Rare earth sintered neodymium-iron-boron magnet, method for producing same and use of praseodymium hydride

Abstract

The application discloses a rare earth sintered Nd-Fe-B magnet, a preparation method thereof and a use of praseodymium hydride. The rare earth sintered Nd-Fe-B magnet has an element composition of (R1, R2)-T-B-M; the rare earth sintered Nd-Fe-B magnet is composed of a sintered body containing main phase crystal grains and a grain boundary phase; the main phase crystal grains are composed of (R1, R2)2T 14 B phase; the Pr concentration C1 of the edge of the main phase crystal grains is higher than the Pr concentration C2 of the center of the main phase crystal grains; 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 20-60 nm. The coercive force and the remanence of the rare earth sintered Nd-Fe-B magnet reach a good balance.

Description

Technical Field

[0001] This invention provides a rare earth sintered NdFeB magnet, its preparation method, and the uses of praseodymium hydride. Background Technology

[0002] With the increasing demand for hybrid electric vehicles, pure electric vehicles, and energy-saving air conditioning compressors, the demand for permanent magnet materials with high coercivity and low temperature coefficient is also increasing. Using a large amount of heavy rare earth elements can improve the coercivity and temperature coefficient of permanent magnet materials. However, this will significantly increase the cost and sacrifice some remanence and magnetic energy product. The preparation method uses Nd... 14.1 Co 1.34 Cu 0.04 Fe bal B 5.84 The alloy sheet was hydrogen-crushed into coarse powder with a particle size of 10–100 μm; the coarse powder was then processed by air jet milling in a nitrogen atmosphere to form fine powder with an average particle size of 3.38 μm; and the fine powder with an average particle size of 1.8 μm was further processed by hydrogen-hydrogenation. x The powder and fine powder are mixed and isostatically pressed under a magnetic field of 1800 kA / m and a pressure of 300 MPa. The green body is sintered under vacuum at 1040–1060 °C for 2 h, then gas-cooled and quenched, and finally tempered at 900 °C and 500 °C for 2 h each. This method requires the use of heavy rare earth element Dy, and DyH is directly... x The powder is mixed with the fine powder. Although this method can significantly improve the coercivity of the magnet, it reduces the remanence too much, resulting in an inability to achieve a good balance between coercivity and remanence.

[0003] Adding Co and Ni elements can improve the temperature coefficient of magnets, but excessive addition of Co and Ni elements will reduce the performance of the magnets. Furthermore, Co and Ni are strategic elements and are relatively expensive. CN111696742A discloses a method for preparing heavy rare earth-free high-performance NdFeB permanent magnet materials: providing anisotropic magnet materials (Nd, Pr). x Fe (100-x-y-z) B y M z Provide auxiliary phase material Pr a Ni 100-b Anisotropic magnetic materials and auxiliary phase materials are uniformly mixed to obtain mixed magnetic powder, which is then subjected to orientation molding, sintering, and tempering treatments to obtain heavy rare earth-free high-performance NdFeB materials. CN104575899A discloses a method for preparing sintered NdFeB magnets, in which main alloy powder and rare earth cobalt compound powder are directly mixed and then molded, resulting in a larger average thickness of the grain boundary phase in the obtained magnet. These methods can improve the coercivity of the magnet, but cannot suppress the decrease in remanence, resulting in an inability to achieve a good balance between coercivity and remanence. Summary of the Invention

[0004] On the one hand, the present invention provides a (R1,R2)-TBM rare-earth sintered NdFeB magnet, which achieves a good balance between coercivity and remanence. Furthermore, the rare-earth sintered NdFeB magnet of the present invention has a low temperature coefficient of remanence and a low temperature coefficient of coercivity.

[0005] On the other hand, the present invention provides a method for preparing rare earth sintered NdFeB magnets. This method differs from traditional methods in that it suppresses the reduction of remanence, thereby achieving a good balance between the coercivity and remanence of the rare earth sintered NdFeB magnets.

[0006] In another aspect, the present invention provides a use for praseodymium hydride.

[0007] On one hand, the present invention provides a (R1,R2)-TBM rare earth sintered NdFeB magnet.

[0008] The rare earth sintered NdFeB magnet is composed of a sintered body containing main phase grains and grain boundary phases;

[0009] The main phase grains are composed of (R1,R2)2T 14 The main phase is composed of phase B; the Pr concentration C1 at the edge of the main phase grain is higher than the Pr concentration C2 at the center of the main phase grain.

[0010] The R1 concentration of the grain boundary phase is higher than that of the main phase grains; and the average thickness of the grain boundary phase is 20–60 nm.

[0011] R1 is selected from one or more of Nd and Gd elements, and Nd accounts for more than 50 at% of the total number of atoms of R1;

[0012] R2 is a Pr element;

[0013] T is selected from one or more of Fe, Co and Ni elements, and Co and Ni account for less than 3 at% of the total number of T atoms;

[0014] B represents boron.

[0015] M is selected from one or more of the elements Al, Cu, Ga, Zn, Bi, Zr, Ti, Nb, V, Mo and W, and the total number of M atoms is less than 5 at% of the sintered body.

[0016] In the rare-earth sintered NdFeB magnet of the present invention, preferably, the Pr concentration gradually decreases from the edge of the main phase grain to the center of the main phase grain.

