JPS63192205A - Manufacture of permanent magnet of rare earth alloy - Google Patents

Abstract

PURPOSE:To form the title permanent magnet having high magnetic characteristics stably with excellent reproducibility by giving explosive power to the fine powder of an alloy for a rare earth magnet or the green compact of fine powder, mutually contact-bonding fine powder to form a molded form and executing magnetic characteristic-imparting heat treatment to the molded form. CONSTITUTION:The fine powder of a rare earth magnet or the green compact of fine powder is not magnetic-field orientation-treated or is magnetic-field orientation-treated and is given explosive power, fine powder is contact-bonded mutually to shape a molded form, and the molded form is magnetic characteristic-imparting thermally treated. Since the molded form acquired by explosive power is molded impulsively and instantaneously, oxygen is not increased by adsoprtion, and the molded form having high density of 97% or more of theoretical density is obtained, thus omitting a subsequent sintering process, then resulting in the usage of raw material fine powder having grain size larger than grain size according to a conventional method by twice or decuple. When raw material fine powder having large grain size is employed, the increase of impurity content such as oxygen and carbon can be prevented. Accordingly, the rare earth magnet having superior magnetic characteristics can be shaped stably with excellent reproducibility through one or more of heat treatment.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a method for stably manufacturing rare earth alloy permanent magnets (hereinafter referred to as rare earth magnets) having excellent magnetic properties with good reproducibility. .

[Conventional technology]

Conventionally, magnets containing rare earth metals such as samarium-cobalt and neodymium-iron-boron have been highly evaluated for their high magnetic properties, have been significantly developed in recent years, and are now widely put into practical use.

These rare earth magnets are produced by, for example, melting raw metals mixed in a predetermined ratio in a vacuum induction furnace or vacuum arc melting, and casting the resulting molten metal into an ingot, which is then heated using a nitrogen or argon gas. Coarse powder obtained by coarsely pulverizing to several tens of meshes in an active gas atmosphere using a Stampf mill, hammer mill, roller mill, etc., or by reducing a rare earth metal oxide in the coexistence of other metal powders, A fine powder of several micrometers in size is prepared by finely pulverizing it in an organic solvent such as toluene or in an inert gas using a ball mill, vibration mill, jet mill, or attritor, and then this fine powder is prepared. A green compact obtained by compression molding powder under a magnetic field or no magnetic field is held at a predetermined temperature within the range of 1000 to 1250°C for 30 to 60 minutes in a vacuum or an inert gas atmosphere such as argon. It is manufactured by sintering under the following conditions.

[Problem that the invention seeks to solve]

The rare earth alloy, especially the rare earth alloy in powder form.

Since it is very easily oxidized, in order to prevent oxidation of the rare earth alloy, during the pulverization step when pulverizing it to prepare raw material powder for rare earth magnets, the pulverizing step is performed using the above-mentioned method, crab element or The process must be carried out in an inert gas such as argon or an organic solvent such as toluene, but even with this method, the rare earth alloy such as the inert gas or organic solvent must be used before the raw material powder is prepared. There is a problem that oxygen and carbon in the surrounding atmosphere combine with this rare earth alloy and mix into the raw material powder, thereby significantly reducing the magnetic properties of the magnet.In particular, the amount of these impurities is
It increases in inverse proportion to the particle size of the fine powder.

On the other hand, the magnetic properties of rare earth magnets deteriorate as the crystal grain size in the sintered body increases, so it is necessary to take into account the grain growth that occurs during the sintering process and reduce the grain size of the raw fine powder as much as possible. In fact, the current situation is that the raw material fine powder is manufactured as small as practically possible.

In this way, it is necessary to make the grain size of the raw material fine powder as small as possible in consideration of the grain growth that occurs during the sintering process, but if the raw material fine powder is made small in particle size, oxygen A contradictory phenomenon occurs in which the amount of carbon and carbon impurities increases, significantly impairing the magnetic properties of rare earth magnets, and it is extremely difficult to stably produce rare earth magnets with high characteristics without quality variations. there were.

[Failure to solve the problem]

Therefore, from the above-mentioned viewpoint, the present inventors conducted research in order to stably manufacture rare earth magnets with high magnetic properties with good reproducibility, and as a result, they found that fine powder of rare earth a-stone or compacted powder thereof Furthermore, they discovered that rare earth magnets with high magnetic properties can be stably produced with good reproducibility by using explosive force to press fine powders together to form a compact.

This invention was made based on the above-mentioned knowledge, and involves applying explosive force to fine powder of a rare earth magnet or its green compact, with or without applying a magnetic field orientation treatment, to press the fine powder together. This method is characterized in that a rare earth magnet is produced by forming a molded body and subjecting this molded body to heat treatment to impart magnetic properties.

Since the molded body obtained by the explosive force is instantaneously shaped by the explosive force, there is no increase in oxygen due to adsorption compared to conventional sintered bodies, and there is no increase in oxygen content.

Already at this stage, a product with a high density of 9 gussets or more, which is the theoretical density, can be obtained, so the subsequent sintering process can be omitted. There is no need to reduce the particle size of the raw material fine powder as much as possible in consideration of the grain growth that occurs, and it is possible to use a raw material fine powder with a particle size that is 2 to 10 times larger than the particle size of the raw material fine powder used in the conventional method. can be used.

In this way, if it is possible to use fine raw material powder with a large particle size, it is possible to prevent an increase in the content of impurities such as oxygen and carbon in the compact, and eliminate factors that impair magnetic properties. .

