WO2022191349A1 - Method for manufacturing hot-deformed permanent magnet - Google Patents

Abstract

The present invention relates to a method for manufacturing a hot-deformed permanent magnet, comprising the steps of: preparing NdFeB magnetic powder; mixing the NdFeB magnetic powder and ReF₃ (Re is a rare earth metal other than the rare earth metals contained in NdFeB) powder; hot press-forming a mixture in which the ReF3 powder is attached to the surface of the NdFeB magnetic powder; hot deforming a hot press-formed product; performing primary post-heat treatment on the hot-deformed anisotropic permanent magnet; and performing secondary post-heat treatment on the anisotropic permanent magnet that has been primary post-heat treated.

Description

Manufacturing method of hot-deformed permanent magnet

The present invention relates to a method for manufacturing a hot-deformed permanent magnet, by mixing NdFeB magnetic powder and ReF ₃ powder to adhere ReF ₃ powder to the surface of NdFeB magnetic powder, first hot pressing and second hot deformation ) and 1st and 2nd post-heat treatment to make the crystal grains of the columnar grains uniform, increase the c-axis orientation, and produce a magnet with high coercive force and high maximum energy or residual magnetic flux density. it's about

Demand for NdFeB sintered magnets for motors such as hybrid cars is gradually increasing, and it is required to further increase the coercive force (Hcj). In order to increase the coercive force (Hcj) of the NdFeB sintered magnet, a method of substituting a part of Nd with Dy or Tb is known, but the resources of Dy and Tb are scarce and ubiquitous. The problem is that the residual magnetic flux density (Br) or the maximum energy product ((BH)max) of the magnet decreases.

Recently, when Dy or Tb is attached to the surface of a NdFeB sintered magnet by sputtering and heated to 700 to 1000°C, the coercive force (Hcj) can be increased without substantially lowering the residual magnetic flux density (Br) of the magnet. was found to be

Dy and Tb adhering to the magnet surface are sent to the inside of the sintered body through the grain boundaries of the sintered body, and diffuse from the grain boundary to the inside of each particle of the main phase R ₂ Fe ₁₄ B (R is a rare earth element) (grain boundary diffusion) ). At this time, since the R-rich phase at the grain boundary is liquefied by heating, the diffusion rate of Dy or Tb in the grain boundary is much faster than the diffusion rate from the grain boundary to the inside of the columnar grains.

By adjusting the heat treatment temperature and time using this difference in diffusion rate, a state with high Dy or Tb concentration can be realized only in the region (surface region) extremely close to the grain boundaries of the columnar grains in the sintered body throughout the sintered body. have. Since the coercive force (Hcj) of the NdFeB sintered magnet is determined according to the state of the surface region of the columnar particles, the NdFeB sintered magnet having crystal grains with high Dy or Tb concentrations in the surface region has a high coercive force. Also, as the concentration of Dy or Tb increases, the residual magnetic flux density (Br) of the magnet decreases, but since such a region is only the surface region of each columnar particle, the residual magnetic flux density (Br) of the columnar grains as a whole hardly decreases. does not In this way, NdFeB sintered magnets with high coercive force (Hcj) and residual magnetic flux density (Br) that do not substitute Dy or Tb and high-performance magnets that do not change much can be manufactured. This method is called grain boundary diffusion.

On the other hand, the method of manufacturing an anisotropic neodymium-based permanent magnet is usually produced by metal melting, rapid cooling, milling, magnetic powder is formed while applying a magnetic field, followed by sintering at a high temperature (1000 ° C. or higher) and post-heat treatment. manufactured through In this process, as another method of securing the high coercive force of the magnetic powder, there is a method of refining the size of the crystal grains to the size of a single sphere.

It is to pulverize the crystal grains of the magnetic powder into small pieces by a physical method to make them fine. There is also a need to maintain the magnetic powder of crystal grains until the final product is produced.

However, in the process of manufacturing finely pulverized magnetic powder having a fine particle size with a magnet, due to high heat treatment of over 1000 °C, the growth of fine grains occurs in the surface portion, which is a portion with high energy and many defects, and the grain size of the surface portion Since the nucleation of reverse magnetic domains in the particles cannot be suppressed due to the dialogue, the coercive force is significantly lowered, and it is difficult to obtain crystal grains aligned in one direction due to the non-uniform particle size, so the residual magnetic flux density is also significantly lowered.

