CN104952607A - Manufacturing method of light rare earth-copper alloy NdFeB magnet with grain boundary being low melting point - Google Patents

Abstract

The invention discloses a preparation method of an NdFeB magnet whose grain boundary is a light rare earth-copper alloy with a low melting point, and belongs to the field of rare earth permanent magnet materials. The preparation steps are as follows: crush the ingot of NdFeB main alloy with a ratio of 2:14:1 into 3-5 μm powder particles, add light rare earth-copper alloy with a weight fraction of 3-8% and an average particle size of 0.1-3 μm The powder is mixed evenly, and the product is obtained after magnetic field pressing, isostatic pressing, sintering and densification, and then heat treatment. The light rare earth-copper alloy is not only a liquid phase sintering aid, but also a grain boundary phase, and has good wettability with the 2:14:1 main phase. The advantage is that the light rare earth-copper alloy is evenly distributed on the grain boundary of the 2:14:1 main phase, which effectively hinders the exchange coupling between the 2:14:1 main phase grains, which is conducive to obtaining high coercive force and can Low-temperature sintering is realized, and high-temperature tempering heat treatment is omitted, which simplifies the process and saves energy.

Description

Preparation method of neodymium-iron-boron magnet whose grain boundary is light rare earth-copper alloy with low melting point

technical field

The invention belongs to the field of rare earth permanent magnet materials, and in particular relates to a preparation method of a neodymium-iron-boron magnet whose low melting point grain boundary is a light rare earth-copper alloy.

Background technique

The sintered NdFeB magnet known as the "Magnetic King" has become the core functional material in the fields of electric power, telecommunications, automobiles, computers, biomedicine and household appliances, and is being used in the manufacture of hundreds of kilowatts of electric (or hybrid electric) vehicles. Generators, motors, and permanent magnet motors for wind power generation in the megawatt range.

The microstructure of sintered Nd-Fe-B magnets usually has the following characteristics: (1) consists of 2:14:1 phase and Nd-rich phase at grain boundaries; (2) Nd-rich phase is distributed along grain boundaries or at the intersection of grain boundaries, The Nd-rich phases distributed along the grain boundaries are in the form of flakes, and the Nd-rich phases at the intersection of grain boundaries are in the shape of polygonal blocks; (3) There are few other impurity phases and pores. The Nd2Fe14B phase has a very high saturation magnetic induction (1.61T) and anisotropy field (>70kOe), and the magnetic properties of the sintered NdFeB permanent magnet material are provided by the 2:14:1 phase. The composition and volume percentage of the main phase of 2:14:1 determine the magnetic properties of the magnet to a large extent. At the same time, the structure of the sintered NdFeB permanent magnet material also determines the magnetic properties of the material to a large extent. For example, the grain orientation and density of the 2:14:1 phase of a magnet determine the remanence and energy product of the magnet to a large extent, while the grain size and boundary structure have a great influence on the coercive force of the magnet.

The orientation and density of sintered NdFeB magnets have reached more than 98%, so its remanence and magnetic energy product have reached more than 90% of the theoretical value, while the coercive force is less than 30% of the theoretical value, mainly due to the actual There is a large gap between the microstructure and the ideal microstructure: the main phase grains are not uniform and small, resulting in low coercive force; the magnetocrystalline anisotropy constant K1 of the surface layer of the main phase grains in 2:14:1 is low, and the microstructure is defective. Many, large scattered magnetic fields, the most likely to form reverse magnetization domain nuclei, resulting in low coercive force; the grain boundary Nd-rich phase cannot be continuously distributed in a thin layer between the 2:14:1 phase grains, and magnetic isolation cannot be effectively realized. The 2:14:1 phase is very easy to generate reverse magnetization domains between grains, which reduces the coercive force of the magnet. Therefore, in order to obtain a sintered NdFeB magnet with high coercivity, the grain size of the 2:14:1 phase must be reduced, the anisotropy of the surface layer of the 2:14:1 grain must be strengthened, and the Nd-rich phase must be guaranteed to be Thin layers are evenly distributed around all Nd2Fe14B grains.

