LU504521B1

LU504521B1 - Soft magnetic composite with multilayer core-shell structure and preparation method therefor

Info

Publication number: LU504521B1
Application number: LU504521A
Authority: LU
Inventors: Liping Liang
Original assignee: Qingdao Univ Of Technology Linyi Management Committee Office
Priority date: 2023-05-09
Filing date: 2023-06-16
Publication date: 2023-12-18
Also published as: CN116543995A

Abstract

Disclosed is a soft magnetic composite with a multilayer core-shell structure and a preparation method therefor. The preparation method includes: pretreating iron powder, and coating a surface of the iron powder with phosphoric acid-organic resin; and then coating inorganic nanoparticles with a silane coupling agent, mixing the coated inorganic nanoparticles with a lubricant, then placing a mixture in a die of a hot-pressing sintering furnace for hot-forming, then removing pressure, and discharging a magnet after cooling. According to the present invention, the pure iron powder is used as a magnetic matrix, and high-melting-point oxides, carbides and nitrides are used as isolation layers for insulation coating, such that the soft magnetic composite with the core-shell structure is obtained; and by changing a pressing mode, damage of an insulation layer in a pressing process is effectively avoided, and pressing residual stress is reduced, such that a magnet loss is reduced.

Description

BL-5705

SOFT MAGNETIC COMPOSITE WITH MULTILAYER CORE-SHELL HUS0452

STRUCTURE AND PREPARATION METHOD THEREFOR

TECHNICAL FIELD

[01] The present invention relates to the technical field of preparation of soft magnetic composites, and particularly provides a soft magnetic composite with a multilayer core-shell structure and a preparation method therefor.

BACKGROUND ART

[02] Soft magnetic composite (SMC for short) is prepared by coating the surface of soft magnetic particles with a high resistivity isolation layer, pressing and heat treatment.

Based on the advantages of the material, such as environmental friendliness and easy to manufacture, near-net forming and three-dimensional magnetocaloric isotropy, at present, pure iron-based SMC can replace laminated silicon steel sheets as stator material to make three-dimensional magnetic circuit electric motors, which can effectively promote the efficient and lightweight development of electric motors and promote the low-carbon and low-energy upgrading in new energy vehicles, construction machinery, electric aircraft and other fields.

[03] The main raw materials of iron-based SMCs include pure iron powder and high resistivity isolation materials, among which pure iron powder is mostly water atomized iron powder and reduced iron powder, and high resistivity isolation materials include organic resin, phosphoric acid and other compounds. As magnetic particles, the properties and mass fraction of pure iron powder determine the saturation magnetization, permeability and other magnetic properties of the material. The isolation layer is a high resistivity material, and the loss of the material can be effectively reduced by coating.

[04] At present, there are many researches on coating the iron powder with a phosphoric acid isolation layer and then overlapping with organic resin to form multi-layer coating. However, in the subsequent compression moulding process, in order to achieve the required density, residual stress is formed in the material, which increases the material loss and decreases the magnetic properties. In order to remove the 1

BL-5705 residual stress inside the material, it is necessary to perform one-step stress relief 504527 annealing after compression moulding, and the temperature is generally 450-650°C. For example, in the prior art, iron powder is coated with phosphoric acid and organic resin binder, moulded at 900-1100 MPa, and then annealed at 450-650°C. However, the temperature resistance of the coating is poor, and the integrity of the coating is destroyed after heat treatment, which makes the bare iron powder make contact with each other, thus reducing the resistivity of the magnet and increasing the eddy current loss.

[05] In the prior art, some soft magnetic composites with organic-inorganic insulation coating are prepared, which takes into account the advantages of organic and inorganic coating. For example, iron powder is coated with phosphoric acid and organic resin, mixed with MgO, ZnO and other oxides by mechanical ball milling, pressed at 900-1100 Mpa, and then annealed at 450-650°C to prepare magnets. However, due to the high hardness of MgO, ZnO and other oxides, the phosphoric acid layer is punctured to destroy the integrity of the coating during the pressing process, which increases the hysteresis loss of the magnet, and the sharp corners reduces the magnetic properties of the magnet.

