JP7586881B2 - Sintered rare earth neodymium-iron-boron magnets, their manufacturing method and use of praseodymium hydride - Google Patents

Description

The present invention provides rare earth sintered neodymium-iron-boron magnets, their manufacturing method, and uses of praseodymium hydride.

With the increasing demand for hybrid cars, electric cars and energy-saving air conditioner compressors, the demand for permanent magnet materials with high coercivity and low temperature coefficient is also increasing. The use of large amounts of heavy rare earth elements can improve the coercivity and temperature coefficient of permanent magnet materials, but this brings about a significant increase in cost and partially sacrifices the remanence and magnetic energy product. An alloy sheet with the atomic composition of each element is Nd _14.1 Co _1.34 Cu _0.04 Fe _bal B _5.84 is manufactured, the alloy sheet is hydrogen-milled into coarse powder with a particle size of 10-100 μm, the coarse powder is jet-milled in a nitrogen atmosphere to make fine powder with an average particle size of 3.38 μm, and D _y H _x powder with an average particle size of 1.8 μm is mixed with the fine powder, and hydrostatically isostatically pressed under a magnetic field of 1800 kA/m and a pressure of 300 MPa. The green body is sintered under vacuum conditions at 1040-1060 ° C for 2 h, then gas-cooled and quenched, and then tempered at 900 ° C and 500 ° C for 2 h, respectively. This method requires the use of heavy rare earth Dy, and the D _y H _x powder is directly mixed with the fine powder. This method can greatly improve the coercive force of the magnet, but it also reduces the residual magnetic flux density so much that the balance between the coercive force and the residual magnetic flux density is lost.

Although the temperature coefficient of a magnet can be improved by adding Co and Ni elements, excessive addition of Co and Ni elements leads to a decrease in magnet performance, and Co and Ni elements are strategic elements and relatively expensive. CN111696742A discloses a method for producing a high-performance neodymium-iron-boron permanent magnet material that does not contain heavy rare earth elements, which comprises preparing an anisotropic magnet material (Nd, Pr) _x Fe _(100-x-y-z) B _y M _z and an auxiliary phase material Pr _a Ni _100-b , uniformly mixing the anisotropic magnet material and the auxiliary phase material to form a mixed magnetic powder, and then carrying out orientation press molding, sintering and tempering treatments in this order to obtain a high-performance neodymium-iron-boron material that does not contain heavy rare earth elements. CN104575899A discloses a method for producing a sintered neodymium-iron-boron magnet in which a main alloy powder and a rare earth cobalt compound powder are directly mixed and then molded, thereby increasing the average thickness of the grain boundary phase of the resulting magnet. These methods can improve the coercive force of the magnet, but cannot prevent a decrease in the residual magnetic flux density, making it difficult to achieve a good balance between the coercive force and the residual magnetic flux density.

In one aspect, the present invention provides a (R1, R2)-TB-M rare earth sintered neodymium-iron-boron magnet that achieves a good balance between the coercivity and remanence of the rare earth sintered neodymium-iron-boron magnet. Furthermore, the rare earth sintered neodymium-iron-boron magnet of the present invention has a low temperature coefficient of remanence and a low temperature coefficient of coercivity.

In another aspect, the present invention provides a method for producing an (R1, R2)-TB-M rare earth sintered neodymium-iron-boron magnet. Unlike conventional methods, this method suppresses the decrease in residual magnetic flux density, thereby achieving a good balance between the coercive force and residual magnetic flux density of the rare earth sintered neodymium-iron-boron magnet.

In another aspect, the present invention provides the use of praseodymium hydride.

In one embodiment, the present invention is a (R1,R2)-TBM rare earth sintered neodymium-iron-boron magnet, comprising:
The rare earth sintered neodymium-iron-boron magnet is composed of a sintered body containing main phase crystal grains and a grain boundary phase,
the main phase crystal grains are made of a (R1, R2) ₂ T ₁₄ B phase, and a Pr concentration C ₁ at an edge of the main phase crystal grain is higher than a Pr concentration C ₂ at a center of the main phase crystal grain;
The R1 concentration of the grain boundary phase is higher than the R1 concentration of the main phase crystal grains, and the average thickness of the grain boundary phase is 20 to 60 nm;
R1 is one or more elements selected from Nd and Gd, and Nd accounts for 50 at % or more of the total number of atoms of R1;
R2 is a Pr element;
T is one or more elements selected from Fe, Co, and Ni, and Co and Ni account for 3 at % or less of the total number of atoms of T;
B is elemental boron;
The present invention provides an (R1, R2)-TBM rare earth sintered neodymium-iron-boron magnet, in which M is one or more elements selected from the group consisting of Al, Cu, Ga, Zn, Bi, Zr, Ti, Nb, V, Mo, and W, and the total atomic number of M is 5 at % or less of the sintered body.

In the rare earth sintered neodymium-iron-boron magnet of the present invention, the Pr concentration preferably gradually decreases from the edge of the main phase crystal grains toward the center of the main phase crystal grains.

In the rare earth sintered neodymium-iron-boron magnet according to the present invention, the Pr concentration _C1 at the edge of the main phase crystal grain is preferably 0.25 wt % or more higher than the Pr concentration _C2 at the center of the main phase crystal grain.

In the rare earth sintered neodymium-iron-boron magnet of the present invention, the composition of the sintered body is preferably R1: 28-31 wt%, R2: 0.1-5 wt%, B: 0.6-1.6 wt%, Co: 0.1-3.9 wt%, Cu: 0.05-1.0 wt%, Zr: 0.06-0.25 wt%, Ga: 0.1-0.3 wt%, and the balance is essentially Fe.