[0017] In the rare earth sintered NdFeB magnet of the present invention, preferably, the Pr concentration C1 at the edge of the main phase grain is more than 0.25 wt% higher than the Pr concentration C2 at the center of the main phase grain.

[0018] According to the rare earth sintered NdFeB magnet of the present invention, preferably, the composition of the sintered body is: 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 remainder is substantially Fe.

[0019] According to the rare earth sintered NdFeB magnet of the present invention, preferably, the Zr content in the sintered body is 0.1-0.16 wt%, and the Ga content is 0.15-0.25 wt%.

[0020] The rare-earth sintered NdFeB magnet of the present invention preferably does not contain heavy rare-earth elements.

[0021] According to the rare earth sintered NdFeB magnet of the present invention, preferably, the remanence of the rare earth sintered NdFeB magnet is 14.50 kGs or more, the intrinsic coercivity is 14 kOe or more, the remanence temperature coefficient in the range of 20 to 150°C is less than 0.113% / °C, and the coercivity temperature coefficient in the range of 20 to 150°C is less than 0.573% / °C.

[0022] On the other hand, the present invention provides a method for preparing the above-mentioned rare earth sintered NdFeB magnet, characterized by comprising the following steps:

[0023] (a) The raw materials R1, T, B and M of rare earth sintered NdFeB magnets are smelted to obtain a master alloy sheet;

[0024] (b) The master alloy sheet is crushed into coarse alloy powder with an average particle size D50 of 20 to 500 μm;

[0025] (c) The alloy coarse powder and the praseodymium-containing powder are ground in an air jet mill to form magnetic powder with an average particle size D50 of 1 to 10 μm; wherein the praseodymium-containing powder is praseodymium hydride or Pr-M alloy powder.

[0026] (d) The magnetic powder is pressed in a magnetic field and then subjected to isostatic pressing to obtain a blank;

[0027] (e) The blank is subjected to vacuum heat treatment and two-stage tempering to obtain rare earth sintered permanent magnets.

[0028] According to the preparation method of the present invention, preferably, the amount of praseodymium powder used is 0.1 to 5.0 wt% based on the weight of the alloy coarse powder.

[0029] In another aspect, the present invention provides the use of praseodymium hydride in improving the balance coefficient of remanence and coercivity of rare earth sintered NdFeB magnets, wherein alloy coarse powder and praseodymium hydride powder are ground into magnetic powder in an air jet mill; the amount of praseodymium hydride powder is 0.1 to 5.0 wt% based on the weight of the alloy coarse powder.

[0030] The composition of the alloy coarse powder is R1-TBM;

[0031] R1 is selected from one or more of Nd and Gd elements, and Nd accounts for more than 50 at% of the total number of atoms of R1;

[0032] T is selected from one or more of Fe, Co and Ni elements, and Co and Ni account for less than 3 at% of the total number of T atoms;

[0033] B represents boron.

[0034] M is selected from one or more of the elements Al, Cu, Ga, Zn, Bi, Zr, Ti, Nb, V, Mo and W, and the total number of M atoms is less than 5 at% of the sintered body;

[0035] The formula for calculating the balance coefficient E between remanence and coercivity is as follows:

[0036] E = X2 / X1;

[0037] X1 = (Br1 - Br2) / Br1;

[0038] X2 = (Hcj2 - Hcj1) / Hcj1;

[0039] Br1 represents the remanence of rare earth sintered NdFeB magnets obtained without the addition of praseodymium hydride powder in the air jet milling process, in kGs;

[0040] Br2 represents the remanence of rare earth sintered NdFeB magnets obtained by adding praseodymium hydride powder in the air jet milling process, in kGs;

[0041] Hcj1 represents the coercivity of rare earth sintered NdFeB magnets obtained without the addition of praseodymium hydride powder in the air jet milling process, and the unit is kOe;

[0042] Hcj2 represents the coercivity of rare earth sintered NdFeB magnets obtained by adding praseodymium hydride powder in the air jet milling process, and the unit is kOe.

[0043] The rare-earth sintered NdFeB magnet of the present invention exhibits high coercivity and remanence, achieving a good balance between the two. Furthermore, the rare-earth sintered NdFeB magnet of the present invention has a low temperature coefficient of remanence and a low temperature coefficient of coercivity. Attached Figure Description

[0044] Figure 1This is a scanning electron microscope image of the rare earth sintered NdFeB magnet obtained in Example 1. Detailed Implementation

[0045] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0046] In this invention, remanence refers to the magnetic flux density at the point where the magnetic field strength on the saturation hysteresis loop is zero, usually denoted as Br or Mr, and the unit is Tesla (T) or Gauss (Gs). 1 Gs = 0.0001 T.

[0047] In this invention, coercivity, also known as intrinsic coercivity, refers to the magnetic field strength when the magnetic field is monotonically reduced to zero and then increased in the opposite direction from the saturated magnetization state of the magnet, causing its magnetization intensity to decrease to zero along the saturation hysteresis loop. It is usually denoted as Hcj, and its unit is Oersted (Oe) or Ampere per meter (A / m). 1 Oe = 79.6 A / m. Hcj is the intrinsic coercivity at room temperature.