[Prior art literature]

[Patent Literature]

(Patent Document 1) [Patent Document 1] Korea Patent Publication No. 10-2015-0033423 (2015.04.01)

(Patent Document 2) [Patent Document 2] Japanese Patent Laid-Open No. 62-074048 (April 4, 1987)

(Patent Document 3) [Patent Document 3] Korean Patent No. 10-1447301 (2014.09.26)

The present invention relates to a method of manufacturing a hot deformable permanent magnet, by mixing NdFeB magnetic powder and ReF ₃ powder to adhere ReF ₃ powder to the surface of NdFeB magnetic powder, first hot pressing and second hot deformation ) and 1st and 2nd post-heat treatment to make the crystal grains of the columnar grains uniform, increase the degree of c-axis orientation, and produce a magnet with high coercive force and high maximum energy or residual magnetic flux density. provide

In order to achieve the above object, the method for manufacturing a hot-deformed permanent magnet according to the present invention comprises the steps of preparing NdFeB magnetic powder; mixing the NdFeB magnetic powder and ReF ₃ (Re is other rare earth metals except for the rare earth included in NdFeB) powder; hot pressing the mixture in which the ReF3 powder is attached to the surface of the NdFeB magnetic powder; hot deformation of the isotropic permanent magnet formed by the hot pressing; first post-heating the hot-deformed anisotropic permanent magnet; Secondary post-heat treatment of the anisotropic permanent magnet subjected to the first post-heat treatment;

In the method for manufacturing a hot-deformed permanent magnet according to the present invention, the NdFeB magnetic powder is a melt spun powder, and the particle size of the NdFeB magnetic powder is 100 to 300 μm.

The NdFeB magnetic powder is Nd _30.1 Fe _bal. It is characterized in that it has a composition ratio of Co _5.0 Ga _0.6 B _0.9 .

In the method of manufacturing a hot-deformed permanent magnet according to the present invention, the ReF ₃ powder is DyF ₃ and has a particle size of 50 to 150 nm.

In the method for manufacturing a hot-deformed permanent magnet according to the present invention, the Nd _30.1 Fe _bal. 1.0 to 2.0 parts by weight of the DyF ₃ powder is mixed with 100 parts by weight of Co _5.0 Ga _0.6 B _0.9 magnetic powder.

The step of hot pressing in the method for manufacturing a hot deformable permanent magnet according to the present invention is performed at a temperature of 600 to 800 °C for 10 to 30 minutes, a pressure of 50 to 100 MPa, and a density of 95% or more.

In the method for manufacturing a hot-deformed permanent magnet according to the present invention, the hot deformation is performed at a temperature of 700 to 850° C. for 5 to 20 minutes, a pressure of 50 to 200 MPa, and the height of the isotropic permanent magnet is 60 to It is characterized in that it deforms by 80%.

The step of hot deformation in the manufacturing method of the hot deformable permanent magnet according to the present invention; After that, the first post-heat treatment at 600 to 700 ° C. for 1 to 2 hours to remove residual stress and homogenize the tissue Tea post-heat treatment step; characterized in that it is added.

The first post-heat treatment step in the method for manufacturing a hot-deformed permanent magnet according to the present invention; Then, the second post-heat treatment at 600 to 800 ° C. for 1 to 2 hours to make magnetic homogenization, magnetic grain homogenization, sintering density maximization, magnetic phase / A secondary heat treatment step for controlling the fraction of the non-magnetic phase; characterized in that it is added.

According to the method for manufacturing a hot-deformed permanent magnet according to the present invention, a small amount of ReF ₃ (Re is other rare earth metals except for the rare earth contained in NdFeB) powder different from the NdFeB magnetic powder, which is the parent metal, is mixed in a small amount to increase the degree of freedom in the selection of the rare earth metal. can be raised

According to the method for manufacturing a hot-deformed permanent magnet according to the present invention, there is no need for a high-temperature sintering process through hot pressing and hot-deformation secondary pressurization, and the magnetization direction of crystal grains is aligned in one direction without applying a magnetic field due to hot deformation. Therefore, the magnetic field application process is unnecessary.

According to the method for manufacturing a hot-deformed permanent magnet according to the present invention, a magnet with a high coercive force and a high maximum energy or residual magnetic flux density by homogenizing the crystal grains of the columnar grains and increasing the c-axis orientation by performing primary and secondary heat treatment can be manufactured.

1 is a flowchart of a manufacturing method according to the present invention.

