respectively 0.12%/°C and 0.43%/°C within the temperature range of 20 to 180°C.
Example 5: A sintered neodymium/iron/boron-based permanent magnet comprising 6.0wt.% of Dy and 0.7wt.% of Tb.
By using a process similar to Example 1, a sintered neodymium/iron/boron-based permanent magnet comprising 6.0wt.% Dy, 0.7wt.% Tb, 19.68 wt.% Nd, 4.92 wt.% Pr, 0.24 wt.% Ce, 0.2 wt.% Y, 65.14wt.% Fe, 0.97wt.% B, 1.0wt.% Co, 0.4wt.% Zr, 0.4wt.% Al and 0.35wt.% Cu was obtained.
It possesses the following magnetic properties at 20°C: remanence of 1.19T, intrinsic coercivity of 2086KA/m, energy product of 278KJ/m3; at 180°C: remanence of 0.94T, intrinsic coercivity of 655KA/m, energy product of 172KJ/m . Its temperature coefficients of remanence and intrinsic coercivty are respectively 0.13%/°C and 0.43%/°C within the temperature range of 20 to 180°C.
The results of measuring the magnetic properties and thermal stability for the neodymium/iron/boron-based permanent magnets obtained in the above examples are summarized in table 1 below. Table 1
As can be seen from the above results, the permanent magnet according to the invention only contains a limited amount of Dy and very little or even no Tb, and yet has a high remanence and coercivity at a temperature up to 180°C, and the remanence and coercivity decay less as the temperature increases. The sintered neodymium/iron/boron-based permanent magnet according to the invention retains its good magnetic properties at a temperature up to 180°C, and therefore is capable of providing high enough magnetic field in the EV/HEV motors.
Although the permanent magnet of the invention has been described in great detail with respect to its application in electric motors, it would be easily appreciated by one of ordinary skilled in the art that the magnent can also be applied in generators, due to similar working principles to electric motors, in order to overcome some or all technical disadvantages as mentioned above. Likewise, the permanent magnet of the invention can also be applied in integrated starter-generators for electric vehicles and hybrid electric vehicles, as well as other integrated electromotors.
While the invention has been described with reference to a preferred embodiment, it will be understood that variation and modification can be made without departing the spirit and scope of the invention. Such variation and modification should be included in the scope of the appended claims.

Claims

What is claimed is:
1. A neodymium/iron/boron-based permanent magnet, comprising:
16 to 25 wt.% of Nd,
4 to 10 wt.% of Dy,
O to 1.2 wt.% of Tb,
2 to 13 wt.% of component R, wherein component R is selected from Pr, Ce, Gd, or Y, or any combination thereof,
1.4 to 9 wt.% of component T, wherein component T is selected from Co, Cu, or Al, or any combination thereof,
0.1 to 0.6 wt.% of component M, wherein component M is selected from Zr, Ti, or Mo, or any combination thereof,
0.9 to 1.1 wt.% of B, and
the balance of Fe.
2. The permanent magnet according to claim 1, wherein the permanent magent has an intrinsic coercivity of 2050 to 2745KA/m at 20°C.
3. The permanent magnet according to claim 1, wherein the permanent magent has a temperature coefficient of intrinsic coercivity of 0.38 to 0.43%/°C.
4. The permanent magnet according to claim 1, wherein Dy is present in an amount of 5 to 8 wt.%.
5. The permanent magnet according to claim 1, wherein Tb is present in an amount of 0 to 1 wt.%.
6. The permanent magnet according to claim 1, wherein component R is Pr, Ce, or Y, or any combination thereof, and is present in an amount of 4 to 6 wt.%.
7. The permanent magnet according to claim 1, wherein component T is a combination of Co, Cu, and Al, and is present in an amount of 1.5 to 4.0 wt.%.
8. The permanent magnet according to claim 1, wherein component M is Zr, and is present in an amount of 0.15 to 0.4 wt.%.
9. A method of manufacturing a neodymium/iron/boron-based permanent magnet, comprising the steps of: (1) forming an alloy strip, the alloy comprising 16 to 25 wt.% of Nd, 4 to 10 wt.% of Dy, 0 to 1.2 wt.% of Tb, 2 to 13 wt.% of component R, which is selected from Pr, Ce, Gd, or Y, or any combination thereof, 1.4 to 9 wt.% of component T, which is selected from Co, Cu, or Al, or any combination thereof, 0.1 to 0.6 wt.% of component M, which is selected from Zr, Ti, or Mo, or any combination thereof, 0.9 to 1.1 wt.% of B, and the balance of Fe;
(2) forming fine powders from the alloy strip;
(3) aligning the fine powders in a magnetic field, and compacting into a green body;
(4) further pressing and compacting the green body into a higher density body by cold isostatic pressing;
(5) sintering the higher density body, followed by heat treatment and aging.
10. The method according to claim 9, wherein the fine powders have particle sizes ranging from Ιμιη to ΙΟμιη, with a mean particle size of about 3.5μιη.
11. The method according to claim 9, wherein in the cold isostatic pressing, the pressue is about 300MPa, and the duration is about 30s.
12. An electric motor, comprising the neodymium/iron/boron-based permanent magnet according to any one of claims 1 to 8 or obtained by the method according to any one of claims 9 to 11.
13. A generator, comprising the neodymium/iron/boron-based permanent magnet according to any one of claims 1 to 8 or obtained by the method according to any one of claims 9 to 11.
14. An integrated electromotor, comprising the neodymium/iron/boron-based permanent magnet according to any one of claims 1 to 8, or obtained by the method according to any one of claims 9 to 11.
EP12800074.2A 2011-06-17 2012-06-15 PERMANENT MAGNET BASED ON NEODYM / IRON / BORE Ceased EP2721618A4 (en)

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