Anisotropic magnetic material and preparation method and application thereof

Abstract

The invention discloses an anisotropic magnetic material and a preparation method and application thereof, and relates to the technical field of viscous magnet materials, and the anisotropic magnetic material comprises an inner core, a first coating layer and a second coating layer in the direction from the center of a particle to the outer surface layer of the particle; the inner core comprises a neodymium iron boron material, the first coating layer comprises a rare earth alloy, and the second coating layer comprises a phosphoric acid compound. Through coating of the first coating layer and the second coating layer, microcracks of the inner core are effectively repaired, compact particles are formed, and the instability and high-temperature oxidation risk of a grain boundary phase are reduced, so that the high-temperature stability of the anisotropic magnetic material is remarkably improved on the premise that the magnetic performance is not greatly sacrificed.

Description

Technical Field

[0001] The present invention relates to the technical field of bonded magnet materials, and in particular, to an anisotropic magnetic material, a preparation method thereof, and an application thereof. Background Art

[0002] Bonded magnets have the advantages of free formability and high dimensional accuracy, etc., and are widely used in the fields of consumer electronics products and new energy vehicles. Especially for anisotropic bonded magnets with higher magnetic properties, they meet the development trends of miniaturization and light weight of end products in emerging fields. Currently, the HDDR (i.e., hydrogen absorption - disproportionation - dehydrogenation - recombination) process is mainly used to prepare anisotropic NdFeB magnetic powder. Its preparation process is simple, the production cost is low, and it is easy to realize industrialization. However, under high - temperature conditions, due to the intensified lattice vibration of anisotropic NdFeB magnetic powder, the migration of magnetic domain walls is likely to occur, resulting in the rearrangement of magnetic domains. This rearrangement will lead to a decrease in the remanence and coercivity of the magnet, and the weakening of magnetic properties. In addition, due to the defects of the hydrogen - induced phase - change process, micro - cracks are likely to form on the surface of the prepared anisotropic NdFeB magnetic powder. These micro - cracks will intensify at high temperatures and become the penetration paths for corrosive media such as oxygen and water, thereby accelerating the oxidation and corrosion of the material and further reducing the magnetic properties. As a result, when the bonded magnet prepared from anisotropic NdFeB magnetic powder serves at a higher temperature, problems such as a decrease in magnetic properties and magnetic flux loss will occur. Summary of the Invention

[0003] The main object of the present invention is to provide an anisotropic magnetic material, a preparation method thereof, and an application thereof, so as to solve the problem of the decrease in magnetic properties of anisotropic magnetic materials under high - temperature service conditions in the prior art.

[0004] To achieve the above object, according to one aspect of the present invention, an anisotropic magnetic material is provided. Along the direction from the particle center to the particle outer surface layer, the anisotropic magnetic material includes a core, a first coating layer, and a second coating layer;

[0005] The core contains NdFeB material, the first coating layer contains rare - earth alloy, and the second coating layer contains phosphoric acid - based compounds.

[0006] Furthermore, the core contains NdFeB matrix material and strengthening elements;

[0007] Wherein, the strengthening elements include first rare - earth elements and / or transition metal elements;

[0008] Preferably, the first rare - earth elements include at least one of La - series elements, Sc, and Y, and the transition metal elements include at least one of Co, Ni, Cu, Al, Zr, Ga, Nb, Ti, Cr, V, and Zn;

[0009] Preferably, the neodymium iron boron material comprises, by mass percentage: 27% - 30% of Nd, 0.9% - 1.2% of B, 0.1% - 20% of Co, 0 - 2% of a first rare earth element, and the balance is Fe

[0010] Further, the first coating layer contains a second rare earth element and a low melting point metal element;

[0011] Among them, the second rare earth element includes at least one of La series elements, Sc, and Y, and the melting point of the low melting point metal element ≤ 1100 °C;

[0012] Preferably, the mass ratio of the low melting point metal element to the second rare earth element is (20 - 40):(60 - 80). Preferably, the second rare earth element includes at least one of Nd and Pr;

[0013] Preferably, the low melting point metal element includes at least one of Cu, Al, Ga, In, and Zn;

[0014] Preferably, the rare earth alloy comprises, by mass content: 60% - 80% of Nd, 0 - 20% of Pr, 0 - 20% of Tb, 0 - 20% of Dy, 0 - 20% of Cu, and 0 - 10% of Al.

[0015] Further, the phosphoric acid compound includes at least one of phosphoric acid, phosphate, and organic phosphoric acid derivatives;

[0016] Preferably, the phosphoric acid compound includes at least one of phosphoric acid, disodium hydrogen phosphate, zinc phosphate, aluminum phosphate, metaphosphoric acid, and phosphate ester.

[0017] Further, the D50 particle size of the anisotropic magnetic material is 40 - 250 μm; and / or,

[0018] The D50 particle size of the inner core is 30 - 200 μm; and / or,

[0019] The thickness of the first coating layer is 0.1 - 200 nm; and / or,

[0020] The thickness of the second coating layer is 0.1 - 200 nm; and / or,

[0021] The mass ratio of the first coating layer to the inner core is (1 - 5):100; and / or,

[0022] The mass ratio of the sum of the masses of the first coating layer and the inner core to the mass of the second coating layer is 100:(0.01 - 1).

[0023] In the second aspect of the present invention, there is provided a method for preparing the anisotropic magnetic material of the first aspect, comprising the following steps:

[0024] S1. Mix the core material with a solution containing a rare earth alloy to obtain a first mixture; perform heat treatment on the first mixture to obtain a first intermediate;

[0025] S2. Mix the first intermediate with a solution containing a phosphoric acid compound to obtain a second mixture; perform passivation treatment on the second mixture to obtain an anisotropic magnetic material.

[0026] Furthermore, the solution containing the rare earth alloy is formed by mixing the rare earth alloy with a first organic solvent. Among them, the rare earth alloy includes a second rare earth element and a low melting point metal element, and the first organic solvent includes acetone or ethanol.

[0027] The solution containing the phosphoric acid compound is formed by mixing the phosphoric acid compound with a second organic solvent. Among them, the phosphoric acid compound includes at least one of phosphoric acid, phosphate, and phosphoric acid organic derivatives, and the second organic solvent includes at least one of acetone, ethanol, methyl acetate, and ethyl acetate;

[0028] Preferably, the second rare earth element includes at least one of La series elements, Sc, and Y;

[0029] Preferably, the melting point of the low melting point metal element ≤ 1100 °C;

[0030] More preferably, the second rare earth element includes at least one of Nd and Pr;

[0031] More preferably, the low melting point metal element includes at least one of Cu, Al, Ga, In, and Zn;

[0032] Preferably, the phosphoric acid compound includes at least one of phosphoric acid, disodium hydrogen phosphate, zinc phosphate, aluminum phosphate, metaphosphoric acid, and phosphate ester;

[0033] Preferably, the mass content of the rare earth alloy in the solution containing the rare earth alloy is 10% - 20%;

[0034] Preferably, the mass content of the first organic solvent in the solution containing the rare earth alloy is 80% - 90%;

[0035] Preferably, the mass content of the phosphoric acid compound in the solution containing the phosphoric acid compound is 0.01 - 1%.

[0036] Furthermore, the heat treatment includes a first-stage heat treatment and a second-stage heat treatment carried out in sequence; among them, the temperature of the first-stage heat treatment < the temperature of the second-stage heat treatment;

[0037] Preferably, the temperature of the first-stage heat treatment is 80 - 120 °C, and the time of the first-stage heat treatment is 10 - 20 min;

[0038] Preferably, the temperature of the second heat treatment is 700 - 850 °C, and the time of the second heat treatment is 0.5 - 2.5 h;

[0039] Preferably, the temperature of the passivation treatment is 30 - 80 °C, and the time of the passivation treatment is 1 - 3 h.

