JPS63286516A - Manufacture of permanent magnet - Google Patents

Abstract

PURPOSE:To manufacture a high-efficiency permanent magnet improved in residual magnetic flux density, etc., by subjecting an alloy containing rare-earth elements, transition metals, and boron as principal components to melting, to casting, and then to hot working at a specific temp. CONSTITUTION:An alloy containing rare-earth elements (including Y), transition metals, and boron as principal components is melted and cast. After casting, hot working is applied at >=800 deg.C to refine crystals. Subsequently, if necessary, a heat treatment stage is added, or further, the alloy after the above heat treatment is crushed and the resulting powder is kneaded together with an organic binder, which is compacted so as to be formed into a resin-bonded-type magnet. In this way, the high-efficiency permanent magnet improved in coercive force and maximum energy product can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION C. Industrial Application Field The present invention relates to a method for manufacturing a permanent magnet whose basic components are rare earth elements, iron, and boron.

[Conventional technology]

Permanent magnets are one of the important electrical and electronic materials used in a wide range of fields, from various household appliances to peripheral terminal equipment for large computers.

With the recent demand for smaller and more efficient electrical products,
Permanent magnets are also required to have increasingly higher performance. Typical permanent magnets currently in use are alnico, hard ferrite, and rare earth-transition metal magnets. In particular, R-Co permanent magnets, which are rare earth-transition metal magnets, and R
Since -Fe-B permanent magnets provide high magnetic performance, much research and development has been carried out on them.

Conventionally, there are methods for manufacturing these R-Fe-B permanent magnets as shown in the following documents.

(1) Sintering method based on powder metallurgy.

(Reference 12 Reference 2) (2) A quenched thin strip manufacturing device used for manufacturing amorphous alloys produces quenched thin flakes with a thickness of about 30 μm, and the quenched thin flakes are made into magnets using a resin bonding method using the melt spinning method. Resin bonding method used. (Reference 31 Reference 4) (3) A method of mechanically orienting the rapidly cooled flakes used in the method (2) above using a two-step hot press method. (Reference 42 Reference 5) Here, sentence #1: JP-A-59-46008; Reference 2: M,
Sagawa, S., Fuji imural N., T.
Ogawa, H. Yamamoto.

and Y, Matsuura;
A p p+, Phys, Vol, 55
(8) 15Mar.

h 1984. p2083゜Document 3: JP-A-59-211549; Document 4: R
, W, Lee; AppI, Phys, Lett, V
ol, 4E3 (8), 15 APril 198
5, p790; Document 5: Japanese Patent Application Laid-open No. 100402/1983 Next, the above conventional method will be explained.

First, in the sintering method (1), an alloy ingot is produced by melting and casting, and then pulverized to obtain magnet powder with an appropriate particle size (several μm). Magnetic powder is kneaded with a binder, which is a molding aid, and press-molded in a magnetic field to complete a molded product. The compact was sintered in argon at a temperature of around 1100°C for 1 hour.
It is then rapidly cooled down to Muromasa. After sintering, the coercive force is further improved by heat treatment at a temperature of around 600°C.

In the resin bonding method (2) using quenched flakes by the melt spinning method, first, a quenched ribbon of R-Fe-B alloy is produced at an optimal rotation speed of a quenched ribbon manufacturing apparatus. Obtained thickness 3
A 0 μm ribbon ribbon is an aggregate of crystals with a diameter of 1000 Å or less, is brittle and easily broken, and since the crystal grains are distributed in the same direction, it is also magnetically isotropic. By pulverizing the ribbon to an appropriate particle size, kneading it with a resin, and press-molding it, it is possible to fill it to about 85% by volume at a pressure of about 7 ton/cm'.

In the manufacturing method (3), first, a ribbon-like quenched ribbon or piece of ribbon is heated in a vacuum or in an inert atmosphere for about 70 minutes.
Place in a graphite or other heat-resistant press mold preheated to 0°C. When the lipo has reached the desired temperature - axial pressure is applied. Although the temperature and time are not specified, suitable conditions for sufficient plasticity are T-725±25°C and pressure of P~1.4 ton/cm.At this stage, the magnet is slightly oriented in the pressing direction. However, it is generally isotropic.The following hot pressing is carried out in a large area mold.Most commonly, 700
℃ and 0.7 ton/cm'' for a few seconds. The sample then has an initial thickness of 172 mm and is oriented parallel to the pressing direction, making the alloy anisotropic. This method is called a two-step hot pressing method.This method produces an R-Fe-B magnet that is dense and exhibits anisotropy.

