Composite magnetic material and method for producing the same

Abstract

This invention discloses a composite magnetic material and its preparation method. The composite magnetic material comprises the following components by weight percentage: 80-96% rare earth magnetic powder, 2-10% binder, 0.1-5% stress-regulating layer, and the balance being additives. The rare earth magnetic powder is Nd-Fe-B based magnetic powder, Sm-Fe-N based magnetic powder, or a combination of both. The stress-regulating layer is composed of an inorganic phase or an organic-inorganic composite phase, and is formed on the surface of the rare earth magnetic powder in a continuous or semi-continuous coating structure, or anchored on the surface of the rare earth magnetic powder in a discrete nanostructure. The stress-regulating layer and the rare earth magnetic powder differ in their coefficient of thermal expansion and / or elastic modulus, and the difference is sufficient to keep the near-surface layer of the rare earth magnetic powder in a state of residual stress after molding. The technical solution of this invention can improve the stability of magnetic properties to a certain extent and slow down the attenuation of magnetic properties under temperature changes or external stress.

Description

Technical Field

[0001] This invention relates to the technical field of magnetic materials, and in particular to a composite magnetic material and its preparation method. Background Technology

[0002] With the miniaturization and high performance of electronic devices, magnetic materials, especially rare-earth permanent magnets, are widely used in motors, sensors, communication equipment, and automotive electronics. Typical rare-earth magnetic materials include neodymium iron boron (NdFeB) and samarium cobalt (SCo) systems, which possess high energy products and high magnetic anisotropy, making them among the best-performing permanent magnet materials currently available. To meet the demands of complex structure forming and mass production, composite magnetic materials composed primarily of rare-earth magnetic powder, supplemented with binders and functional additives, have been gradually developed in recent years, and are formed through injection molding and compression molding. These composite magnetic materials combine processability with certain magnetic properties, and have become an important development direction for magnetic materials.

[0003] In existing technologies, improvements to rare-earth composite magnetic materials mainly focus on controlling magnetic powder particle size, surface treatment, optimizing the bonding system, and improving dispersibility. For example, introducing coupling agents or nano-additives improves the interfacial compatibility between magnetic powder and the matrix, thereby enhancing mixing uniformity and molding performance; or optimizing the magnetic powder ratio and orientation process enhances the overall magnetic properties of the magnet. However, under these technical approaches, the improvement of material performance mainly relies on composition adjustment or macroscopic orientation control, with relatively limited means of regulating the internal structural state of the material. In practical applications, this improvement method, primarily based on component optimization, often struggles to further improve the magnetic anisotropy and stability of the material while maintaining good processing performance, especially as magnetic properties are prone to decay under temperature changes or complex stress environments. Therefore, how to achieve more effective structural control in composite magnetic material systems to further improve their magnetic anisotropy and overall magnetic properties has become an urgent technical problem to be solved. Summary of the Invention

[0004] The main objective of this invention is to propose a composite magnetic material that addresses the technical problems of existing rare-earth bonded composite magnetic materials, such as easy attenuation of magnetic properties, limited improvement in magnetic anisotropy and thermal stability under temperature changes or complex stress environments.

[0005] To achieve the above objectives, the present invention proposes a composite magnetic material comprising the following components by weight percentage: 80-96% rare earth magnetic powder, 2-10% binder, 0.1-5% stress-regulating layer, and the balance being additives, wherein the sum of the contents of each component is 100%, wherein: The rare earth magnetic powder is Nd-Fe-B based magnetic powder, Sm-Fe-N based magnetic powder, or a combination of both. The stress regulation layer is composed of an inorganic phase or an organic-inorganic composite phase. The stress regulation layer is formed on the surface of the rare earth magnetic powder in a continuous or semi-continuous coating structure, or is anchored on the surface of the rare earth magnetic powder in a discrete nanostructure. The stress-regulating layer and the rare earth magnetic powder differ in their coefficient of thermal expansion and / or elastic modulus, and the difference is sufficient to cause the near-surface layer of the rare earth magnetic powder to be in a state of residual stress after molding.

[0006] In one embodiment, the stress-regulating layer is composed of silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, yttrium oxide, cerium oxide, or a combination of two or more of these.

[0007] In one embodiment, the thickness of the stress-regulating layer is 1-100 nm.

[0008] In one embodiment, the stress-regulating layer has a coverage of 30%-100% on the surface of the rare earth magnetic powder.

[0009] In one embodiment, the relative difference in the coefficient of thermal expansion between the stress-regulating layer and the rare-earth magnetic powder is not less than 10%, or the relative difference in the elastic modulus between the stress-regulating layer and the rare-earth magnetic powder is not less than 10%, wherein the relative difference is the ratio of the difference between the two to the smaller of the two values.