In the rare earth sintered neodymium-iron-boron magnet of the present invention, the Zr content in the sintered body is preferably 0.1 to 0.16 wt %, and the Ga content is preferably 0.15 to 0.25 wt %.

The rare earth sintered neodymium-iron-boron magnet of the present invention preferably does not contain heavy rare earth elements.

The rare earth sintered neodymium-iron-boron magnet of the present invention preferably has a residual magnetic flux density of 14.50 kGs or more, an intrinsic coercivity of 14.0 kOe or more, a residual magnetic flux density temperature coefficient within the range of 20 to 150°C of less than 0.113%/°C, and a coercivity temperature coefficient within the range of 20 to 150°C of less than 0.573%/°C.

In another embodiment, the present invention provides a method for producing a composition comprising:
(a) melting the raw materials R1, T, B and M of a rare earth sintered neodymium-iron-boron magnet to obtain a master alloy sheet;
(b) crushing the master alloy sheet into coarse alloy powder having an average particle size D50 of 20-500 μm;
(c) pulverizing the coarse alloy powder with a praseodymium-containing powder by jet milling to obtain a magnetic powder having an average particle size D50 of 1 to 10 μm, the praseodymium-containing powder being a praseodymium hydride or Pr-M alloy powder;
(d) pressing the magnetic powder in a magnetic field and obtaining a green body through hydrostatic isostatic pressing;
(e) subjecting the green body to a vacuum heat treatment and two-stage tempering to obtain a rare earth sintered permanent magnet;
The present invention also provides a method for producing the rare earth sintered neodymium-iron-boron magnet, comprising the steps of:

According to the manufacturing method of the present invention, the amount of praseodymium-containing powder used is preferably 0.1 to 5.0 wt % based on the mass of the alloy coarse powder.

In another aspect, the present invention provides a method for improving the balance factor between the residual magnetic flux density and the coercive force of a rare earth sintered neodymium-iron-boron magnet, comprising: pulverizing a coarse alloy powder with a praseodymium hydride powder by jet milling into a magnetic powder; and using an amount of the praseodymium hydride powder of 0.1 to 5.0 wt % based on the mass of the coarse alloy powder;
The composition of the alloy coarse powder is R1-TB-M,
R1 is one or more elements selected from Nd and Gd, and Nd accounts for 50 at % or more of the total number of atoms of R1;
T is one or more elements selected from Fe, Co, and Ni, and Co and Ni account for 3 at % or less of the total number of atoms of T;
B is elemental boron;
M is one or more elements selected from Al, Cu, Ga, Zn, Bi, Zr, Ti, Nb, V, Mo and W, and the total atomic number of M is 5 at % or less of the sintered body;
The balance coefficient E between the residual magnetic flux density and the coercive force is calculated as follows:
E = X2/X1
X1=(Br1-Br2)/Br1
X2=(Hcj2-Hcj1)/Hcj1
(Br1 represents the residual magnetic flux density of the rare earth sintered neodymium-iron-boron magnet obtained without adding praseodymium hydride powder in the jet milling process, and is expressed in kGs.
Br2 represents the residual magnetic flux density of the rare earth sintered neodymium-iron-boron magnet obtained by adding praseodymium hydride powder in the jet milling process, and is expressed in kGs.
Hcj1 represents the coercivity of the rare earth sintered neodymium-iron-boron magnet obtained without adding praseodymium hydride powder in the jet milling process, and is expressed in kOe.
Hcj2 represents the coercivity of the rare earth sintered neodymium-iron-boron magnet obtained by adding praseodymium hydride powder in the jet milling process, and is expressed in kOe.
The use of praseodymium hydride to improve the balance factor between remanence and coercivity in rare earth sintered neodymium-iron-boron magnets is provided.

The rare earth sintered neodymium-iron-boron magnet of the present invention has a relatively high coercivity and residual magnetic flux density, achieving a good balance between the two. Furthermore, the rare earth sintered neodymium-iron-boron magnet of the present invention has a relatively low temperature coefficient of residual magnetic flux density and temperature coefficient of coercivity.

FIG. 1 is a scanning electron microscope photograph of the rare earth sintered neodymium-iron-boron magnet obtained in Example 1.

The present invention is described in more detail below, but is not limited to this.

In the present invention, the residual magnetic flux density means the numerical value of the magnetic flux density corresponding to zero magnetic field strength at the saturation magnetic hysteresis line, and is usually expressed as Br or Mr, with the unit being Tesla (T) or Gauss (Gs). 1 Gs = 0.0001 T.

In the present invention, coercivity, also called intrinsic coercivity, refers to the magnetic field strength when the magnetic field is monotonically decreased from the saturation magnetization state of a magnet to zero and then increased in the opposite direction, decreasing the magnetization strength to zero along the saturation magnetic hysteresis line, and is usually written as Hcj, with units of oersted (Oe) or amperes per meter (A/m). 1 Oe = 79.6 A/m. Hcj is the intrinsic coercivity at room temperature.

In the present invention, the inert gas includes helium gas, neon gas, argon gas, krypton gas, xenon gas, etc. Vacuum refers to the degree of absolute vacuum, and the smaller the value, the higher the degree of vacuum.

In the present invention, the average particle size D50 refers to the equivalent diameter of the largest particle when the cumulative distribution in the particle size distribution curve is 50%.

In the present invention, "at%" refers to atomic percentage.

The purpose of the present invention is to achieve a good balance between the residual magnetic flux density and coercive force of a magnet. The formula for calculating the balance coefficient E between the residual magnetic flux density and coercive force is as follows:

E = X2/X1
X1=(Br1-Br2)/Br1
X2=(Hcj2-Hcj1)/Hcj1
Br1 represents the remanence, in kGs, of a rare earth sintered neodymium-iron-boron magnet obtained without the addition of any modifier powder. In some embodiments, Br1 represents the remanence, in kGs, of a rare earth sintered neodymium-iron-boron magnet obtained without the addition of any praseodymium hydride powder in the jet milling process.