[0040] In the third aspect of the present invention, there is provided a mixed adhesive powder for bonded magnets, including the anisotropic magnetic material of the first aspect or the anisotropic magnetic material prepared by the preparation method of the second aspect.

[0041] In the fourth aspect of the present invention, there is provided a bonded magnet, which is formed by pressing and molding the mixed adhesive powder for bonded magnets of the third aspect.

[0042] By applying the technical solution of the present invention, through the coating of the first coating layer and the second coating layer, the microcracks of the inner core are effectively filled, dense particles are formed, the instability of the grain boundary phase and the risk of high-temperature oxidation are reduced, so that the high-temperature stability of the anisotropic magnetic material is significantly improved without significantly sacrificing the magnetic properties, and the problem of the decrease in magnetic properties of the anisotropic magnetic material under high-temperature service conditions is effectively solved. Description of the Drawings

[0043] Figure 1 It is a schematic diagram of the microstructure of the anisotropic magnetic material in an embodiment of the present invention;

[0044] Figure 2 It is a test curve of the irreversible flux loss of the bonded magnets formed by the anisotropic magnetic materials in Example 4 and Comparative Example 1 at 130 °C with the holding time;

[0045] Figure 3 It is a test curve of the irreversible flux loss of the bonded magnets formed by the anisotropic magnetic materials in Example 4 and Comparative Example 1 after holding at 25 - 120 °C for 100 h.

[0046] Description of the Reference Numerals:

[0047] 101 - inner core; 102 - first coating layer; 103 - second coating layer. Detailed Embodiments

[0048] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0049] As described in the background art of the present invention, there is a problem in the prior art that the magnetic properties of anisotropic magnetic materials deteriorate under high-temperature service conditions. To solve the above problems, in a typical embodiment of the present invention, as Figure 1 shown, an anisotropic magnetic material is provided. Along the direction from the particle center to the particle outer surface layer, the anisotropic magnetic material includes a core 101, a first coating layer 102, and a second coating layer 103; the core 101 contains a neodymium iron boron material, the first coating layer 102 contains a rare earth alloy, and the second coating layer 103 contains a phosphoric acid compound.

[0050] The core 101 is the main part of the anisotropic magnetic material and mainly contains a neodymium iron boron (NdFeB) material. The NdFeB material is a high-performance permanent magnet material, with Nd (neodymium), Fe (iron), and B (boron) as the main components. The tetragonal crystal phase of the NdFeB material has strong magnetic anisotropy, which helps to enhance the coercivity and magnetic energy product of the anisotropic magnetic material, thereby enhancing the magnetic properties of the magnet. The neodymium iron boron material can be prepared by the HDDR (hydrogenation-disproportionation-dehydrogenation-recombination) process.

[0051] The first coating layer 102 is located between the core 101 and the second coating layer 103 and is mainly composed of a rare earth alloy. The rare earth alloy can penetrate into the microcracks on the surface of the core particles to fill these defects, thereby forming a denser particle structure. At the same time, the first coating layer 102 forms a coating on the surface of the core 101, eliminating the high-energy positions on the grain surface, suppressing the generation of reverse magnetic domains, improving the heat resistance of the magnetic material, and also improving the magnetic isolation effect between magnetic particles, further enhancing the coercivity of the magnetic material.

[0052] The second coating layer 103 is the outermost protective layer of the magnetic material particles and is mainly composed of a phosphoric acid compound. The second coating layer 103 is used to provide a dense passivation film, which has good corrosion resistance and thermal stability, effectively preventing the magnetic material particles from oxidizing in high-temperature or corrosive environments, avoiding a sharp decline in magnetic properties under high-temperature conditions, maintaining the magnetic properties of the magnetic material stable, and enhancing corrosion resistance and thermal stability.

[0053] Compared with the prior art, through the synergistic effect of this multi-layer structure from the particle interior to the outer surface layer, the present invention uses the core 101 containing the neodymium iron boron material to provide basic magnetic properties, uses the first coating layer 102 containing the rare earth alloy to improve the structure of the magnetic material particles and enhance magnetic isolation, and uses the second coating layer 103 containing the phosphoric acid compound to provide surface passivation protection, avoiding the situation where microcracks cannot be repaired without phosphoric acid treatment of the first coating layer. Under the combined action of the three, the comprehensive performance of the anisotropic magnetic material is significantly improved, especially the high-temperature resistance and antioxidant ability of the magnetic material are enhanced, and its service life in high-temperature environments is extended.

[0054] The structure and composition of the core 101 directly affect the remanence (Br) and coercivity (Hcj) of the magnet. In some embodiments, the core 101 comprises a neodymium iron boron material composed of a NdFeB matrix phase and a rare earth-rich phase. Among them, the NdFeB matrix phase is Nd 2 Fe 14 B tetragonal crystal phase, which is the basic magnetic phase of the neodymium iron boron material. The tetragonal crystal phase has strong magnetic anisotropy, which is the basis for the high magnetic energy product and coercivity of the magnet, thus ensuring that the magnetic material has a high magnetization saturation and coercivity. The rare earth-rich phase helps to increase the anisotropy field of the magnet, thereby further enhancing the magnetic properties of the magnet. The rare earth-rich phase mainly appears in the form of an excessive amount of Nd element in the Nd 2 Fe 14 B phase, or exists in the form of other rare earth metal phases, such as intermetallic compounds of Nd or oxides of Nd, etc. The presence of the rare earth-rich phase helps to adjust and enhance the anisotropy field of the material, thereby increasing the coercivity of the magnet and enabling it to maintain a strong magnetic state after the external magnetic field is removed.

[0055] In some embodiments, the mass ratio of the NdFeB matrix phase to the rare earth-rich phase is (97 - 99):(1 - 3). The matrix phase provides the main magnetization ability and magnetic anisotropy, while the rare earth-rich phase enhances the magnetic stability and coercivity of the material by adjusting the magnetic anisotropy field. By defining the mass ratio of the NdFeB matrix phase to the rare earth-rich phase in the core, such a multi-level and multi-phase structure enables the core to have good chemical stability while having high-intensity magnetic properties.

[0056] In addition to containing Nd (neodymium), Fe (iron), and B (boron), in some embodiments, the core 101 of the present invention comprises a NdFeB matrix material and a strengthening element, that is, the neodymium iron boron material includes a NdFeB matrix material and a strengthening element, so as to adjust the anisotropy field of the magnet and further improve its magnetic properties.

[0057] In some embodiments, the enhancing element includes a first rare earth element and / or a transition metal element. For example, the first rare earth element includes at least one of Dy (dysprosium), Pr, Tb (terbium), La, and Ce, and the transition metal element includes at least one of Co, Ni, Cu, and Al. Among them, the addition of two heavy rare earth elements, Dy (dysprosium) and Tb (terbium), can significantly improve the thermal stability of the magnet, especially the coercive force at high temperatures; the addition of light rare earth elements such as La and Ce can reduce costs without affecting the coercive force and remanence of the magnet as much as possible. The introduction of transition elements can enhance the coercive force, improve the magnetic properties and thermal stability of magnetic materials. Specifically, the introduction of Co can improve the thermal stability of magnetic materials, while the addition of Cu helps to improve the fluidity of magnetic materials, and Al can improve the corrosion resistance of magnetic materials. The present invention can select different enhancing elements according to actual needs.

[0058] In some embodiments, the mass ratio of the NdFeB matrix material to the reinforcement element is (98-99): (1-2). The present invention can further improve its comprehensive magnetic properties and adapt to specific working conditions by adjusting the ratio of the reinforcement element in the core.