SUMMARY

[06] In order to solve the problems existing in the prior art, the present invention provides a soft magnetic composite with a multilayer core-shell structure and a preparation method therefor, according to the present invention, pure iron powder is used as a magnetic matrix, and high-melting-point oxides, nitrides and carbides are used as isolation layers for insulation coating, such that the soft magnetic composite with the core-shell structure is obtained, and by changing a pressing mode, damage of an insulation layer in a pressing process is effectively avoided, and pressing residual stress is reduced, such that a magnet loss is reduced, magnetic performance is improved, and finally the high-performance SMC magnet with a uniform structure is obtained.

[07] In order to solve the above technical problems, a technical solution provided by the present invention is as follows: 2

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[08] The preparation method for soft magnetic composite with multilayer 504527 core-shell structure is provided in the present invention and specifically as follows: firstly, surface treatment is performed on iron powder by mechanical ball milling to improve surface activity of the iron powder, and ball milling speed is based on the fact that the surface activity may be improved without obviously reducing a particle size of the iron powder; in order to satisfy the above conditions, the step uses a high-energy ball mill and a cemented carbide grinding ball, with a rotation speed of 250-500 rpm and a treatment time of 5-20 minutes.

[09] The pretreated iron powder is coated with phosphoric acid and organic resin, orthophosphoric acid, acetone, ethanol or deionized water are prepared into a phosphoric acid solution, then the phosphoric acid solution and the iron powder are uniformly mixed, the coated iron powder is dried at 60-80°C to form a phosphoric acid passivation layer to be sieved, thermoplastic resin and ethanol or acetone are prepared into a solution to coat the iron powder for the second time, and the drying and sieving steps are repeated to prepare phosphoric acid-resin coated iron powder. Then, nanoparticles of high-melting-point ceramic compounds such as MgO, ZnO, SiO, SiC,

TiO,, SiN and AIN, a silane coupling agent and the acetone or ethanol are prepared into a solution, a nano-particle suspension is formed by mechanical stirring or ultrasonic stirring, and then the phosphoric acid-resin coated iron powder is added into the solution, such that the nanoparticles may be well adsorbed on a resin coating on a surface of the iron powder by means of the silane coupling agent to form a high-melting-point coating, thus obtaining the SMC with multilayer core-shell structure.

[10] Coated insulating iron powder, zinc stearate having a concentrating of 0.1-0.25%, micropowder wax and other lubricants are uniformly mixed by a mixer, and formed by hot pressing sintering, pressing pressure is 100-250 MPa, pressing sintering temperature is divided into two stages: firstly, a mixture is heated to 200-250°C, temperature and pressure are kept for 20-30 minutes, volatilization of organic substances in the magnet is promoted, then the temperature is raised to 400-450°C, the temperature and the pressure are kept for 5-10 minutes, and the magnet is cooled and discharged. 3

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[11] Raw materials of the present invention are the pure iron powder, atomized iron 504527 powder or reduced iron powder, component purity is greater than 99.0%, and the water atomized iron powder with smooth appearance and higher purity is preferred.

[12] Compared with the prior art, the present invention has the following beneficial effects:

[13] The multi-layer coating method of the present invention may effectively improve binding force of a high-melting-point nano-compound and the surface of the iron powder and distribution uniformity, thus improving integrity and uniformity of the insulation layer. In addition, heat resistance of the insulation layer may be effectively improved by adding the high-melting-point nano-compound; in the present invention, the hot-pressing sintering process is used to replace the forming and stress-relieving heat treatment in one step, a traditional mould pressing heat treatment is replaced with a hot-pressing sintering method, the iron powder may be in a thermoplastic state in the pressing process, such that the iron powder is easier to flow and deform, density is improved, forming pressure is greatly reduced, and usage amount of the lubricant may be reduced; and further, forming the material at lower pressure may effectively reduce heat treatment temperature. Therefore, by means of the present invention, the forming and heating treatment may be synthesized in one step, and the pure iron-based SMC with high resistivity and low loss may be obtained by means of low energy consumption.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[14] In order to make the technical problems, technical solution and advantages of the present invention more clear, the present invention will be described in detail below with reference to specific examples.

[15] Unless otherwise specified, reagents and materials used in the examples and comparative examples may be obtained through commercial channels. A silane coupling agent is a commercial product, there is no special requirement for the silane coupling agent, and the silane coupling agent may be kh-570, kh-560, kh-550, A-151, A-171, etc.

