Alloy soft magnetic powder for differential mode inductors, its preparation process and applications

Abstract

This application provides an alloy soft magnetic powder for differential mode inductors, its preparation process, and its application, solving the problem that existing magnetic powder cores have poor DC bias performance and cannot meet the miniaturization requirements of high-frequency differential mode inductors. The preparation method of the alloy soft magnetic powder for differential mode inductors in this application includes the following steps: (1) multi-level gradient powder ratio: a three-level particle size ratio is adopted; (2) composite insulation coating process; (3) magnetic field assisted pressing: isostatic pressing is carried out under a vertical magnetic field of 0.5-1 T, and the pressing pressure is divided into three stages: 500 MPa×30 s→1000 MPa×60 s→1500 MPa×120 s; (4) gradient annealing and magnetic field annealing synergistic treatment.

Description

Technical Field

[0001] This invention relates to the field of magnetic materials technology, and in particular to an alloy soft magnetic powder for differential mode inductors, its preparation process, and its applications. Background Technology

[0002] Metallic soft magnetic powder cores are widely used in high-frequency power electronic devices due to their combination of high saturation magnetic induction (Bs) and high resistivity. However, the DC bias performance of existing conventional magnetic powder cores is significantly lower than that of iron-nickel based magnetic powder cores (such as iron-nickel 50 and iron-nickel-molybdenum), as shown in the following ways:

[0003] Severe permeability decay: Under a DC bias field (100 Oe), the permeability retention rate of conventional magnetic cores is less than 50%;

[0004] High loss: Under high-frequency operating conditions (100kHz), the superposition of eddy current loss and hysteresis loss leads to excessive temperature rise;

[0005] Process defects: The existing insulation coating process (phosphoric acid alcohol method) is prone to uneven coating, and the pressing pressure and annealing parameters have not been synergistically optimized.

[0006] Existing magnetic cores have poor DC bias performance, which cannot meet the miniaturization requirements of high-frequency differential mode inductors. Summary of the Invention

[0007] This application provides an alloy soft magnetic powder for differential mode inductors, its preparation process, and its application, which solves the problem that existing magnetic powder cores have poor DC bias performance and cannot meet the miniaturization requirements of high-frequency differential mode inductors.

[0008] The first aspect of this application provides a method for preparing alloy soft magnetic powder for differential mode inductors, comprising the following steps:

[0009] (1) Multi-level gradient powder ratio: Three-level particle size ratio is adopted, in which 50-100μm coarse particles account for 50-70%, 20-50μm medium particles account for 20-30%, and 10-20μm fine particles account for 5-20%, and the volume ratio of coarse particles to medium particles is 2.5-3.5;

[0010] (2) Composite insulation coating process: Phosphoric acid aqueous solution and nano SiO2 sol are mixed at a mass ratio of 1:0.2-0.5, and coated in a fluidized bed at a coating temperature of 250-300 ℃ and a coating time of 40-60 min to form a gradient insulation layer with a thickness of 0.8-1.5 μm;

[0011] (3) Magnetic field-assisted pressing: Isostatic pressing is carried out under a vertical magnetic field of 0.5-1 T. The pressing pressure is divided into three stages: 500 MPa×30 s→1000 MPa×60 s→1500 MPa×120 s, and the final density is ≥7.5 g / cm³.

[0012] (4) Combined processing of gradient annealing and magnetic field annealing:

[0013] First stage: Under nitrogen protection, the temperature is increased to 500℃ at a rate of 5℃ / min and held for 1 h;

[0014] Second stage: Switch to hydrogen atmosphere, heat to 650℃ at 2℃ / min and hold for 2 h, while applying a 0.2T transverse alternating magnetic field;

[0015] The third stage: cooling to 200°C at a rate of 3°C / min, followed by natural cooling. In a preferred embodiment, the composition of the alloy soft magnetic powder is as follows:

[0016] Iron: 80-93%; Silicon: 5-10 wt%; Aluminum: 1-5 wt%; and additives: 1-5 wt%; the additives include one or more of passivating agents, insulating agents, and lubricants.

[0017] In a preferred embodiment, the alloy soft magnetic powder further includes a nickel-cobalt-iron alloy, which accounts for 0.05%-3 wt% of the alloy soft magnetic powder.

[0018] In a preferred embodiment, the nano-SiO2 sol in step (2) has a particle size of 10-20 nm, and 0.1-0.5 wt% boric acid is incorporated into the sol as an interfacial bonding enhancer.

[0019] In a preferred embodiment, the magnetic field direction in step (3) is perpendicular to the pressing direction, and the magnetic field frequency is 10-50 Hz.

[0020] In a preferred embodiment, the alternating magnetic field frequency in the second stage of step (4) is 1-5Hz, and the magnetic field strength changes periodically in the range of 0.1-0.3T.

[0021] The second aspect of this application provides an alloy soft magnetic powder for differential mode inductors, prepared according to any of the methods described above.

[0022] In a preferred embodiment, the DC bias characteristic of the alloy soft magnetic powder used for the differential mode inductor is ≥95%.

[0023] The third aspect of this application provides a differential mode inductor device that uses the aforementioned alloy soft magnetic powder as the magnetic core.

[0024] In a preferred embodiment, the magnetic core has a multi-air-gap distributed structure with an air-gap spacing of 0.1-0.3 mm and an air-gap number to magnetic circuit length ratio of ≥3 / 10 cm.