[0059] In some embodiments, the NdFeB material includes, by mass percentage, 27% to 30% Nd, 0.9% to 1.2% B, 0% to 20% Co, 0% to 2% of the first rare earth element, and the remainder is Fe. In this way, by finely controlling the composition of the NdFeB material in the core, the magnetic properties and thermal stability of the magnet can be precisely controlled to meet the needs of different application fields.

[0060] In some embodiments, the NdFeB material may be prepared using a HDDR process. Specifically, the NdFeB material may be prepared by the following method:

[0061] The first step is to place the master alloy in a vacuum or argon environment and keep it at a temperature range of 1050° C. to 1150° C. for 10 to 20 hours, thereby completing the homogenization heat treatment step;

[0062] In the second step, the master alloy containing heat treatment is placed in an environment with a hydrogen partial pressure of 0.01 to 0.3 MPa, the temperature is maintained at 30 to 200 ° C for 1 to 3 hours, and then maintained in a vacuum for 0.5 to 1 hour for hydrogenation reaction to generate coarse-grained Re 2 Fe 14 BH x Powder particles;

[0063] The third step is a hydrogen absorption-disproportionation step, in which the hydrogenated powder particles are heated to 800-860°C in a 30-100 kPa hydrogen environment and kept warm for 3-5 hours to absorb hydrogen and disproportionate.

[0064] The fourth process, dehydrogenation-combination step: reduce the hydrogen pressure to 1-10 kPa, maintain at 800-860 °C for 0.5-1 h for low-vacuum dehydrogenation, then evacuate to below 0.1 Pa for dehydrogenation for 1-2 h to complete the combination reaction, and finally fill with argon and cool to room temperature to obtain the NdFeB material. The first coating layer 102 can be used to improve the surface properties of the magnetic material particles, enhance the magnetic isolation effect between magnetic particles, thereby improving the heat resistance and magnetic property stability of the overall material. The composition and properties of the first coating layer 102 have a direct impact on the comprehensive performance of the magnetic material. In some embodiments, the first coating layer 102 contains a second rare earth element and a low-melting-point metal element, that is, the rare earth alloy includes a second rare earth element and a low-melting-point metal element. The second rare earth element mainly provides properties such as magnetism, stability, and anisotropy in the rare earth alloy. The low melting point property of the low-melting-point metal element gives it good ductility and fluidity, helping to fill the microcracks on the surface of the core particles and improving the compactness of the magnetic material. At the same time, the low-melting-point metal element can also react with the NdFeB matrix phase or the rare earth-rich phase on the surface of the core particles, thus contributing to the formation of the first coating layer 102 and maximizing the role of the first coating layer.

[0065] Specifically, the second rare earth element includes at least one of La series elements, Sc, and Y. For example, the second rare earth element includes at least one of La (lanthanum), Ce (cerium), Pr (praseodymium), Nd (neodymium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), Lu (lutetium), Y (yttrium), and Sc (scandium). In some preferred embodiments, the second rare earth element includes at least one of Nd and Pr.

[0066] In some embodiments, the melting point of the low-melting-point metal element ≤ 1100 °C. In some preferred embodiments, the low-melting-point metal element includes at least one of Cu, Al, Ga, In, and Zn. The addition of these low-melting-point metal elements can improve the fluidity, facilitate filling the microcracks on the surface of the core particles, and is conducive to subsequent processing and shaping.

[0067] In some embodiments, the mass ratio of the low-melting-point metal element to the second rare earth element is (20-40):(60-80). Reasonably controlling the mass ratio of the second rare earth element to the low-melting-point metal element can form a dense and strongly adhesive first coating layer, effectively preventing the oxidation and corrosion of the magnetic material in different environments, especially in high-temperature and humid environments, improving the long-term stability and service life of the material. In addition, an appropriate proportion of the rare earth alloy helps to form a stable and uniform coating layer, simplifies the preparation process, and improves production efficiency.

[0068] In the specific implementation process of the present invention, the rare earth alloy includes at least one of NdCu material, PrNdCu material, NdCuAl material, and PrNdCuAl material. Specifically, the rare earth alloy includes, by mass content: Nd 60% - 80wt%, Pr 0 - 20wt%, Cu 0 - 20wt%, and Al 0 - 10wt%.

[0069] The second coating layer 103 is mainly composed of phosphoric acid compounds. Phosphoric acid compounds refer to compounds containing phosphate groups (PO 4 3- ). Phosphoric acid compounds can be organic phosphates or inorganic phosphates. In some embodiments, the phosphoric acid compounds include at least one of phosphoric acid, phosphates, and organic derivatives of phosphoric acid. Among them, phosphates refer to salt compounds containing the PO 4 3- group, and organic derivatives of phosphoric acid refer to compounds formed after one or more hydrogen atoms in phosphoric acid molecules are replaced by other atoms or groups. In the specific implementation process of the present invention, it can be selected according to actual needs.

[0070] In some embodiments, the phosphoric acid compounds can include at least one of phosphoric acid, disodium hydrogen phosphate, zinc phosphate, aluminum phosphate, metaphosphoric acid, and phosphate esters. The second coating layer formed by these phosphoric acid compounds, in addition to providing heat resistance and corrosion resistance protection, can also improve the fluidity and filling properties of the magnetic material. Especially when preparing bonded magnets, when the anisotropic magnetic material and the binder are mixed to form a mixed glue powder, the second coating layer 103 is in direct contact with the binder. The second coating layer can help the magnetic material disperse and fill better, ensuring the high density and high performance of the bonded magnet. In addition, when the phosphoric acid compounds form the second coating layer, the formation temperature is relatively low and will not damage the structure of the first coating layer, thus ensuring the integrity and stability of the overall structure of the magnetic material.

[0071] In some specific embodiments, the first coating layer 102 is composed of NdCuAl material, the second coating layer 103 is composed of phosphoric acid, the mass content of the first coating layer 102 is 1% - 3% of the core, and the mass content of the second coating layer 103 is 0.1% - 0.5% of the sum of the masses of the core and the first coating layer 102. This can further optimize the high-temperature resistance of the magnetic material.

[0072] Specifically, in the above specific embodiments, on the one hand, the NdCuAl material penetrates into the grain boundaries of the main phase of the core. On the other hand, the NdCuAl material fills the microcracks in the core particles resulting from hydrogen-induced phase transformation. The sharp corners of the microcracks have high stress and large stray fields, which are prone to form reverse magnetization nuclei. After the NdCuAl material epitaxially grows on the tetragonal main phase, it lubricates the edges of the grains, dissolves the sharp corners of the microcracks, and forms a complete first coating layer. This first coating layer has a lower electrode potential, improving the corrosion resistance of the main phase.

[0073] In the above specific embodiments, the mass content of the first coating layer 102 is 1% - 3% of the core, enabling the first coating layer 102 to be uniformly formed and preventing the problem of uneven distribution of the grain boundary phase caused by the growth of grains on the surface layer of the particles.

[0074] In the above specific embodiments, phosphoric acid can undergo an oxidation-reduction reaction with the NdCuAl material in the first coating layer 102 to generate a dense phosphate crystal coating film, which prevents the oxidation corrosion of the surface layer NdCuAl material in a high-temperature environment below 150°C, thereby preventing the decomposition of the main phase and the demagnetization caused by the large stray field at the microcracks.

[0075] In the above specific embodiments, the mass content of the second coating layer 103 is 0.1% - 0.5% of the sum of the masses of the core 101 and the first coating layer 102, preferably 0.1% - 0.3%. This ensures that the second coating layer 103 is a crystal-dense layer with a smooth and uniform thickness, preventing the coating layer from being uneven or incomplete, and at the same time avoiding an excessive thickness of the coating layer, which would increase the non-magnetic components per unit volume and reduce the magnetic properties of the magnetic material.