[16] The present invention provides a soft magnetic composite with a multilayer 4

BL-5705 core-shell structure and a preparation method therefor, and the specific examples are as 504527 follows.

[17] Example 1

[18] A preparation method for a soft magnetic composite with a multilayer core-shell structure includes:

[19] Step 1: performing mechanical ball milling pretreatment on water atomized iron powder at rotation speed of a ball mill of 500 revolutions per minute for pretreatment time of 6 minutes;

[20] Step 2: uniformly mixing an orthophosphoric acid-ethanol solution with the pretreated iron powder at a volume ratio of 1:60, drying a mixture at 70°C for 60 minutes, and performing sieving with a 60-mesh sieve to prevent caking from affecting subsequent coating;

[21] Step 3: uniformly mixing an epoxy resin-ethanol solution with phosphoric acid coated iron powder at a volume ratio of 1:30, drying a mixture at 70°C for 60 minutes anew, and then performing sieving to obtain organic-inorganic composite coated insulating iron powder;

[22] Step 4: mixing MgO nanoparticles with acetone in a mass ratio of 1:150 to prepare a suspension, adding a silane coupling agent accounting for 0.3% of mass of the acetone, preparing a MgO nanoparticle suspension by means of mechanical stirring, adding the iron powder into the suspension, performing uniform mixing under mechanical stirring, and then performing drying and sieving to obtain insulating iron powder with a nano MgO shell layer;

[23] Step 5: adding a zinc stearate lubricant accounting for 0.15 wt% of mass of the insulating iron powder, and performing uniform mixing by a mixer to obtain powder; and

[24] Step 6: putting the powder into a die of a hot-pressing sintering furnace, keeping pressing pressure at 100 MPa, keeping heating temperature at 200°C for 20 minutes at first, then raising the temperature to 400°C, keeping the temperature for 5 minutes, then removing the pressure and the temperature, and discharging a magnet after cooling.

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[25] Example 2 504527 26] A preparation method for a soft magnetic composite with a multilayer core-shell structure includes:

[27] Steps 1-3 are the same as those in Example 1;

[28] Step 4: mixing ZnO nanoparticles with acetone in a mass ratio of 1:150 to prepare a solution, adding a silane coupling agent accounting for 0.3% of mass of the acetone, preparing a ZnO nanoparticle suspension by means of mechanical stirring, adding the iron powder into the suspension, performing uniform mixing under mechanical stirring, and then performing drying and sieving to obtain insulating iron powder with a nano ZnO shell layer;

[29] Step 5: adding a zinc stearate lubricant accounting for 0.15 wt% of mass of the insulating iron powder, and performing uniform mixing by a mixer to obtain powder; and

[30] Step 6: putting the powder into a die of a hot-pressing sintering furnace, keeping pressing pressure at 110 MPa, keeping heating temperature at 200°C for 20 minutes at first, then raising the temperature to 400°C, keeping the temperature for 5 minutes, then removing the pressure and the temperature, and discharging a magnet after cooling.

[31] Example 3

[32] A preparation method for a soft magnetic composite with a multilayer core-shell structure includes:

[33] Steps 1-3 are the same as those in Example 1;

[34] Step 4: mixing SiC nanoparticles with acetone in a mass ratio of 1:150 to prepare a solution, adding a silane coupling agent accounting for 0.3% of mass of the acetone, preparing a SiC nanoparticle suspension by means of mechanical stirring, adding the iron powder into the suspension, performing uniform mixing under mechanical stirring, and then performing drying and sieving to obtain insulating iron powder with a nano SiC shell layer;

[35] Step 5: adding a zinc stearate lubricant accounting for 0.15 wt% of mass of the insulating iron powder, and performing uniform mixing by a mixer to obtain powder; 6

BL-5705 and LU504521

[36] Step 6: putting the powder into a die of a hot-pressing sintering furnace, keeping pressing pressure at 120 MPa, keeping heating temperature at 200°C for 20 minutes at first, then raising the temperature to 400°C, keeping the temperature for 5 minutes, then removing the pressure and the temperature, and discharging a magnet after cooling.

