CN101901657B - Sintered NdFeB (neodymium iron boron) permanent magnet material and preparation method thereof - Google Patents

Abstract

The invention provides an NdFeB (neodymium iron boron) permanent magnet material, which contains an NdFeB alloy and a cobalt ferrite. The invention also provides a method for preparing the NdFeB permanent magnet material. The method comprises the following steps of: performing magnetic field-oriented compression moulding on a mixture of the NdFeB alloy and the cobalt ferrite; and sintering and tempering the mixture under the condition of vacuum or inert gas protection so as to obtain the NdFeB permanent magnet material. The method can prepare a sintered NdFeB permanent magnet material which has the advantages of corrosion resistance and high working temperature.

Description

A kind of sintered NdFeB permanent magnet material and preparation method thereof

technical field

The invention relates to a sintered NdFeB permanent magnet material and a preparation method thereof.

Background technique

In the 1980s, Japan's Sumitomo Metal Corporation invented NdFeB permanent magnet materials for the first time. Since its inception, NdFeB permanent magnet materials have been widely used in automobiles, computers, electronics, machinery, energy, medical equipment, etc. Numerous fields. In particular, NdFeB has a high cost performance ratio, so it has become an ideal material for the manufacture of magnetic functional devices with high efficiency, small size, and light weight, and has had a revolutionary impact on many application fields. But with the continuous expansion of application fields and technological progress. The performance requirements for permanent magnet materials are increasing day by day, in terms of operating temperature and corrosion resistance.

Since the NdFeB permanent magnet material itself contains highly reactive rare earth elements, it makes NdFeB easy to be oxidized and corroded in the environment, and in the case of use without any surface treatment, the corrosion occurs in a small amount of acid Or the presence of alkaline substances or water tends to carry out from the surface, producing rust, which will cause the degradation and passivity of the magnetism. Also, where such rusted magnets are embedded in magnetic circuits and the like, the rust spreads, potentially contaminating surrounding components. At the same time, since the Curie temperature of sintered NdFeB is only 310°C, the temperature coefficient is relatively large, and the temperature coefficient of remanence is generally -0.09 to -0.12%. The ratio of degrees is called the temperature coefficient of remanence. The larger the temperature coefficient of remanence, the better the high temperature resistance of the material. However, ordinary magnetic materials can only work below 160°C. Therefore, with the increasing demand for rare earth permanent magnets in automobile starter motors and electric vehicle motors, new challenges are posed to the high temperature resistance and corrosion resistance of permanent magnets.

A technical solution for improving the corrosion resistance of sintered NdFeB permanent magnet materials is disclosed in the prior art. The method comprises mixing NdFeB alloy powder with 4 at% of the sintered NdFeB powder to obtain a mixed powder, and then mixing The mixed powder is pressed and molded in the presence of protective gas, and then sintered and magnetized to obtain a sintered NdFeB permanent magnet material with cobalt added. Although the sintered NdFeB permanent magnet material improves the corrosion resistance of the permanent magnet, But the permanent magnet material is not resistant to high temperature, and the working temperature is only 170°C.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the shortcomings that the corrosion resistance and high temperature resistance of permanent magnet materials in the prior art cannot be improved at the same time, and to provide a sintered NdFeB permanent magnet with good corrosion resistance and high temperature resistance. Magnetic materials and methods for their preparation.

In order to achieve the above object, the present invention provides a sintered NdFeB permanent magnet material, which contains NdFeB alloy and cobalt ferrite.

The present invention also provides a preparation method of NdFeB permanent magnet material, the method comprises carrying out magnetic field orientation compression molding of the mixture of NdFeB alloy and cobalt ferrite, and then sintering under the condition of vacuum or inert gas protection and tempering to obtain NdFeB permanent magnet materials.

The sintered NdFeB permanent magnet material that can be prepared by the method for preparing the NdFeB permanent magnet material provided by the invention has good corrosion resistance and high temperature resistance.

Detailed ways

The NdFeB permanent magnet material provided by the invention contains NdFeB alloy and cobalt ferrite.