[0076] The coercivity (Hcj) of the anisotropic magnetic material of the present invention is ≥14 kOe, and the maximum energy product (BHm) is ≥40 MGOe. When the bonded magnet prepared from the anisotropic magnetic material of the present invention is exposed to air at 120 - 130°C for 100 h, its irreversible flux loss is <7%.

[0077] Specifically, the coercivity refers to the reverse magnetic field strength that needs to be applied during the process of returning from the saturated magnetization state to the zero magnetization state in the magnetization curve. The magnitude of the coercivity directly affects the thermal stability of the magnetic material and its anti-demagnetization ability under a strong reverse magnetic field. The anisotropic magnetic material of the present invention can achieve a coercivity above 14 kOe, indicating that it has a very strong anti-demagnetization ability and can still maintain stable magnetism under high-temperature or complex magnetic field environments.

[0078] The magnetic energy product is a measure of the maximum ability of a magnetic material to store magnetic energy after magnetization. It is usually the product of B (residual magnetism) and H (coercive force) at the maximum value in the second quadrant of the hysteresis loop, with the unit of MGOe (megagauss oersteds). The anisotropic magnetic material of the present invention can achieve a magnetic energy product of more than 40 MGOe, indicating that it can store more magnetic energy under the same volume. This is particularly important in applications with high requirements for magnetic properties, such as in motors, sensors, and electronic products, where a high magnetic energy product can bring about a smaller volume, higher efficiency, and stronger magnetic force.

[0079] When the bonded magnet prepared from the anisotropic magnetic material of the present invention is exposed to air at 120 - 130 °C for 100 h, its irreversible flux loss is < 7%. This shows that the anisotropic magnetic material of the present invention has excellent high-temperature resistance and excellent stability in a high-temperature environment. After experiencing long-term high-temperature exposure, the magnetic properties can still remain stable, indicating that the anisotropic magnetic material of the present invention can resist a significant decline in magnetic properties at high temperatures, which means that the anisotropic magnetic material of the present invention effectively prevents oxidation and demagnetization at high temperatures and maintains the magnetic properties of the magnet.

[0080] In some embodiments, the D50 particle size of the anisotropic magnetic material is 40 - 250 μm; and / or, in some embodiments, the D50 particle size of the inner core 101 is 30 - 200 μm; and / or, the thickness of the first coating layer 102 is 0.1 - 200 nm; and / or, the thickness of the second coating layer 103 is 0.1 - 200 nm. By precisely controlling the thickness of each layer, the performance of the magnet can be further optimized. This control of particle size and thickness also makes it easier to achieve uniform distribution of the magnetic material during the preparation of the viscous magnet, improving the processing accuracy and yield of the viscous magnet. Among them, the D50 particle size can also be understood as the volume median diameter or the median particle size. Specifically, the D50 particle size refers to the particle size value at which the particle size distribution of the material accumulates to 50% by volume.

[0081] Specifically, the D50 particle size of the anisotropic magnetic material is preferably 40 - 200 μm, which is convenient for subsequent mixing with glue to prepare the bonded magnet. It can prevent the magnetic material from having too fine a particle size, which may lead to agglomeration and caking during the glue mixing process and is not conducive to filling the mold, and also prevent the magnetic material from having too coarse a particle size, resulting in large particle gaps and being unable to obtain a high-density magnet. This ensures that the mixed glue powder has appropriate fluidity and filling properties, and fully exerts its high performance.

[0082] Specifically, the D50 particle size of the anisotropic magnetic material is 40 to 250 μm, such as 40 μm, 50 μm, 100 μm, 150 μm, 200 μm, 230 μm, 250 μm, or the range composed of any two of them; and / or, the D50 particle size of the inner core 101 is 30 to 200 μm, such as 30 μm, 40 μm, 50 μm, 100 μm, 150 μm, 200 μm, or the range composed of any two of them; and / or, the thickness of the first coating layer 102 is 0.1 to 200 nm, such as 0.1 nm, 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 50 nm, 100 nm, 150 nm, 200 nm, or the range composed of any two of them; and / or, the thickness of the second coating layer 103 is 0.1 to 200 nm, such as 0.1 nm, 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 50 nm, 100 nm, 150 nm, 200 nm, or the range composed of any two of them.

[0083] In some embodiments, the mass ratio of the first coating layer 102 to the inner core 101 is (1 to 5):100; and / or, the mass ratio of the sum of the masses of the first coating layer 102 and the inner core 101 to the mass of the second coating layer 103 is 100:(0.01 to 1). For example, the mass of the inner core 101 is m1, the mass of the first coating layer 102 is m2, and the mass of the second coating layer 103 is m3, m2 / m1 = 1 to 5, m3 / (m1 + m2) = 0.01 to 1. There is a synergistic effect between the first coating layer 102 and the second coating layer 103. A reasonable mass ratio can ensure that a composite protective film is formed on the surface of the inner core particles. The first coating layer 102 fills the microcracks, and the second coating layer 103 forms a passivation film. By limiting the mass ratio within the above range, the combination of the two can minimize the loss of magnetic properties at high temperatures, enabling the magnetic material to not only maintain its excellent magnetic properties but also significantly improve its heat resistance and corrosion resistance, and find the best balance between cost and performance.

[0084] Specifically, the mass ratio of the first coating layer 102 to the inner core 101 is (1 to 5):100, such as 1:100, 1.5:100, 2:100, 2.5:100, 3:100, 3.5:100, 4:100, 4.5:100, 5:100, or the range composed of any two of them. The mass ratio of the sum of the masses of the first coating layer 102 and the inner core 101 to the mass of the second coating layer 103 is 100:(0.01 to 1), such as 100:0.01, 100:0.02, 100:0.03, 100:0.04, 100:0.05, 100:0.06, 100:0.07, 100:0.08, 100:0.09, 100:0.1, or the range composed of any two of them.

[0085] In a second aspect of the present invention, there is provided a method for preparing an anisotropic magnetic material, comprising the following steps:

[0086] S1. Mixing a core material with a solution containing a rare earth alloy to obtain a first mixture; subjecting the first mixture to a heat treatment to obtain a first intermediate;

[0087] S2. Mixing the first intermediate with a solution containing a phosphoric acid compound to obtain a second mixture; subjecting the second mixture to a passivation treatment to obtain the anisotropic magnetic material.

[0088] Specifically, in step S1, the core material is mixed with the solution containing the rare earth alloy so that the surface of the core material particles contacts and adsorbs the rare earth alloy. The solution containing the rare earth alloy can be dissolved in a first organic solvent to ensure that the components of the rare earth alloy are evenly distributed and adhered to the surface of the core material, obtaining the first mixture. The first mixture is placed in a heat treatment device and treated under specific temperature and time conditions. The purpose of the heat treatment is to cause the rare earth alloy to undergo grain boundary diffusion, and at the same time melt and penetrate into the microcracks on the surface of the core material particles to fill these defects, and at the same time form a dense first coating layer on the particle surface. This process helps to improve the density and stability of the magnetic material particles, reduce the high-energy positions on the surface, inhibit the formation of reverse magnetic domains, and enhance the coercivity and heat resistance of the magnetic material. The heat treatment temperature generally needs to be controlled above the melting point of the rare earth alloy, but should not be too high to avoid the growth of the main phase grains or over-diffusion of the alloy.

[0089] In step S2, after the formation of the first coating layer, the first intermediate is mixed with the solution of the phosphoric acid compound so that the surface of the first intermediate contacts the phosphoric acid compound, obtaining the second mixture. The solution containing the phosphoric acid compound can be carried out in a second organic solvent for subsequent drying. The second mixture is subjected to a passivation treatment to obtain a second intermediate. Among them, the passivation treatment refers to forming a phosphoric acid compound passivation film (i.e., the second coating layer) on the surface of the first intermediate through a chemical reaction in an acidic environment. This film has good corrosion resistance and heat resistance, and can effectively prevent the oxidation corrosion of the magnetic material in a high-temperature environment and maintain the magnetic properties of the magnetic material. The passivation treatment generally needs to be carried out at a lower temperature to ensure the uniformity and bonding strength of the film layer.