[0025] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:

[0026] 1. The proposed solution employs a "multi-level gradient powder ratio" design, which significantly improves the overall performance of alloy soft magnetic powder by optimizing particle size distribution. The gradient distribution of coarse, medium, and fine particles achieves a "closely packed" effect: coarse particles act as a framework, providing structural support; medium particles fill the gaps between coarse particles; and fine particles further fill micropores, reducing residual porosity. This increases the pressing density, reduces porosity, and the close contact between particles reduces air gaps in the magnetic circuit, lowering magnetic reluctance. This reduces magnetic domain distortion and magnetic leakage. Simultaneously, the gradient packing reduces direct contact points between particles, blocking eddy current paths.

[0027] 2. Magnetic field-assisted pressing: Under a 1T vertical magnetic field, the easy magnetization axis of the powder is aligned along the direction of the magnetic field, which reduces the resistance to the movement of magnetic domain walls, significantly improves the magnetic permeability, and reduces attenuation.

[0028] 3. Pressure Stages: 500MPa Stage: Initially eliminates voids between powder particles, preventing particle breakage and providing a uniform substrate for magnetic field orientation. 1000MPa Stage: Further compaction, creating tight contact between particles and enhancing magnetic circuit continuity. 1500MPa Stage: Densification is completed under high pressure, while the magnetic field maintains grain orientation stability, preventing lattice distortion caused by high pressure. This also improves DC bias characteristics. Detailed Implementation

[0029] The following detailed description of the high DC bias composite magnetic core for reactors and its fabrication process of the present invention, with reference to specific embodiments, is provided in further detail.

[0030] Example 1:

[0031] This embodiment provides an alloy soft magnetic powder for differential mode inductors. The alloy soft magnetic powder is composed of: 80 wt% iron powder, 10 wt% silicon powder, 5 wt% aluminum powder, 1 wt% iron phosphate (passivating agent), 1 wt% magnesium phosphate (insulating agent), and 3 wt% zinc stearate (lubricant).

[0032] The preparation method of alloy soft magnetic powder includes the following steps:

[0033] Iron powder, silicon powder, and aluminum powder were vacuum dried at 80 °C for 1.5 h.

[0034] The dried iron powder, silicon powder, aluminum powder, zinc stearate (lubricant), and ferric phosphate (passivating agent) were mixed in proportion and ball-milled at a low speed (200 r / min) to ensure uniform dispersion of the components.

[0035] The particles were prepared into three particle size ratios: 50-100 μm coarse particles, accounting for 60% by mass; 20-50 μm medium particles, accounting for 20% by mass; and 10-20 μm fine particles, accounting for 20% by mass; with a volume ratio of coarse to medium particles of 3.

[0036] Composite insulation coating process: Magnesium phosphate solution and nano-SiO2 sol (particle size of 15 nm) are mixed at a mass ratio of 1:0.2, and coated in a fluidized bed at a coating temperature of 250 ℃ for 60 min to form a gradient insulation layer with a thickness of 1.2 μm.

[0037] Magnetic field-assisted pressing: Isostatic pressing is performed under a 1 T vertical magnetic field, with the magnetic field direction perpendicular to the pressing direction and a magnetic field frequency of 30 Hz. The pressing pressure is divided into three stages: first, 500 MPa is maintained for 30 s, then 1000 MPa is maintained for 60 s, and finally, 1500 MPa is maintained for 120 s (500 MPa × 30 s → 1000 MPa × 60 s → 1500 MPa × 120 s), with a final density of 8 g / cm³.

[0038] Combined gradient annealing and magnetic field annealing:

[0039] First stage: Under nitrogen protection, the temperature is increased to 500℃ at a rate of 5℃ / min and held for 1 h;

[0040] Nitrogen gas is used to isolate oxygen, preventing the alloy from oxidizing at high temperatures to form non-magnetic oxides and ensuring the high saturation magnetic induction (Bs) and initial magnetic permeability of the soft magnetic powder. Second stage: Switch to hydrogen atmosphere, heat to 650 ℃ at 2 ℃ / min and hold for 2 h, while applying a 0.2 T transverse alternating magnetic field;

[0041] Hydrogen can participate in the densification of the insulating layer, strengthen the bonding between the insulating layer and magnetic powder particles, reduce interface defects, and lower high-frequency eddy current losses.

[0042] Temperature gradient control has a significant impact on the uniformity of the microstructure. Since the raw material powder of this invention uses a variety of particle size combinations, it is easy to deform due to the rapid heating and pressing process. By controlling the gradient annealing process, the deformation of the material caused by the rapid heating during the annealing process can also be prevented.

[0043] Third stage: Cool to 200 ℃ at 3 ℃ / min and then allow to cool naturally.

[0044] Slow cooling (3℃ / min) allows the soft magnetic alloy to undergo an ordered phase transition, optimizing domain wall mobility and improving permeability. Natural cooling to room temperature further balances internal stress and avoids the risk of hydrogen embrittlement.

[0045] Performance testing:

[0046] 1. The permeability was measured to be 70 μH / m using a BH analyzer (Iwatsu SY-8219).

[0047] After being treated at 100 ℃ for 48 h, the attenuation rate was tested.

[0048]

[0049] The attenuation rate is 30%.