[0010] In one embodiment, the stress-regulating layer is fixed to the surface of the rare-earth magnetic powder by an interface connecting component, wherein the interface connecting component is a silane coupling agent, a titanate coupling agent, a phosphate coupling agent, an aluminate coupling agent, or a combination of two or more thereof.

[0011] In one embodiment, the adhesive is one or more of a thermoplastic resin or a thermosetting resin.

[0012] In one embodiment, the adhesive is polyphenylene sulfide, polyamide, epoxy resin, phenolic resin, polyimide, or a combination of two or more thereof.

[0013] Another object of the present invention is to provide a method for preparing composite magnetic materials, comprising the following: The weight percentage of the components as described in the above embodiments; The stress-regulating layer material is mixed with rare earth magnetic powder, surface coated or surface anchored to form a stress-regulating layer on the surface of rare earth magnetic powder. The rare earth magnetic powder with the stress-regulating layer formed thereon is mixed evenly with binder and additives; The resulting mixture is subjected to heating molding, extrusion granulation or compression molding, and then cooled or cured after molding to obtain a composite magnetic material.

[0014] Another object of the present invention is to provide application areas for composite magnetic materials, such as in motor magnets, sensor magnets or automotive electronic magnetic components.

[0015] The composite magnetic material of this invention comprises rare-earth magnetic powder, a binder, a stress-regulating layer, and additives. The rare-earth magnetic powder accounts for 80-96% by weight, serving as the main phase providing the primary magnetic properties; specifically, it is Nd-Fe-B based magnetic powder, Sm-Fe-N based magnetic powder, or a combination of both. The binder accounts for 2-10% by weight, imparting the necessary molding ability to the material, enabling the magnetic powder to be formed into magnets of the desired shape through injection molding, compression molding, or other methods. The stress-regulating layer accounts for 0.1-5% by weight; it is not simply an inert filler but is formed on the surface of the rare-earth magnetic powder in a continuous or semi-continuous coating structure, or anchored to the surface of the rare-earth magnetic powder in a discrete nanostructure, thus being positioned closest to the surface of the magnetic powder. This composition and spatial distribution mean that the material's interior is no longer simply a conventional composite of magnetic powder and resin, but rather introduces an additional structural unit on the magnetic powder surface that can participate in interfacial constraints. Because the stress-regulating layer differs from the rare-earth magnetic powder in terms of coefficient of thermal expansion and / or elastic modulus, asynchronous shrinkage and deformation responses occur between the magnetic powder surface layer and its outermost layer during the cooling or curing process after molding. This difference does not remain at the level of simple material parameters but transforms into a localized residual stress state acting on the near-surface layer of the magnetic powder. Since the stress-regulating layer is located on the surface of the magnetic powder rather than being randomly dispersed away from it, this stress can directly act on the near-surface region of the magnetic matrix, rather than being ineffectively consumed in the binder phase.

[0016] The performance variations of rare-earth bonded magnets often depend not only on the content and orientation of the magnetic powder but also on the stability of the interface state surrounding the powder. Under temperature changes or external stress, the surface layer of the magnetic powder in traditional systems is more prone to inconsistent local structural responses, which makes the magnetic properties more susceptible to decay with fluctuations in service conditions. The surface stress modulation structure employed here effectively establishes a maintainable near-surface constraint environment around each magnetic powder particle, preventing the particle surface from being completely free and instead maintaining a certain constrained deformation state under the combined action of the interface layer. For hard magnetic phases such as Nd-Fe-B and Sm-Fe-N based magnetic powders, which are highly sensitive to local structural states, the introduction of the surface constraint state helps to reduce interface relaxation and local structural fluctuations caused by temperature fluctuations or mechanical stress disturbances during service, thereby making the magnetic response of the powder surface layer more stable. Meanwhile, the amount of stress-regulating layer is controlled within the range of 0.1-5% by weight. This ensures that it plays a practical role on the surface of the magnetic powder while avoiding significant dilution of the magnetic matrix due to an excessively high proportion of non-magnetic phases. The magnetic powder still maintains a high proportion of 80-96% by weight, so the material as a whole remains dominated by rare-earth hard magnetic phases, without deviating from the basic requirements of bonded magnets for magnetic properties and formability. Because this regulation occurs on the surface and near the surface of the magnetic powder, rather than relying solely on simple additions or subtractions at the formulation level or a single improvement in macroscopic orientation, it can more directly adjust the internal structural state of the composite material while maintaining the processing adaptability of the bonded magnet. This allows for more targeted mitigation of magnetic property decay under temperature changes or complex stress conditions, and improves the stability of magnetic properties. Detailed Implementation