Wan et al. added Pr-Cu alloy (Pr68Cu32) to prepare Dy-free sintered Nd-Fe-B magnets by double alloy method. The coercive force of the magnet was increased from 14kOe from the introduction of Pr-Cu grain boundary phase to the introduction of Pr-Cu 21kOe of the grain boundary phase. But its main alloy is Nd12.2Pr2.6Fe76.3Co2.1B6.0Nb0.2Al0.5Cu0.1 alloy, Nd/Pr reaches 14.8% atomic fraction, much higher than 11.76% atomic fraction of 2:14:1 positive fraction, also That is, the magnet itself contains 2:14:1 phase and Nd/Pr-rich phase, and Pr-Cu alloy is introduced at the grain boundary, and there are more non-magnetic phases (including Nd/Pr-rich phase and Pr-Cu alloy phase) at the grain boundary, and the remaining The magnetic drop is more, from about 13000Gs to about 11000Gs. (Wan F, Zhang Y, Han J, et al. Coercivity enhancement in Dy-free Nd–Fe–B sintered magnets by using Pr-Cu alloy[J]. Journal of Applied Physics,2014,115(20):203910.)

As we all know, the grain boundary Nd-rich phase in sintered Nd-B permanent magnet materials is very important. Although the Nd-rich phase itself does not provide magnetism, it mainly plays two roles: one is to realize liquid phase sintering to densify the magnet, which is the magnet. The basis for obtaining high magnetic flux density; second, it is distributed around the 2:14:1 main phase grains, which acts as a demagnetic coupling to the main phase grains and achieves high coercive force.

The light rare earth (La, Ce, Pr, Nd)-Cu alloy (light rare earth content 50-90% atomic percentage) of a certain composition range has a low melting point (about 400-800 ° C), which can realize low-temperature liquid phase sintering; Rare earth (La, Ce, Pr, Nd)-Cu alloys are non-magnetic and have good wettability with the 2:14:1 phase, and can achieve uniform thin-layer distribution around the grains of the 2:14:1 main phase.

Contents of the invention

The invention provides a neodymium-iron-boron magnet whose grain boundary is light rare earth-copper alloy with low melting point and a preparation method thereof. It is characterized in that the light rare earth-copper alloy powder with a certain weight fraction is mixed evenly with the NdFeB main alloy powder with a nearly positive ratio of 2:14:1, and is obtained after magnetic field pressing, isostatic pressing, vacuum sintering and densification, and heat treatment. product.

The present invention mainly uses two characteristics of light rare earth-copper alloy to greatly improve the structure of sintered NdFeB magnets to obtain high magnetic properties, especially high coercive force: ① light rare earth-copper alloy and 2:14:1 phase have Good wettability can achieve uniform thin-layer distribution around the 2:14:1 main phase grains, preventing exchange coupling between 2:14:1 grains; ② light rare earth-copper binary alloy (light rare earth Atomic percentage 50-90%) has a low melting point (about 400-800°C), which can realize low-temperature liquid phase sintering and fine-grained structure.

A method for preparing an NdFeB magnet whose grain boundary is a light rare earth-copper alloy with a low melting point, which is characterized in that a 2:14:1 NdFeB alloy is used as the main alloy, and a light rare earth-copper alloy with a certain composition range As an auxiliary alloy, sintered NdFeB magnets are prepared by double alloy method, in which light rare earth-copper alloy is not only a liquid phase sintering aid, but also a grain boundary phase, and has good wettability with the main phase of 2:14:1;

The specific process steps are:

1. Nearly divided 2:14:1 NdFeB main alloy ingot is broken into 3-5μm powder particles;

2. Break the light rare earth-copper auxiliary alloy ingot into powder particles of 0.1-3μm;

3. Add light rare earth-copper alloy powder with a weight fraction of 3-8% to the 2:14:1 NdFeB main alloy powder, and mix evenly;

4. Orientation pressing and isostatic pressing of the mixed powder under a magnetic field greater than 1.8T;

5. Vacuum sinter the compact at 800-1000°C for 1-4h, with a vacuum degree of 10 ^-3 Pa;

6. Temper the sintered magnet at 300-500°C for 1-4h, vacuum degree 10 ^-3 Pa;

7. Get the product.

The present invention has the advantage that:

1. It can achieve low temperature sintering and refine the grain;

2. The light rare earth-copper grain boundary phase is evenly distributed in the grain boundary of the 2:14:1 main phase, which effectively hinders the exchange coupling between the 2:14:1 main phase grains;

3. High temperature tempering heat treatment is omitted, the process is simplified and energy is saved.

detailed description

Embodiment one:

The main alloy components of NdFeB based on the 2:14:1 phase are designed respectively Nd11.76Fe82.36B5.88 (atomic percentage) and Pr75Cu25 (atomic percentage), and the ingredients are distributed according to the design. The main alloy considers the burning loss of rare earth Nd3 % (percentage by weight), auxiliary alloy considers the burning loss of rare earth Pr 5% (percentage by weight), and the main alloy and auxiliary alloy flakes with a thickness of 300 μm and 150 μm are prepared by flake ingot technology, and the average particle is prepared by hydrogen breaking and jet milling The main alloy powder and auxiliary alloy powder with a size of 3.5 μm and 1.5 μm are added to the main alloy powder with an auxiliary alloy powder with a weight fraction of 4%, and the two powders are mixed evenly in a mixer. After uniform mixing, the The powder is oriented and pressed in a magnetic field of 1.8T and isostatically pressed at 200MPa. The obtained compact is placed in a vacuum sintering furnace, sintered at 950°C for 3h, and then tempered at 400°C for 3h. The new sintered NdFeB The magnet has the comprehensive properties of N45M: the intrinsic coercive force reaches 13.9kOe, the remanence reaches 13.7kGs, and the magnetic energy product reaches 45.2MGOe.

Embodiment two:

Based on the 2:14:1 phase of NdFeB main alloy composition Nd8.82Pr2.94Fe80.00Co1.36Zr1.00B5.88 (atomic percentage) and Pr50Nd20Cu30 (atomic percentage), according to the design of the ingredients, the main alloy considers rare earth Nd /Pr burning loss 3% (weight percentage), auxiliary alloy considers rare earth Pr/Nd burning loss 5% (weight percentage), prepares main alloy flakes with a thickness of 300 μm respectively by the scale ingot casting process, and uses the melt rapid quenching process Prepare an auxiliary alloy thin strip with a thickness of 50 μm, prepare the main alloy powder with an average particle size of 3.0 μm by hydrogen blasting and jet milling, prepare auxiliary alloy powder with an average particle size of 0.6 μm by ball milling, add Auxiliary alloy powder with a weight fraction of 6%, mix the two powders uniformly in a mixer, and the uniformly mixed powder is oriented and pressed in a magnetic field of 2.0T and isostatically pressed at 200MPa. Put it into a vacuum sintering furnace, sinter at 900°C for 3 hours, and then temper at 380°C for 3 hours. The new sintered NdFeB magnet has the comprehensive properties of N40SH: the intrinsic coercive force reaches 20.7kOe, the residual magnetism reaches 13.1kGs, and the magnetic energy The product reaches 40.9MGOe.