Br2 represents the residual magnetic flux density, in kGs, of the rare earth sintered neodymium-iron-boron magnet obtained by adding the modifier powder. In some embodiments, Br2 represents the residual magnetic flux density, in kGs, of the rare earth sintered neodymium-iron-boron magnet obtained by adding the praseodymium hydride powder to the jet milling process.

Hcj1 represents the coercivity of a rare earth sintered neodymium-iron-boron magnet obtained without the addition of any modifier powder, in kOe. In some embodiments, Hcj1 represents the coercivity of a rare earth sintered neodymium-iron-boron magnet obtained without the addition of any additive praseodymium hydride powder to the jet milling process, in kOe.

Hcj2 represents the coercivity of the rare earth sintered neodymium-iron-boron magnet obtained by adding the modifier powder, in kOe. In some embodiments, Hcj2 represents the coercivity of the rare earth sintered neodymium-iron-boron magnet obtained by adding the praseodymium hydride powder to the jet milling process, in kOe.

In the present invention, it has been discovered that by adding praseodymium-containing powder to the jet milling process in which coarse alloy powder is pulverized into fine magnetic powder, the thickness of the grain boundary phase of the resulting magnet can be maintained within a certain range, and praseodymium exhibits a gradient distribution within the main phase particles, making it possible to achieve a good balance between the residual magnetic flux density and coercive force of the magnet. Based on this, the present invention is completed.

<Rare earth sintered neodymium-iron-boron magnet>
The rare earth sintered neodymium-iron-boron magnet according to the present invention has the elemental composition shown in the following formula.
(R1,R2)-TBM

A rare earth sintered neodymium-iron-boron magnet is composed of a sintered body containing main phase crystal grains and a grain boundary phase. In some embodiments, a rare earth sintered neodymium-iron-boron magnet is synonymous with a sintered body.

R1 is one or more elements selected from Nd and Gd. Nd is 50 at% or more of the total number of R1 atoms, preferably 80 at% or more of the total number of R1 atoms, and more preferably 95 at% or more of the total number of R1 atoms. According to one embodiment of the present invention, R1 is Nd.

R2 is the element Pr.

T is one or more elements selected from Fe, Co, and Ni. Co and Ni are 3 at% or less of the total number of atoms of T, preferably Co and Ni are 2 at% or less of the total number of atoms of T, and more preferably Co and Ni are 1 to 1.5 at% of the total number of atoms of T. According to one embodiment of the present invention, T is Fe and Co.

B is the element boron.

M is one or more elements selected from Al, Cu, Ga, Zn, Bi, Zr, Ti, Nb, V, Mo and W. Preferably, M is Cu, Zr and Ga. The total atomic number of M is 5 at% or less of the sintered body, preferably 4 at% or less, more preferably 3 at% or less, and most preferably 0.1-2 at%. According to one embodiment of the present invention, the total atomic number of M is 0.3-1 at% of the sintered body.

In the rare earth sintered neodymium-iron-boron magnet according to the present invention, the main phase crystal grains are composed of an (R1, R2) ₂ T ₁₄ B phase. The inventors have found that the Pr concentration C ₁ at the edge of the main phase crystal grain is higher than the Pr concentration C ₂ at the center of the main phase crystal grain. The Pr concentration C ₁ at the edge of the main phase crystal grain is 0.25 wt% or more higher than the Pr concentration C ₂ at the center of the main phase crystal grain. Preferably, the Pr concentration C ₁ at the edge of the main phase crystal grain is 0.40 wt% or more higher than the Pr concentration C ₂ at the center of the main phase crystal grain, and more preferably, the Pr concentration C ₁ at the edge of the main phase crystal grain is 0.50 wt% or more higher than the Pr concentration C ₂ at the center of the main phase crystal grain. In some embodiments, the concentration difference (C ₁ -C ₂ ) between the Pr concentration C ₁ at the edge of the main phase crystal grain and the Pr concentration C ₂ at the center of the main phase crystal grain is in the range of 0.25 to 0.70 wt%, preferably in the range of 0.40 to 0.70 wt%, and more preferably in the range of 0.45 to 0.65 wt%. According to one embodiment of the present invention, the concentration difference (C ₁ -C 2 ) between the Pr concentration C ₁ at the edge of the main phase crystal grain and the Pr concentration C ₂ at the center of the main phase crystal grain is 0.53 to 0.57 wt%. If the Pr concentration difference is too small, it is disadvantageous for improving the coercive force, and if the Pr _{concentration} difference is too large, it has a bad influence on the residual magnetic flux density, the residual magnetic flux density temperature coefficient, and the coercive force temperature coefficient. The Pr concentration difference in the above range is advantageous for achieving a good balance between the coercive force and the residual magnetic flux density of the magnet.

According to one embodiment of the present invention, the Pr concentration gradually decreases from the edge of the main phase crystal grain along the center of the main phase crystal grain. Thus, the Pr concentration exhibits a gradient distribution. This further ensures a good balance between the coercivity and residual magnetic flux density of the magnet.

The R1 concentration A1 of the grain boundary phase is higher than the R1 concentration A2 of the main phase crystal grains. The average thickness L of the grain boundary phase is 20 to 60 nm, preferably 20 to 40 nm, and more preferably 22 to 27 nm. If the thickness of the grain boundary phase is too small, the coercivity of the magnet cannot be significantly improved, and if the thickness of the grain boundary phase is too large, the residual magnetic flux density is significantly reduced, and the residual magnetic flux density temperature coefficient and the coercivity temperature coefficient are significantly increased. A grain boundary phase thickness in the above range is advantageous for achieving a good balance between the coercivity and residual magnetic flux density of the magnet.