[0017] 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. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially. Furthermore, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, or solution B, or a solution where both A and B are satisfied simultaneously. In addition, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] One object of the present invention is to provide a composite magnetic material comprising the following components by weight percentage: 80-96% rare earth magnetic powder, 2-10% binder, 0.1-5% stress-regulating layer, and the balance being additives, wherein the sum of the contents of each component is 100%, wherein: The rare earth magnetic powder is Nd-Fe-B based magnetic powder, Sm-Fe-N based magnetic powder, or a combination of both. The stress regulation layer is composed of an inorganic phase or an organic-inorganic composite phase. The stress regulation layer is formed on the surface of the rare earth magnetic powder in a continuous or semi-continuous coating structure, or is anchored on the surface of the rare earth magnetic powder in a discrete nanostructure. The stress-regulating layer and the rare earth magnetic powder differ in their coefficient of thermal expansion and / or elastic modulus, and the difference is sufficient to cause the near-surface layer of the rare earth magnetic powder to be in a state of residual stress after molding.

[0019] Specifically, the stress-regulating layer acts directly on the surface of each individual particle, rather than on the outer surface of the overall powder pack. Its design aims to establish a local constraint or interface regulation layer near the surface of the magnetic powder particles, enabling each particle's surface to form a controlled residual stress environment during molding and cooling. A continuous or semi-continuous coating structure means the stress-regulating layer can form a covering layer on the particle surface; this covering can be complete or localized, ensuring that local areas of the particle surface are constrained. Discrete nanostructure anchoring indicates that the stress-regulating layer is attached to the magnetic powder particle surface as nanoscale particles or island-like structures. These particles are spatially discontinuous but form localized stress concentration zones, thereby applying local constraints to the near-surface of the particles without affecting the overall packing characteristics of the magnetic powder.

[0020] The stress-regulating layer, composed of an inorganic phase or an organic-inorganic composite phase, generates interfacial stress during molding heating and cooling due to the difference in thermal expansion coefficients or elastic moduli between itself and the magnetic powder. This difference typically requires a relative difference in thermal expansion coefficients or elastic moduli of more than 10%. This ensures that the near-surface layer of the magnetic powder maintains a certain compressive or tensile stress state after injection molding, compression molding, or extrusion cooling to room temperature. For example, for Nd-Fe-B magnetic powder, when the surface is coated with silica nanoparticles, the difference in thermal expansion coefficients between silica and the magnetic powder is approximately 20%. The residual compressive stress formed on the particle surface during cooling can reach tens of megapascals. This stress is sufficient to limit the relaxation of the microstructure of the particle surface lattice without damaging the overall structure of the magnetic powder. For Sm-Fe-N magnetic powder, when the surface is coated with alumina or composite nanoparticles, by controlling the coating thickness within the range of 5-50 nanometers, stable local residual stress can be formed during cooling, allowing the magnetic powder surface to maintain high local structural stability under varying service temperatures. Through this design, the micro-stress environment near the surface of each particle is effectively controlled, thereby forming a repeatable and stable structural state in the composite material, providing a physical basis for maintaining the local magnetic properties of the magnetic powder, while taking into account the overall molding and processing performance.

[0021] In a preferred embodiment, the stress-regulating layer is composed of silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, yttrium oxide, cerium oxide, or a combination of two or more of these.

[0022] In a preferred embodiment, the thickness of the stress-regulating layer is 1-100 nm. This is intended to ensure that the layer can form effective interfacial constraints on the surface of the magnetic powder particles without significantly diluting the magnetic bulk due to excessive thickness. If the thickness is too thin, for example, less than 1 nm, the coating layer may be discontinuous or unable to form stable local stress regions, thus insufficient to apply effective residual stress to the near-surface layer of the magnetic powder during molding cooling or curing. If the thickness is too thick, for example, exceeding 100 nm, it may increase the proportion of non-magnetic phases in the composite material, reduce the volume fraction of magnetic powder, affect the overall magnetic properties, and negatively impact interparticle bonding and molding density.

[0023] In practical applications, for Nd-Fe-B based magnetic powders, a silica stress-regulating layer can be formed on the particle surface using a sol-gel method, with the thickness controlled within the range of 5-20 nanometers. This ensures that the continuous or semi-continuous coating layer can uniformly cover the particle surface and generate a residual compressive stress of approximately 10-30 MPa during injection molding and cooling, thereby improving the stability of the particle surface. For Sm-Fe-N based magnetic powders, when alumina nanoparticles or organic-inorganic composite nanoparticles are anchored on the particle surface, the thickness can be controlled within the range of 10-50 nanometers. This allows for the establishment of a stable local stress state during cooling and solidification, while also considering the flowability between particles and the processability of the composite material. Furthermore, multilayer deposition or stepwise coating methods can be used to vary the local thickness of the stress-regulating layer within the range of 1-100 nanometers, creating a gradient stress regulation effect to further optimize the structural stability of the magnetic powder surface and the retention of magnetic properties under thermal cycling.