[0050] 2. Use an LCR meter (Keysight E4980A) to test the DC bias characteristics. The specific steps are as follows:

[0051] Connect the wound magnetic powder core to the LCR tester and connect it to a DC power supply.

[0052] Measure the initial inductance value: Measure the initial inductance value L0 of the magnetic sample without DC bias.

[0053] Apply DC bias: Under a DC bias field of 100 Oe (Oersted), measure the inductance value L under the magnetic field strength.

[0054]

[0055] L is the inductance value after the DC magnetic field is superimposed, and L0 is the inductance value without the DC magnetic field.

[0056] The DC bias characteristic is 95%.

[0057] This application employs a "multi-level gradient powder ratio" design, which significantly improves the overall performance of alloy soft magnetic powder by optimizing particle size distribution. The gradient distribution of coarse, medium, and fine particles achieves a "close-packed" effect: coarse particles act as a framework, providing structural support; medium particles fill the gaps between coarse particles; and fine particles further fill micropores, reducing residual porosity. Increased compaction density reduces porosity, and close contact between particles reduces air gaps in the magnetic circuit, lowering magnetic reluctance. This reduces magnetic domain distortion and magnetic leakage. Simultaneously, the gradient filling reduces direct contact points between particles, blocking eddy current paths.

[0058] Magnetic field-assisted pressing, under a 1 T vertical magnetic field, aligns the easy magnetization axis of the powder along the direction of the magnetic field, reduces the resistance to the movement of magnetic domain walls, significantly improves the magnetic permeability, and reduces attenuation.

[0059] Pressure is applied in stages: 500 MPa stage: Initially eliminates voids between powder particles, preventing particle breakage and providing a uniform substrate for magnetic field orientation. 1000 MPa stage: Further compaction, creating tight contact between particles and enhancing magnetic circuit continuity. 1500 MPa stage: Densification is completed under high pressure, while the magnetic field maintains grain orientation stability, preventing lattice distortion caused by high pressure. DC bias characteristics are also improved.

[0060] The combined processing of gradient annealing and magnetic field annealing has the following advantages:

[0061] 1. Improve DC bias performance.

[0062] Through hydrogen reduction and magnetic field modulation, the magnetic domains are arranged in an orderly manner and the grain boundaries are purified, which significantly improves the retention rate of magnetic permeability under a 100 Oe bias field.

[0063] 2. Reduce high-frequency losses.

[0064] Insulation layer uniformity optimization (nitrogen + hydrogen synergy) reduces leakage current; grain homogenization (magnetic field suppresses abnormal growth) reduces eddy current loss; stress release reduces hysteresis loss.

[0065] 3. Coordination of process parameters.

[0066] Matching annealing temperature, magnetic field, and pressing pressure enables high-density, low-defect magnetic cores, meeting the requirements of miniaturized differential-mode inductors for high Bs and low losses.

[0067] Example 2:

[0068] This embodiment provides an alloy soft magnetic powder for differential mode inductors. The composition of the alloy soft magnetic powder is: 90 wt% iron powder, 5 wt% silicon powder, 1 wt% aluminum powder, 1 wt% iron phosphate (passivating agent), 2 wt% magnesium phosphate (insulator), and 2 wt% zinc stearate (lubricant).

[0069] The preparation method of alloy soft magnetic powder includes the following steps:

[0070] Iron powder, silicon powder, and aluminum powder were vacuum dried at 80 °C for 1.5 h.

[0071] The dried iron powder, silicon powder, aluminum powder, zinc stearate (lubricant), and ferric phosphate (passivating agent) were mixed in proportion and ball-milled at a low speed (200 r / min) to ensure uniform dispersion of the components.

[0072] The particles were prepared in three sizes: 50-100μm coarse particles, accounting for 70% by mass; 20-50μm medium particles, accounting for 20% by mass; and 10-20μm fine particles, accounting for 10% by mass; with a volume ratio of coarse to medium particles of 3.5.

[0073] Composite insulation coating process: Magnesium phosphate solution and nano-SiO2 sol (particle size of 20 nm) are mixed at a mass ratio of 1:0.5, and coated in a fluidized bed at a coating temperature of 250 ℃ for 60 min to form a gradient insulation layer with a thickness of 0.5 μm.

[0074] Magnetic field-assisted pressing: Isostatic pressing is performed under a 1 T vertical magnetic field, with the magnetic field direction perpendicular to the pressing direction and a magnetic field frequency of 10 Hz. The pressing pressure is divided into three stages: first, 500 MPa is maintained for 30 s, then 1000 MPa is maintained for 60 s, and finally, 1500 MPa is maintained for 120 s (500 MPa × 30 s → 1000 MPa × 60 s → 1500 MPa × 120 s), with a final density of 8 g / cm³.

[0075] Combined gradient annealing and magnetic field annealing:

[0076] First stage: Under nitrogen protection, the temperature is increased to 500℃ at a rate of 5℃ / min and held for 1 h;

[0077] Second stage: Switch to hydrogen atmosphere, heat to 650℃ at 2℃ / min and hold for 2h, while applying a 0.2T transverse alternating magnetic field;

[0078] Third stage: Cool to 200 ℃ at 3 ℃ / min and then allow to cool naturally.

[0079] Performance testing:

[0080] 1. The permeability was measured to be 68 μH / m using a BH analyzer (Iwatsu SY-8219).

[0081] After being treated at 100 ℃ for 48 h, the attenuation rate was tested.

[0082]

[0083] The attenuation rate is 30%.