Through a large number of experiments, the inventor found that by adding cobalt ferrite particles and making them uniformly distributed at the grain boundaries of NdFeB, the excessive growth of NdFeB crystal grains and magnetic domain sizes can be suppressed, that is, the pinning effect , so as to effectively increase the working temperature, and the addition of cobalt itself can form a stable intergranular additional structure with neodymium, increase corrosion resistance and have a higher working temperature sintered NdFeB permanent magnet material. In the present invention, the content of heavy metal cobalt is reduced to a certain extent compared with normal addition due to the addition of nano-cobalt ferrite, and the cost is reduced, and an appropriate amount of oxygen in cobalt ferrite can improve the high temperature resistance of permanent magnet materials, and at the same time due to The presence of cobalt ferrite greatly improves the corrosion resistance of sintered NdFeB permanent magnet materials.

Wherein, in the present invention, the content of cobalt ferrite is 0.1-20% by weight of the NdFeB alloy, preferably 0.5-10%.

And the neodymium-iron-boron alloy mentioned in the present invention has following composition:

Nd _a Re _b Fe _(100-abcd) B _c M _d ,

Wherein, a, b, c, d represent the atomic percentage. 1≤a≤10, 5≤b≤12, 5≤d≤8, 0≤d≤15, the balance is Fe, Re is at least one of Pr, Dy, Tb, Ho, Gd, La, Ce, Y element, and M is one or more selected from Co, Al, Cu, Zr, Ga, Nb, Mo.

The added cobalt ferrite is uniformly dispersed in the host material, and the general formula of the cobalt ferrite is Con _{Fe 3 -n} O ₄ , wherein the value of n is any value from 0.1 to 2.0.

The average particle diameter of the cobalt ferrite is preferably 20-60 nm. Cobalt ferrite particles are uniformly distributed at the grain boundary of the NdFeB main phase through a proper process, so as to form a pinning effect. The content of cobalt should not exceed 20% of the total weight of sintered NdFeB, if it exceeds, the coercive force will be severely reduced.

In order to achieve the above object, the present invention also provides a method for preparing a sintered NdFeB permanent magnet, the method comprising: preparing an alloy ingot, wherein the alloy ingot includes an NdFeB alloy, and crushing the alloy ingot into powder Add cobalt ferrite powder, orient the powder in an external magnetic field, and press the mixed powder into a block compact, and then sinter and temper under vacuum or inert gas protection conditions to obtain NdFeB permanent magnets Material.

The process of manufacturing NdFeB permanent magnet materials by sintering method generally includes formulation, smelting, crushing, powder making, magnetic powder orientation pressing molding, vacuum sintering, machining and electroplating. In the present invention, it is necessary to mix the NdFeB alloy powder and the cobalt ferrite powder uniformly after powder making and before magnetic powder orientation pressing.

Specific steps are as follows:

1) Crushing and grinding the NdFeB alloy to obtain alloy material powder. The method of crushing the NdFeB alloy can be hydrogen explosion method or the method of crushing by a crusher, and the method of powder making can be by jet mill or protective atmosphere ball milling to make powder with an average diameter of 2-10 microns.

The NdFeB alloy can be NdFeB ingot alloy and NdFeB quick-setting sheet, which can be obtained commercially, or can be made of NdFeB ingot alloy by casting process, or made by quick-setting sheet process NdFeB quick-setting flakes, its composition is:

Nd _a Re _b Fe _(100-abcd) B _c M _d ,

Wherein, a, b, c, d represent the atomic percentage. 1≤a≤10, 5≤b≤12, 5≤d≤8, 0≤d≤15, the balance is Fe, Re is at least one of Pr, Dy, Tb, Ho, Gd, La, Ce, Y element, and M is one or more selected from Co, Al, Cu, Zr, Ga, Nb, Mo.

The method for making ingot alloys by the casting process is well known to those skilled in the art. The smelted alloy melt can be cast into a water-cooled copper mold. The NdFeB ingot alloy is mainly composed of columnar crystals. Separated by thin layers of neodymium-rich phase, the distance between adjacent neodymium-rich phase layers is about 100-1500 microns.

The method for making quick-setting flakes by the quick-setting flake process is well known to those skilled in the art. The molten alloy after smelting can be poured onto the surface of a rotating copper roller, and the surface rotation speed of the copper roller is about 1-2 m/s , the alloy melt is cooled rapidly to form flakes with a thickness of 0.2-0.5 mm and a width of different sizes, and the width of the columnar crystals in the flakes is 5-25 microns.