[0024] In a preferred embodiment, the stress-regulating layer has a coverage of 30%-100% on the surface of the rare-earth magnetic powder.

[0025] When the coverage rate is less than 30%, the stress-regulating layer is not distributed continuously or uniformly on the particle surface, making it difficult for local residual stress to form a stable network. This results in insufficient lattice confinement on the particle surface, thus limiting its improvement on the structural stability and magnetic properties of the near-surface layer of magnetic powder. Conversely, excessively high coverage rates, while forming a complete coating layer, increase the proportion of non-magnetic components and reduce the volume fraction of magnetic powder, potentially lowering the overall magnetic properties of the composite magnet. It also affects the dense bonding between particles and the molding and processing performance.

[0026] In practical implementation, for Nd-Fe-B magnetic powder, sol-gel or chemical deposition methods can be used to control the coverage of the silica stress-regulating layer on the particle surface within the range of 50%-80%. This achieves semi-continuous or continuous coating, ensuring effective residual compressive stress during cooling and solidification, while avoiding excessive dilution of the magnetic powder volume fraction. For Sm-Fe-N magnetic powder, when using nano-alumina particles to anchor the surface, the coverage can be controlled at 70%-100%. The discrete distribution between particles creates localized stress concentration zones, thus maintaining the structural stability of the near-surface layer and the magnetic properties under thermal cycling after molding. The coverage can also be adjusted according to particle size and surface roughness to ensure sufficient interfacial constraint on each particle surface, while also considering the overall processability and density of the composite magnet.

[0027] In a preferred embodiment, the relative difference in the coefficient of thermal expansion between the stress-regulating layer and the rare-earth magnetic powder is not less than 10%, or the relative difference in the elastic modulus between the stress-regulating layer and the rare-earth magnetic powder is not less than 10%, wherein the relative difference is the ratio of the difference between the two to the smaller of the two values.

[0028] The relative difference refers to the ratio of the difference between the coefficient of thermal expansion or the modulus of elasticity of the stress-regulating layer and the magnetic powder to the smaller of the two values. This avoids inconsistencies in the interpretation of the difference range due to different numerical benchmarks. By setting a threshold of no less than 10%, sufficient inconsistency in the thermal or mechanical response between the interface layer and the magnetic powder can be ensured, thereby forming quantifiable compressive or tensile stress during cooling or curing. This constrains the near-surface layer of the magnetic powder and prevents it from losing its regulating effect due to similar material properties.

[0029] For example, the coefficient of thermal expansion of Nd-Fe-B magnetic powder is approximately 6 × 10⁻⁶. -6 / K, while when silicon oxide is used as the stress-regulating layer, its coefficient of thermal expansion is approximately 12×10. -6 / K, the difference between the two is 6×10 -6 / K, the relative difference is 6×10 -6 / 6×10 -6 =100%, significantly higher than 10%, enabling the formation of stable interfacial stress during cooling to room temperature. For example, regarding elastic modulus, the elastic modulus of Nd-Fe-B magnetic powder is approximately 160 GPa, while that of alumina nanoparticles is approximately 380 GPa, a difference of 220 GPa. The relative difference is 220 / 160≈137%, also much greater than 10%, ensuring that the magnetic powder surface can effectively withstand the constraint effect generated by the stress-regulating layer under molding stress or temperature changes. For Sm-Fe-N magnetic powder, the coefficient of thermal expansion is approximately 5×10⁻⁶. -6 / K, titanium dioxide nanoparticles were chosen as the stress modulation layer, with a thermal expansion coefficient of approximately 8 × 10⁻⁶. -6 The relative difference of / K is approximately 60%, which is within the required range and can generate sufficient residual stress. Using these specific values, the fabrication personnel can clearly select suitable inorganic or organic-inorganic composite materials as the stress regulation layer to ensure that the interfacial difference is sufficient to generate the target residual stress after molding, thereby achieving stable control of the near-surface structure of the magnetic powder.

[0030] In a preferred embodiment, the stress regulation layer is fixed to the surface of the rare earth magnetic powder by an interface connecting component, wherein the interface connecting component is a silane coupling agent, a titanate coupling agent, a phosphate coupling agent, an aluminate coupling agent, or a combination of two or more thereof.