The sintered body of the present invention includes elements such as R1, R2, B, Co, Cu, Zr, Ga, and Fe. In some embodiments, the sintered body of the present invention consists of R1, R2, B, Co, Cu, Zr, Ga, and Fe.

Based on the mass of the sintered body, the content of R1 may be 28 to 31 wt%, preferably 28 to 30 wt%, and more preferably 28 to 29 wt%.

Based on the mass of the sintered body, the content of R2 may be 0.1-5 wt%, preferably 1.0-3 wt%, more preferably 1.5-2.5 wt%, and most preferably 1.7-2.0 wt%.

Based on the mass of the sintered body, the B content may be 0.6 to 1.6 wt%, preferably 0.7 to 1.3 wt%, and more preferably 0.9 to 1.0 wt%.

Based on the mass of the sintered body, the Co content may be 0.1 to 3.9 wt%, preferably 0.7 to 1.3 wt%, and more preferably 0.9 to 1.0 wt%.

Based on the mass of the sintered body, the Cu content may be 0.05-1.0 wt%, preferably 0.10-0.70 wt%, and more preferably 0.12-0.20 wt%.

Based on the mass of the sintered body, the Zr content may be 0.06 to 0.25 wt%, preferably 0.1 to 0.16 wt%, and more preferably 0.13 to 0.15 wt%.

Based on the mass of the sintered body, the Ga content may be 0.1-0.3 wt%, preferably 0.15-0.25 wt%, and more preferably 0.18-0.20 wt%.

The remainder is Fe.

By controlling each element within the above range, it is advantageous to obtain a rare earth sintered neodymium-iron-boron magnet that achieves a good balance between coercivity and residual magnetic flux density.

According to one embodiment of the present invention, the rare earth sintered neodymium-iron-boron magnet of the present invention does not contain heavy rare earth elements. The heavy rare earth elements are terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), rubidium (Tm), ytterbium (Yb) and rubidium (Lu). This reduces costs and better ensures a good balance between coercivity and residual magnetic flux density.

The rare earth sintered neodymium-iron-boron magnet of the present invention has a residual magnetic flux density of 14.50 kGs or more, preferably 14.60 kGs or more, and more preferably 14.65 kGs or more. The residual magnetic flux density may be less than 16.1 kGs, preferably less than 15.8 kGs, and more preferably 15.5 kGs. The intrinsic coercivity is 14.0 kOe or more, preferably 16.3 kOe or more, and more preferably 16.5 kOe or more. The intrinsic coercivity may be less than 29 kOe, preferably less than 25 kOe, and more preferably less than 19 kOe. The residual magnetic flux density temperature coefficient within the temperature range of 20 to 150°C is less than 0.113%/°C, preferably less than 0.110%/°C, and more preferably less than 0.109%/°C. The temperature coefficient of remanence may be greater than 0, preferably greater than 0.05%/°C, more preferably greater than 0.08%/°C. The temperature coefficient of coercivity in the range of 20-150°C is less than 0.573%/°C, preferably less than 0.570%/°C, more preferably less than 0.565%/°C. The temperature coefficient of coercivity is greater than 0, preferably greater than 0.1%/°C, more preferably greater than 0.3%/°C.

The rare earth sintered neodymium-iron-boron magnet of the present invention may have a balance coefficient E between residual magnetic flux density and coercivity of 25 or more, preferably 35 or more, and more preferably 39 or more. The balance coefficient E may be 150 or less, preferably 100 or less, and more preferably 80 or less. The definition of the balance coefficient E is as described above.

<Method of manufacturing rare earth sintered neodymium-iron-boron magnet>
The method for producing a rare earth sintered neodymium-iron-boron magnet according to the present invention includes (a) a melting step, (b) a crushing step, (c) a jet milling step, (d) a molding step, and (e) a sintering and aging treatment step, which are described in detail below.

The melting step includes melting the raw material of the rare earth sintered neodymium-iron-boron magnet, including R1, T, B, and M, to obtain a master alloy sheet. Preferably, the raw material of the rare earth sintered neodymium-iron-boron magnet is composed of R1, T, B, and M. R1 is one or more selected from Nd and Gd elements. Nd is 50 at% or more of the total number of R1 atoms, preferably Nd is 80 at% or more of the total number of R1 atoms, and more preferably Nd is 95 at% or more of the total number of R1 atoms. According to one embodiment of the present invention, R1 is Nd. T is one or more selected from Fe, Co, and Ni elements. Co and Ni are 3 at% or less of the total number of T atoms, preferably Co and Ni are 2 at% or less of the total number of T atoms, and more preferably Co and Ni are 1 to 1.5 at% of the total number of T atoms. According to one embodiment of the present invention, T is Fe and Co. B is a boron element. M is one or more elements selected from Al, Cu, Ga, Zn, Bi, Zr, Ti, Nb, V, Mo, and W. Preferably, M is Cu, Zr, or Ga. The total atomic number of M is 5 at% or less of the raw material, preferably 4 at% or less, more preferably 3 at% or less, and most preferably 0.1 to 2 at%. According to one embodiment of the present invention, the total atomic number of M is 0.3 to 1 at% of the raw material.