Furthermore, even if the compact formed by the above-mentioned explosive force is sintered, sintering can be done at a lower temperature and for a shorter time than in the conventional method, and grain growth in such a sintering process is extremely unlikely. , the same effect as when the sintering step is omitted can be obtained.

Here, the particle size that is 2 to 10 times larger than the conventional method is
Specifically, it refers to particles with an average particle size of 5 to 50 μm.

The molded body formed as described above is heat-treated at least once in a magnetic field or in a non-magnetic field at a temperature in the range of 300°C to 1250°C to improve its magnetic properties. Rare earth magnets with magnetic properties can be stably manufactured with good reproducibility.

[Example] Next, the method for manufacturing a rare earth magnet of the present invention will be specifically explained with reference to Examples.

Example 1 Nd14.3DY0. produced by vacuum arc melting.
160 g each of neodymium/iron/boron alloy ingots for magnets having the component composition of 7F877B8 were taken, ground in a stamp mill in a nitrogen atmosphere, classified with a 24-mesh sieve, and the coarse powder was placed in a degassed CFC solvent. Finely pulverized using a rotating ball mill, and measured using a Fischer subsitive sizer: average particle size: 3 μm, 5.9 μm,
7.2μms 11.2μm, 15.4μm, 201
μm, 25.0 μm raw material fine powder was prepared, and among this raw material fine powder, the average particle size near, 2 μm, 115.4 μm, 2
6 pieces of each fine powder of 0.1μm and 25.0μm
511, each of these is filled into a thin-walled steel cylindrical container in an argon atmosphere, compression molded and sealed, and the steel cylindrical container filled with each of these fine powders is placed in an explosion molding apparatus shown in Fig. 1. This explosive forming device is charged into.

Between the shock absorbing plate 1 and the mold 2, a steel cylindrical container 5 filled with raw material fine powder 4 is charged into the charging part 3 of the mold 2, a fryer 6 is placed on top of the container, and a fryer 6 is placed above it. The explosive 7 is detonated by a detonator 8 to form a compact, and the steel cylindrical container 5 filled with each of the fine powders is detonated using an explosive 260II to form a magnet. The fine alloy powder is crimped, and then the steel layer adhering to the outer periphery of the crimped body is mechanically scraped off, the crimped body is cut out to form a molded body, and this molded body is introduced into a vacuum furnace where the degree of vacuum is adjusted. 1Oiu*H,! i+ vacuum at 650℃ 2
The method of the present invention was carried out by carrying out heat treatment to impart magnetism over time, and cooling by introducing argon gas at the end of the treatment, thereby producing rare earth magnets 1 to 4 of the present invention. The magnetic properties of these rare earth magnets are shown in Table 1.

For comparison, each of the same fine powders was subjected to a pressure of 1.5 ton/c.
I! Press molding under L2 pressure, - side 10m
11 cubic powder compacts were molded, and these compacts were placed in a vacuum of 10-mmHll at a temperature of 1090°C.
After sintering by holding for 1 hour, the sintered body was quenched, and then the sintered body was heated to a temperature of 65 in a vacuum of 1 O-5wHI.
A comparative rare earth magnet 1-4 was produced by carrying out a comparative method by performing heat treatment at 0° C. for 2 hours.

The magnetic properties of comparative rare earth magnets 1 to 4 obtained as a result are also shown in Table 1.

Example 2 The production method of Example 1 was carried out under exactly the same conditions except that the raw material fine powder was oriented in an Oersted magnetic field and a non-magnetic aluminum cylinder was used as the cylindrical container 5. A rare earth magnet was manufactured by implementing the invented method.

The magnetic properties of the rare earth magnets 5 to 8 of the present invention and comparative rare earth magnets 5 to 8 thus obtained are shown in Table 2.

〔Effect of the invention〕

From the results shown in Tables 1 and 2, it can be seen that the rare earth magnets 1 to 8 of the present invention manufactured by the method of the present invention have oxygen contents that are compared to comparative rare earth magnets 1 to 8 manufactured by the comparative method. It is clear that the coercive force is significantly smaller and the coercive force is also significantly larger. Furthermore, regarding the maximum energy product, the rare earth magnets 1 to 8 of the present invention manufactured by the method of the present invention are constant regardless of the average particle size of the raw material fine powder, whereas the comparative rare earth magnets manufactured by the comparative method Magnets 1 to 8 are significantly influenced by the average particle size of the raw material fine powder, and it is clear that the larger the average particle size, the smaller the maximum energy product. It can be seen that this is an excellent manufacturing method with little variation.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an apparatus for explosively molding fine powder of rare earth magnets or green compacts thereof. DESCRIPTION OF SYMBOLS 1...Shock absorbing plate, 2...Mold, 3...Charging part, 4...Fine powder, 5...Cylindrical container,
6...flyer, 7...explosives,
8... Detonator for detonation.

Claims (2)

[Claims] (1) Applying explosive force to a fine powder of a rare earth magnet alloy or a compact thereof, and pressing the fine powders together to form a compact;
A method for producing a rare earth alloy permanent magnet, which comprises subjecting the compact to heat treatment to impart magnetic properties. (2) The method for producing a permanent magnet made of a rare earth alloy according to claim 1, characterized in that the fine powder of the alloy for rare earth magnets or the green compact thereof is subjected to a magnetic field orientation treatment.