[0090] Through the above two-step coating treatment, the present invention can prepare an anisotropic magnetic material with excellent thermal stability and magnetic properties. The first coating layer can improve the density of magnetic material particles and reduce surface defects, while the second coating layer forms a protective film on the surface, further improving corrosion resistance and high-temperature stability. The surface treatment method provided by the present invention not only has a simple process, is easy to control, but also has a low cost and is suitable for large-scale industrial production. The finally obtained anisotropic magnetic material can be applied to the preparation of various high-performance magnets to meet the requirements for high magnetic properties and adaptability to complex working conditions of magnetic materials.

[0091] In some embodiments, after the second coating layer is formed, a second intermediate is obtained; the second intermediate can be dried, and the second intermediate can be dried in a drying device to remove residual organic solvents. The drying process can be carried out under vacuum conditions or in a controlled atmosphere to avoid oxidation or unnecessary side reactions. The drying temperature is set to ensure complete volatilization of the solvent.

[0092] In some embodiments, the solution containing the rare earth alloy is formed by mixing the rare earth alloy with a first organic solvent. Among them, the rare earth alloy includes a second rare earth element and a low melting point metal element, and the first organic solvent includes acetone or ethanol. The solution containing the rare earth alloy can be a suspension, as long as it ensures uniform mixing of the core material and the rare earth alloy in the first organic solvent. In the specific implementation process of the present invention, the mass content of the rare earth alloy in the solution containing the rare earth alloy is 10% - 20%; the mass content of the first organic solvent in the solution containing the rare earth alloy is 80% - 90%;

[0093] In some embodiments, the solution containing the phosphoric acid compound is formed by mixing the phosphoric acid compound with a second organic solvent. Among them, the phosphoric acid compound includes at least one of phosphoric acid, phosphate, and organic derivatives of phosphoric acid, and the second organic solvent includes at least one of acetone, ethanol, methyl acetate, and ethyl acetate. The phosphoric acid compound is dissolved in the second organic solvent to form a solution. In the specific implementation process of the present invention, the mass content of the phosphoric acid compound in the solution containing the phosphoric acid compound is 0.01 - 1 wt%.

[0094] Among them, the second rare earth element includes at least one of La series elements, Sc, and Y. For example, the second rare earth element includes at least one of La (lanthanum), Ce (cerium), Pr (praseodymium), Nd (neodymium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), Lu (lutetium), Y (yttrium), and Sc (scandium). In some preferred embodiments, the second rare earth element includes at least one of Nd and Pr.

[0095] In the specific implementation process of the present invention, the rare earth alloy includes at least one of NdCu material, PrNdCu material, NdCuAl material, and PrNdCuAl material. Specifically, the rare earth alloy includes, by mass content: Nd 60% - 80%, Pr 0 - 20%, Tb 0 - 20%, Dy 0 - 20%, Cu 0 - 20%, Al 0 - 10%. The phosphoric acid-based chemical compound refers to a compound containing a phosphate group (PO 4 3- ). The phosphoric acid-based chemical compound can be an organic phosphate or an inorganic phosphate. In some embodiments, the phosphoric acid-based compound includes at least one of phosphoric acid, phosphate, and phosphoric acid organic derivatives. Specifically, the phosphoric acid-based compound can include at least one of phosphoric acid, disodium hydrogen phosphate, zinc phosphate, aluminum phosphate, metaphosphoric acid, and phosphate ester.

[0096] In some embodiments, the melting point of the low-melting metal element ≤ 1100°C. In some preferred embodiments, the low-melting metal element includes at least one of Cu, Al, Ga, In, and Zn. The addition of these low-melting metal elements can improve fluidity, facilitate filling of microcracks on the surface of the core particles, and is conducive to processing and shaping.

[0097] The heat treatment of the present invention includes two consecutive stages. In some embodiments, the heat treatment includes a first-stage heat treatment and a second-stage heat treatment carried out in sequence; wherein, the temperature of the first-stage heat treatment < the temperature of the second-stage heat treatment. The temperature of the first-stage heat treatment is relatively low. In the mixture of the core material and the rare earth alloy, a first organic solvent is added to ensure uniform dispersion of the rare earth alloy. The low temperature of the first-stage heat treatment can promote the evaporation of the first organic solvent, avoiding damage to the core surface or uneven distribution of the rare earth alloy caused by excessive boiling of the solvent during subsequent high-temperature treatment. The rare earth alloy begins to interact with the microstructure of the core material at a relatively low temperature, and may form a preliminary alloy layer on the surface of the core particles. This alloy layer can start to fill the microcracks, but there will be no violent diffusion or formation of an alloy phase with too large a thickness. A certain amount of rare earth alloy has been adsorbed on the core surface. The temperature of the second-stage heat treatment is relatively high, which can promote the further diffusion of the rare earth alloy into the interior of the core material particles, fill the microcracks, form a denser particle structure, and enhance mechanical strength and heat resistance. Under high-temperature conditions, the interaction between the rare earth alloy and the core material may promote phase transformation of the crystal phase, forming a more stable alloy phase, which is crucial for improving the magnetic properties (such as coercivity and magnetic energy product) of the magnetic material.

[0098] Through this two-step heat treatment and this method of gradually increasing temperature and staged treatment, the present invention can more precisely control the microstructure of the material, avoiding the adverse effects that may be brought about by single high-temperature heat treatment, such as excessive grain growth and uneven alloy distribution.

[0099] The present invention does not limit the specific conditions of the two-stage heat treatment, as long as the above requirements are met. For example, in some embodiments, the temperature of the first-stage heat treatment is 80-120°C, and the time of the first-stage heat treatment is 10-20 min; and / or, the temperature of the second-stage heat treatment is 700-850°C, and the time of the second-stage heat treatment is 0.5-2.5 h. By limiting the temperature of the heat treatment to meet the above requirements, it is ensured that grain boundary diffusion is sufficient during the heat treatment process, the grain boundary phase distribution is uniform, the microcracks in the core particles are completely filled, and at the same time, the growth of the main phase grains and the formation of triangular grain boundaries are avoided, further improving the magnetic properties. According to Fick's law of diffusion, during the heat treatment process, rare earth alloy diffusion with a high concentration first occurs rapidly on the surface layer of the core particles, and then diffuses to the grain boundaries of the particles over time at different positions. Finally, the liquid rare earth alloy fills the microcracks inside the particles. By limiting the time of the heat treatment to meet the above requirements, a uniformly distributed grain boundary phase and a uniform coating layer can be ensured.

[0100] Specifically, the temperature of the first-stage heat treatment is 80-120°C, such as 80°C, 90°C, 100°C, 110°C, 120°C, or the range composed of any two of them; the time of the first-stage heat treatment is 10-20 min, such as 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min, 20 min, or the range composed of any two of them; the temperature of the second-stage heat treatment is 700-850°C, such as 700°C, 720°C, 740°C, 750°C, 780°C, 800°C, 820°C, 840°C, 850°C, or the range composed of any two of them; the time of the second-stage heat treatment is 0.5-2.5 h, such as 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, or the range composed of any two of them.

[0101] The passivation treatment is used to promote the formation of the second coating layer. In order to avoid the passivation treatment from damaging the first coating layer, in some embodiments, the temperature of the passivation treatment is 30-80°C, and the time of the passivation treatment is 1-3 h. In this way, a uniform and dense second coating layer can be achieved at a relatively low temperature, and at the same time, the first coating layer will not be damaged. By limiting the time of the passivation treatment to meet the above requirements, complete coating and complete solvent volatilization can be achieved.