Figure 2 is before mixing Nd _30.1 Fe _bal. It is a photomicrograph of the powder of Co _5.0 Ga _0.6 B _0.9 composition.

3 is a micrograph of DyF3 powder before mixing.

4 is after mixing, Nd _30.1 Fe _bal. This is a photo of DyF3 powder attached to the surface of the powder having a composition of Co _5.0 Ga _0.6 B _0.9 .

5 is a crystal analysis data of an isotropic permanent magnet obtained by hot-pressing a mixture containing 1.6 parts by weight of DyF3 at 750°C and a pressure of 70 MPa for 20 minutes.

6 is a hot deformation process diagram at 70% deformation at the height of the permanent magnet, deformation rate 0.002 S ^-1 , deformation temperature 800° C., and deformation pressure 160 Mpa

7 is an X-ray diffraction analysis data showing that the grain alignment is improved after the primary heat treatment of the anisotropic permanent magnet.

8 is a pole figure in the (006) direction after the primary heat treatment of the anisotropic permanent magnet.

9 is a graph showing the thickness of the grain boundary after two-stage post-heat treatment of the anisotropic permanent magnet to which DyF ₃ powder is added and the composition of the grain boundary after the second-stage post-heat treatment of the anisotropic permanent magnet to which DyF ₃ powder is added.

Hereinafter, the present invention will be described in more detail. Hereinafter, "upper", "downward", "front" and "rear" and other directional terms are defined based on the state shown in the drawings.

[Manufacturing method]

(1) preparing rare earth NdFeB-based powder

The raw material, NdFeB-based powder (Nd _30.1 Fe _bal. Co _5.0 Ga _0.6 B _0.9 ) was melted, and the melt was injected into a cooling roll rotating at high speed to prepare a ribbon-shaped alloy. The ribbon-shaped ingot produced by the rolling process is milled with a stamp mill and pulverized to a size of about 100 to 300 μm to prepare neodymium-based magnetic powder.

(2) Preparation of ReF ₃ powder

ReF ₃ powder (Re is other rare earth metals except for the rare earth contained in NdFeB), and a particle size of 50 to 150 nm is prepared.

(3) Kneading of NdFeB-based powder and ReF ₃ powder

1.6 parts by weight of DyF ₃ powder having an average particle diameter of 100 nm-300 nm is mixed with 100 parts by weight of NdFeB-based powder (Nd _30.1 Fe _bal. Co _5.0 Ga _0.6 B _0.9 ), and kneaded in a 3D mixer for 1 hour.

(4) hot pressing

By kneading, a mixture having DyF ₃ powder adhered to the surface of the NdFeB powder (Nd _30.1 Fe _bal. Co _5.0 Ga _0.6 B _0.9 ) is hot-pressed at a temperature of 600 to 800° C. for 10 to 30 minutes, and a pressure of 50 to 100 MPa.

The hot pressing holding time is preferably 15 to 25 minutes, more preferably 20 minutes.

By the hot pressing, an isotropic permanent magnet having a density of 95% or more can be manufactured.

(5) hot deformation

The isotropic permanent magnet manufactured by the hot pressing is performed at a temperature of 700 to 850° C. for 5 to 20 minutes, a pressure of 50 to 200 MPa, and the height of the anisotropic permanent magnet is deformed by 60 to 80%.

The hot deformation holding time is preferably 8 to 12 minutes, more preferably 10 minutes.

By the hot deformation, an anisotropic permanent magnet can be manufactured.

(5) 1st post-heat treatment

A primary post-heat treatment is performed to remove residual stress and align the grains of the anisotropic permanent magnet manufactured by the hot deformation. The primary post-heat treatment is performed at 600 to 700° C. for 1 to 2 hours to remove residual stress and homogenize the tissue.

(5) Secondary post-heat treatment

After the first post-heat treatment, a second post-heat treatment is performed to equalize the magnetic structure, equalize the magnetic grain boundary, maximize the sintering density, and control the fraction of the non-magnetic phase. The secondary post-heat treatment is maintained in a high vacuum at 600 to 800° C. for 1 to 2 hours.

Hereinafter, a more specific embodiment of the present invention will be described with reference to a test example.

[ Example 1 ]

In this example, Nd _30.1 Fe _baL. 1.6 parts by weight of DyF ₃ powder having an average particle diameter of 100 nm-300 nm was mixed with a 200 μm average particle diameter powder having a composition of Co _5.0 Ga _0.6 B _0.9 and kneaded in a 3D mixer for 1 hour.