The raw material of the rare earth sintered neodymium-iron-boron magnet according to the present invention includes elements such as R1, B, Co, Cu, Zr, Ga and Fe. In some embodiments, the raw material of the rare earth sintered neodymium-iron-boron magnet according to the present invention consists of R1, B, Co, Cu, Zr, Ga and Fe. Based on the mass of the raw material of the rare earth sintered neodymium-iron-boron magnet, the content of R1 may be 28-31 wt%, preferably 28-30 wt%, and more preferably 28-29 wt%. The content of B may be 0.6-1.6 wt%, preferably 0.7-1.3 wt%, and more preferably 0.9-1.0 wt%. The content of Co may be 0.1-3.9 wt%, preferably 0.7-1.3 wt%, and more preferably 0.9-1.0 wt%. The Cu content may be 0.05-1.0 wt%, preferably 0.10-0.70 wt%, and more preferably 0.12-0.20 wt%. The Zr content may be 0.06-0.25 wt%, preferably 0.1-0.16 wt%, and more preferably 0.13-0.15 wt%. The Ga content may be 0.1-0.3 wt%, preferably 0.15-0.25 wt%, and more preferably 0.18-0.20 wt%. The balance is Fe. According to one embodiment of the present invention, the raw material for the rare earth sintered neodymium-iron-boron magnet of the present invention may not contain heavy rare earth elements. The heavy rare earth elements are terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), rubidium (Tm), ytterbium (Yb) and rubidium (Lu).

The raw materials are mixed according to the composition of the rare earth sintered neodymium-iron-boron magnet. In some embodiments, the raw materials consist of Nd, B, Co, Cu, Zr, Ga and Fe. The Nd content may be 28-31 wt%, preferably 28-30 wt%, and more preferably 28-29 wt%. The B content may be 0.6-1.6 wt%, preferably 0.7-1.3 wt%, and more preferably 0.9-1.0 wt%. The Co content may be 0.1-3.9 wt%, preferably 0.7-1.3 wt%, and more preferably 0.9-1.0 wt%. The Cu content may be 0.05-1.0 wt%, preferably 0.10-0.70 wt%, and more preferably 0.12-0.20 wt%. The Zr content may be 0.06-0.25 wt%, preferably 0.1-0.16 wt%, and more preferably 0.13-0.15 wt%. The Ga content may be 0.1-0.3 wt%, preferably 0.15-0.25 wt%, and more preferably 0.18-0.20 wt%. The balance is Fe.

Melting may be performed in a vacuum melting furnace. The average thickness of the resulting master alloy sheet may be 0.05 to 1.00 mm, preferably 0.1 to 0.8 mm, and more preferably 0.2 to 0.5 mm.

Crushing step: Crush the mother alloy sheet into coarse alloy powder. The average particle size D50 of the coarse alloy powder is 20-500 μm, preferably 50-300 μm, more preferably 80-150 μm. The coarse alloy powder can be obtained by adopting a method called hydrogen crushing, for example, the mother alloy sheet can be subjected to hydrogen absorption and dehydrogenation treatment in a hydrogen crushing furnace to form coarse alloy powder.

Jet Milling Process In a traditional jet milling process, the coarse alloy powder is directly ground into a fine alloy powder. In the present invention, the praseodymium-containing powder is added to the jet milling process to facilitate at least a portion of the fine alloy powder being coated with the praseodymium-containing powder. The coarse alloy powder and the praseodymium-containing powder are ground into a magnetic powder by jet milling. The magnetic powder has an average particle size D50 of 1-10 μm, preferably 2-7 μm, and more preferably 3-5 μm.

The praseodymium-containing powder according to the present invention may be praseodymium hydride or Pr-M alloy powder. In the Pr-M alloy powder, M is one or more elements selected from Al, Cu, Ga, Zn, Bi, Zr, Ti, Nb, V, Mo, and W. Preferably, M is Cu, Zr, and Ga. The Pr-M alloy powder is not a Pr-Ni alloy powder or a Pr-Co alloy powder. These two types of alloy powder are expensive, but are not significantly effective in improving the balance between the residual magnetic flux density and the coercive force of the magnet, and are even inferior to the Pr-M alloy powder of the present invention.

According to one embodiment of the present invention, the praseodymium-containing powder is praseodymium hydride powder. Such powder is not only inexpensive and easily available, but also has a very significant effect of improving the balance between the residual magnetic flux density and the coercive force of the magnet. Such a technical effect is unexpected.

According to another embodiment of the present invention, the Pr-M alloy powder is a Pr-Cu alloy powder. The Pr in the Pr-Cu alloy powder is 50 at% or more, preferably 60 at% or more, and more preferably 65 to 75 at%.

Based on the mass of the alloy coarse powder, the amount of praseodymium-containing powder used is 0.1 to 5.0 wt%, preferably 1.0 to 4.0 wt%, and more preferably 1.5 to 2.5 wt%.

The jet milling process may be carried out in a nitrogen atmosphere.

Compaction process: The magnetic powder is pressed in a magnetic field and then subjected to hydrostatic isostatic pressing to obtain a green body.

The molding step may be carried out by press molding in a molding press, preferably under nitrogen protection.

The magnetic field strength is greater than 1.0T, preferably greater than 1.5T, and more preferably greater than 1.7T.

The density of the green body may be from 2.5 to 5.5 g/cm ³ , preferably from 3.5 to 5.0 g/cm ³ , and more preferably from 4.0 to 4.5 g/cm ³ .

Sintering and aging process The green body undergoes a vacuum heat treatment and a two-stage tempering process to obtain a rare earth sintered permanent magnet.

The vacuum conditions of the vacuum heat treatment mean that the absolute vacuum is less than 0.5 Pa, preferably less than 0.3 Pa, and more preferably less than 0.1 Pa. The heat treatment temperature may be 850 to 1300°C, preferably 950 to 1200°C, and more preferably 1000 to 1100°C. The heat treatment time may be 2 to 10 hours, preferably 3 to 8 hours, and more preferably 4 to 7 hours.