[0084] 2. The DC bias characteristic measurement method is the same as in Example 1, and the result is 95%.

[0085] Example 3:

[0086] This embodiment provides an alloy soft magnetic powder for differential mode inductors. The alloy soft magnetic powder is composed of: 85 wt% iron powder; 5 wt% silicon powder; 5 wt% aluminum powder; 1 wt% iron phosphate (passivating agent); 2 wt% magnesium phosphate (insulator); and 2 wt% zinc stearate (lubricant).

[0087] The preparation method of alloy soft magnetic powder includes the following steps:

[0088] Iron powder, silicon powder, and aluminum powder were vacuum dried at 80°C for 1.5 h.

[0089] The dried iron powder, silicon powder, aluminum powder, zinc stearate (lubricant), and ferric phosphate (passivating agent) were mixed in proportion and initially mixed by ball milling at low speed (200 r / min) to ensure uniform dispersion of the components.

[0090] The particles were prepared in three sizes: 50-100μm coarse particles, accounting for 70% by mass; 20-50μm medium particles, accounting for 20% by mass; and 10-20μm fine particles, accounting for 10% by mass; with a volume ratio of coarse to medium particles of 3.5.

[0091] Composite insulation coating process: magnesium phosphate solution and nano-SiO2 sol (particle size of 18 nm) are mixed at a mass ratio of 1:0.5, and coated in a fluidized bed at a coating temperature of 250℃ for 60 min to form a gradient insulation layer with a thickness of 0.5 μm.

[0092] Magnetic field-assisted pressing: Isostatic pressing is performed under a 1 T vertical magnetic field, with the magnetic field direction perpendicular to the pressing direction and a magnetic field frequency of 20 Hz. The pressing pressure is divided into three stages: first, 500 MPa is maintained for 30 s, then 1000 MPa is maintained for 60 s, and finally, 1500 MPa is maintained for 120 s (500 MPa × 30 s → 1000 MPa × 60 s → 1500 MPa × 120 s), with a final density of 8 g / cm³.

[0093] Combined gradient annealing and magnetic field annealing:

[0094] First stage: Under nitrogen protection, the temperature is increased to 500℃ at a rate of 5℃ / min and held for 1 h;

[0095] Second stage: Switch to hydrogen atmosphere, heat to 650 ℃ at 2 ℃ / min and hold for 2 h, while applying a 0.2 T transverse alternating magnetic field;

[0096] Third stage: Cool to 200 ℃ at 3 ℃ / min and then allow to cool naturally.

[0097] Performance testing:

[0098] 1. The permeability was measured to be 72 μH / m using a BH analyzer (Iwatsu SY-8219).

[0099] After being treated at 100 degrees Celsius for 48 hours, the attenuation rate was tested.

[0100]

[0101] The attenuation rate is 28%.

[0102] 2. The DC bias characteristic measurement method is the same as in Example 1, and the result is 96%.

[0103] Example 4:

[0104] This embodiment provides an alloy soft magnetic powder for differential mode inductors. The composition of the alloy soft magnetic powder is: 84 wt% iron powder, 5 wt% silicon powder, 5 wt% aluminum powder, 1 wt% iron phosphate (passivating agent), 2 wt% magnesium phosphate (insulator), 2 wt% zinc stearate (lubricant), and 1 wt% nickel-cobalt-iron alloy.

[0105] The preparation method of alloy soft magnetic powder includes the following steps:

[0106] Iron powder, silicon powder, and aluminum powder were vacuum dried at 80 °C for 1.5 h.

[0107] The dried iron powder, silicon powder, aluminum powder, nickel-cobalt-iron alloy (mass ratio of nickel, cobalt, and iron: 30:20:50) are mixed with zinc stearate (lubricant) and ferric phosphate (passivating agent) in a certain proportion, and then mixed by ball milling at low speed (200 r / min) to ensure uniform dispersion of the components.

[0108] The particles were prepared in three sizes: 50-100μm coarse particles, accounting for 70% by mass; 20-50μm medium particles, accounting for 20% by mass; and 10-20μm fine particles, accounting for 10% by mass; with a volume ratio of coarse to medium particles of 3.5.

[0109] Composite insulation coating process: magnesium phosphate solution and nano-SiO2 sol (particle size of 20 nm) are mixed at a mass ratio of 1:0.5, and coated in a fluidized bed at a coating temperature of 250℃ for 60 min to form a gradient insulation layer with a thickness of 0.5 μm.

[0110] Magnetic field-assisted pressing: Isostatic pressing is performed under a 1 T vertical magnetic field, with the magnetic field direction perpendicular to the pressing direction and a magnetic field frequency of 20 Hz. The pressing pressure is divided into three stages: first, 500 MPa is maintained for 30 s, then 1000 MPa is maintained for 60 s, and finally, 1500 MPa is maintained for 120 s (500 MPa × 30 s → 1000 MPa × 60 s → 1500 MPa × 120 s), with a final density of 8 g / cm³.

[0111] Combined gradient annealing and magnetic field annealing:

[0112] First stage: Under nitrogen protection, the temperature is increased to 500℃ at a rate of 5℃ / min and held for 1 h;

[0113] Second stage: Switch to hydrogen atmosphere, heat to 650 ℃ at 2 ℃ / min and hold for 2 h, while applying a 0.2 T transverse alternating magnetic field;

[0114] Third stage: Cool to 200 ℃ at 3 ℃ / min and then allow to cool naturally.