[0048] In this invention, the inert gases include helium, neon, argon, krypton, and xenon. Vacuum refers to absolute vacuum; the smaller the value, the higher the vacuum level.

[0049] In this invention, the average particle size D50 represents the equivalent diameter of the largest particle when the cumulative distribution in the particle size distribution curve is 50%.

[0050] In this invention, "at%" refers to the atomic percentage.

[0051] This invention aims to achieve a good balance between the remanence and coercivity of a magnet. The formula for calculating the balance coefficient E between remanence and coercivity is as follows:

[0052] E = X2 / X1;

[0053] X1 = (Br1 - Br2) / Br1;

[0054] X2 = (Hcj2 - Hcj1) / Hcj1;

[0055] Br1 represents the remanence of rare-earth sintered NdFeB magnets obtained without the addition of modified powder, in kGs. In some embodiments, Br1 represents the remanence of rare-earth sintered NdFeB magnets obtained without the addition of praseodymium hydride powder in the air jet milling process, in kGs.

[0056] Br2 represents the remanence of rare-earth sintered NdFeB magnets obtained by adding modified powder, in kGs. In some embodiments, Br2 represents the remanence of rare-earth sintered NdFeB magnets obtained by adding praseodymium hydride powder in the air jet milling process, in kGs.

[0057] Hcj1 represents the coercivity of rare-earth sintered NdFeB magnets obtained without the addition of modified powder, in kOe. In some embodiments, Hcj1 represents the coercivity of rare-earth sintered NdFeB magnets obtained without the addition of praseodymium hydride powder in the air jet milling process, in kOe.

[0058] Hcj2 represents the coercivity of rare-earth sintered NdFeB magnets obtained by adding modified powder, in kOe. In some embodiments, Hcj2 represents the coercivity of rare-earth sintered NdFeB magnets obtained by adding praseodymium hydride powder in the air jet milling process, in kOe.

[0059] This invention discovers that adding praseodymium-containing powder to the air jet milling process of pulverizing coarse alloy powder into fine magnetic powder can maintain the thickness of the grain boundary phase of the resulting magnet within a certain range, and the praseodymium exhibits a gradient distribution within the main phase particles, thereby achieving a good balance between the remanence and coercivity of the magnet. Based on this, this invention was completed.

[0060] Rare Earth Sintered NdFeB Magnets

[0061] The rare-earth sintered NdFeB magnet of the present invention has the elemental composition shown in the following formula:

[0062] (R1,R2)-TBM

[0063] Rare earth sintered NdFeB magnets are composed of sintered bodies containing main phase grains and grain boundary phases. In some embodiments, rare earth sintered NdFeB magnets and sintered bodies have the same meaning.

[0064] R1 is selected from one or more of Nd and Gd. Nd accounts for 50 at% or more of the total number of atoms in R1; preferably, Nd accounts for 80 at% or more of the total number of atoms in R1; more preferably, Nd accounts for 95 at% or more of the total number of atoms in R1. According to one embodiment of the present invention, R1 is Nd.

[0065] R2 is a Pr element.

[0066] T is selected from one or more of Fe, Co, and Ni. Co and Ni account for less than 3 at% of the total atomic number of T; preferably, Co and Ni account for less than 2 at% of the total atomic number of T; more preferably, Co and Ni account for 1 to 1.5 at% of the total atomic number of T. According to one embodiment of the present invention, T is Fe and Co.

[0067] B represents boron.

[0068] M is selected from one or more elements chosen from Al, Cu, Ga, Zn, Bi, Zr, Ti, Nb, V, Mo, and W. Preferably, M is Cu, Zr, or Ga. The total number of M atoms is 5 at% or less in the sintered body; 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 invention, the total number of M atoms is 0.3 to 1 at%.

[0069] In the rare-earth sintered NdFeB magnet of the present invention, the main phase grains are composed of (R1,R2)2T 14 The main phase is composed of phase B. This invention has found that the Pr concentration C1 at the edge of the main phase grain is higher than the Pr concentration C2 at the center of the main phase grain. The Pr concentration C1 at the edge of the main phase grain is at least 0.25 wt% higher than the Pr concentration C2 at the center of the main phase grain. Preferably, the Pr concentration C1 at the edge of the main phase grain is at least 0.40 wt% higher than the Pr concentration C2 at the center of the main phase grain; more preferably, the Pr concentration C1 at the edge of the main phase grain is at least 0.50 wt% higher than the Pr concentration C2 at the center of the main phase grain. In some embodiments, the concentration difference (C1-C2) between the Pr concentration C1 at the edge of the main phase grain and the Pr concentration C2 at the center of the main phase 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 (C1-C2) between the Pr concentration C1 at the edge of the main phase grain and the Pr concentration C2 at the center of the main phase grain is 0.53-0.57 wt%. If the Pr concentration difference is too small, it is detrimental to improving coercivity; if the Pr concentration difference is too large, it will adversely affect remanence, the temperature coefficient of remanence, and the temperature coefficient of coercivity. A Pr concentration difference within the above range helps to achieve a good balance between the coercivity and remanence of the magnet.