[0031] Specific preparation methods can be achieved through solution coating or impregnation. For example, magnetic powder is dispersed in an organic solvent, and an appropriate amount of silane coupling agent is added to form a self-assembled layer on the surface of the magnetic powder. Then, nano-oxide or organic-inorganic composite particles are added to the system and uniformly dispersed by ultrasonic or mechanical stirring, allowing the stress-regulating layer particles to adhere to the surface of the magnetic powder under the action of the coupling agent. Subsequently, heating or drying treatment is used to allow the coupling agent to complete a chemical reaction or solidify, firmly fixing the stress-regulating layer to the surface of the magnetic powder. Another method is to introduce the coupling agent and the stress-regulating layer precursor into the solution system through chemical deposition, directly generating a well-bonded stress-regulating layer on the surface of the magnetic powder. These methods ensure that the surface of each magnetic powder particle is uniformly covered with a stress-regulating layer, and the presence of interfacial bonding components ensures that the coating layer remains stable and does not fall off during subsequent injection molding, compression molding, or extrusion molding and cooling processes, thus forming a stable structure that can maintain residual stress near the surface of the particles.

[0032] In a preferred embodiment, the adhesive is one or more of a thermoplastic resin or a thermosetting resin.

[0033] In a preferred embodiment, the adhesive is polyphenylene sulfide, polyamide, epoxy resin, phenolic resin, polyimide, or a combination of two or more thereof.

[0034] Another object of the present invention is to provide a method for preparing composite magnetic materials, comprising the following: The weight percentage of the components as described in the above embodiments; The stress-regulating layer material is mixed with rare earth magnetic powder, surface coated or surface anchored to form a stress-regulating layer on the surface of rare earth magnetic powder. The rare earth magnetic powder with the stress-regulating layer formed thereon is mixed evenly with binder and additives; The resulting mixture is subjected to heating molding, extrusion granulation or compression molding, and then cooled or cured after molding to obtain a composite magnetic material.

[0035] Specifically, this preparation process is based on rare-earth magnetic powder. By constructing a stress-regulating structure on the particle surface and combining it with a bonding system, a stable interfacial state is formed after the material is molded. First, the rare-earth magnetic powder and the stress-regulating layer raw material are processed, which can be achieved by dry or wet methods. In a wet system, the magnetic powder can be dispersed in water or an organic solvent and a uniform suspension system can be formed by mechanical stirring or ultrasonic dispersion. In a dry system, high-speed mixing or ball milling can be used to ensure sufficient contact of the raw materials. In this process, an interfacial connecting component is preferably introduced, which preferentially acts on the surface of the magnetic powder particles to form an interfacial connecting layer with reactive or adsorption capabilities. Subsequently, the stress-regulating layer raw material is added, which combines with the magnetic powder surface under the action of the interfacial connecting component, thereby forming a continuous or semi-continuous coating structure on the particle surface, or anchoring it to the particle surface in the form of discrete nanostructures. For situations requiring a more uniform coating, sol-gel reaction or in-situ deposition can be used to generate a nanoscale thin layer of inorganic phase on the surface of magnetic powder. For discrete structures, the dispersion state and amount of nanoparticles can be controlled to allow them to adhere to the particle surface in a discontinuous manner, thereby achieving the construction of local interface structures.

[0036] After the stress-regulating layer is formed, the treated rare-earth magnetic powder is mixed with binders and additives. This process can be carried out in a Banbury mixer, twin-screw extruder, or high-speed mixing equipment. Heating gradually softens or melts the binder, resulting in a uniform distribution among the magnetic powder particles. The additives at this stage primarily improve the interfacial compatibility between the magnetic powder and the binder, as well as the flowability of the system, ensuring the stress-regulating layer maintains a stable adhesion during mixing and preventing detachment or agglomeration. Simultaneously, by controlling the mixing temperature and shear conditions, the components are macroscopically uniformly distributed while preserving the particle surface structure.

[0037] The resulting mixture is then subjected to molding processes, which can be selected based on the specific application, such as injection molding, compression molding, or extrusion granulation. During the molding process, the material is heated to the melting or solidification temperature of the binder, making the system flowable and filling the mold or forming a granular structure under applied pressure. After molding, the material is gradually transformed from a high-temperature state to a room-temperature stable state through natural cooling, controlled cooling rate, or curing. During this cooling or curing process, due to the difference in thermal expansion behavior or mechanical response between the stress-regulating layer and the rare-earth magnetic powder, asynchronous shrinkage or deformation occurs between the particle surface and its surface structure, resulting in a stable residual stress distribution near the surface of the magnetic powder. This residual stress is maintained after cooling, keeping the surface of each magnetic powder particle in a confined state, thereby forming a structure with interface regulation characteristics within the composite material, ultimately obtaining a composite magnetic material.

[0038] Another object of the present invention is to provide application areas for composite magnetic materials, such as in motor magnets, sensor magnets or automotive electronic magnetic components.

[0039] Example 1 A composite magnetic material comprises, by weight percentage: 92% Nd-Fe-B based magnetic powder, 6% polyphenylene sulfide, 0.6% stress-regulating layer, and 1.4% additives. The Nd-Fe-B based magnetic powder is anisotropic magnetic powder with an average particle size of 5-8 μm; the stress-regulating layer is a silica nanophase; the additives include 0.8% silane coupling agent and 0.6% lubricant, wherein the silane coupling agent is γ-aminopropyltriethoxysilane, and the lubricant is methyl stearate.

