A method for preparing a low-cost high-magnetic-property powder metallurgy soft magnetic material

Abstract

The application discloses a preparation method of a low-cost high-magnetic-performance powder metallurgy soft magnetic material, which comprises the following steps: mixing ferrophosphorus, paraffin powder and iron powder to obtain mixed powder, pressing and forming the mixed powder to obtain a compact, pre-sintering the compact to obtain a pre-sintered compact, re-pressing the pre-sintered compact and then sintering, and obtaining the powder metallurgy soft magnetic material; the preparation method of the application uses ferrophosphorus, paraffin powder and iron powder as raw materials, controls the particle size of the raw materials, does not need to granulate and spheroidize, directly mixes, and then can obtain mixed powder with excellent fluidity; the mixed powder is pressed and formed to obtain a compact with high density; the compact is preliminarily pre-sintered, re-pressed to further improve the density, and then sintered, so that the powder metallurgy soft magnetic material with high magnetic performance is obtained.

Description

TECHNICAL FIELD

[0001] The application relates to a soft magnetic material, in particular to a preparation method of a low-cost high-magnetic-performance powder metallurgy soft magnetic material. BACKGROUND

[0002] The soft magnetic material has the characteristics of high saturation magnetic induction intensity, high magnetic permeability and the like, and is widely applied to the electric power and electronic industries. With the development of industrial technology, the application of the soft magnetic material is more and more extensive, the shape of the soft magnetic material part is more and more complex, and the size is also more and more small. In the process of preparing the soft magnetic material part by using the traditional mechanical processing method, the problems of low processing efficiency, low material utilization rate and high cost are increasingly prominent.

[0003] The powder metallurgy process has the characteristics of near net shape, the mechanical processing allowance is small, and the material utilization rate can reach more than 95%, so the powder metallurgy process is an ideal process for preparing the soft magnetic material part. The magnetic performance of the soft magnetic material is greatly related to the component design and the preparation process of the material. Due to the characteristics of the powder metallurgy process, the prepared soft magnetic material part inevitably has pores, so that the magnetic performance of the soft magnetic material part is not high. Therefore, it is of great significance to prepare the low-cost soft magnetic material with excellent mechanical performance and magnetic performance by studying the component design and the preparation process of the soft magnetic material.

[0004] The Chinese patent (ZL201310400060.8) adopts injection molding to prepare the soft magnetic product, the production cost is high, and the sintering process needs to be degreased, so the process is complex. The Chinese patent (ZL201410330449.4) adopts dry pressing to prepare the soft magnetic material, but the particle size of the powder used is small, the spray granulation needs to be carried out before the molding, and the sintering and degreasing of the molded body are needed to prepare the soft magnetic material with high magnetic performance, so the production cost is high. SUMMARY

[0005] In view of the defects of the prior art, the purpose of the application is to provide a preparation method of a low-cost high-magnetic-performance powder metallurgy soft magnetic material. The preparation method of the application effectively reduces the porosity of the material and improves the density of the material by the cooperation of the raw materials, the molding mode and the sintering process, and finally the obtained powder metallurgy soft magnetic material has excellent mechanical performance and magnetic performance. The preparation method of the application is simple and controllable, the cost is low, and the method is suitable for industrialized mass production.

[0006] In order to achieve the above-mentioned purpose, the application adopts the following technical scheme:

[0007] The preparation method of the low-cost high-magnetic-performance powder metallurgy soft magnetic material mixes ferrophosphorus, paraffin powder and iron powder to obtain mixed powder, presses and molds the mixed powder to obtain a compact, pre-sinter the compact to obtain a pre-sintered compact, re-presses the pre-sintered compact and then sinter, and the powder metallurgy soft magnetic material is obtained.

[0008] The particle size D50 of the phosphorus tri-iron is 15-50 μm, the particle size D50 of the paraffin powder is 25-75 μm, and the particle size D50 of the iron powder is 55-150 μm;

[0009] The pre-sintering temperature is 780-850 ℃;

[0010] The pressure of the re-pressing is 650-750 MPa, and the down-pressing rate is 3%-5%.

[0011] The gap between the pre-sintering blank and the mold is controlled to be 5-10 filaments during the re-pressing.