[0102] Specifically, the temperature of the passivation treatment is 30-80°C, such as 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, or the range composed of any two of them; the time of the passivation treatment is 1-3 h, such as 1 h, 2 h, 3 h, or the range composed of any two of them.

[0103] In the third aspect of the present invention, there is provided a mixed glue powder for bonded magnets, which comprises the anisotropic magnetic material of the first aspect or the anisotropic magnetic material prepared by the preparation method provided in the second aspect.

[0104] Due to the inclusion of the above-mentioned anisotropic magnetic material with excellent properties, when the mixed glue powder for bonded magnets is used to prepare bonded magnets, the bonded magnets can have excellent thermal stability and magnetic properties.

[0105] The mixed glue powder for bonded magnets of the present invention further comprises a resin. The resin serves as a binder for bonding the magnetic materials into a whole. There are various choices for the resin, which can be a thermosetting resin (such as epoxy resin, phenolic resin, etc.) or a thermoplastic resin (such as polyester, polyamide, polyurethane, etc.). The resin not only provides physical bonding between the magnetic materials, but also endows the bonded magnets with good mechanical strength, dimensional stability and chemical corrosion resistance. In addition, the addition of the resin can make the magnetic materials have better processability, such as injection molding or compression molding, which is convenient for manufacturing magnets that meet specific shape requirements. In some embodiments, the mass ratio of the anisotropic magnetic material to the resin is (97-99):(1-3).

[0106] In the fourth aspect of the present invention, there is provided a bonded magnet, which is formed by pressing the mixed glue powder for bonded magnets provided in the third aspect.

[0107] Due to the inclusion of the above-mentioned mixed glue powder for bonded magnets with excellent properties, the bonded magnet has excellent thermal stability and magnetic properties. When the bonded magnet is exposed to air at 120-130 °C for 100 h, its irreversible flux loss < 7%.

[0108] The resin for the bonded magnet involved in the present invention is dispersed on the surface of the treated magnetic powder as a binder, wherein the weight of the magnetic powder is 97-99 wt%, and the remaining part is composed of the binder resin and other additives. As the above-mentioned mixture containing the binder, various choices can be made according to the forming method, such as injection molding, extrusion molding and compression molding. Thermosetting resins, such as epoxy resins and phenolic resins, are used for compression molding; thermoplastic resins, such as nylon and polyphenylene sulfide (PPS), are used for injection molding. In addition, when manufacturing the mixture used for the bonded magnet, in order to improve the fluidity, formability, and fully exhibit the magnetic properties of the magnetic powder, commercially available lubricants, coupling agents and other additives can be used in addition to the binder. Among them, stearic acid and its derivatives, inorganic lubricants, oils, etc. can be used as the lubricant, and 0.01-0.5 wt% can be used relative to the whole bonded magnet. Secondly, silane-based coupling agents can be used as the coupling agent, and 0.01-1.0 wt% can be used.

[0109] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0110] In the following examples, the NdFeB material is prepared by the HDDR process. The specific preparation method is as follows:

[0111] In the first step, the master alloy is placed in a vacuum or argon environment and kept at a temperature in the range of 1050 °C to 1150 °C for 10 to 20 hours to complete the homogenization heat treatment step;

[0112] In the second step, the heat-treated master alloy is placed in an environment with a hydrogen partial pressure of 0.01 to 0.3 MPa, kept at a temperature of 30 to 200 °C for 1 to 3 hours, and then kept in a vacuum for 0.5 to 1 hour for the hydrogenation reaction to generate coarse-grained Re 2 Fe 14 BH x powder particles;

[0113] In the third step, the hydrogen absorption-disproportionation step, the hydrogenated powder particles are heated to 800 to 860 °C in a hydrogen environment of 30 to 100 kPa and kept warm for 3 to 5 hours for hydrogen absorption disproportionation;

[0114] In the fourth step, the dehydrogenation-recombination step, the hydrogen pressure is reduced to 1 to 10 kPa, low-vacuum dehydrogenation is carried out at 800 to 860 °C for 0.5 to 1 h, and then the vacuum is pumped to below 0.1 Pa for dehydrogenation for 1 to 2 h to complete the recombination reaction. Finally, argon is filled and cooled to room temperature to obtain NdFeB bonded magnetic powder.

[0115] Example 1

[0116] The preparation method of the anisotropic magnetic material in this example includes the following steps:

[0117] S1. Add 1000 g of NdFeB material, 10 g of rare earth alloy NdCuAl material, and 150 g of acetone, a first organic solvent, to a blender and mix evenly to obtain a first mixture; heat the first mixture to 100 °C under vacuum conditions and keep it warm for 15 min, then raise the temperature to 750 °C and keep it for 60 min, and then cool to room temperature to form a first coating layer on the inner core surface to obtain a first intermediate; among them, based on a mass fraction of 100%, the mass composition of each element in the NdFeB material is: Nd 29.5 wt%, Co 3.0 wt%, B 1.05 wt%, Nb 0.3 wt%, Ga 0.3 wt%, and the balance is Fe. The mass composition of each element in the rare earth alloy NdCuAl material is: Nd 80 wt%, Cu 10 wt%, Al 10 wt%;

[0118] S2. Mix 500 g of the first intermediate, 0.75 g of anhydrous orthophosphoric acid with an acetone solvent, stir evenly to obtain a second mixture; transfer the second mixture to a vacuumable mixer, stir while evacuating, and keep it at a temperature of 45 °C until the acetone has completely evaporated, forming a second coating layer to obtain the anisotropic magnetic material of this example.

[0119] Example 2

[0120] The difference from Example 1 is that in S1, the temperature is raised to 820 °C and maintained for 60 min; in S2, 0.75 g of anhydrous orthophosphoric acid is replaced by 1 g of anhydrous orthophosphoric acid.

[0121] Example 3

[0122] The difference from Example 1 is that in S1, 10 g of rare earth alloy NdCuAl is replaced by 20 g of rare earth alloy NdCuAl; in S2, 0.75 g of anhydrous orthophosphoric acid is replaced by 0.6 g of anhydrous orthophosphoric acid.

[0123] Example 4

[0124] The difference from Example 1 is that in S1, 10 g of rare earth alloy NdCuAl is replaced by 20 g of rare earth alloy NdCuAl, and the temperature is raised to 790 °C and maintained for 60 min; in S2, 0.75 g of anhydrous orthophosphoric acid is replaced by 0.85 g of anhydrous orthophosphoric acid.

[0125] Example 5

[0126] The difference from Example 1 is that in S1, 10 g of rare earth alloy NdCuAl is replaced by 30 g of rare earth alloy NdCuAl; in S2, 0.75 g of anhydrous orthophosphoric acid is replaced by 0.5 g of anhydrous orthophosphoric acid.

[0127] Example 6

[0128] The difference from Example 1 is that in S1, 10 g of rare earth alloy NdCuAl is replaced by 30 g of rare earth alloy NdCuAl, and the temperature is raised to 790 °C and maintained for 60 min.

[0129] Example 7

[0130] The difference from Example 1 is that in S1, 10 g of rare earth alloy NdCuAl is replaced by 15 g of rare earth alloy NdCuAl, and the temperature is raised to 800 °C and maintained for 60 min.

[0131] Example 8

[0132] The difference from Example 1 is that in S1, 10 g of rare earth alloy NdCuAl is replaced with 15 g of rare earth alloy NdCuAl, and the temperature is raised to 810 °C and maintained for 60 min; in S2, 0.75 g of anhydrous orthophosphoric acid is replaced with 0.85 g of anhydrous orthophosphoric acid.

[0133] Example 9

[0134] The difference from Example 1 is that in S1, 10 g of rare earth alloy NdCuAl is replaced with 25 g of rare earth alloy NdCuAl, and the temperature is raised to 790 °C and maintained for 60 min; in S2, 0.75 g of anhydrous orthophosphoric acid is replaced with 0.5 g of anhydrous orthophosphoric acid.