Figure 2 is Nd _30.1 Fe _{baL before mixing.} It is a photomicrograph of the powder of Co _5.0 Ga _0.6 B _0.9 composition. 3 is a micrograph of DyF ₃ powder before mixing. 4 is after mixing, Nd _30.1 Fe _bal. This is a photograph of DyF ₃ powder attached to the surface of the powder having a composition of Co _5.0 Ga _0.6 B _0.9 .

By kneading, Nd _30.1 Fe _bal. An isotropic permanent magnet having a density of 95% or more was prepared by hot pressing a mixture having DyF ₃ powder attached to the surface of the powder having a composition of Co _5.0 Ga _0.6 B _0.9 at 750° C. for 20 minutes at 70 Mpa pressure and in a high vacuum atmosphere.

FIG. 5 is crystal analysis data of an isotropic permanent magnet obtained by hot-pressing a mixture containing 1.6 parts by weight of DyF ₃ at 750° C. and a pressure of 70 MPa for 20 minutes. In FIG. 5 , it can be seen that DyF ₃ is added Nd ₂ Fe ₁₄ B ₁ phase analysis results through X-ray diffraction analysis.

<Table 1> Density according to hot pressing temperature

Table 1 is a table comparing the density according to the hot pressing temperature. It can be seen that when the hot pressing temperature is 700° C. or higher, the hot pressing density can be controlled to 96% or higher.

The isotropic permanent magnet manufactured by the hot pressing was hot deformed at 800° C. for 10 minutes at a pressure of 160 Mpa, in a high vacuum atmosphere at a deformation rate of 0.002 s ⁻¹ . A permanent magnet was manufactured.

6 is a hot deformation process diagram at 70% deformation at the height of a permanent magnet, a deformation rate of 0.002 S ^-1 , a deformation temperature of 800° C., and a deformation pressure of 160 Mpa.

A primary post-heat treatment is performed to remove residual stress and align the grains of the anisotropic permanent magnet manufactured by the hot deformation. For the first post-heat treatment, the hot-deformed anisotropic permanent magnet was maintained in high vacuum at 600°C for 1 hour.

7 is X-ray diffraction analysis data showing that the texture coefficient (I( ₀₀₆₎ /I ₍₁₀₅₎ ) value is increased and grain alignment is improved after the first heat treatment of the anisotropic permanent magnet.

8 is a pole figure data in the (006) direction after the primary heat treatment of the anisotropic permanent magnet. In FIG. 8 , it can be seen that crystal anisotropy has occurred in the (006) direction after the first post-heat treatment.

The crystalline phase of a hot-deformed permanent magnet having a tetragonal (tetragonal structure) structure according to the primary post-heat treatment is added for the purpose of grain boundary diffusion during hot deformation. (001) direction), the grain alignment is increased, and it is determined that the residual magnetization value is improved.

After the residual stress of the anisotropic permanent magnet is removed and the grains are aligned according to the first post heat treatment, a second post heat treatment is performed to equalize the magnetic structure, equalize the magnetic grain boundary, maximize the sintering density, and control the fraction of the non-magnetic phase. For the secondary post-heat treatment, the anisotropic permanent magnet subjected to the first post-heat treatment was maintained at 700° C. for 2 hours in a high vacuum.

During the secondary post-heat treatment, non-magnetic phase movement occurred between grains and grain boundaries, and magnetic structure homogenization, magnetic grain boundary homogenization, and sintering density improvement occurred, so that residual magnetization was greatly improved.

9 is a graph showing the thickness of grain boundaries after two-stage post heat treatment of an anisotropic permanent magnet to which DyF ₃ powder is added.

9 is a graph showing the thickness of the grain boundary after two-stage post-heat treatment of the anisotropic permanent magnet to which DyF ₃ powder is added and the composition of the grain boundary after two-stage post-heat treatment of the anisotropic permanent magnet to which DyF ₃ powder is added.

After the 1st and 2nd post-heat treatment, the grain boundary thickness was uniformly manufactured to a thickness of 2 nm, a stable crystal phase was formed, and a pinning force that inhibits the magnetic domain wall movement was generated due to an increase in the Nd-rich phase and a decrease in the Fe-rich phase, resulting in a high residual magnetization value. , the coercive force was improved.