[37] Example 4

[38] A preparation method for a soft magnetic composite with a multilayer core-shell structure includes:

[39] Steps 1-3 are the same as those in Example 1;

[40] Step 4: mixing SiC nanoparticles with acetone in a mass ratio of 1:150 to prepare a solution, adding a silane coupling agent accounting for 0.3% of mass of the acetone, preparing a SiC nanoparticle suspension by means of mechanical stirring, adding the iron powder into the suspension, performing uniform mixing under mechanical stirring, and then performing drying and sieving to obtain insulating iron powder with a nano SiC shell layer;

[41] Step 5: adding a zinc stearate lubricant accounting for 0.15 wt% of mass of the insulating iron powder, and performing uniform mixing by a mixer to obtain powder; and

[42] Step 6: putting the powder into a die of a hot-pressing sintering furnace, keeping pressing pressure at 250 MPa, keeping heating temperature at 200°C for 20 minutes at first, then raising the temperature to 400°C, keeping the temperature for 5 minutes, then removing the pressure and the temperature, and discharging a magnet after cooling.

[43] Example 5

[44] A preparation method for a soft magnetic composite with a multilayer core-shell structure includes:

[45] Step 1: performing mechanical ball milling pretreatment on reduced iron powder at rotation speed of a ball mill of 250 revolutions per minute for pretreatment time of 20 minutes; 7

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[46] Step 2: uniformly mixing an orthophosphoric acid-ethanol solution with the 504527 pretreated iron powder at a volume ratio of 1:60, drying a mixture at 70°C for 60 minutes, and performing sieving to prevent caking from affecting subsequent coating;

[47] Step 3: uniformly mixing an epoxy resin-ethanol solution with phosphoric acid coated iron powder at a volume ratio of 1:30, drying a mixture at 70°C for 60 minutes anew, and then performing sieving to obtain organic-inorganic composite coated insulating iron powder;

[48] Step 4: mixing SiO; nanoparticles with ethanol in a mass ratio of 1:150 to prepare a suspension, adding a silane coupling agent accounting for 0.3% of mass of the ethanol, preparing a SiO» nanoparticle suspension by means of mechanical stirring, adding the iron powder into the suspension, performing uniform mixing under mechanical stirring, and then performing drying and sieving to obtain insulating iron powder with a nano SiO; shell layer;

[49] Step 5: adding a micropowder wax lubricant accounting for 0.1 wt% of mass of the insulating iron powder, and performing uniform mixing by a mixer to obtain powder; and

[50] Step 6: putting the powder into a die of a hot-pressing sintering furnace, keeping pressing pressure at 150 MPa, keeping heating temperature at 250°C for 30 minutes at first, then raising the temperature to 450°C, keeping the temperature for 5 minutes, then removing the pressure and the temperature, and discharging a magnet after cooling.

[51] Example 6

[52] A preparation method for a soft magnetic composite with a multilayer core-shell structure includes:

[53] Step 1: performing mechanical ball milling pretreatment on reduced iron powder at rotation speed of a ball mill of 400 revolutions per minute for pretreatment time of 15 minutes;

[54] Step 2: uniformly mixing an orthophosphoric acid-ethanol solution with the pretreated iron powder at a volume ratio of 1:60, drying a mixture at 70°C for 60 minutes, and performing sieving to prevent caking from affecting subsequent coating; 8

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[55] Step 3: uniformly mixing an epoxy resin-ethanol solution with phosphoric 1006581 acid coated iron powder at a volume ratio of 1:30, drying a mixture at 70°C for 60 minutes anew, and then performing sieving to obtain organic-inorganic composite coated insulating iron powder,

[56] Step 4: mixing TiO; nanoparticles with ethanol in a mass ratio of 1:150 to prepare a suspension, adding a silane coupling agent accounting for 0.3% of mass of the ethanol, preparing a TiO, nanoparticle suspension by means of mechanical stirring, adding the iron powder into the suspension, performing uniform mixing under mechanical stirring, and then performing drying and sieving to obtain insulating iron powder with a nano TiO; shell layer;

[57] Step 5: adding a micropowder wax lubricant accounting for 0.25 wt% of mass of the insulating iron powder, and performing uniform mixing by a mixer to obtain powder; and

[58] Step 6: putting the powder into a die of a hot-pressing sintering furnace, keeping pressing pressure at 130 MPa, keeping heating temperature at 220°C for 25 minutes at first, then raising the temperature to 420°C, keeping the temperature for 10 minutes, then removing the pressure and the temperature, and discharging a magnet after cooling.