[0040] The stress-regulating layer was constructed using a wet coating method. First, Nd-Fe-B magnetic powder was added to anhydrous ethanol and mechanically stirred at room temperature with ultrasonic treatment to ensure uniform dispersion. Then, a silane coupling agent was added, causing hydrolysis and condensation reactions on the surface of the magnetic powder particles to form an interfacial bonding layer. While maintaining stirring, tetraethyl orthosilicate was slowly added to the system as a precursor, and the reaction temperature was controlled at approximately 40°C, allowing it to undergo hydrolysis and condensation reactions on the magnetic powder surface to generate a silica nanolayer. By controlling the amount of precursor added and the reaction time, the resulting stress-regulating layer was 10-20 nm thick with a coverage of 60%-70%. After the reaction, the system was filtered and dried at 80°C to obtain magnetic powder with the stress-regulating layer on its surface.

[0041] The treated magnetic powder, polyphenylene sulfide, and lubricant were added to a Banbury mixer and melt-mixed at 280°C to ensure the binder was evenly distributed among the magnetic powder particles. After mixing, the material was extruded through a twin-screw extruder, cooled, and pelletized to obtain granular composite material. The pellets were then placed in an injection molding machine and injection molded at 300°C with an injection pressure of 80 MPa. After molding, the material was allowed to cool naturally to room temperature.

[0042] Example 2 A composite magnetic material comprises, by weight percentage: 92% Nd-Fe-B based magnetic powder, 6% polyphenylene sulfide, 0.6% stress-regulating layer, and 1.4% additives. The Nd-Fe-B based magnetic powder is anisotropic magnetic powder with an average particle size of 5-8 μm; the stress-regulating layer is an alumina nanophase; the additives include 0.8% silane coupling agent and 0.6% lubricant, wherein the silane coupling agent is γ-aminopropyltriethoxysilane, and the lubricant is methyl stearate.

[0043] The stress-regulating layer was also constructed using a wet processing method. First, Nd-Fe-B magnetic powder was added to anhydrous ethanol and dispersed mechanically and ultrasonically to form a homogeneous system. A silane coupling agent was added to form an interfacial bonding layer on the surface of the magnetic powder particles. Then, alumina nanoparticles were added to the system, and under continuous stirring and ultrasonication, they were anchored to the surface of the magnetic powder particles by the coupling agent. By controlling the amount of nanoparticles added and the dispersion time, the coverage of alumina on the magnetic powder surface was 60%-70%, corresponding to an equivalent structural thickness of approximately 10-20 nm. After processing, the material was filtered and dried at 80°C to obtain magnetic powder with a stress-regulating layer attached to its surface.

[0044] The treated magnetic powder, polyphenylene sulfide, and lubricant were added to a Banbury mixer and melt-mixed at 280°C. The mixture was then extruded and granulated using a twin-screw extruder. The resulting granules were injection molded at 300°C with an injection pressure of 80 MPa, and then allowed to cool naturally to room temperature.

[0045] Example 3 A composite magnetic material comprises, by weight percentage: 91% Sm-Fe-N based magnetic powder, 7% polyamide, 0.8% stress-regulating layer, and 1.2% additives. The Sm-Fe-N based magnetic powder is anisotropic magnetic powder with an average particle size of 3-6 μm; the stress-regulating layer is a silica nanophase; the additives include 0.7% silane coupling agent and 0.5% lubricant, wherein the silane coupling agent is γ-aminopropyltriethoxysilane, and the lubricant is ethylene bis-stearamide.

[0046] The stress-regulating layer was constructed using a wet coating method. First, Sm-Fe-N magnetic powder was added to anhydrous ethanol and mechanically stirred at room temperature with ultrasonic treatment to ensure uniform dispersion. Then, a silane coupling agent was added, causing adsorption and hydrolysis reactions on the surface of the magnetic powder particles to form an interfacial bonding layer. Under continuous stirring, tetraethyl orthosilicate was added as a precursor to the system, and the reaction temperature was controlled at approximately 35°C, allowing it to undergo hydrolysis and condensation reactions on the surface of the magnetic powder particles to generate a silica nanolayer. By adjusting the amount of precursor and the reaction time, the thickness of the stress-regulating layer was 15-30 nm, with a coverage of 70%-85%. After the reaction, the system was filtered and dried at 70°C to obtain magnetic powder with a stress-regulating layer on its surface.