[0070] According to one embodiment of the present invention, the Pr concentration gradually decreases from the edge of the main phase grain to the center of the main phase grain. Thus, the Pr concentration exhibits a gradient distribution. This further ensures a good balance between the coercivity and remanence of the magnet.

[0071] The R1 concentration A1 of the grain boundary phase is higher than the R1 concentration A2 of the main phase grains. The average thickness L of the grain boundary phase is 20–60 nm; preferably 20–40 nm; more preferably 22–27 nm. If the grain boundary phase thickness is too small, the coercivity of the magnet cannot be significantly improved; if the grain boundary phase thickness is too large, the remanence will decrease significantly, and the temperature coefficient of remanence and the temperature coefficient of coercivity will increase significantly. The grain boundary phase thickness within the above range helps to achieve a good balance between the coercivity and remanence of the magnet.

[0072] The sintered body of the present invention comprises elements such as R1, R2, B, Co, Cu, Zr, Ga, and Fe. In some embodiments, the sintered body of the present invention is composed of R1, R2, B, Co, Cu, Zr, Ga, and Fe.

[0073] Based on the weight of the sintered body, the content of R1 can be 28–31 wt%; preferably 28–30 wt%; more preferably 28–29 wt%.

[0074] Based on the weight of the sintered body, the content of R2 can 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%.

[0075] Based on the weight of the sintered body, the content of B can be 0.6 to 1.6 wt%; preferably 0.7 to 1.3 wt%; more preferably 0.9 to 1.0 wt%.

[0076] Based on the weight of the sintered body, the Co content can be 0.1–3.9 wt%; preferably 0.7–1.3 wt%; more preferably 0.9–1.0 wt%.

[0077] Based on the weight of the sintered body, the Cu content can be 0.05–1.0 wt%; preferably 0.10–0.70 wt%; more preferably 0.12–0.20 wt%.

[0078] Based on the weight of the sintered body, the Zr content can be 0.06 to 0.25 wt%; preferably 0.1 to 0.16 wt%; more preferably 0.13 to 0.15 wt%.

[0079] Based on the weight of the sintered body, the Ga content can be 0.1 to 0.3 wt%; preferably 0.15 to 0.25 wt%; more preferably 0.18 to 0.20 wt%.

[0080] The remainder is Fe.

[0081] Controlling the elements within the above-mentioned ranges is beneficial to obtaining rare-earth sintered NdFeB magnets with a good balance between coercivity and remanence.

[0082] According to one embodiment of the present invention, the rare-earth sintered NdFeB 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), thulium (Tm), ytterbium (Yb), and lutetium (Lu). This reduces costs and better ensures a good balance between coercivity and remanence.

[0083] The remanence of the rare-earth sintered NdFeB magnet of the present invention is 14.50 kGs or more; preferably 14.60 kGs or more; more preferably 14.65 kGs or more. The remanence can be less than 16.1 kGs, preferably less than 15.8 kGs; more preferably 15.5 kGs. The intrinsic coercivity is 14.0 kOe or more; preferably 16.3 kOe or more; more preferably 16.5 kOe or more. The intrinsic coercivity can be less than 29 kOe; preferably less than 25 kOe; more preferably less than 19 kOe. The remanence temperature coefficient in the temperature range of 20–150 °C is less than 0.113% / °C; preferably less than 0.110% / °C; more preferably less than 0.109% / °C. The remanence temperature coefficient can be greater than 0, preferably greater than 0.05% / °C, more preferably greater than 0.08% / °C. The temperature coefficient of coercivity is less than 0.573% / ℃ in the range of 20–150℃; preferably, less than 0.570% / ℃; more preferably, less than 0.565% / ℃. The temperature coefficient of coercivity is greater than 0, preferably greater than 0.1% / ℃, and more preferably greater than 0.3% / ℃.

[0084] The balance coefficient E between remanence and coercivity of the rare-earth sintered NdFeB magnet of the present invention can be 25 or higher, preferably 35 or higher, and more preferably 39 or higher. The balance coefficient E can be 150 or lower, preferably 100 or lower, and more preferably 80 or lower. The definition of the balance coefficient E is as described above.

[0085] <Preparation Method of Rare Earth Sintered NdFeB Magnets>

[0086] The method for preparing rare-earth sintered NdFeB magnets of the present invention includes the following steps: (a) smelting process; (b) crushing process; (c) air jet milling process; (d) forming process; and (e) sintering and aging treatment process. These are described in detail below.

[0087] Smelting process

[0088] The raw materials for rare-earth sintered NdFeB magnets, including R1, T, B, and M, are smelted to obtain a master alloy sheet. Preferably, the raw materials for rare-earth sintered NdFeB magnets consist of R1, T, B, and M. R1 is selected from one or more of Nd and Gd elements. Nd is 50 at% or more of the total atomic number of R1; preferably, Nd is 80 at% or more of the total atomic number of R1; more preferably, Nd is 95 at% or more of the total atomic number of R1. According to one embodiment of the invention, R1 is Nd. T is selected from one or more of Fe, Co, and Ni elements. Co and Ni are 3 at% or less of the total atomic number of T; preferably, Co and Ni are 2 at% or less of the total atomic number of T; more preferably, Co and Ni are 1 to 1.5 at% of the total atomic number of T. According to one embodiment of the invention, T is Fe and Co. B is boron. M is selected from one or more of Al, Cu, Ga, Zn, Bi, Zr, Ti, Nb, V, Mo, and W elements. Preferably, M is Cu, Zr, or Ga. The total number of M atoms 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 invention, the total number of M atoms is 0.3 to 1 at%.