<Table 2>

When comparing Examples 1, 2, and 3 with Comparative Groups 1 and 2 in Table 2, it can be seen that the residual magnetization (kG) value is significantly different depending on whether post-heat treatment 2 is performed. This is considered to improve the residual magnetization power by not only controlling the fraction of the non-magnetic phase between grains and grain boundaries in Post-Heat Treatment 2, but also improving the grain alignment.

Comparing Examples 1, 2, and 3, it was confirmed that the coercive force and residual magnetization values tend to decrease as the amount of DyF ₃ added, which is the added powder, decreased, and the highest magnetic properties were exhibited at 1.6 parts by weight of DyF ₃ added. .

The content conditions for Examples 2 and 3 and Comparative Examples 2 to 4 are shown in Table 2.

Examples 2 and 3 were prepared in amounts of 0.2 parts by weight and 0.4 parts by weight of the added powder DyF ₃ decreased by 0.2 parts by weight compared to Example 1, and the coercive force was 3 to 5 as compared to Example 1 as the amount decreased by 0.2 parts by weight. % tends to decrease, and the residual magnetization value tends to decrease by 0.5 to 1.2% as compared with Example Group 1 as the addition amount decreases by 0.2 parts by weight.

Comparing Comparative Group 1 with Example Groups 1, 2, and 3, the higher the amount of DyF ₃ added, the better the residual magnetization value and coercive force.

Comparing Example 1 and Comparative Group 2, the coercive force increased by 1.46 kOe and the residual magnetization by 2.84 kG after the post-heat treatment 2 process.

Comparing Comparative Group 3 and Example Group 1, when the post-heat treatment 2 temperature was increased by 100 °C, the coercive force decreased by 5.25 kOe and the residual magnetization decreased by 1.3 kG.

Comparing Comparative Group 4 and Example 1, the coercive force decreased by 10.65 kOe and the residual magnetization decreased by 3.1 kG when the post-heat treatment 2 temperature was increased by 200 °C.

Table 2 shows the presence or absence of secondary post-heat treatment and post-heat treatment temperature for Comparative Groups 2 to 4.

Claims (8)

1. preparing NdFeB magnetic powder;

   mixing the NdFeB magnetic powder and ReF ₃ (Re is other rare earth metals except for the rare earth included in NdFeB) powder;

   hot pressing the mixture in which the ReF3 powder is attached to the surface of the NdFeB magnetic powder;

   hot deformation of the hot press-formed sintered body;

   first post-heating the hot-deformed anisotropic permanent magnet;

   Method of manufacturing a hot-deformed permanent magnet comprising the; secondary post-heat treatment of the anisotropic permanent magnet subjected to the first post-heat treatment.
2. The method of claim 1,

   The NdFeB magnetic powder is Nd _30.1 Fe _bal. It is a melt spun powder having a composition ratio of Co _5.0 Ga _0.6 B _0.9 , and the particle size of the NdFeB magnetic powder is 100 to 300 μm.
3. The method of claim 1,

   The ReF ₃ powder is DyF ₃ , and a method of manufacturing a hot-deformed permanent magnet, characterized in that the particle size is 50 to 150 nm.
4. 4. The method of claim 3,

   The Nd _30.1 Fe _bal. Co _5.0 Ga _0.6 B _0.9 A method of manufacturing a hot deformable permanent magnet, characterized in that 1.0 to 2.0 parts by weight of the DyF ₃ powder is mixed with 100 parts by weight of the magnetic powder.
5. The method of claim 1,

   The hot pressing is performed at a temperature of 600 to 800° C. for 10 to 30 minutes, a pressure of 50 to 100 MPa, and a density of 95% or more.
6. The method of claim 1,

   The hot deformation is performed at a temperature of 700 to 850 °C for 5-20 minutes, a pressure of 50 to 200 MPa, and the height of the sintered body is deformed by 60 to 80%. Way.
7. The method of claim 1,

   The step of hot deformation; After that, the first post heat treatment step of removing residual stress by performing a first post heat treatment at 600 to 700 ° C. for 1 to 2 hours and homogenizing the tissue; A method of manufacturing a hot-deformed permanent magnet.
8. 8. The method of claim 7,

   The first post-heat treatment step; Then, a second post-heat treatment step for magnetic homogenization, magnetic grain homogenization, sintering density maximization, magnetic phase / non-magnetic phase fraction control by second post-heat treatment at 600 to 800 ° C. for 1 to 2 hours A method of manufacturing a hot-deformed permanent magnet, characterized in that it is added.

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