Embodiment three:

Nd8.82Pr2.94Fe81.3Al1.00B5.88 (atomic percent) and La20Ce55Cu25 (atomic percent) based on the 2:14:1 phase of the NdFeB main alloy composition, according to the design composition, where the main alloy considers rare earth Nd/Pr The burning loss of 3% (weight percentage), auxiliary alloy considers the burning loss of rare earth La/Ce 5% (weight percentage), the main alloy flakes with a thickness of 300 μm are prepared by the scale ingot casting process, and the thickness is prepared by the melt rapid quenching process Auxiliary alloy strips of 50 μm are prepared by hydrogen breaking and jet milling to prepare main alloy powders with an average particle size of 3.0 μm, and auxiliary alloy powders with an average particle size of 0.5 μm are prepared by ball milling, and the weight fraction is added to the main alloy powders 5% auxiliary alloy powder, mix the two powders uniformly in the mixer, and the uniformly mixed powder is oriented and pressed in a magnetic field of 2.0T and isostatically pressed at 200MPa, and the obtained compact is placed in a vacuum In the sintering furnace, sintering at 850°C for 3 hours, and then tempering and heat treatment at 320°C for 3 hours, the new sintered NdFeB magnet has the comprehensive properties of N42H: the intrinsic coercive force reaches 17.3kOe, the remanence reaches 13.2kGs, and the magnetic energy product reaches 42.4 MGOe.

Claims (6)

1. a kind of grain boundary is the preparation method of the neodymium-iron-boron magnet of low-melting point light rare earth-copper alloy, it is characterized in that nearly normal fraction 2:14:1 neodymium-iron-boron alloy is used as main alloy, and the light rare earth-copper alloy of certain composition scope is used Copper alloy is used as auxiliary alloy, and sintered NdFeB magnets are prepared by double alloy method, in which light rare earth-copper alloy is not only a liquid phase sintering aid, but also a grain boundary phase, and has good wettability with the main phase of 2:14:1 sex; The preparation steps are: a. Design and divide 2:14:1 NdFeB main alloy and light rare earth-copper auxiliary alloy composition and cast ingots respectively; b. Nearly divided into 2:14:1 NdFeB main alloy and light rare earth-copper auxiliary alloy to make powder respectively; c. Mix a certain fraction of light rare earth-copper alloy powder with nearly positive 2:14:1 NdFeB main alloy powder; d. The mixed powder is densified by magnetic field pressing, isostatic pressing and vacuum sintering; e. The product is obtained after tempering heat treatment; The light rare earth in the light rare earth-copper alloy is one or more of La, Ce, Pr and Nd, and the atomic percentage of the light rare earth is 50-90%. 2. A kind of grain boundary is the preparation method of the neodymium-iron-boron magnet of low melting point light rare earth-copper alloy as claimed in claim 1, it is characterized in that: step c described 2:14:1 neodymium-iron-boron main alloy powder particle size 3-5μm, light rare earth-copper alloy powder particle size 0.1-3μm. 3. a kind of grain boundary is the preparation method of the neodymium-iron-boron magnet of low melting point light rare earth-copper alloy as described in claim 1, it is characterized in that: the weight percent of the light rare earth-copper alloy powder described in step c is 3- 8%. 4. A method for preparing an NdFeB magnet whose grain boundaries are light rare earth-copper alloys with a low melting point as claimed in claim 1, wherein the sintering temperature in step d is 800-1000°C, and the sintering time is 1 -4h, vacuum degree 10 ^-3 Pa. 5. A method for preparing an NdFeB magnet whose grain boundary is a light rare earth-copper alloy with a low melting point as claimed in claim 1, wherein the tempering heat treatment temperature in step e is 300-500°C, and the heat treatment time is 300-500°C. For 1-4h, the vacuum degree is 10 ^-3 Pa. 6. A kind of preparation method of the NdFeB magnet whose grain boundary is light rare earth-copper alloy with low melting point as claimed in claim 1 is characterized in that: the light rare earth-copper grain boundary phase is evenly distributed in the main phase of 2:14:1 The grain boundaries effectively hinder the exchange coupling between the 2:14:1 main phase grains, thereby obtaining high coercive force.