The primary tempering temperature may be 600 to 1050°C, preferably 700 to 1000°C, and more preferably 800 to 950°C. The primary tempering time may be 1 to 6 h, preferably 2 to 5 h, and more preferably 3 to 4 h. The primary tempering is performed under vacuum conditions. Vacuum conditions means that the absolute vacuum is less than 0.5 Pa, preferably less than 0.3 Pa, and more preferably less than 0.1 Pa.

The secondary tempering temperature may be 300-700°C, preferably 400-600°C, more preferably 450-550°C. The secondary tempering time may be 3-10h, preferably 4-8h, more preferably 5-7h. The secondary tempering is performed under vacuum conditions. Vacuum conditions means that the absolute vacuum is less than 0.5 Pa, preferably less than 0.3 Pa, more preferably less than 0.1 Pa.

<Use of Praseodymium Hydride>
The present invention provides the use of praseodymium hydride to improve the balance factor between remanence and coercivity of rare earth sintered neodymium-iron-boron magnets. The balance factor between remanence and coercivity can be expressed as E and is calculated by the following formula:

E = X2/X1
X1=(Br1-Br2)/Br1
X2=(Hcj2-Hcj1)/Hcj1
Br1 represents the residual magnetic flux density of the rare earth sintered neodymium-iron-boron magnet obtained without adding praseodymium hydride powder in the jet milling process, and is expressed in kGs.
Br2 represents the residual magnetic flux density of the rare earth sintered neodymium-iron-boron magnet obtained by adding praseodymium hydride powder in the jet milling process, and is expressed in kGs.
Hcj1 represents the coercivity of the rare earth sintered neodymium-iron-boron magnet obtained without adding praseodymium hydride powder in the jet milling process, and is expressed in kOe.
Hcj2 represents the coercivity of the rare earth sintered neodymium-iron-boron magnet obtained by adding praseodymium hydride powder in the jet milling process, and is expressed in kOe.

The balance coefficient E between the residual magnetic flux density and the coercive force of the rare earth sintered neodymium-iron-boron magnet of the present invention may be 25 or more, preferably 35 or more, and more preferably 39 or more. The balance coefficient E may be 150 or less, preferably 100 or less, and more preferably 80 or less.

In the use according to the present invention, the alloy coarse powder and the praseodymium hydride powder are pulverized into coarse powder by jet milling. Based on the mass of the alloy coarse powder, the amount of the praseodymium hydride powder used is 0.1-5.0 wt%, preferably 1.0-4.0 wt%, and more preferably 2.0-3.0 wt%. In addition to the jet milling process, the use according to the present invention may further include a melting process, a crushing process, a molding process, and a sintering and aging process. The specific process conditions are as described above.

The composition of the alloy coarse powder according to the present invention is R1-TB-M, preferably R1-TB-M.

R1 is one or more elements selected from Nd and Gd. Nd is 50 at% or more of the total number of R1 atoms, preferably 80 at% or more of the total number of R1 atoms, and more preferably 95 at% or more of the total number of R1 atoms. According to one embodiment of the present invention, R1 is Nd.

T is one or more elements selected from Fe, Co, and Ni. Co and Ni account for 3 at% or less of the total number of atoms of T, preferably Co and Ni account for 2 at% or less of the total number of atoms of T, and more preferably Co and Ni account for 1 to 1.5 at% of the total number of atoms of T. According to one embodiment of the present invention, T is Fe and Co.

B is the element boron.

M is one or more elements selected from Al, Cu, Ga, Zn, Bi, Zr, Ti, Nb, V, Mo and W. Preferably, M is Cu, Zr and Ga. The total atomic number of M is 5 at% or less, preferably 4 at% or less, more preferably 3 at% or less, and most preferably 0.1-2 at% of the alloy coarse powder. According to one embodiment of the present invention, the total atomic number of M is 0.3-1 at% of the alloy coarse powder.

The alloy coarse powder according to the present invention includes elements such as R1, B, Co, Cu, Zr, Ga, and Fe. In some embodiments, the alloy coarse powder according to the present invention consists of R1, B, Co, Cu, Zr, Ga, and Fe. Based on the mass of the alloy coarse powder, the content of R1 may be 28-31 wt%, preferably 28-30 wt%, and more preferably 28-29 wt%. The content of B may be 0.6-1.6 wt%, preferably 0.7-1.3 wt%, and more preferably 0.9-1.0 wt%. The content of Co may be 0.1-3.9 wt%, preferably 0.7-1.3 wt%, and more preferably 0.9-1.0 wt%. The Cu content may be 0.05-1.0 wt%, preferably 0.10-0.70 wt%, and more preferably 0.12-0.20 wt%. The Zr content may be 0.06-0.25 wt%, preferably 0.1-0.16 wt%, and more preferably 0.13-0.15 wt%. The Ga content may be 0.1-0.3 wt%, preferably 0.15-0.25 wt%, and more preferably 0.18-0.20 wt%. The balance is Fe. According to one embodiment of the present invention, the alloy coarse powder according to the present invention does not contain a heavy rare earth element. The heavy rare earth elements are terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), rubidium (Tm), ytterbium (Yb), and rubidium (Lu).

According to one embodiment of the present invention, the alloy coarse powder may be composed of Nd, B, Co, Cu, Zr, Ga and Fe. The Nd content may be 28-31 wt%, preferably 28-30 wt%, more preferably 28-29 wt%. The B content may be 0.6-1.6 wt%, preferably 0.7-1.3 wt%, more preferably 0.9-1.0 wt%. The Co content may be 0.1-3.9 wt%, preferably 0.7-1.3 wt%, more preferably 0.9-1.0 wt%. The Cu content may be 0.05-1.0 wt%, preferably 0.10-0.70 wt%, more preferably 0.12-0.20 wt%. The Zr content may be 0.06-0.25 wt%, preferably 0.1-0.16 wt%, and more preferably 0.13-0.15 wt%. The Ga content may be 0.1-0.3 wt%, preferably 0.15-0.25 wt%, and more preferably 0.18-0.20 wt%. The balance is Fe.