[0135] Example 10

[0136] The difference from Example 1 is that in S1, 10 g of rare earth alloy NdCuAl is replaced with 25 g of rare earth alloy NdCuAl, and the temperature is raised to 780 °C and maintained for 60 min; in S2, 0.75 g of anhydrous orthophosphoric acid is replaced with 0.6 g of anhydrous orthophosphoric acid.

[0137] Example 11

[0138] The difference from Example 1 is that in S1, the temperature is raised to 830 °C and maintained for 60 min.

[0139] Example 12

[0140] The difference from Example 1 is that in S1, the temperature is raised to 830 °C and maintained for 60 min; in S2, 0.75 g of anhydrous orthophosphoric acid is replaced with 1 g of anhydrous orthophosphoric acid.

[0141] Example 13

[0142] The difference from Example 1 is that in S1, 10 g of rare earth alloy NdCuAl is replaced with 15 g of rare earth alloy NdCuAl, and the temperature is raised to 830 °C and maintained for 60 min.

[0143] Example 14

[0144] The difference from Example 1 is that in S1, 10 g of rare earth alloy NdCuAl is replaced with 15 g of rare earth alloy NdCuAl, and the temperature is raised to 830 °C and maintained for 60 min; in S2, 0.75 g of anhydrous orthophosphoric acid is replaced with 0.85 g of anhydrous orthophosphoric acid.

[0145] Example 15

[0146] The difference from Example 1 is that the NdCuAl material is replaced with an NdCu material, and the elemental composition of the NdCu material is: Nd 80 wt%, Cu 20 wt%.

[0147] Example 16

[0148] The difference from Example 1 is that the NdCuAl material is replaced by the PrNdCu material, and the elemental composition of the PrNdCu material is: Nd 60wt%, Pr 20wt%, Cu 20wt%.

[0149] Example 17

[0150] The difference from Example 1 is that the NdCuAl material is replaced by the PrNdCuAl material, and the elemental composition of the PrNdCuAl material is: Nd 60wt%, Pr 20wt%, Cu 10wt%, Al 10wt%.

[0151] Example 18

[0152] The difference from Example 1 is that the anhydrous orthophosphoric acid is replaced by disodium hydrogen phosphate.

[0153] Example 19

[0154] The difference from Example 1 is that the anhydrous orthophosphoric acid is replaced by zinc phosphate.

[0155] Example 20

[0156] The difference from Example 1 is that the anhydrous orthophosphoric acid is replaced by a mixture of methylphosphonic acid, diethylphosphinic acid, and trimethylphosphoric acid.

[0157] Example 21

[0158] The difference from Example 1 is that 10 g of the rare earth alloy NdCuAl material is replaced by 50 g of the rare earth alloy NdCuAl material.

[0159] Example 22

[0160] The difference from Example 1 is that 10 g of the rare earth alloy NdCuAl material is replaced by 8 g of the rare earth alloy NdCuAl material.

[0161] Example 23

[0162] The difference from Example 1 is that 10 g of the rare earth alloy NdCuAl material is replaced by 60 g of the rare earth alloy NdCuAl material.

[0163] Example 24

[0164] The difference from Example 1 is that 0.75 g of anhydrous orthophosphoric acid is replaced by 0.05 g of anhydrous orthophosphoric acid.

[0165] Example 25

[0166] The difference from Example 1 is that 0.75 g of anhydrous orthophosphoric acid is replaced by 5 g of anhydrous orthophosphoric acid.

[0167] Example 26

[0168] The difference from Example 1 is that 0.75 g of anhydrous orthophosphoric acid is replaced with 0.02 g of anhydrous orthophosphoric acid.

[0169] Example 27

[0170] The difference from Example 1 is that 0.75 g of anhydrous orthophosphoric acid is replaced with 8 g of anhydrous orthophosphoric acid.

[0171] Comparative Example 1

[0172] The neodymium iron boron material is directly used as the anisotropic magnetic material of this comparative example.

[0173] Comparative Example 2

[0174] 500 g of neodymium iron boron material, 0.6 g of anhydrous orthophosphoric acid and acetone solvent are mixed and stirred evenly to obtain a mixture; the mixture is transferred to a vacuumable mixer, and vacuum is pumped while stirring, and it is kept warm at a temperature of 50 °C until the acetone volatilizes completely, obtaining the anisotropic magnetic material of this comparative example.

[0175] Comparative Example 3

[0176] 500 g of neodymium iron boron material, 0.85 g of anhydrous orthophosphoric acid and acetone solvent are mixed and stirred evenly to obtain a mixture; the mixture is transferred to a vacuumable mixer, and vacuum is pumped while stirring, and it is kept warm at a temperature of 50 °C until the acetone volatilizes completely, obtaining the anisotropic magnetic material of this comparative example.

[0177] Comparative Example 4

[0178] 500 g of neodymium iron boron material, 1 g of anhydrous orthophosphoric acid and acetone solvent are mixed and stirred evenly to obtain a mixture; the mixture is transferred to a vacuumable mixer, and vacuum is pumped while stirring, and it is kept warm at a temperature of 50 °C until the acetone volatilizes completely, obtaining the anisotropic magnetic material of this comparative example.

[0179] Comparative Example 5

[0180] 1000 g of neodymium iron boron material, 10 g of rare earth alloy NdCuAl, and 150 g of acetone first organic solvent are mixed and stirred evenly to obtain a first mixture; the first mixture is heated to 100 °C and kept warm for 15 min under vacuum conditions, then heated to 750 °C and kept for 60 min, and then cooled to room temperature to form a first coating layer with a thickness of 100 nm on the inner core surface, obtaining the anisotropic magnetic material of this comparative example; among them, the element ratio of the rare earth alloy NdCuAl is: Nd 80 wt%, Cu 10 wt%, Al 10 wt%.

[0181] Test Examples

[0182] 1. Measurement of Residual Magnetism (Br), Coercivity (Hcj), and Maximum Energy Product (BHm)

[0183] The residual magnetism, coercivity, and maximum energy product of the magnetic powder are measured according to the method in Appendix D of GB / T 41967-2022 Anisotropic Neodymium-Iron-Boron Permanent Magnet Powder.

[0184] 2. Thermal Stability Test

[0185] Preparation of Bonded Magnet:

[0186] Mix 98% by mass of magnetic powder, 1% of epoxy resin, 0.5 wt% of stearic acid lubricant, and 0.5 wt% of silane coupling agent, and compress and form to obtain a bonded magnet.

[0187] Use the prepared bonded magnet to magnetize it in an environment with a magnetic field greater than 3T at room temperature T 0 environment, and measure the initial magnetic flux Φ(T0). Next, adsorb the magnet on a pure iron plate with a thickness of 1.0 mm ± 0.1 mm, and the easy magnetization direction of the magnet should be perpendicular to the surface of the iron plate. Then, in the atmospheric environment, heat it to the set temperature T and keep it for a certain time. Finally, take it out and cool it to room temperature to measure the magnetic flux Φ(T). The formula for calculating the flux loss is Flux loss = (Φ(T) - Φ(T 0 )) / Φ(T 0 ) × 100%, and measure it according to the semi-open circuit method of GB / T40794-2021. Expose the bonded magnet in air at 20 - 120 °C and 130 °C for 100 h, and measure the irreversible flux loss.

[0188] The specific preparation parameters of the examples and comparative examples are shown in Table 1, and the test results are shown in Table 2.

[0189] Table 1

[0190]

[0191] In Table 1, the mass of the inner core is m1, the mass of the first coating layer is m2, and the mass of the second coating layer is m3.