[0115] Performance testing:

[0116] 1. The permeability was measured to be 77 μH / m using a BH analyzer (Iwatsu SY-8219).

[0117] After being treated at 100 ℃ for 48 hours, the attenuation rate was tested.

[0118]

[0119] The attenuation rate is 20%.

[0120] 2. The DC bias characteristic measurement method is the same as in Example 1, and the result is 98%.

[0121] By incorporating nickel-cobalt-iron alloys, the permeability can be significantly improved, the permeability decay rate reduced, and DC bias performance enhanced through optimization of lattice structure, magnetic domain behavior, and saturation characteristics. By adjusting the ratio of nickel to cobalt in the alloy, the introduction of nickel and cobalt can reduce the magnetocrystalline anisotropy of the iron-based alloy, enhance the domain wall mobility, and the high Curie temperature of cobalt can broaden the operating temperature range of soft magnetic materials.

[0122] Example 5:

[0123] This embodiment provides an alloy soft magnetic powder for differential mode inductors. The composition of the alloy soft magnetic powder is as follows: 84 wt% iron powder, 5 wt% silicon powder, 5 wt% aluminum powder, 1 wt% iron phosphate (passivating agent), 2 wt% magnesium phosphate (insulator), 2 wt% zinc stearate (lubricant), 0.5 wt% nickel-cobalt-iron alloy I (mass ratio of nickel, cobalt, and iron: 30:20:50), and 0.5 wt% nickel-cobalt-iron alloy II (mass ratio of nickel, cobalt, and iron: 55:5:40). In this embodiment, the total amount of alloy soft magnetic powder is 5 kg.

[0124] The preparation method of alloy soft magnetic powder includes the following steps:

[0125] Iron powder, silicon powder, and aluminum powder were vacuum dried at 80 °C for 1.5 h.

[0126] The dried iron powder, silicon powder, aluminum powder, nickel-cobalt-iron alloy I, zinc stearate (lubricant), and iron phosphate (passivating agent) were mixed in proportion and ball-milled at low speed (200 r / min) for 2 hours to ensure uniform dispersion of the components. Then, nickel-cobalt-iron alloy II was added and ball-milled at high speed (400 r / min). The high-speed ball milling time was 1 / 4 of the low-speed mixing time.

[0127] The particles were prepared in three sizes: 50-100μm coarse particles, accounting for 70% by mass; 20-50μm medium particles, accounting for 20% by mass; and 10-20μm fine particles, accounting for 10% by mass; with a volume ratio of coarse to medium particles of 3.5.

[0128] Composite insulation coating process: magnesium phosphate solution and nano-SiO2 sol (particle size of 20 nm) are mixed at a mass ratio of 1:0.5, and coated in a fluidized bed at a coating temperature of 250℃ for 60 min to form a gradient insulation layer with a thickness of 0.5 μm.

[0129] Magnetic field-assisted pressing: Isostatic pressing is performed under a 1 T vertical magnetic field, with the magnetic field direction perpendicular to the pressing direction and a magnetic field frequency of 20 Hz. The pressing pressure is divided into three stages: first, 500 MPa is maintained for 30 s, then 1000 MPa is maintained for 60 s, and finally, 1500 MPa is maintained for 120 s (500 MPa × 30 s → 1000 MPa × 60 s → 1500 MPa × 120 s), with a final density of 8 g / cm³.

[0130] Combined gradient annealing and magnetic field annealing:

[0131] First stage: Under nitrogen protection, the temperature is increased to 500℃ at a rate of 5℃ / min and held for 1 h;

[0132] Second stage: Switch to hydrogen atmosphere, heat to 650 ℃ at 2 ℃ / min and hold for 2 h, while applying a 0.2 T transverse alternating magnetic field;

[0133] Third stage: Cool to 200 ℃ at 3 ℃ / min and then allow to cool naturally.

[0134] Performance testing:

[0135] 1. The permeability was measured to be 76 μH / m using a BH analyzer (Iwatsu SY-8219).

[0136] After being treated at 100 ℃ for 48 hours, the attenuation rate was tested.

[0137]

[0138] The attenuation rate is 16%.

[0139] 2. The DC bias characteristic measurement method is the same as in Example 1, and the result is 99%.

[0140] By adding nickel-cobalt-iron alloy, the permeability can be significantly improved, the permeability attenuation rate reduced, and the DC bias performance improved by optimizing the crystal structure, magnetic domain behavior, and saturation characteristics. Controlling the timing, rotation speed, and mixing time of the second nickel-cobalt-iron alloy during ball milling creates a non-uniform distribution of the first and second nickel-cobalt-iron alloys in the mixture, forming a compositional gradient. This elemental gradient distribution suppresses eddy current losses and reduces the permeability attenuation rate.

[0141] Example 6:

[0142] This embodiment provides an alloy soft magnetic powder for differential mode inductors. The composition of the alloy soft magnetic powder is as follows: 85 wt% iron powder, 5 wt% silicon powder, 5 wt% aluminum powder, 1 wt% iron phosphate (passivating agent), 2 wt% magnesium phosphate (insulating agent), 1.95 wt% zinc stearate (lubricant), and 0.05 wt% nickel-cobalt-iron alloy.