[59] Example 7

[60] In the present example, SiC is replaced with equivalent amount of SiN, and other conditions are the same as those in Example 4.

[61] In order to further highlight the beneficial effects of the present invention, due to the limited space, comparative examples are constructed by taking Example 4 as an example as follows.

[62] Comparative example 1

[63] A preparation method for a soft magnetic composite includes:

[64] Steps 1-3 are the same as those in Example 4;

[65] Step 4: uniformly mixing 0.3% of SiC nanoparticles with organic-inorganic composite coated insulating iron powder by a mechanical ball milling method to obtain insulating iron powder; 9

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[66] Step 5: adding a zinc stearate lubricant accounting for 0.6 wt% of mass of the 504527 insulating iron powder, and performing uniform mixing by a mixer to obtain powder; and

[67] Step 6: pressing and molding the powder prepared in step 5 by a normal temperature press at 1000 MPa; and

[68] Step 7: placing a pressed blank in a nitrogen annealing furnace for annealing at 200°C for 30 minutes, then raising the temperature to 600°C for 15 minutes, and performing discharging after cooling.

[69] Comparative example 2

[70] A preparation method for a soft magnetic composite includes:

[71] Step 1: performing mechanical ball milling pretreatment on water atomized iron powder at rotation speed of a ball mill of 500 revolutions per minute for pretreatment time of 6 minutes;

[72] Step 2: mixing an orthophosphoric acid-ethanol solution with the pretreated water atomized homogeneous iron powder at a volume ratio of 1:60, drying a mixture at 70°C for 60 minutes, and performing sieving to prevent caking from affecting subsequent coating;

[73] Step 3: uniformly mixing an epoxy resin-ethanol solution with phosphoric acid coated iron powder at a volume ratio of 1:30, drying a mixture at 70°C for 60 minutes anew, and then performing sieving to obtain organic-inorganic composite coated insulating iron powder;

[74] Step 4: adding a zinc stearate lubricant accounting for 0.15 wt% of mass of the insulating iron powder, and performing uniform mixing by a mixer to obtain powder; and

[75] Step 5: putting the powder into a die of a hot-pressing sintering furnace, keeping pressing pressure at 100 MPa, keeping heating temperature at 200°C for 20 minutes at first, then raising the temperature to 400°C, keeping the temperature for 5 minutes, then removing the pressure and the temperature, and discharging a magnet after cooling.

[76] Comparative example 3

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[77] A preparation method for a soft magnetic composite includes: 1006581

[78] Steps 1-3 are the same as those in Example 4;

[79] Step 4: adding a zinc stearate lubricant accounting for 0.6 wt% of mass of the insulating iron powder, and performing uniform mixing by a mixer to obtain powder; and

[80] Step 5: pressing and molding the powder by a normal temperature press at 1000 MPa; and

[81] Step 6: placing a pressed blank in a nitrogen annealing furnace for annealing at 200°C for 30 minutes, then raising the temperature to 400°C for 15 minutes, and performing discharging after cooling.

[82] Comparative example 4

[83] In the present comparative example, step 3 1s omitted, and other conditions are the same as those in Example 4.

[84] Comparative example 5

[85] In the present comparative example, a silane coupling agent in step 4 1s omitted, and other conditions are the same as those in Example 4.

[86] Comparative example 6

[87] A preparation method for a soft magnetic composite includes:

[88] Steps 1-3 are the same as those in Example 4;

[89] Step 4: adding a zinc stearate lubricant accounting for 0.6 wt% of mass of the insulating iron powder, and performing uniform mixing by a mixer to obtain powder; and

[90] Step 5: pressing and molding the powder by a normal temperature press at 1000 MPa; and

[91] Step 6: placing a pressed blank in a nitrogen annealing furnace for annealing at 200°C for 30 minutes, then raising the temperature to 600°C for 15 minutes, and performing discharging after cooling.

[92] Comparative example 7

[93] A preparation method for a soft magnetic composite includes:

[94] Steps 1-3 are the same as those in Example 4; 11

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[95] Step 4: adding a zinc stearate lubricant accounting for 0.6 wt% of mass of the 504527 insulating iron powder, and performing uniform mixing by a mixer to obtain powder; and

[96] Step 5: warm compacting and forming the powder at heating temperature of 100°C and pressure of 800 Mpa, maintaining the pressure for 30 min, and removing a mould;

[97] Step 6: placing a pressed blank in a nitrogen annealing furnace for annealing at 200°C for 30 minutes, then raising the temperature to 600°C for 15 minutes, and performing discharging after cooling.