[0012] The preparation method of the application uses phosphorus tri-iron, paraffin powder and iron powder as raw materials. Phosphorus can improve the strength of the material, reduce the sintering temperature, and in soft magnetic materials, phosphorus can improve the resistance value, reduce the eddy current effect and reduce the heat generation. In the application, phosphorus is introduced in the form of phosphorus tri-iron, and the powder flowability is improved by adding paraffin powder. The mixed powder is directly mixed with iron powder without granulation. Only the particle size of the raw material needs to be controlled. The mixed powder obtained after mixing has excellent flowability and is fully mixed and uniform. The mixed powder is pressed into a compact, and a compact with high density can be obtained. Therefore, by further controlling the shrinkage rate of pre-sintering by controlling the temperature during pre-sintering, and by controlling the pressure of re-pressing and the gap between the re-pressing mold, and by controlling the down-pressing rate of re-pressing to be 3%-5%, it is found that when the down-pressing rate of re-pressing is controlled to be 3%-5%, the density of the powder metallurgy soft magnetic material obtained after sintering is the highest, and the magnetic performance is the best.

[0013] It is found that the temperature of pre-sintering needs to be effectively controlled to finally obtain a soft magnetic material with high density. If the pre-sintering temperature is too high, the shrinkage rate is too high, which not only affects the down-pressing rate during re-pressing, but also consumes the driving force for subsequent sintering, so that the density cannot be effectively improved during sintering. If the temperature is too low, the shrinkage rate is too low, which will also affect the down-pressing rate after re-pressing, thereby affecting the final density.

[0014] In addition, it is found that during re-pressing, the gap between the pre-sintering blank and the mold needs to be controlled within the range of the application to effectively improve the density of the pre-sintering blank. If the gap between the pre-sintering blank and the mold is small, the pressure of re-pressing is consumed by the friction between the pre-sintering blank and the mold during the deformation process of the pre-sintering blank, and the density cannot be effectively improved. If the gap is large, the radial deformation amount of the pre-sintering blank will be too large, and the density cannot be effectively improved.

[0015] In the preferred scheme, the mixed powder consists of the following components in mass percentage: phosphorus tri-iron (Fe3P) 1.45-1.87%, paraffin powder 0.6-0.8%, and the rest is iron powder.

[0016] The amount of each substance in the mixed powder is controlled within the above range to achieve the best performance. If the paraffin powder is too much, the green compact density will be reduced, and if it is too little, the powder flowability will be reduced, affecting the molding and the final performance. If the ferrophosphorus is too little, the phosphorus content cannot meet the requirements of liquid phase sintering, and the density cannot be effectively improved, and the magnetic performance is reduced. If too much ferrophosphorus is added, not only the compression performance of the powder will be affected, but also the sintering deformation will be increased, and the material will be embrittled.

[0017] In a preferred embodiment, the particle size D50 of the ferrophosphorus is 25-30 μm, the particle size D50 of the paraffin powder is 35-50 μm, and the particle size D50 of the iron powder is 60-100 μm.

[0018] In the present application, by using the above particle size grading, adding paraffin powder, and controlling the amount of ferrophosphorus, only by mixing the raw materials in a mixer, a powder with excellent flowability and compressibility can be obtained, so that granulation is not required, and a green compact with high density can be obtained.

[0019] In a preferred embodiment, the mixing is carried out in a mixer, the rotation speed of the mixer is 20-30 rpm, and the mixing time is 2-4 h.

[0020] In a preferred embodiment, the pressure for the compression molding is 500-600 MPa, and the holding time is 4-8 s.

[0021] By controlling the pressure for the compression molding within the above range, a green compact with optimal high density is obtained. During the pre-sintering process, the shrinkage is controlled by the pre-sintering temperature, and the re-compression reduction rate is controlled within the range of 3-5%. After sintering, the density can be maximized, and a soft magnetic material with almost near-net-shape can be obtained, greatly reducing the processing cost.

[0022] In a preferred embodiment, the pre-sintering is carried out in a mixed atmosphere of N2 and H2, and the pre-sintering time is 1-2 h. The pre-sintering in the present application is carried out in a mixed atmosphere of N2 and H2. N2 mainly functions to prevent the material from being oxidized during sintering, and H2 mainly functions to maintain a slightly reducing atmosphere in the sintering furnace. By controlling the pre-sintering time within the above range, the density of the final soft magnetic material is the highest in cooperation with the pre-sintering temperature.

[0023] Further preferably, the volume flow ratio of N2 to H2 during the pre-sintering is 5-7:1. By controlling the volume flow ratio of N2 to H2 within the above range, the performance of the final soft magnetic material is the best.