[0143] The preparation method of alloy soft magnetic powder includes the following steps:

[0144] Iron powder, silicon powder, and aluminum powder were vacuum dried at 80°C for 1.5 h.

[0145] The dried iron powder, silicon powder, aluminum powder, nickel-cobalt-iron alloy, zinc stearate (lubricant), and ferric phosphate (passivating agent) are mixed in proportion and initially mixed by ball milling at low speed (200 r / min) to ensure uniform dispersion of the components.

[0146] The particles were prepared in three sizes: 50-100μm coarse particles, accounting for 70% by mass; 20-50μm medium particles, accounting for 20% by mass; and 10-20μm fine particles, accounting for 10% by mass; with a volume ratio of coarse to medium particles of 3.5.

[0147] Composite insulation coating process: magnesium phosphate solution and nano-SiO2 sol (particle size of 10 nm) are mixed at a mass ratio of 1:0.5, and coated in a fluidized bed at a coating temperature of 250 ℃ for 60 min to form a gradient insulation layer with a thickness of 0.5 μm.

[0148] Magnetic field-assisted pressing: Isostatic pressing is performed under a 1 T vertical magnetic field, with the magnetic field direction perpendicular to the pressing direction and a magnetic field frequency of 30 Hz. The pressing pressure is divided into three stages: first, 500 MPa is maintained for 30 s, then 1000 MPa is maintained for 60 s, and finally, 1500 MPa is maintained for 120 s (500 MPa × 30 s → 1000 MPa × 60 s → 1500 MPa × 120 s), with a final density of 8 g / cm³.

[0149] Combined gradient annealing and magnetic field annealing:

[0150] First stage: Under nitrogen protection, the temperature is increased to 500℃ at a rate of 5℃ / min and held for 1 h;

[0151] Second stage: Switch to hydrogen atmosphere, heat to 650 ℃ at 2 ℃ / min and hold for 2 h, while applying a 0.2 T transverse alternating magnetic field;

[0152] Third stage: Cool to 200 ℃ at 3 ℃ / min and then allow to cool naturally.

[0153] Performance testing:

[0154] 1. The permeability was measured to be 76 μH / m using a BH analyzer (Iwatsu SY-8219).

[0155] After being treated at 100 ℃ for 48 hours, the attenuation rate was tested.

[0156]

[0157] The attenuation rate is 20%.

[0158] 2. The DC bias characteristic measurement method is the same as in Example 1, and the result is 97%.

[0159] Example 7:

[0160] This embodiment provides an alloy soft magnetic powder for differential mode inductors. The composition of the alloy soft magnetic powder is as follows: 85 wt% iron powder, 5 wt% silicon powder, 5 wt% aluminum powder, 1 wt% iron phosphate (passivating agent), 2 wt% magnesium phosphate (insulator), 1.95 wt% zinc stearate (lubricant), and 0.05 wt% nickel-cobalt-iron alloy.

[0161] The preparation method of alloy soft magnetic powder includes the following steps:

[0162] Iron powder, silicon powder, and aluminum powder were vacuum dried at 80°C for 1.5 h.

[0163] The dried iron powder, silicon powder, aluminum powder, nickel-cobalt-iron alloy, zinc stearate (lubricant), and ferric phosphate (passivating agent) are mixed in proportion and then ball-milled at a low speed (200 r / min) to ensure uniform dispersion of the components.

[0164] The particles were prepared in three sizes: 50-100μm coarse particles, accounting for 70% by mass; 20-50μm medium particles, accounting for 20% by mass; and 10-20μm fine particles, accounting for 10% by mass; with a volume ratio of coarse to medium particles of 3.5.

[0165] Composite insulation coating process: Magnesium phosphate solution and nano-SiO2 sol (particle size of 15 nm) are mixed at a mass ratio of 1:0.5, and 0.1 wt% boric acid is added to the nano-SiO2 sol as an interfacial bonding enhancer. Fluidized bed coating is used, the coating temperature is 250 ℃, and the coating time is 60 min to form a gradient insulation layer with a thickness of 0.5 μm.

[0166] Magnetic field-assisted pressing: Isostatic pressing is performed under a 1 T vertical magnetic field, with the magnetic field direction perpendicular to the pressing direction and a magnetic field frequency of 40 Hz. The pressing pressure is divided into three stages: first, 500 MPa is maintained for 30 s, then 1000 MPa is maintained for 60 s, and finally, 1500 MPa is maintained for 120 s (500 MPa × 30 s → 1000 MPa × 60 s → 1500 MPa × 120 s), with a final density of 8 g / cm³.

[0167] Combined gradient annealing and magnetic field annealing:

[0168] First stage: Under nitrogen protection, the temperature is increased to 500℃ at a rate of 5℃ / min and held for 1 h;

[0169] Second stage: Switch to hydrogen atmosphere, heat to 650 ℃ at 2 ℃ / min and hold for 2 h, while applying a 0.2 T transverse alternating magnetic field;

[0170] Third stage: Cool to 200 ℃ at 3 ℃ / min and then allow to cool naturally.

[0171] Performance testing:

[0172] 1. The permeability was measured to be 76 μH / m using a BH analyzer (Iwatsu SY-8219).

[0173] After being treated at 100 ℃ for 48 h, the attenuation rate was tested.

[0174]

[0175] The attenuation rate is 17%.

[0176] 2. The DC bias characteristic measurement method is the same as in Example 1, and the result is 98%.