[0089] The raw materials for the rare-earth sintered NdFeB magnets of the present invention include elements such as R1, B, Co, Cu, Zr, Ga, and Fe. In some embodiments, the raw materials for the rare-earth sintered NdFeB magnets of the present invention are composed of R1, B, Co, Cu, Zr, Ga, and Fe. Based on the weight of the raw materials of the rare-earth sintered NdFeB magnets, the content of R1 can be 28-31 wt%; preferably 28-30 wt%; more preferably 28-29 wt%. The content of B can be 0.6-1.6 wt%; preferably 0.7-1.3 wt%; more preferably 0.9-1.0 wt%. The content of Co can be 0.1-3.9 wt%; preferably 0.7-1.3 wt%; more preferably 0.9-1.0 wt%. The content of Cu can be 0.05-1.0 wt%; preferably 0.10-0.70 wt%; more preferably 0.12-0.20 wt%. The Zr content can be 0.06–0.25 wt%; preferably 0.1–0.16 wt%; more preferably 0.13–0.15 wt%. The Ga content can be 0.1–0.3 wt%; preferably 0.15–0.25 wt%; more preferably 0.18–0.20 wt%. The remainder is Fe. According to one embodiment of the present invention, the raw material for the rare earth sintered NdFeB 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), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0090] The raw materials are prepared according to the composition of rare-earth sintered NdFeB magnets. In some embodiments, the raw materials may consist 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%; more preferably 0.13–0.15 wt%. The Ga content can be 0.1–0.3 wt%; preferably 0.15–0.25 wt%; more preferably 0.18–0.20 wt%. The remainder is Fe.

[0091] The melting can be carried out in a vacuum melting furnace. The average thickness of the resulting master alloy sheet can be 0.05 to 1.00 mm; preferably 0.1 to 0.8 mm; more preferably 0.2 to 0.5 mm.

[0092] Crushing process

[0093] The master alloy sheet is crushed 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 hydrogen crushing, for example, by subjecting the master alloy sheet to hydrogen absorption and dehydrogenation treatment in a hydrogen crushing furnace to form coarse alloy powder.

[0094] air jet milling process

[0095] In traditional air jet milling processes, coarse alloy powder is directly ground into fine alloy powder. This invention, however, adds praseodymium-containing powder during the air jet milling process to promote at least partial coating of the fine alloy powder by the praseodymium-containing powder. The coarse alloy powder and the praseodymium-containing powder are then ground into magnetic powder in an air jet mill. The average particle size D50 of the magnetic powder is 1–10 μm; preferably 2–7 μm; more preferably 3–5 μm.

[0096] The praseodymium-containing powder of the present invention can be praseodymium hydride or Pr-M alloy powder. In the Pr-M alloy powder, M is selected from 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 cannot be Pr-Ni alloy powder or Pr-Co alloy powder. On the one hand, these two alloy powders are expensive; on the other hand, their effect on improving the balance of remanence and coercivity of magnets is not significant, and is even inferior to the Pr-M alloy powder of the present invention.

[0097] According to one embodiment of the present invention, the praseodymium-containing powder is praseodymium hydride powder. Such a powder is not only inexpensive and readily available, but also remarkably effective in improving the balance between remanence and coercivity of magnets. Such technical effects are unexpected.

[0098] 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; more preferably 65 to 75 at%.

[0099] Based on the weight of the alloy coarse powder, the amount of praseodymium-containing powder is 0.1 to 5.0 wt%; preferably 1.0 to 4.0 wt%; more preferably 1.5 to 2.5 wt%.

[0100] The air jet milling process can be carried out in a nitrogen atmosphere.

[0101] Molding process

[0102] The magnetic powder is pressed in a magnetic field and then subjected to isostatic pressing to obtain the green body.

[0103] The molding process can be carried out by pressing in a molding press. Preferably, it is carried out under nitrogen protection.

[0104] The magnetic field strength is greater than 1.0T; preferably greater than 1.5T; more preferably greater than 1.7T.

[0105] The density of the green body can be 2.5–5.5 g / cm³. 3 Preferably, it is 3.5–5.0 g / cm³. 3 More preferably, it is 4.0–4.5 g / cm³. 3 .

[0106] Sintering and aging treatment processes

[0107] Rare earth sintered permanent magnets are obtained by vacuum heat treatment and two-stage tempering of the billet.

[0108] The vacuum conditions for vacuum heat treatment refer to an absolute vacuum level of less than 0.5 Pa; preferably less than 0.3 Pa; more preferably less than 0.1 Pa. The heat treatment temperature can be 850–1300 °C; preferably 950–1200 °C; more preferably 1000–1100 °C. The heat treatment time can be 2–10 h; preferably 3–8 h; more preferably 4–7 h.

[0109] The primary tempering temperature can be 600–1050℃; preferably 700–1000℃; more preferably 800–950℃. The primary tempering time can be 1–6 hours; preferably 2–5 hours; more preferably 3–4 hours. The primary tempering is carried out under vacuum conditions. Vacuum conditions refer to an absolute vacuum degree of less than 0.5 Pa; preferably less than 0.3 Pa; more preferably less than 0.1 Pa.