[0047] The treated magnetic powder, polyamide, and lubricant were added to a twin-screw extruder and melt-blended at 260°C to ensure uniform dispersion of the components. After blending, the material was extruded, cooled, and pelletized to obtain granular composite material. The pellets were then placed in an injection molding machine and injection molded at 270°C with an injection pressure of 75 MPa. After molding, the material was allowed to cool naturally to room temperature.

[0048] Comparative Example 1 A composite magnetic material comprises, by weight percentage: 92% Nd-Fe-B based magnetic powder, 6% polyphenylene sulfide, and 2.0% additives. The Nd-Fe-B based magnetic powder is anisotropic magnetic powder with an average particle size of 5-8 μm; the additives include 0.8% silane coupling agent and 1.2% lubricant, wherein the silane coupling agent is γ-aminopropyltriethoxysilane, and the lubricant is methyl stearate.

[0049] Nd-Fe-B magnetic powder was added to anhydrous ethanol and mechanically stirred and ultrasonically treated at room temperature to ensure uniform dispersion. A silane coupling agent was then added to form an adsorption layer on the surface of the magnetic powder particles. After treatment, the system was filtered and dried at 80°C to obtain the treated magnetic powder.

[0050] The aforementioned magnetic powder, polyphenylene sulfide, and lubricant were added to a Banbury mixer and melt-mixed at 280°C to ensure uniform dispersion of the components. After mixing, the material was extruded through a twin-screw extruder, cooled, and pelletized to obtain granular composite material. The pellets were then placed in an injection molding machine and injection molded at 300°C with an injection pressure of 80 MPa. After molding, the material was allowed to cool naturally to room temperature.

[0051] Comparative Example 2 A composite magnetic material comprises, by weight percentage: 92% Nd-Fe-B based magnetic powder, 6% polyphenylene sulfide, 0.6% silica nanoparticles, and 1.4% additives. The Nd-Fe-B based magnetic powder is anisotropic magnetic powder with an average particle size of 5-8 μm; the silica nanoparticles have an average particle size of 20-50 nm; the additives include 0.8% silane coupling agent and 0.6% lubricant, wherein the silane coupling agent is γ-aminopropyltriethoxysilane, and the lubricant is methyl stearate.

[0052] Nd-Fe-B magnetic powder, silica nanoparticles, and additives were directly added to a high-speed mixer and mechanically mixed at room temperature to initially disperse the components uniformly. However, the silica nanoparticles did not form a coating or anchoring structure on the surface of the magnetic powder. Subsequently, the mixture was added to an internal mixer and melt-mixed at 280°C to ensure that the binder was uniformly distributed among the magnetic powder particles.

[0053] After mixing, the material is extruded through a twin-screw extruder, cooled, and pelletized to obtain granular composite material. The pellets are then placed in an injection molding machine and injection molded at 300°C with an injection pressure of 80 MPa. After molding, the material is allowed to cool naturally to room temperature.

[0054] Test Method Description To compare the performance of the samples obtained in each embodiment and comparative example, the obtained granules were prepared into standard test specimens by injection molding. The injection molding temperature was 300℃, and the injection pressure was 80MPa. The resulting samples were processed into block specimens with dimensions of approximately 10mm×10mm×5mm for subsequent magnetic property testing. To ensure the comparability of the test results, all samples were prepared under the same molding conditions and tested after being placed at room temperature for 24 hours.

[0055] Magnetic property testing was conducted using a vibrating sample magnetometer. Remanence, intrinsic coercivity, and maximum energy product of the samples were measured at room temperature. An external magnetic field strength within ±2T was applied during testing. The demagnetization curve of the samples was measured, and the relevant magnetic property parameters were automatically calculated by the testing system. To minimize testing errors, each sample was tested at least three times, and the average value was taken as the final result.

[0056] To evaluate the performance stability of the material under temperature variation conditions, heat treatment tests were conducted on each sample. The samples were placed in a constant temperature chamber and held at 150℃ for 2 hours, then naturally cooled to room temperature. The magnetic properties were then measured again using the same method. By comparing the changes in coercivity and remanence before and after heat treatment, the magnetic property retention rate was calculated to characterize the material's stability under thermal conditions.

[0057] All tests were conducted under identical environmental conditions, and the testing equipment was calibrated before use to ensure data accuracy and repeatability. The above testing methods enable effective comparison of the magnetic properties and stability of different samples under the same conditions.

[0058] Test Results Table 1. Magnetic property test results of each embodiment and comparative sample. As shown in Table 1, under the same test conditions, there are significant differences in the magnetic properties of different samples and their changes after heat treatment. The remanence and maximum energy product of Examples 1 and 2 at room temperature are similar, while the intrinsic coercivity is slightly higher than that of the comparative sample. This indicates that with the introduction of the stress-regulating layer, the basic magnetic properties of the material are not significantly weakened while maintaining a high magnetic powder content. Further comparison of Examples 1 and 2 reveals that when the stress-regulating layer material is changed from silicon dioxide to alumina, the changes in various magnetic property parameters are minimal, indicating that this structural design does not depend on a single material system and can achieve stable construction under different inorganic phase conditions.