[0024] In a preferred embodiment, the holding time during the re-compression is 5-10 s.

[0025] Preferably, the sintering is carried out in a mixed atmosphere of N2 and H2, the sintering temperature is 1100-1250℃, and the sintering time is 6-9h.

[0026] Further preferably, the volume flow ratio of N2 to H2 during the sintering is 5-7:1. The performance is optimal when the volume flow ratio of N2 to H2 is controlled within this range.

[0027] In the present application, after the re-pressing, long-time sintering is carried out, and finally the powder metallurgy soft magnetic material with high density is obtained through physical and chemical reactions such as powder inter-particle mass transfer and recrystallization. In the sintering process, only the sintering atmosphere and the final sintering temperature and time need to be controlled, and thus the soft magnetic material with high density and excellent comprehensive performance can be obtained.

[0028] In actual operation, after the sintering is completed, the necessary parts of the powder metallurgy soft magnetic material are processed according to the drawing requirements, and then the soft magnetic product is manufactured.

[0029] Preferably, the density of the powder metallurgy soft magnetic material is ≥7.34g / cm 3 , the tensile strength is ≥350MPa, the yield strength is ≥220MPa, the hardness is 45-80HRB, the maximum permeability is ≥2.3mH / m, the saturation magnetic induction is ≥1.6T, and the coercive force is ≤180A / m.

[0030] Further preferably, the density of the powder metallurgy soft magnetic material is ≥7.57g / cm 3 , the tensile strength is ≥473MPa, the yield strength is ≥326MPa, the hardness is 40-80HRB, the maximum permeability is ≥2.42mH / m, the saturation magnetic induction is ≥1.68T, and the coercive force is ≤176A / m.

[0031] Advantages

[0032] 1. The soft magnetic material prepared in the present application does not add expensive nickel, cobalt and other metal powders, and at the same time, the powder with a larger particle size which does not need spray granulation pretreatment is used. The preparation cost is lower than that of adding expensive metal powder and needing pretreatment, and the mechanical properties and magnetic properties of the prepared soft magnetic material are superior to those of not adding expensive metal powder and needing pretreatment.

[0033] 2. The dry pressing is used to prepare the soft magnetic material in the present application, which has a lower cost compared to injection molding, and does not need to be degreased during the sintering process, which can further reduce the production cost.

[0034] 3. The re-pressing and re-sintering process is used in the present application to improve the density of the soft magnetic material, and the soft magnetic material with excellent mechanical properties and magnetic properties can be prepared. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 Metallographic chart of soft magnetic material obtained in Example 2.

[0036] Figure 2 Metallographic chart of soft magnetic material obtained in Example 2.

[0037] Figure 3 Graph of magnetic property of soft magnetic material obtained in Example 2.

[0038] Figure 4 Metallographic chart of soft magnetic material obtained in Comparative Example 1.

[0039] Figure 5 Graph of magnetic property of soft magnetic material obtained in Comparative Example 1.

[0040] Figure 6 Graph of magnetic property of soft magnetic material obtained in Comparative Example 3. DETAILED DESCRIPTION

[0041] Example 1

[0042] A mixed powder of 1.45% of phosphide iron (particle size D50 of 30 μm), 0.6% of paraffin powder (particle size D50 of 45 μm), and the rest of iron powder (particle size D50 of 100 μm) was mixed in a mixer at 20 rpm for 4 h, and then formed at a forming pressure of 600 MPa and a pressure holding time of 5 s. The formed product was pre-sintered at 800 °C for 2 h in a sintering furnace in an atmosphere of N2+H2 (volume flow ratio of N2:H2=7:1), and then re-pressed at a pressure of 700 MPa and a pressure holding time of 5 s in a mold. The re-pressing pressure reduction ratio was 5%, and the gap between the pre-sintered product and the mold was controlled to be 10 μm during the re-pressing. Then, the re-pressed product was sintered at 1150 °C for 8 h in a sintering furnace in an atmosphere of N2+H2 (volume flow ratio of N2:H2=7:1), to thereby produce a soft magnetic material having low cost, excellent mechanical properties, and excellent magnetic properties.

[0043] The density of the obtained soft magnetic material was 7.57 g / cm 3 , the tensile strength was 473 MPa, the yield strength was 326 MPa, the hardness was 70 HRB, the maximum permeability was 2.42 mH / m, the saturation magnetic flux density was 1.69 T, and the coercive force was 176 A / m.