[0192] Table 2

[0193]

[0194]

[0195] Figure 1 This is a schematic diagram of the microstructure of the anisotropic magnetic material in an embodiment of the present invention. Along the direction from the particle center to the outer surface layer, the anisotropic magnetic material includes an inner core, a first coating layer, and a second coating layer, and the first coating layer can fill into the microcracks of the inner core particles.

[0196] Figure 2 Curves of the irreversible flux loss of the bonded magnets formed of the anisotropic magnetic materials in Example 4 and Comparative Example 1 at 130 °C as a function of the holding time. According to Figure 2 it can be seen that for the bonded magnet of Example 4 compared with that of Comparative Example 1, the irreversible flux loss at 100 hours can be increased by about 9%. Figure 3 Curves of the irreversible flux loss of the bonded magnets formed of the anisotropic magnetic materials in Example 4 and Comparative Example 1 when holding at 25 - 120 °C for 100 h. According to Figure 3 it can be known that for the bonded magnet of Example 4 compared with that of Comparative Example 1, the irreversible flux loss at 120 °C can be increased by about 8%.

[0197] According to Table 2, it can be seen that compared with Comparative Examples 1 - 5, the anisotropic magnetic materials in Examples 1 - 27 exhibit substantially equivalent magnetic properties in terms of remanence and maximum magnetic energy product. The coercivity of the anisotropic magnetic materials in Examples 1 - 27 is higher than that of the comparative examples, indicating that the demagnetization resistance of the anisotropic magnetic materials in the examples is enhanced.

[0198] Compared with Comparative Examples 1 - 5, the irreversible flux loss of the anisotropic magnetic materials in Examples 1 - 27 after being placed at 130 °C for 100 h is 2.90% - 9.30%, while the flux loss range of the comparative examples is 10.5% - 12.0%. It can be seen that the flux loss of the examples is much lower than that of the comparative examples, which indicates that the heat resistance of the anisotropic magnetic materials in the examples at high temperatures (such as 130 °C) is significantly improved, and the stability of the magnetic properties is better. This shows that the decrease in the magnetic properties of the anisotropic magnetic materials in the examples at high temperatures is effectively suppressed, which benefits from the protective effect of the surface double-layer coating on the core particles, thereby improving the service performance of the magnets under complex working conditions.

[0199] Without significantly reducing the magnetic properties of the anisotropic magnetic materials, the present invention significantly improves its stability and heat resistance in high-temperature environments, which is particularly important for the applications of magnets that need to work under high-temperature conditions.

[0200] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. Anisotropic magnetic material, characterized in that: Along the direction from the center of the particle to the outer surface of the particle, the anisotropic magnetic material comprises a core (101), a first coating layer (102) and a second coating layer (103); The core (101) comprises a neodymium iron boron material, the first coating layer (102) comprises a rare earth alloy, and the second coating layer (103) comprises a phosphoric acid compound.

2. The anisotropic magnetic material according to claim 1, characterized in that: The core (101) comprises a NdFeB matrix material and a reinforcement element; Wherein, the enhancement element includes a first rare earth element and / or a transition metal element; Preferably, the first rare earth element includes at least one of La series elements, Sc, and Y, and the transition metal element includes at least one of Co, Ni, Cu, Al, Zr, Ga, Nb, Ti, Cr, V, and Zn; Preferably, the NdFeB material comprises, in terms of mass percentage, 27% to 30% Nd, 0.9% to 1.2% B, 0.1% to 20% Co, 0 to 2% of the first rare earth element, and the remainder being Fe.

3. The anisotropic magnetic material according to claim 1 or 2, characterized in that: The first coating layer (102) contains a second rare earth element and a low melting point metal element; Wherein, the second rare earth element includes at least one of La series elements, Sc, and Y, and the melting point of the low melting point metal element is ≤1100°C; Preferably, the mass ratio of the low melting point metal element to the second rare earth element is (20-40): (60-80); Preferably, the second rare earth element includes at least one of Nd and Pr; Preferably, the low melting point metal element includes at least one of Cu, Al, Ga, In, and Zn; Preferably, the rare earth alloy comprises, by mass content, 60% to 80% Nd, 0% to 20% Pr, 0% to 20% Tb, 0% to 20% Dy, 0% to 20% Cu, and 0% to 10% Al.

4. The anisotropic magnetic material according to any one of claims 1 to 3, characterized in that: The phosphoric acid compound includes at least one of phosphoric acid, phosphate, and organic phosphoric acid derivatives; Preferably, the phosphate compound includes at least one of phosphoric acid, disodium hydrogen phosphate, zinc phosphate, aluminum phosphate, metaphosphoric acid, and phosphate ester.

5. The anisotropic magnetic material according to any one of claims 1 to 4, characterized in that: The D50 particle size of the anisotropic magnetic material is 40 to 250 μm; and / or, The D50 particle size of the core (101) is 30 to 200 μm; and / or, The thickness of the first coating layer (102) is 0.1 to 200 nm; and / or, The thickness of the second coating layer (103) is 0.1 to 200 nm; and / or, The mass ratio of the first coating layer (102) to the core (101) is (1-5):100; and / or, The mass ratio of the sum of the masses of the first coating layer (102) and the core (101) to the mass of the second coating layer (103) is 100:(0.01-1).

6. A method for preparing anisotropic magnetic material according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1, mixing the core material with a solution containing a rare earth alloy to obtain a first mixture; heat-treating the first mixture to obtain a first intermediate; S2, mixing the first intermediate with a solution containing a phosphoric acid compound to obtain a second mixture; and passivating the second mixture to obtain anisotropic magnetic material.

7. The preparation method according to claim 6, characterized in that: The solution containing the rare earth alloy is a mixture of the rare earth alloy and a first organic solvent, wherein the rare earth alloy includes a second rare earth element and a low melting point metal element, and the first organic solvent includes acetone or ethanol; The solution containing the phosphoric acid compound is a mixture of the phosphoric acid compound and a second organic solvent, wherein the phosphoric acid compound includes at least one of phosphoric acid, phosphate, and an organic phosphoric acid derivative, and the second organic solvent includes at least one of acetone, ethanol, methyl acetate, and ethyl acetate; Preferably, the second rare earth element includes at least one of La series elements, Sc, and Y; Preferably, the melting point of the low-melting-point metal element is ≤1100°C; More preferably, the second rare earth element includes at least one of Nd and Pr; More preferably, the low melting point metal element includes at least one of Cu, Al, Ga, In, and Zn; Preferably, the phosphoric acid compound includes at least one of phosphoric acid, disodium hydrogen phosphate, zinc phosphate, aluminum phosphate, metaphosphoric acid, and phosphate ester; Preferably, the mass content of the rare earth alloy in the solution containing the rare earth alloy is 10% to 20%; Preferably, the mass content of the first organic solvent in the solution containing the rare earth alloy is 80% to 90%; Preferably, the mass content of the phosphoric acid compound in the solution containing the phosphoric acid compound is 0.01-1%.

8. The preparation method according to claim 6, characterized in that: The heat treatment includes a first stage heat treatment and a second stage heat treatment performed sequentially; wherein the temperature of the first stage heat treatment is less than the temperature of the second stage heat treatment; Preferably, the temperature of the first heat treatment is 80-120°C, and the time of the first heat treatment is 10-20 minutes; Preferably, the temperature of the second heat treatment is 700-850°C, and the time of the second heat treatment is 0.5-2.5h; Preferably, the temperature of the passivation treatment is 30-80° C., and the time of the passivation treatment is 1-3 hours.

9. A rubber powder for bonded magnets, characterized in that: The invention comprises the anisotropic magnetic material according to any one of claims 1 to 5 or the anisotropic magnetic material prepared by the preparation method according to any one of claims 6 to 8.

10. A bonded magnet, characterized in that: The bonded magnet according to claim 9 is formed by pressing the mixed rubber powder.

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