The method of hydrogen crushing through a hydrogen crushing furnace is well known to those skilled in the art. For example, put a neodymium-iron-boron alloy with a fresh surface into a stainless steel container, and after vacuuming, fill it with high-purity hydrogen to reach about one atmospheric pressure. After 20-30 minutes, you will hear the popping sound of the alloy and the temperature of the container rises. This is because the alloy forms a hydride and bursts after absorbing hydrogen, and then vacuum dehydrogenates at 400-600°C for 2-10 hours.

The method of crushing NdFeB ingot alloy or NdFeB quick-setting flakes through a crusher is well known to those skilled in the art, for example, a jaw crusher is used for primary crushing, and then an intermediate crusher is used for intermediate crushing.

The jet milling method is well known to those skilled in the art, using airflow to accelerate the powder particles to supersonic speed, causing them to collide with each other and break up.

2) Mixing the NdFeB alloy powder and cobalt ferrite uniformly to obtain mixed powder.

The cobalt ferrite should be dispersed first, and the added amount is 0.5-10% of the total weight of the NdFeB main body powder. The average particle diameter of the cobalt ferrite is 10-150 nm, and preferably the average particle diameter of the ferrite is 20-60 nm.

Preferably, the preparation method of the mixture comprises mixing the NdFeB alloy and the cobalt ferrite in the presence of an antioxidant, or mixing the NdFeB alloy and the cobalt ferrite in the presence of an antioxidant and a lubricant. Mixing; the amount of the antioxidant is 0.1-5% by weight of the host material, and the amount of the lubricant is 0-5% by weight of the host material. The antioxidant is not particularly limited, and the type and usage of the antioxidant are known to those skilled in the art, such as polyethylene oxide alkyl ether, polyethylene oxide monofatty ester, polyethylene oxide olefin base One or more of the ethers can be specifically antioxidants produced by Shenyang Chemical Industry. The lubricant is not particularly limited, and the types and usages of the lubricant are known to those skilled in the art, such as gasoline, oleic acid, stearic acid, polyalcohol and polyethylene glycol, sorbitan, glycerol stearate One or more of the esters.

The mixing method is well known to those skilled in the art, and can be uniformly mixed in a mixer.

3) Magnetic field orientation compression molding of the obtained mixed powder to obtain a parison.

The method of pressing the mixed powder into a blank in a magnetic field is a conventional method. Preferably, it is pressed into a parison in a magnetic field orientation forming press. The conditions are that the forming orientation magnetic field is 1.2-3T, and the forming blank is subjected to isostatic pressing Press 10-200 MPa for 10-60 seconds. Further increasing the magnetic field can improve the orientation degree of the magnetic powder. The compression molding of the parison is completed in a completely sealed glove box, so that the magnetic powder is isolated from the air. On the one hand, it avoids the danger of fire due to oxidation and heat of the magnet, and on the other hand, it reduces the oxygen content of the final magnet.

4) The parison is sintered and tempered under the condition of vacuum or inert gas protection to prepare the NdFeB permanent magnet material.

The method of sintering and tempering is a conventional method. Preferably, the parison is sintered at 1030-1120°C for 2-8 hours under the condition of vacuum or inert gas protection, and then tempered at 800-920°C for 1-3 hours. , and then tempered at 500-650°C for 2-4 hours to obtain sintered NdFeB permanent magnet materials. A second tempering can further increase the coercive force. Since the melting point of the cobalt ferrite is above 1200° C., the cobalt ferrite will not decompose and melt when sintered at the temperature.

The inert gas may be any gas that does not participate in the reaction, preferably one or more of helium, argon, neon, krypton, and xenon.

Example 1

This embodiment is used to illustrate the NdFeB permanent magnet material provided by the present invention and its preparation method.

1) NdFeB alloy adopts quick-setting sheet technology, the surface line speed of copper roller is 1.5 m/s, the composition is (PrNd) _10.61 Dy _3.5 Fe _77.55 B _5.87 Co _1.68 Al _0.5 Cu _0.16 Ga _0.13 (a%), strip The sheet thickness is about 0.3mm.

2) Hydrogen crushing in a hydrogen crushing furnace, absorb hydrogen to saturation at room temperature, dehydrogenate at 550°C for 6 hours to make hydrogen crushed powder, and then use jet mill under nitrogen protection to make powder with an average particle diameter of 3.5 microns.