[0044] Example 2

[0045] The mixed powder of 1.60% of phosphorus tri-iron (particle size D50 is 25 μm), 0.6% of paraffin powder (particle size D50 is 50 μm), and the rest of iron powder (particle size D50 is 60 μm) is mixed in a mixer at 20 revolutions per minute for 4 hours, and then formed under a forming pressure of 550 MPa and a pressure maintaining time of 5 seconds. After that, the pre-sintering is carried out in a sintering furnace under the atmosphere of N2+H2 (volume flow ratio of N2:H2=7:1) at 850°C for 1.5 hours. After taking out, the re-pressing is carried out in a mold under a pressure of 680 MPa and a pressure maintaining time of 8 seconds, and the re-pressing reduction rate is 5%. During the re-pressing, the gap between the pre-sintered blank and the mold is controlled to be 8 wires. Then, the sintering is carried out in the sintering furnace under the atmosphere of N2+H2 (volume flow ratio of N2:H2=7:1) at 1100°C for 9 hours, so as to prepare a soft magnetic material with low cost, excellent mechanical properties and magnetic properties.

[0046] Figure 1 With Figure 2 The metallographic graph of the soft magnetic material prepared in Example 2 is shown in the figure, from which it can be seen that the material has high density and low porosity.

[0047] Figure 3 The magnetic performance curve graph of the soft magnetic material prepared in Example 2 is shown in the figure.

[0048] The density of the obtained soft magnetic material is 7.61 g / cm 3 , the tensile strength is 500 MPa, the yield strength is 350 MPa, the hardness is 75 HRB, the maximum permeability is 2.72 mH / m, the saturation magnetic induction is 1.73 T, and the coercive force is 170 A / m.

[0049] Example 3

[0050] The mixed powder of 1.60% of phosphorus tri-iron (particle size D50 is 25 μm), 0.6% of paraffin powder (particle size D50 is 50 μm), and the rest of iron powder (particle size D50 is 60 μm) is mixed in a mixer at 20 revolutions per minute for 4 hours, and then formed under a forming pressure of 550 MPa and a pressure maintaining time of 5 seconds. After that, the pre-sintering is carried out in a sintering furnace under the atmosphere of N2+H2 (volume flow ratio of N2:H2=7:1) at 850°C for 1.5 hours. After taking out, the re-pressing is carried out in a mold under a pressure of 680 MPa and a pressure maintaining time of 8 seconds, and the re-pressing reduction rate is 5%. During the re-pressing, the gap between the pre-sintered blank and the mold is controlled to be 8 wires. Then, the sintering is carried out in the sintering furnace under the atmosphere of N2+H2 (volume flow ratio of N2:H2=7:1) at 1100°C for 9 hours, so as to prepare a soft magnetic material with low cost, excellent mechanical properties and magnetic properties.

[0051] The density of the obtained soft magnetic material is 7.61 g / cm 3513 MPa, yield strength of 378 MPa, hardness of 73 HRB, maximum permeability of 2.48 mH / m, saturation magnetic induction of 1.68 T, and coercive force of 175 A / m.

[0052] Comparative Example 1

[0053] Other conditions are the same as those in Example 1, except that no pre-sintering and re-pressing are performed, and the green compact is directly sintered in a N2+H2 atmosphere of a sintering furnace at 1200℃ for 9h to prepare a low-cost soft magnetic material. The density of the obtained soft magnetic material is 7.06 g / cm 3 , tensile strength of 452 MPa, yield strength of 310 MPa, hardness of 46 HRB, maximum permeability of 1.39 mH / m, saturation magnetic induction of 1.38 T, and coercive force of 190 A / m, Figure 4 is a metallographic phase diagram of the soft magnetic material prepared in Comparative Example 1, and the black color is a pore. It can be seen from the diagram that the density is obviously reduced, Figure 5 is a magnetic performance curve diagram of the soft magnetic material prepared in Comparative Example 1.

[0054] Comparative Example 2

[0055] Other conditions are the same as those in Example 1, except that the mass fraction of the phosphide iron in the mixed powder is 2.00%;

[0056] The density of the obtained soft magnetic material is 7.24 g / cm 3 , tensile strength of 328 MPa, yield strength of 216 MPa, hardness of 50 HRB, maximum permeability of 2.23 mH / m, saturation magnetic induction of 1.56 T, and coercive force of 172 A / m.