In the jet milling process, the raw material containing the alloy coarse powder and the praseodymium hydride powder is pulverized into a magnetic powder by jet milling. The average particle size D50 of the magnetic powder may be 1 to 10 μm, preferably 2 to 7 μm, and more preferably 3 to 5 μm. The jet milling process may be performed in a nitrogen atmosphere.

Example 1
Melting step: The raw materials were mixed in the following composition by mass percentage: Nd 29.0%, B 1.0%, Co 1.0%, Cu 0.15%, Zr 0.15%, Ga 0.2%, and the balance Fe. The raw materials were melted in a vacuum smelting rapid solidification furnace to produce an alloy sheet with an average thickness of 0.3 mm.

Hydrogen crushing process: The alloy sheet was subjected to hydrogen absorption and dehydrogenation treatment in a hydrogen crushing furnace to produce coarse alloy powder with an average particle size D50 of 100 μm.

Jet milling process: 2.0 wt% praseodymium hydride powder was added to the alloy coarse powder and mixed uniformly. The mixture was then pulverized into magnetic powder with an average particle size D50 of 4.0 μm by jet milling using nitrogen gas as a medium.

Molding process: The magnetic powder was applied to a nitrogen-protected molding press and oriented by applying a 1.8 T magnetic field to mold it into a green body, and the density of the green body was 4.3 g/ ^cm3 .

Sintering and aging process: The green body was placed in a vacuum sintering furnace with an absolute vacuum of less than 0.1 Pa and sintered at 1070°C for 5 hours to obtain a sintered magnet. The sintered magnet was then subjected to a first-stage tempering process at 900°C for 3 hours and a second-stage tempering process at 500°C for 5 hours under conditions of an absolute vacuum of less than 0.1 Pa to obtain a rare earth sintered neodymium-iron-boron magnet.

The rare earth sintered neodymium-iron-boron magnet was machined into a sample pillar of D10 x 10 mm, and the magnetic properties of the magnet were measured at room temperature and 150°C using a BH tester, and the residual magnetic flux density temperature coefficient α and coercivity temperature coefficient β were calculated within the range of 20 to 150°C.

The microstructure of the rare earth sintered neodymium-iron-boron magnet was observed using a Sigma 500 field emission scanning electron microscope (see Figure 1), and composition analysis was performed using an EDS detector.

Tables 1 and 2 show the average thickness L of the grain boundary phase, the Pr concentration difference (C ₁ -C ₂ ) between the main phase crystal grain edge and the main phase crystal grain center, and magnetic performance parameters of the rare earth sintered neodymium-iron-boron magnets.

Examples 2 to 3 and Comparative Examples 1 to 2
In the jet milling process, the amount of praseodymium hydride powder used was changed, and the other processes were the same as in Example 1. The average thickness L of the grain boundary phase, the Pr concentration difference (C ₁ -C ₂ ) between the main phase crystal grain edge and the main phase crystal grain center, and the magnetic performance parameters of the rare earth sintered neodymium-iron-boron magnets are shown in Tables 1 and 2.

Example 4
In the jet milling process, 3.0% wt of Pr68Cu32 alloy was added, and other processes were the same as in Example 1. The average thickness L of the grain boundary phase, the Pr concentration difference (C ₁ -C ₂ ) between the main phase crystal grain edge and the main phase crystal grain center, and magnetic performance parameters of the rare earth sintered neodymium-iron-boron magnet are shown in Tables 1 and 2.

Comparative Example 3
In the melting process, the raw materials were blended according to mass percent of Nd 29.0%, Pr 2.0%, B 1.0%, Co 1.0%, Cu 0.15%, Zr 0.15%, Ga 0.2% and the balance Fe, and in the jet milling process, no praseodymium hydride powder was added, and the other processes were the same as in Example 1. The average thickness L of the grain boundary phase, the Pr concentration difference (C ₁ -C ₂ ) between the main phase crystal grain edge and the main phase crystal grain center and the magnetic performance parameters of the rare earth sintered neodymium-iron-boron magnet are shown in Tables 1 and 2.

Comparative Examples 4 to 9
Sintered neodymium-iron-boron magnets were manufactured according to Examples 1 to 6 of CN111696742A. The average thickness L of the grain boundary phase, the Pr concentration difference (C ₁ -C ₂ ) between the main phase crystal grain edge and the main phase crystal grain center, and magnetic performance parameters of the rare earth sintered neodymium-iron-boron magnets are shown in Table 2.

Comparative Examples 10 to 13
Sintered neodymium-iron-boron magnets were manufactured according to Examples 1 to 4 of CN104575899A. The average thickness L of the grain boundary phase, the Pr concentration difference ( _C1 - _C2 ) between the main phase crystal grain edge and the main phase crystal grain center, and magnetic performance parameters of the rare earth sintered neodymium-iron-boron magnets are shown in Table 2.

注：Ｂｒ１は、改質粉末を添加せずに得られた希土類焼結ネオジム－鉄－ボロン磁石の残留磁束密度を表し，単位がｋＧｓであり、Ｂｒ２は、改質粉末を添加して得られた希土類焼結ネオジム－鉄－ボロン磁石の残留磁束密度を表し、単位がｋＧｓであり、Ｈｃｊ１は、改質粉末を添加せずに得られた希土類焼結ネオジム－鉄－ボロン磁石の保磁力を表し、単位がｋＯｅであり、Ｈｃｊ２は、改質粉末を添加して得られた希土類焼結ネオジム－鉄－ボロン磁石の保磁力を表し、単位がｋＯｅである。

Note: Br1 represents the residual magnetic flux density of the rare earth sintered neodymium-iron-boron magnet obtained without adding any modifying powder, and is expressed in kGs; Br2 represents the residual magnetic flux density of the rare earth sintered neodymium-iron-boron magnet obtained with the addition of a modifying powder, and is expressed in kGs; Hcj1 represents the coercive force of the rare earth sintered neodymium-iron-boron magnet obtained without adding any modifying powder, and is expressed in kOe; and Hcj2 represents the coercive force of the rare earth sintered neodymium-iron-boron magnet obtained with the addition of a modifying powder, and is expressed in kOe.