3) Add CoFe ₂ O ₄ with an average particle diameter of 50 nanometers to the NdFeB alloy powder, and add an antioxidant (produced by Shenyang Chemical). The dosage of the cobalt ferrite is 1% of the weight of the NdFeB alloy powder, and the dosage of the antioxidant poly is 0.5% of the weight of the NdFeB alloy powder.

4) In a glove box filled with nitrogen, the mixed powder is pressed into a blank by a magnetic field press, the forming orientation magnetic field strength is 1.6T, the pressure is 100 MPa, and the pressing time is 30 seconds.

5) The compacted blank is sintered in a vacuum sintering furnace with a vacuum degree of 2×10 ^-2 Pa, sintered at 1080°C for 3 hours, and then undergoes a tempering heat treatment at 850°C for 2 hours, and a second tempering at 500°C Fire for 3 hours to obtain NdFeB permanent magnet material T1.

Comparative example 1

In this comparative example, nano-cobalt ferrite is not added, and the rest of the process is exactly the same as that of Example 1 to obtain the NdFeB permanent magnet material CT1.

Example 2

This embodiment is used to illustrate the NdFeB permanent magnet material provided by the present invention and its preparation method.

Carry out as in Example 1, the difference is that Co ₂ Fe ₁ O ₄ cobalt ferrite is used to replace the cobalt ferrite in Example 1, and the amount of cobalt ferrite added is 5% of the weight of the NdFeB alloy powder. %. The NdFeB permanent magnet material T2 was prepared.

Example 3

This embodiment is used to illustrate the NdFeB permanent magnet material provided by the present invention and its preparation method.

Carry out according to Example 1, except that the average particle diameter of CoFe ₂ O ₄ is 100 nanometers to prepare NdFeB permanent magnet material T3.

Example 4

This embodiment is used to illustrate the NdFeB permanent magnet material provided by the present invention and its preparation method.

Carry out according to Example 1, except that the amount of CoFe ₂ O ₄ is 10% by weight of the NdFeB alloy, and the NdFeB permanent magnet material T4 is obtained.

Comparative example 2

This embodiment is used to illustrate the NdFeB permanent magnet material provided by the present invention and its preparation method.

Sample T5 was prepared according to the method described in Example 1, except that the cobalt ferrite in Example 1 was replaced by Co, wherein the average particle diameter of Co was 50 nanometers, and the NdFeB permanent magnet material CT2 was obtained.

Example 5-10

These examples are used to detect the magnetic properties of the NdFeB permanent magnet material T1-4 prepared by the present invention and the NdFeB permanent magnet material CT1 and CT2 prepared by Comparative Example 1-2. The NIM200C measurement system for different temperature curves of magnetic materials measures the magnetic properties of the test samples.

No implementation corresponding to the exclusive right of preparation method without antioxidant

Corrosion Test

The prepared NdFeB permanent magnet material T1-4 and the NdFeB permanent magnet material prepared in Comparative Example 1-2 were made into cylindrical samples with a diameter of 10 mm and a length of 7 mm. -70CP type unsaturated accelerated life testing machine for HAST test, the test conditions are 130 ℃, humidity 95%, steam pressure 2.7bar, time is 10 days, T1-4 and CT1, CT2 lost magnet mass is recorded in the attached table.

Maximum working temperature test

The prepared NdFeB permanent magnet material T1-4, as well as CT1 and CT2 are made into cylindrical samples with a diameter of 10mm and a length of 7mm. The NIM200C measuring system for different temperature curves of permanent magnet materials of the China Institute of Metrology is used to test the samples. From 60°C, the unit is 2°C, and when it reaches a certain temperature, the intrinsic demagnetization will bend from a straight line, indicating that the maximum working temperature of the NdFeB material has been reached. The test results are shown in Table 1:

Table 1

project W _loss (mg/cm2) Inflection point temperature T1 2.1 190°C T2 1.8 186°C T3 2.5 186°C T4 1.5 188°C T5 2.0 182°C

CT1 8.2 160°C CT2 2.7 170℃

As can be seen from Table 1, the loss magnet mass of the sintered NdFeB permanent magnet material sample T1 prepared by Example 1 provided in the present invention is 2.1, while the loss magnet mass of CT2 prepared in Comparative Example 2 is 2.7, The inflection point temperature of T1 is 190°C, and the inflection point temperature of CT2 is 170°C. It can be seen that the sintered NdFeB permanent magnet material provided by the present invention has the advantages of good corrosion resistance and high temperature resistance.