[0057] Comparative Example 3

[0058] Other conditions are the same as those in Example 2, except that the particle size D50 of the iron powder in the mixed powder is 160 μm. The density of the obtained soft magnetic material is 7.10 g / cm 3 , tensile strength of 482 MPa, yield strength of 316 MPa, hardness of 68 HRB, maximum permeability of 1.57 mH / m, saturation magnetic induction of 1.40 T, and coercive force of 179 A / m. Figure 6 is a magnetic performance curve diagram of the soft magnetic material prepared in Comparative Example 3.

[0059] Comparative Example 4

[0060] Other conditions are the same as those in Example 2, except that the gap between the pre-sintered compact and the mold is controlled to be 2 wires during re-pressing. The density of the obtained soft magnetic material is 7.17 g / cm 3, the tensile strength is 412 MPa, the yield strength is 286 MPa, the hardness is 61 HRB, the maximum permeability is 1.84 mH / m, the saturation magnetic induction is 1.52 T, and the coercive force is 184 A / m.

[0061] Comparative Example 5

[0062] The other conditions are the same as in Example 1, except that the pre-sintering temperature is 1000°C, and the density of the soft magnetic material obtained is 7.18 g / cm 3 , the tensile strength is 453 MPa, the yield strength is 336 MPa, the hardness is 58 HRB, the maximum permeability is 2.12 mH / m, the saturation magnetic induction is 1.53 T, and the coercive force is 178 A / m.

[0063] Comparative Example 6

[0064] The other conditions are the same as in Example 2, except that the sintering time is 5 h, and the density of the soft magnetic material obtained is 7.12 g / cm 3 , the tensile strength is 366 MPa, the yield strength is 261 MPa, the hardness is 65 HRB, the maximum permeability is 1.61 mH / m, the saturation magnetic induction is 1.41 T, and the coercive force is 196 A / m.

Claims

1. A method for producing a low-cost high-magnetic-property powder metallurgy soft magnetic material, characterized by: The phosphorus tri-iron, paraffin powder and iron powder are mixed to obtain a mixed powder, the mixed powder is pressed to obtain a green compact, the green compact is pre-sintered to obtain a pre-sintered compact, the pre-sintered compact is re-pressed and then sintered, and thus a powder metallurgy soft magnetic material is obtained; The particle size D50 of the phosphorus tri-iron is 15-50 μm, the particle size D50 of the paraffin powder is 25-75 μm, and the particle size D50 of the iron powder is 55-150 μm; The pre-sintering is performed in a mixed atmosphere of N2 and H2, the temperature of the pre-sintering is 780-850 ℃, and the time of the pre-sintering is 1-2 h; During the pre-sintering, the volume flow ratio of N2 to H2 is 5-7:

1. The re-pressing pressure is 650-750 MPa, and the reduction rate is 3%-5%. During the re-pressing, the gap between the pre-sintered compact and the mold is controlled to be 5-10 μm. The sintering is performed in a mixed atmosphere of N2 and H2, the temperature of the sintering is 1100-1250 ℃, and the time of the sintering is 6-9 h. During the sintering, the volume flow ratio of N2 to H2 is 5-7:

1.

2. The method according to claim 1, wherein the method is characterized by: The mixed powder comprises, by mass percentage, 1.45-1.87% of phosphorus tri-iron, 0.6-0.8% of paraffin powder, and the rest of iron powder.

3. The method according to claim 1 or 2, characterized in that: The particle size D50 of the phosphorus tri-iron is 25-30 μm, the particle size D50 of the paraffin powder is 35-50 μm, and the particle size D50 of the iron powder is 60-100 μm.

4. The method according to claim 1 or 2, characterized in that: The mixing is performed in a mixer, the rotation speed of the mixer is 20-30 r / min, and the mixing time is 2-4 h.

5. The method according to claim 1 or 2, characterized in that: The pressing pressure is 500-600 MPa, and the pressure maintaining time is 4-8 s.

6. The method according to claim 1 or 2, characterized in that: The pressure maintaining time during the re-pressing is 5-10 s.

7. The method according to claim 1 or 2, characterized in that: Density of the powder metallurgical soft magnetic material ≥ 7.34 g / cm3 3 Tensile strength ≥ 350 MPa, yield strength ≥ 220 MPa, hardness 45-80 HRB, maximum magnetic permeability ≥ 2.3 mH / m, saturation magnetic induction ≥ 1.6 T, coercivity ≤ 180 A / m.

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