As can be seen from Tables 1 and 2, the present invention involves pulverizing the alloy coarse powder with praseodymium-containing powder into magnetic powder by jet milling, and then through processes such as molding and sintering to obtain a rare earth sintered neodymium-iron-boron magnet, which allows the magnet to achieve both residual magnetic flux density and coercive force, achieving a perfect balance between the two, with a balance factor of 25 or more. In this case, the Pr concentration C1 at the edge of the main phase crystal grains is 0.25 wt% or more higher than the Pr concentration C2 at the center of the main phase crystal grains, and the average thickness of the grain boundary phase is 20 to 60 nm. When an appropriate amount of praseodymium hydride powder is used, the balance factor between residual magnetic flux density and coercive force is high, at 35 or more (see Example 1).

As can be seen from Table 3, the magnets of Comparative Examples 1 to 13 cannot simultaneously satisfy the following conditions: (1) The Pr concentration C1 at the edge of the main phase crystal grain is 0.25 wt% or more higher than the Pr concentration C2 at the center of the main phase crystal grain. (2) The average thickness of the grain boundary phase is 20 to 60 nm.

As can be seen from Table 2, in Comparative Example 1, no praseodymium hydride powder was added, and the residual magnetic flux density and coercive force were relatively low. In Comparative Example 2, the amount of praseodymium hydride powder used was too much, and the residual magnetic flux density was reduced too much, resulting in a relatively low balance factor. In Comparative Example 3, even though Pr was added in the raw material mixing process, the coercive force was not significantly improved, and the balance factor was relatively low. In Comparative Examples 4 to 9, PrNi alloy powder was directly mixed with fine magnetic powder, and the coercive force was significantly improved, but the residual magnetic flux density was reduced too much, resulting in a balance factor of less than 20. In Comparative Examples 11 and 12, (PrNd)Co alloy powder was directly mixed with fine magnetic powder, and the coercive force could be improved, but the residual magnetic flux density was reduced too much, resulting in a balance factor of less than 10. In Comparative Examples 10 and 13, DyCo or TbCo alloy powder was directly mixed with fine magnetic powder, and the coercive force was clearly improved, but the residual magnetic flux density was further reduced and the balance factor was very low.

The present invention is not limited to the above-described embodiment, and any modifications, improvements, substitutions, etc. that may occur to a person skilled in the art are included within the scope of the present invention, provided they do not deviate from the spirit of the present invention.

Claims (5)

(R1, R2)-TBM rare earth sintered neodymium-iron-boron magnet,
The rare earth sintered neodymium-iron-boron magnet is composed of a sintered body containing main phase crystal grains and a grain boundary phase,
the main phase crystal grains are made of a (R1, R2) ₂ T ₁₄ B phase, and a Pr concentration C ₁ at an edge of the main phase crystal grain is higher than a Pr concentration C ₂ at a center of the main phase crystal grain;
The R1 concentration of the grain boundary phase is higher than the R1 concentration of the main phase crystal grains, and the average thickness of the grain boundary phase is 20 to 40 nm;
R1 is one or more elements selected from Nd and Gd, and Nd accounts for 50 at % or more of the total number of atoms of R1;
R2 is a Pr element;
T is one or more elements selected from Fe, Co, and Ni, and Co and Ni account for 3 at % or less of the total number of atoms of T;
B is elemental boron;
M is one or more elements selected from Al, Cu, Ga, Zn, Bi, Zr, Ti, Nb, V, Mo and W, and the total atomic number of M is 5 at % or less of the sintered body;
The composition of the sintered body is R1: 28 to 31 wt%, R2: 0.1 to 5 wt%, B: 0.6 to 1.6 wt%, Co: 0.1 to 3.9 wt%, Cu: 0.05 to 1.0 wt%, Zr: 0.06 to 0.25 wt%, Ga: 0.1 to 0.3 wt%, and the balance is substantially Fe;
The rare earth sintered neodymium-iron-boron magnet has a residual magnetic flux density of 14.50 kGs or more, an intrinsic coercive force of 14.0 kOe or more, a temperature coefficient of residual magnetic flux density within the range of 20 to 150°C of less than 0.113%/°C, and a temperature coefficient of coercive force within the range of 20 to 150°C of less than 0.573%/°C.
The (R1, R2)-TBM rare earth sintered neodymium-iron-boron magnet is characterized by the above. The rare earth sintered neodymium-iron-boron magnet described in claim 1, characterized in that the Pr concentration gradually decreases from the edge of the main phase crystal grains toward the center of the main phase crystal grains. 2. The rare earth sintered neodymium-iron-boron magnet according to claim 1, wherein the Pr concentration _C1 at the edge of the main phase crystal grain is 0.25 wt % or more higher than the Pr concentration _C2 at the center of the main phase crystal grain. 2. The rare earth sintered neodymium-iron-boron magnet according to claim 1 , characterized in that the Zr content in the sintered body is 0.1 to 0.16 wt %, and the Ga content is 0.15 to 0.25 wt %. 5. The rare earth sintered neodymium-iron-boron magnet according to claim 1, which does not contain any heavy rare earth element.