[0110] The secondary tempering temperature can be 300–700℃; preferably 400–600℃; more preferably 450–550℃. The secondary tempering time can be 3–10 hours; preferably 4–8 hours; more preferably 5–7 hours. The secondary tempering is carried out under vacuum conditions. Vacuum conditions refer to an absolute vacuum degree of less than 0.5 Pa; preferably less than 0.3 Pa; more preferably less than 0.1 Pa.

[0111] <Uses of Praseodymium Hydrogen>

[0112] This invention provides an application of praseodymium hydride in improving the remanence and coercivity balance coefficient of rare-earth sintered NdFeB magnets. The balance coefficient of remanence and coercivity can be expressed as E, which is calculated using the following formula:

[0113] E = X2 / X1;

[0114] X1 = (Br1 - Br2) / Br1;

[0115] X2 = (Hcj2 - Hcj1) / Hcj1;

[0116] Br1 represents the remanence of rare earth sintered NdFeB magnets obtained without the addition of praseodymium hydride powder in the air jet milling process, in kGs;

[0117] Br2 represents the remanence of rare earth sintered NdFeB magnets obtained by adding praseodymium hydride powder in the air jet milling process, in kGs;

[0118] Hcj1 represents the coercivity of rare earth sintered NdFeB magnets obtained without the addition of praseodymium hydride powder in the air jet milling process, and the unit is kOe;

[0119] Hcj2 represents the coercivity of rare earth sintered NdFeB magnets obtained by adding praseodymium hydride powder in the air jet milling process, and the unit is kOe.

[0120] The balance coefficient E between remanence and coercivity of the rare-earth sintered NdFeB magnet of the present invention can be 25 or more, preferably 35 or more, and more preferably 39 or more. The balance coefficient E can be 150 or less, preferably 100 or less, and more preferably 80 or less.

[0121] In the application of this invention, alloy coarse powder and praseodymium hydride powder are ground into coarse powder in an air jet mill. Based on the weight of the alloy coarse powder, the amount of praseodymium hydride powder is 0.1–5.0 wt%; preferably 1.0–4.0 wt%; more preferably 2.0–3.0 wt%. In addition to the air jet milling process, the application of this invention may also include a smelting process, a crushing process, a forming process, and a sintering and aging treatment process. Specific process conditions are as described above.

[0122] The alloy coarse powder of the present invention has an R1-TBM composition, preferably R1-TBM.

[0123] R1 is selected from one or more of Nd and Gd. Nd accounts for 50 at% or more of the total number of atoms in R1; preferably, Nd accounts for 80 at% or more of the total number of atoms in R1; more preferably, Nd accounts for 95 at% or more of the total number of atoms in R1. According to one embodiment of the present invention, R1 is Nd.

[0124] T is selected from one or more of Fe, Co, and Ni. Co and Ni account for less than 3 at% of the total atomic number of T; preferably, Co and Ni account for less than 2 at% of the total atomic number of T; more preferably, Co and Ni account for 1 to 1.5 at% of the total atomic number of T. According to one embodiment of the present invention, T is Fe and Co.

[0125] B represents boron.

[0126] M is selected from one or more elements chosen from Al, Cu, Ga, Zn, Bi, Zr, Ti, Nb, V, Mo, and W. Preferably, M is Cu, Zr, or Ga. The total number of M atoms is 5 at% or less of the alloy powder; 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 number of M atoms is 0.3 to 1 at%.

[0127] The alloy coarse powder of the present invention comprises elements such as R1, B, Co, Cu, Zr, Ga, and Fe. In some embodiments, the alloy coarse powder of the present invention is composed of R1, B, Co, Cu, Zr, Ga, and Fe. Based on the weight of the alloy coarse powder, the content of R1 can be 28-31 wt%; preferably 28-30 wt%; more preferably 28-29 wt%. The content of B can be 0.6-1.6 wt%; preferably 0.7-1.3 wt%; more preferably 0.9-1.0 wt%. The content of Co can be 0.1-3.9 wt%; preferably 0.7-1.3 wt%; more preferably 0.9-1.0 wt%. The content of Cu can be 0.05-1.0 wt%; preferably 0.10-0.70 wt%; more preferably 0.12-0.20 wt%. The content of Zr can be 0.06-0.25 wt%; preferably 0.1-0.16 wt%; more preferably 0.13-0.15 wt%. The Ga content can be 0.1–0.3 wt%; preferably 0.15–0.25 wt%; more preferably 0.18–0.20 wt%. The remainder is Fe. According to one embodiment of the present invention, the alloy coarse powder 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), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0128] 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%; more preferably 0.13–0.15 wt%. The Ga content can be 0.1–0.3 wt%; preferably 0.15–0.25 wt%; more preferably 0.18–0.20 wt%. The remainder is Fe.

[0129] In the air jet milling process, raw materials comprising alloy coarse powder and praseodymium hydride powder are milled into magnetic powder in an air jet mill. The average particle size D50 of the magnetic powder can be 1–10 μm; preferably 2–7 μm; more preferably 3–5 μm. The air jet milling process can be carried out in a nitrogen atmosphere.