[0059] In the performance comparison after heat treatment, the differences between the example samples and the comparative samples were more pronounced. After holding at 150℃, Examples 1 to 3 all retained over 94% of their intrinsic coercivity, while Comparative Examples 1 and 2 showed significantly lower retention rates. Comparative Example 1 did not introduce a stress-regulating layer, and the magnetic powder surface lacked an interfacial constraint structure, making it more prone to local structural changes during heat treatment, resulting in a larger decrease in coercivity. Although Comparative Example 2 incorporated inorganic nanoparticles, these particles were randomly distributed in the system because they did not form a coating or anchoring structure on the magnetic powder surface, making it difficult for them to exert an effective effect near the surface of the magnetic powder, thus limiting the improvement in thermal stability. In contrast, the stress-regulating layer in the examples was located on the surface of the magnetic powder particles and achieved stable bonding through interfacial connection of components. During heat treatment, it maintained the constrained state of the particle surface, thereby mitigating changes in magnetic properties.

[0060] Compared to Examples 1 and 2, Example 3 exhibits slightly lower room-temperature magnetic properties, which is related to the inherent magnetic properties of the selected Sm-Fe-N based magnetic powder. However, its retention rate after heat treatment is similar to that of Examples 1 and 2, indicating that this structure can play a stabilizing role in different rare-earth magnetic powder systems. The combined data from all sets show that constructing a stress-regulating layer on the surface of the magnetic powder, enabling it to form a stable interface state during molding and subsequent temperature treatment, helps reduce the attenuation of magnetic properties with temperature changes, thereby improving the material's performance stability.

[0061] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the patent protection scope of the present invention.

Claims

1. A composite magnetic material, characterized in that, The composite magnetic material comprises the following components by weight percentage: 80-96% rare earth magnetic powder, 2-10% binder, 0.1-5% stress-regulating layer, and the balance being additives, wherein the sum of the contents of each component is 100%, wherein: The rare earth magnetic powder is Nd-Fe-B based magnetic powder, Sm-Fe-N based magnetic powder, or a combination of both. The stress regulation layer is composed of an inorganic phase or an organic-inorganic composite phase. The stress regulation layer is formed on the surface of the rare earth magnetic powder in a continuous or semi-continuous coating structure, or is anchored on the surface of the rare earth magnetic powder in a discrete nanostructure. The stress-regulating layer and the rare earth magnetic powder differ in their coefficient of thermal expansion and / or elastic modulus, and the difference is sufficient to cause the near-surface layer of the rare earth magnetic powder to be in a state of residual stress after molding.

2. The composite magnetic material according to claim 1, characterized in that, The stress regulation layer is composed of silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, yttrium oxide, cerium oxide, or a combination of two or more of these.

3. The composite magnetic material according to claim 1, characterized in that, The thickness of the stress-regulating layer is 1-100 nm.

4. The composite magnetic material according to claim 1, characterized in that, The stress-regulating layer has a coverage of 30%-100% on the surface of the rare earth magnetic powder.

5. The composite magnetic material according to claim 1, characterized in that, The relative difference in the coefficient of thermal expansion between the stress-regulating layer and the rare earth magnetic powder is not less than 10%, or the relative difference in the elastic modulus between the stress-regulating layer and the rare earth magnetic powder is not less than 10%, wherein the relative difference is the ratio of the difference between the two to the smaller of the two values.

6. The composite magnetic material according to claim 1, characterized in that, The stress regulation layer is fixed to the surface of the rare earth magnetic powder through an interface connecting component, which is a silane coupling agent, a titanate coupling agent, a phosphate coupling agent, an aluminate coupling agent, or a combination of two or more of them.

7. The composite magnetic material according to claim 1, characterized in that, The adhesive is one or more of thermoplastic resin or thermosetting resin.

8. The composite magnetic material according to claim 7, characterized in that, The adhesive is polyphenylene sulfide, polyamide, epoxy resin, phenolic resin, polyimide, or a combination of two or more of these.

9. A method for preparing a composite magnetic material, characterized in that, include: According to the weight percentage of the components as described in claim 1; The stress-regulating layer material is mixed with rare earth magnetic powder, surface coated or surface anchored to form a stress-regulating layer on the surface of rare earth magnetic powder. The rare earth magnetic powder with the stress-regulating layer formed thereon is mixed evenly with binder and additives; The resulting mixture is subjected to heating molding, extrusion granulation or compression molding, and then cooled or cured after molding to obtain a composite magnetic material.

10. The application of the composite magnetic material according to claim 1 in motor magnets, sensor magnets or automotive electronic magnetic components.

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