Claims (10)

1. sintered Nd-Fe-B permanent magnetic material, this permanent magnetic material contains Nd Fe B alloys and Conjugate ferrite, and wherein, the content of said Conjugate ferrite is the 0.5-10 weight % of said Nd Fe B alloys.

2. sintered Nd-Fe-B permanent magnetic material according to claim 1, wherein, the average particulate diameter of said Conjugate ferrite is the 10-150 nanometer.

3. sintered Nd-Fe-B permanent magnetic material according to claim 1, wherein, said Conjugate ferrite is Co _nFe _3-nO ₄, wherein the n value is 0.1～2.0 arbitrary value.

4. sintered Nd-Fe-B permanent magnetic material according to claim 1, wherein, said Nd Fe B alloys has the composition shown in the following formula:

Nd _aRe _bFe _{(100-a-b-c-d)}B _cM _d

Wherein, a, b, c, d represent atomic percentage, 1≤a≤10; 5≤b≤12,5≤c≤8,0≤d≤15; Surplus is Fe, and Re is at least a element among Pr, Dy, Tb, Ho, Gd, La, Ce, the Y, and M is selected among Co, Al, Cu, Zr, Ga, Nb, the Mo one or more.

5. the preparation method of the described sintered Nd-Fe-B permanent magnetic material of claim 1; This method comprises carries out magnetic field orientating compression moulding with the mixture that contains Nd Fe B alloys and Conjugate ferrite; Under the condition of vacuum or inert gas shielding, carry out sintering and tempering then; Obtain Nd-Fe-Bo permanent magnet material; Wherein, the preparation process of mixture of said Nd Fe B alloys and Conjugate ferrite comprises Nd Fe B alloys and Conjugate ferrite is being mixed in the presence of the oxidation inhibitor or in the presence of oxidation inhibitor and lubricant; The consumption of said oxidation inhibitor is the 0.1-5 weight % of said Nd Fe B alloys, and the consumption of said lubricant is the 0-5 weight % of said Nd Fe B alloys.

6. according to the preparation method of the said sintered Nd-Fe-B permanent magnetic material of claim 5, wherein, the consumption of said Conjugate ferrite is the 0.5-10 weight % of said Nd Fe B alloys.

7. the preparation method of sintered Nd-Fe-B permanent magnetic material according to claim 5, wherein, said Conjugate ferrite is Co _nFe _3-nO ₄Wherein the n value is 0.1～2.0 arbitrary value.

8. the preparation method of sintered Nd-Fe-B permanent magnetic material according to claim 5, wherein, said Nd Fe B alloys has the composition shown in the following formula:

Nd _aRe _bFe _{(100-a-b-c-d)}B _cM _d

Wherein, a, b, c, d represent atomic percentage, 1≤a≤10; 5≤b≤12,5≤c≤8,0≤d≤15; Surplus is Fe, and Re is at least a element among Pr, Dy, Tb, Ho, Gd, La, Ce, the Y, and M is selected among Co, Al, Cu, Zr, Ga, Nb, the Mo one or more.

9. the preparation method of sintered Nd-Fe-B permanent magnetic material according to claim 5, wherein, the average particulate diameter of said Conjugate ferrite is the 10-150 nanometer, the average particulate diameter of said Nd Fe B alloys is the 2-5 micron.

10. the preparation method of sintered Nd-Fe-B permanent magnetic material according to claim 5, wherein, the condition of said magnetic field orientating compression moulding comprises that magnetic field intensity is 1.2-3.0T, and pressure is the 10-200 MPa, and the press time is 10-60 second; The condition of said sintering comprises that sintering temperature is 1030-1120 ℃, and sintering time is 2-8 hour; Said tempering comprises double tempering, and the condition of tempering for the first time comprises that temperature is 800-920 ℃, and tempering time is 1-3 hour; Tempered condition comprises that temperature is 500-650 ℃ for the second time, and tempering time is 2-4 hour.