[0130] Example 1

[0131] Smelting process: The raw materials are prepared by mass percentage according to 29.0% Nd, 1.0% B, 1.0% Co, 0.15% Cu, 0.15% Zr, 0.2% Ga and the balance Fe. The raw materials are placed in a vacuum melting and solidification furnace for smelting to produce alloy sheets with an average thickness of 0.3 mm.

[0132] Hydrogen crushing process: The alloy sheets are subjected to hydrogen absorption and dehydrogenation treatment in a hydrogen crushing furnace to form alloy coarse powder with an average particle size D50 of 100μm.

[0133] Air jet milling process: Based on the alloy coarse powder, 2.0 wt% praseodymium hydride powder is added, mixed evenly, and then ground into magnetic powder with an average particle size D50 of 4.0 μm in an air jet mill with nitrogen as the medium.

[0134] Molding process: Magnetic powder is oriented and molded into a green body under nitrogen protection by applying a 1.8T magnetic field in a molding press. The density of the green body is 4.3 g / cm³. 3 ;

[0135] Sintering and aging treatment process: The blank is placed in a vacuum sintering furnace with an absolute vacuum degree of less than 0.1 Pa and sintered at 1070℃ for 5 hours to obtain a sintered magnet; then, the sintered magnet is subjected to a first-stage tempering at 900℃ for 3 hours and a second-stage tempering at 500℃ for 5 hours under an absolute vacuum degree of less than 0.1 Pa to obtain a rare earth sintered NdFeB magnet.

[0136] The above rare earth sintered NdFeB magnets were processed into D10×10mm sample columns. The magnetic properties of the magnets at room temperature and high temperature of 150℃ were measured using a BH tester, and the remanence temperature coefficient α and coercivity temperature coefficient β in the range of 20~150℃ were calculated.

[0137] The microstructure of the above-mentioned rare-earth sintered NdFeB magnets was observed using a Sigma 500 field emission scanning electron microscope (see [reference]). Figure 1 ), and used an EDS detector for component analysis.

[0138] The average thickness L of the grain boundary phase, the Pr concentration difference (C1-C2) between the edge of the main phase grain and the center of the main phase grain, and the magnetic properties of the rare earth sintered NdFeB magnets are shown in Tables 1 and 2.

[0139] Examples 2-3 and Comparative Examples 1-2

[0140] In the air jet milling process, the amount of praseodymium hydride powder was changed, while the remaining processes were the same as in Example 1. The average thickness L of the grain boundary phase of the rare earth sintered NdFeB magnet, the Pr concentration difference (C1-C2) between the edge of the main phase grain and the center of the main phase grain, and the magnetic performance parameters are shown in Tables 1 and 2.

[0141] Example 4

[0142] In the air jet milling process, 3.0% wt of Pr68Cu32 alloy was added, and the remaining processes were the same as in Example 1. The average thickness L of the grain boundary phase of the rare earth sintered NdFeB magnet, the Pr concentration difference (C1-C2) between the edge of the main phase grain and the center of the main phase grain, and the magnetic performance parameters are shown in Tables 1 and 2.

[0143] Comparative Example 3

[0144] In the smelting process, raw materials were prepared by mass percentage as follows: 29.0% Nd, 2.0% Pr, 1.0% B, 1.0% Co, 0.15% Cu, 0.15% Zr, 0.2% Ga, and the balance Fe. In the air jet milling process, praseodymium hydride powder was not added, and the remaining processes were the same as in Example 1. The average thickness L of the grain boundary phase of the rare earth sintered NdFeB magnet, the Pr concentration difference (C1-C2) between the main phase grain edge and the main phase grain center, and the magnetic performance parameters are shown in Tables 1 and 2.

[0145] Table 1

[0146]

[0147] Comparative Examples 4-9

[0148] Sintered NdFeB magnets were prepared according to Examples 1 to 6 of CN111696742A. The average thickness L of the grain boundary phase, the Pr concentration difference (C1-C2) between the main phase grain edge and the main phase grain center, and the magnetic properties of the rare earth sintered NdFeB magnets are shown in Table 2.

[0149] Comparative Examples 10-13

[0150] Sintered NdFeB magnets were prepared 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 grain edge and the main phase grain center, and the magnetic performance parameters of the rare earth sintered NdFeB magnets are shown in Table 2.

[0151] Table 2

[0152]

[0153] Note: Br1 represents the remanence of rare earth sintered NdFeB magnets without the addition of modified powder, in kGs; Br2 represents the remanence of rare earth sintered NdFeB magnets with the addition of modified powder, in kGs; Hcj1 represents the coercivity of rare earth sintered NdFeB magnets without the addition of modified powder, in kOe; Hcj2 represents the coercivity of rare earth sintered NdFeB magnets with the addition of modified powder, in kOe.

[0154] As shown in Tables 1-2, this invention grinds alloy coarse powder and praseodymium-containing powder into magnetic powder using an air jet mill. Then, through forming and sintering processes, rare-earth sintered NdFeB magnets are obtained. This achieves a perfect balance between remanence and coercivity, with a balance coefficient exceeding 25. At this point, the Pr concentration C1 at the edge of the main phase grains is at least 0.25 wt% higher than the Pr concentration C2 at the center of the main phase grains, and the average thickness of the grain boundary phase is 20–60 nm. If an appropriate amount of praseodymium hydride powder is used, the balance coefficient between remanence and coercivity is even higher, exceeding 35 (see Example 1).