[0177] Adding boric acid promotes the uniform dispersion of nano-SiO2 in the magnesium phosphate matrix, forming a "magnesium phosphate-boric acid-SiO2" gradient structure, resulting in a more uniform insulation layer thickness and reducing local magnetic circuit blockage.

[0178] Example 8:

[0179] This embodiment provides an alloy soft magnetic powder for differential mode inductors. The composition of the alloy soft magnetic powder is as follows: 85 wt% iron powder, 5 wt% silicon powder, 5 wt% aluminum powder, 1 wt% iron phosphate (passivating agent), 2 wt% magnesium phosphate (insulating agent), 1.95 wt% zinc stearate (lubricant), and 0.05 wt% nickel-cobalt-iron alloy.

[0180] The preparation method of alloy soft magnetic powder includes the following steps:

[0181] Iron powder, silicon powder, and aluminum powder were vacuum dried at 80°C for 1.5 h.

[0182] The dried iron powder, silicon powder, aluminum powder, nickel-cobalt-iron alloy, zinc stearate (lubricant), and ferric phosphate (passivating agent) are mixed in proportion and then ball-milled at a low speed (200 r / min) to ensure uniform dispersion of the components.

[0183] The particles were prepared in three sizes: 50-100μm coarse particles, accounting for 70% by mass; 20-50μm medium particles, accounting for 20% by mass; and 10-20μm fine particles, accounting for 10% by mass; with a volume ratio of coarse to medium particles of 3.5.

[0184] Composite insulation coating process: Magnesium phosphate solution and nano-SiO2 sol (particle size of 15 nm) are mixed at a mass ratio of 1:0.5, and 0.5 wt% boric acid is added to the nano-SiO2 sol as an interfacial bonding enhancer. Fluidized bed coating is used, the coating temperature is 250 ℃, and the coating time is 60 min to form a gradient insulation layer with a thickness of 0.5 μm.

[0185] Magnetic field-assisted pressing: Isostatic pressing is performed under a 1 T vertical magnetic field, with the magnetic field direction perpendicular to the pressing direction and a magnetic field frequency of 50 Hz. The pressing pressure is divided into three stages: first, 500 MPa is maintained for 30 s, then 1000 MPa is maintained for 60 s, and finally, 1500 MPa is maintained for 120 s (500 MPa × 30 s → 1000 MPa × 60 s → 1500 MPa × 120 s), with a final density of 8 g / cm³.

[0186] Combined gradient annealing and magnetic field annealing:

[0187] First stage: Under nitrogen protection, the temperature is increased to 500℃ at a rate of 5℃ / min and held for 1 h;

[0188] Second stage: Switch to hydrogen atmosphere, heat to 650 ℃ at 2 ℃ / min and hold for 2 h, while applying a 0.2 T transverse alternating magnetic field;

[0189] Third stage: Cool to 200 ℃ at 3 ℃ / min and then allow to cool naturally.

[0190] Performance testing:

[0191] 1. The permeability was measured to be 76 μH / m using a BH analyzer (Iwatsu SY-8219).

[0192] After being treated at 100 ℃ for 48 hours, the attenuation rate was tested.

[0193]

[0194] The attenuation rate is 17%.

[0195] 2. The DC bias characteristic measurement method is the same as in Example 1, and the result is 97%.

[0196] Example 9:

[0197] This embodiment provides an alloy soft magnetic powder for differential mode inductors. The composition of the alloy soft magnetic powder is as follows: 85 wt% iron powder, 5 wt% silicon powder, 5 wt% aluminum powder, 1 wt% iron phosphate (passivating agent), 2 wt% magnesium phosphate (insulating agent), 1.95 wt% zinc stearate (lubricant), and 0.05 wt% nickel-cobalt-iron alloy.

[0198] The preparation method of alloy soft magnetic powder includes the following steps:

[0199] Iron powder, silicon powder, and aluminum powder were vacuum dried at 80 °C for 1.5 h.

[0200] The dried iron powder, silicon powder, aluminum powder, nickel-cobalt-iron alloy, zinc stearate (lubricant), and ferric phosphate (passivating agent) are mixed in proportion and initially mixed by ball milling at low speed (200 r / min) to ensure uniform dispersion of the components.

[0201] The particles were prepared in three sizes: 50-100μm coarse particles, accounting for 70% by mass; 20-50μm medium particles, accounting for 20% by mass; and 10-20μm fine particles, accounting for 10% by mass; with a volume ratio of coarse to medium particles of 3.5.

[0202] Composite insulation coating process: Magnesium phosphate solution and nano-SiO2 sol (particle size of 15 nm) are mixed at a mass ratio of 1:0.5, and 0.5 wt% boric acid is added to the nano-SiO2 sol as an interfacial bonding enhancer. Fluidized bed coating is used, the coating temperature is 250 ℃, and the coating time is 60 min to form a gradient insulation layer with a thickness of 0.5 μm.

[0203] Magnetic field-assisted pressing: Isostatic pressing is performed under a 1 T vertical magnetic field, with the magnetic field direction perpendicular to the pressing direction and a magnetic field frequency of 50 Hz. The pressing pressure is divided into three stages: first, 500 MPa is maintained for 30 s, then 1000 MPa is maintained for 60 s, and finally, 1500 MPa is maintained for 120 s (500 MPa × 30 s → 1000 MPa × 60 s → 1500 MPa × 120 s), with a final density of 8 g / cm³.