[98] Properties of the soft magnetic composites prepared in the above Examples 1-7 and Comparative Examples 1-7 are tested, in which saturation magnetic flux density

Bs is measured according to GB/T13012-2008 "Methods of measurement of d.c. magnetic properties of magnetically soft materials", power loss Ps is measured according to GB/T3658-2008 "Methods of measurement of a.c. magnetic properties of magnetically soft materials"; and strength is measured according to ISO3325 "Sintered metal materials, including hardmetals--Determination of transverse rupture strength", with results seen in Tables 1-2. Bs: saturation magnetic induction intensity; Hc: coercivity; P: magnetic loss.

[99] Table 1

Serial Bs (T) Hc Intensity

Microhm number 10000 A/m | (A/m) (MPa) meter anges [10 [me [eo ma [on [mes [nee eames [10 [ra [se Jo [sa [so [0 [x eames [10 [ms [so J [wo [si Jom [m 12

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[100] It may be seen from Table 1 that the soft magnetic composite prepared by the present invention has relatively high saturation magnetic induction intensity, fracture strength and high resistivity, and further has low coercivity and magnetic loss.

According to the present invention, traditional mould pressing heat treatment 1s replaced with a hot-pressing sintering method, the iron powder may be in a thermoplastic state in a pressing process, heat treatment temperature may be effectively reduced when a material is formed at lower pressure, a pure iron-based SMC with high resistivity and low loss may be obtained by means of low energy consumption, and in addition, an effect of the water atomized iron powder is better than that of the reduced iron powder (Examples 5-6).

[101] Table 2

Bs (T) Ps (W/kg) Resistivity

Hc Intensity

Serial number 10000 100 200 500 1000 Microhm (A/m) (MPa)

A/m Hz Hz Hz Hz meter

Comparative 1.38 203.7 114 |23.1 145.6 | 930 example 1

Comparative 1.41 183.7 196 | 55.0 113.6 1020 40 example 2

Comparative 1.37 263.7 13.9 1316 | 683 1526 | 950 38 example 3

Comparative 1.36 201.2 108 | 272 | 615 1426 | 995 36 example 4

Comparative 1.38 195.7 112 128.1 62.3 147.3 | 975 35 example 5

Comparative 1.38 193.7 11.4 38.9 | 843 205.6 | 280 39 example 6

Comparative 1.39 191.5 109 [36.3 |76.8 |211.2 |301 38 example 7 13

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[102] From the performance test results, it may be seen that heat resistance of an insulation coating may be effectively improved by adding nano high-melting-point oxides and carbides, for example, Comparative Example 1 may still maintain the high saturation magnetic induction intensity and the low loss when heat treatment is performed at 600°C, which shows that the insulation coating is still relatively complete at the heat-treatment temperature. In the case of not adding high-melting-point compounds, whether pressing at room temperature or warm compaction, it is necessary to perform heat treatment at about 600°C to remove pressing stress, and at the moment, the coating has poor thermal stability and is destroyed, such that the loss increases rapidly (Comparative Examples 6 and 7). In addition, under an innovative pressing method, the integrity of the coating may be maintained at low heating temperature even without adding the high-melting-point oxides, carbides and nitrides, but the addition of the high-melting-point compounds may improve strength of the material by means of dispersion strengthening (Comparative Example 2).

[103] According to the present invention, a hot-pressing sintering process may effectively reduce forming pressure (100-250 MPa), therefore internal residual stress of the material is small, and the required heat treatment temperature is low (400°C).

Compared with the present invention, traditional forming pressure is 900-1100 MPa, the heat treatment temperature needs to be increased to 550-650°C, the heat treatment at the temperature affects the integrity of the coating and increases the loss, and low-temperature heat treatment such as 400°C also increases the material loss because the residual stress in a magnet may not be completely eliminated (Comparative

Example 3). However, when the heat treatment temperature is increased to 600°C, the coating is destroyed and the loss is significantly increased (Comparative Example 6).