[0155] As can be seen from Table 3, the magnets of Comparative Examples 1 to 13 cannot simultaneously meet the following conditions: (1) the Pr concentration C1 at the edge of the main phase grain is more than 0.25 wt% higher than the Pr concentration C2 at the center of the main phase grain; (2) the average thickness of the grain boundary phase is 20 to 60 nm.

[0156] As shown in Table 2, Comparative Example 1, without the addition of praseodymium hydride powder, exhibited lower remanence and coercivity. Comparative Example 2, with its excessive praseodymium hydride powder, resulted in a significant decrease in remanence, leading to a lower equilibrium coefficient. Comparative Example 3, by adding Pr during the raw material mixing process, did not show a significant improvement in coercivity, resulting in a low equilibrium coefficient. Comparative Examples 4-9, by directly mixing PrNi alloy powder with fine magnetic powder, significantly increased coercivity but reduced remanence too much, resulting in an equilibrium coefficient below 20. Comparative Examples 11 and 12, by directly mixing (PrNd)Co alloy powder with fine magnetic powder, improved coercivity but reduced remanence too much, resulting in an equilibrium coefficient below 10. Comparative Examples 10 and 13, by directly mixing DyCo or TbCo alloy powder with fine magnetic powder, significantly improved coercivity but reduced remanence even more, resulting in a very low equilibrium coefficient.

[0157] Table 3

[0158] condition <![CDATA[The Pr concentration difference (C1 - C2) is higher than 0.25 wt%]]> L is 20–60 nm Comparative Example 1 no no Example 1 yes yes Example 2 yes yes Example 3 yes yes Comparative Example 2 no yes Example 4 yes yes Comparative Example 3 no no Comparative Example 4 yes no Comparative Example 5 yes no Comparative Example 6 yes no Comparative Example 7 yes no Comparative Example 8 yes no Comparative Example 9 yes no Comparative Example 10 no no Comparative Example 11 yes no Comparative Example 12 no no Comparative Example 13 yes no

[0159] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. A (R1, R2)-T-B-M rare earth sintered Nd-Fe-B magnet, characterized in that: the rare earth sintered Nd-Fe-B magnet is composed of a sintered body containing main phase grains and a grain boundary phase; R1 is selected from one or more of Nd and Gd elements, and Nd accounts for 50 at% or more of the total number of atoms of R1; R2 is a Pr element; T is Fe and Co elements, and Co accounts for 3 at% or less of the total number of atoms of T; B is a boron element; M is Cu, Ga and Zr elements, and the total number of atoms of M is 5 at% or less of the sintered body; the sintered body has a composition of 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 remainder is substantially Fe; the remanence of the rare earth sintered Nd-Fe-B magnet is 14.50 kGs or more, the intrinsic coercivity is 14.0 kOe or more, the remanence temperature coefficient in the range of 20-150 ℃ is less than 0.113% / ℃, and the coercivity temperature coefficient in the range of 20-150 ℃ is less than 0.573% / ℃. The Pr concentration gradually decreases from the edge of the main phase grain to the center of the main phase grain. said primary phase crystalline grains are of the composition (R1, R2)2T 14 B; the Pr concentration at the edge of said primary phase crystalline grains is higher than the Pr concentration at the center of said primary phase crystalline grains C 1 higher than the Pr concentration at the center of said primary phase crystalline grains C 2 ; C 1 - C 2 0.25-0.57 wt%; the R1 concentration of said grain boundary phase is higher than the R1 concentration of the primary phase crystalline grains; and the average thickness of said grain boundary phase is 20-27 nm; The content of Zr in the sintered body is 0.1-0.16 wt%, and the content of Ga is 0.15-0.25 wt%. The method comprises the following steps: (a) smelting raw materials R1, T, B and M of the rare earth sintered Nd-Fe-B magnet to obtain a master alloy sheet; (b) crushing the master alloy sheet into alloy coarse powder with an average particle size D50 of 20-500 µm; (c) grinding the alloy coarse powder and a Pr-containing powder into magnetic powder with an average particle size D50 of 1-10 µm in an airflow mill; wherein the Pr-containing powder is praseodymium hydride or a Pr-M alloy powder; (d) pressing the magnetic powder in a magnetic field, and then performing isostatic pressing to obtain a green body; (e) performing vacuum heat treatment and two-stage tempering treatment on the green body to obtain a rare earth sintered permanent magnet.

2. The rare earth sintered neodymium-iron-boron magnet according to claim 1, characterized by The amount of the Pr-containing powder is 0.1-5.0 wt% based on the weight of the alloy coarse powder.

3. The rare earth sintered neodymium-iron-boron magnet according to claim 1, characterized in that, ​ 4. The method of producing a rare earth sintered neodymium-iron-boron magnet according to any one of claims 1 to 3, characterized by, ​ ​ ​ ​ ​ ​ 5. The preparation method according to claim 4, characterized in that, ​

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