[0204] Combined gradient annealing and magnetic field annealing:

[0205] First stage: Under nitrogen protection, the temperature is increased to 500℃ at a rate of 5℃ / min and held for 1 h;

[0206] Second stage: Switch to hydrogen atmosphere, heat to 650 ℃ at 2 ℃ / min and hold for 2 h, while applying a 0.2 T transverse alternating magnetic field; the frequency of the alternating magnetic field is 5 Hz, and the magnetic field strength changes from 0.1 T to 0.2 T every 1 min, then to 0.3 T, and then to 0.1 T again, and repeats the cycle.

[0207] Periodic variations within the range of 0.1-0.3 T.

[0208] Third stage: Cool to 200 ℃ at 3 ℃ / min and then allow to cool naturally.

[0209] Performance testing:

[0210] 1. The permeability was measured to be 77 μH / m using a BH analyzer (Iwatsu SY-8219).

[0211] After being treated at 100 ℃ for 48 hours, the attenuation rate was tested.

[0212]

[0213] The attenuation rate is 17%.

[0214] 2. The DC bias characteristic measurement method is the same as in Example 1, and the result is 99%.

[0215] The micro-strain induced by the alternating magnetic field can counteract the residual internal stress from pressing or annealing, optimize lattice integrity, reduce magnetocrystalline anisotropy, and enhance magnetic circuit continuity.

[0216] Differential mode inductors are fabricated using the above-mentioned alloy soft magnetic powder. The magnetic core has a multi-air gap distributed structure with an air gap spacing of 0.1-0.3 mm and an air gap number to magnetic circuit length ratio of ≥3 / 10cm.

[0217] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0218] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from the scope of the invention.

[0219] The spirit and scope of the invention are as follows: Thus, if these modifications and variations of the invention fall within the scope of the claims of the invention and their equivalents, the invention is also intended to include these modifications and variations.

Claims

1. A method for preparing alloy soft magnetic powder for differential mode inductors, characterized in that, Includes the following steps: (1) Multi-level gradient powder ratio: Three-level particle size ratio is adopted, in which 50-100μm coarse particles account for 50-70 wt%, 20-50μm medium particles account for 20-30 wt%, and 10-20μm fine particles account for 5-20 wt%, and the volume ratio of coarse particles to medium particles is 2.5-3.5; (2) Composite insulation coating process: Phosphoric acid aqueous solution and nano SiO2 sol are mixed at a mass ratio of 1:0.2-0.5, and coated in a fluidized bed at a coating temperature of 250-300℃ for 40-60 min to form a gradient insulation layer with a thickness of 0.8-1.5μm; (3) Magnetic field-assisted pressing: Isostatic pressing is carried out under a vertical magnetic field of 0.5-1T. The pressing pressure is divided into three stages: 500MPa×30s→1000MPa×60s→1500MPa×120s, and the final density is ≥7.5g / cm³. (4) Combined processing of gradient annealing and magnetic field annealing: First stage: Under nitrogen protection, the temperature is increased to 500℃ at a rate of 5℃ / min and held for 1 hour; Second stage: Switch to hydrogen atmosphere, heat to 650℃ at 2℃ / min and hold for 2h, while applying a 0.2T transverse alternating magnetic field; The third stage: Cool to 200℃ at 3℃ / min and then allow to cool naturally.

2. The method for preparing alloy soft magnetic powder for differential mode inductors according to claim 1, characterized in that, The alloy soft magnetic powder has the following composition: Iron: 80-93 wt% Silicon: 5-10 wt% Aluminum: 1-5 wt%; and additives: 1-5 wt%. The additives include one or more of passivating agents, insulating agents, and lubricants.

3. The method for preparing alloy soft magnetic powder for differential mode inductors according to claim 2, characterized in that, The alloy soft magnetic powder also includes a nickel-cobalt-iron alloy, which accounts for 0.05%-3 wt% of the alloy soft magnetic powder.

4. The method for preparing alloy soft magnetic powder for differential mode inductors according to claim 1, characterized in that, The nano-SiO2 sol in step (2) has a particle size of 10-20 nm, and 0.1-0.5 wt% boric acid is incorporated into the sol as an interfacial bonding enhancer.

5. The method for preparing alloy soft magnetic powder for differential mode inductors according to claim 1, characterized in that, The direction of the magnetic field in step (3) is perpendicular to the direction of suppression, and the magnetic field frequency is 10-50Hz.

6. The method for preparing alloy soft magnetic powder for differential mode inductors according to claim 1, characterized in that, In the second stage of step (4), the frequency of the alternating magnetic field is 1-5Hz, and the magnetic field strength changes periodically in the range of 0.1-0.3T.

7. A soft magnetic powder alloy for differential mode inductors, characterized in that, Prepared according to any one of claims 1-6.

8. The alloy soft magnetic powder for differential mode inductors according to claim 7, characterized in that, The differential mode inductor uses alloy soft magnetic powder with a DC bias characteristic of ≥95%.

9. A differential-mode inductor, characterized in that, The alloy soft magnetic powder described in any one of claims 7-8 is used as the magnetic core.

10. The differential-mode inductor device according to claim 9, characterized in that, The magnetic core has a multi-air-gap distributed structure with an air-gap spacing of 0.1-0.3 mm and an air-gap number to magnetic circuit length ratio of ≥3 / 10 cm.

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