[104] A coating process of epoxy resin is omitted, nanoparticles are coated directly on a surface of phosphoric acid (Comparative Example 4), adhesion between the nanoparticles and a phosphoric acid layer is poor, and integrity of an isolation layer is poor, which significantly increases a loss.

[105] It may be seen from Comparative Example 5 that after the silane coupling 14

BL-5705 agent is omitted, the high-melting-point compounds are unevenly distributed on a 504527 surface of the coated iron powder, which reduces properties of the material.

[106] In summary, the method of the present invention may effectively improve binding force and distribution uniformity of the high-melting-point nano-compounds and the surface of the iron powder, and improve the binding force of nano-oxides and the surface of the iron powder; and pressing pressure and heating temperature are reduced by the innovative pressing method, so as to improve the integrity of the insulation coating and reduce the loss.

Claims

BL-5705 WHAT IS CLAIMED IS: HUS0452

1. A preparation method for a soft magnetic composite with a multilayer core-shell structure, comprising: Step 1: performing ball milling pretreatment on iron powder; Step 2: coating the pretreated iron powder with phosphoric acid to obtain phosphoric acid coated iron powder; Step 3: coating the phosphoric acid coated iron powder with organic resin to obtain phosphoric acid-resin coated iron powder; Step 4: preparing an inorganic nanoparticle suspension, then adding a certain amount of silane coupling agent, performing uniform mixing, then adding the phosphoric acid-resin coated iron powder, performing uniform mixing, then performing drying and sieving to obtain insulating iron powder with nanoparticles as a shell layer; Step 5: uniformly mixing the insulating iron powder prepared in step 4 with a lubricant to obtain powder; and Step 6: putting the powder prepared in step 5 into a die of a hot-pressing sintering furnace at pressing pressure of 100-250 MPa, in a pressing process, raising temperature to 200-250°C at first, keeping the temperature for 20-30 minutes, then raising the temperature to 400-450°C, keeping the temperature for 5-10 minutes, then removing the pressure, and discharging a magnet after cooling.

2. The preparation method for soft magnetic composite with multilayer core-shell structure according to claim 1, wherein in step 4, inorganic nanoparticles are MgO, ZnO, S103, SiC, TiO, SiN or AIN having a particle size of 100-500 nm.

3. The preparation method for soft magnetic composite with multilayer core-shell structure according to claim 2, wherein in step 4, the inorganic nanoparticles are dispersed in acetone or ethanol to form the suspension; a mass ratio of the inorganic nanoparticles to the acetone or ethanol is 1: 100-150; and using amount of the silane coupling agent is 0.2-0.4% of mass of the acetone or ethanol.

4. The preparation method for soft magnetic composite with multilayer core-shell structure according to claim 3, wherein in step 4, drying temperature is 60-80°C, time is 16

BL-5705 60-120 minutes, and sieving is performed with a 80-mesh sieve. 1006581

5. The preparation method for soft magnetic composite with multilayer core-shell structure according to claim 1, wherein step 1 specifically is as follows: performing mechanical ball milling pretreatment on the iron powder at rotation speed of a ball mill of 250-500 rpm for 5-20 minutes; and the iron powder is pure iron powder, atomized iron powder or reduced iron powder, and component purity is greater than 99.0%.

6. The preparation method for soft magnetic composite with multilayer core-shell structure according to claim 1, wherein step 2 specifically is as follows: preparing a phosphoric acid solution with the acetone, the ethanol or deionized water, then uniformly mixing the phosphoric acid solution with the pretreated iron powder, drying the coated iron powder at 60-80°C to form a phosphoric acid passivation layer, and performing sieving to obtain the phosphoric acid coated iron powder.

7. The preparation method for soft magnetic composite with multilayer core-shell structure according to claim 1, wherein step 3 specifically is as follows: preparing the organic resin and the ethanol or acetone to a solution, then adding the phosphoric acid coated iron powder, performing uniform mixing, performing drying at 60-80°C, and performing sieving to obtain the phosphoric acid-resin coated iron powder.

8. The preparation method for soft magnetic composite with multilayer core-shell structure according to claim 1, wherein in the step 5, the lubricant is zinc stearate and/or micropowder wax, and using amount of the lubricant is 0.1-0.25% of the mass of the insulating iron powder.

9. A soft magnetic composite with a multilayer core-shell structure, being prepared by the method according to any one of claims 1-8. 17