It should be noted that the crystal grains of the ribbon produced by the initial melt spinning method are made smaller than the grain size at which the ribbon exhibits its maximum coercive force, so that coarsening of the crystal grains may occur during subsequent hot pressing. to obtain the optimum particle size.

However, in this method, at high temperatures, for example, 800'C or higher, the crystal grains become significantly coarsened, resulting in an extremely low coercive force iHC, making it impossible to produce a practical permanent magnet.

[Problems to be Solved by the Invention] Although R-Fe-B magnets can be manufactured using the following conventional techniques, these manufacturing methods have the following drawbacks.

In the sintering method (1), it is essential to turn the alloy into powder, but since R-Fe-B alloys are very active against m-chords, oxidation becomes even more intense when they are turned into powder. The oxygen concentration in the sintered body inevitably becomes high. Also, when compacting the powder, compacting aids, such as zinc stearate, must be used, which are removed beforehand during the sintering process, but splaying causes carbon buildup within the magnet body. It remains in shape. This carbon is undesirable because it significantly reduces the magnetic performance of R-Fe-H.

The molded body after press molding with the addition of a molding aid is called a green body. It is very fragile and difficult to handle. Therefore, a major drawback is that it takes a considerable amount of effort to arrange them neatly in the sintering furnace.

Because of these drawbacks, generally speaking, R-Fe-B
Manufacturing sintered magnets of this type not only requires expensive equipment, but also has poor production efficiency, resulting in high magnet manufacturing costs. Therefore, R-Fe, which has relatively low raw material cost,
-It is hard to say that this is a method that can take advantage of the advantages of B-based magnets.

Next, methods (2) and (3) use a vacuum melt spinning device, which currently has very low productivity and is expensive.

The method (2) is isotropic in principle, resulting in a low energy product, and the squareness of the hysteresis loop is also poor, which is disadvantageous in terms of temperature characteristics and usage.

Method (3) is a unique method that uses a hot press in two stages, but it cannot be denied that it is extremely inefficient when considering actual mass production. Furthermore, in this method, if the Al1 temperature is, for example, 800° C. or higher, the crystal grains will become significantly coarsened, and as a result, the coercive force iHc will be extremely reduced, and a practical permanent magnet cannot be obtained.

The present invention solves the above-mentioned drawbacks of the prior art, and its purpose is to create a high-performance, low-cost rare earth-iron permanent magnet by using a casting method as a base process and also using hot working. The purpose of this invention is to provide a method for manufacturing the same.

[Means for solving problems]

The first method of manufacturing a permanent magnet of the present invention is a method of manufacturing a magnet whose basic components are rare earth elements (including Y), transition metals, and boron, in which at least an alloy consisting of the basic components is melted and cast. A method for producing a permanent magnet, the second method comprising the steps of hot working at a temperature of 800° C. or higher after casting.
A method for producing a permanent magnet, which is characterized by adding a step of heat treatment following the step of hot working at a temperature of 800 ° C. or higher after casting in the method of 2. After the process, the method for producing a permanent magnet is characterized by comprising the steps of pulverizing the cast alloy, and then kneading the pulverized alloy powder with a machine binder and press-molding it.

[Effect]

As mentioned above, the sintering method and the quenching method, which are methods for producing rare earth-iron magnets, each have major drawbacks such as difficulty in powder control through pulverization and poor productivity.

In order to improve these drawbacks, the present inventors focused on research on magnetization in the bulk state, and first, the rare earth elements,
It is possible to isomerize by hot processing in the composition range of magnets whose basic components are iron and boron, and it is also possible to obtain resin-bonded magnets by crushing this cast ingot into powder, and kneading and hardening it with a mechanical binder. I found out that it is possible.

The anisotropy caused by hot working in this method is described in the above-mentioned document 4.
Only one step is required, instead of two steps as in the quenching method shown in Figure 2, and the process can be carried out in bulk, resulting in extremely high productivity. Furthermore, since there is no need to crush the cast ingot, the sintering method does not require any strict atmosphere control, and the installation cost is greatly reduced.

Furthermore, resin-bonded magnets also do not have the problem of having isometric properties in principle like magnets produced by the quenching method. It is possible to take advantage of the characteristics of performance and low cost.

With this composition, Nd1Fe, which is the main phase in normal casting,
The aB phase becomes coarse and good magnetic properties cannot be obtained by a slight layering process.

The optimal composition of conventional RF' e -B magnets was R+5FetyBs shown in Document 2.

This composition is shifted to the side rich in R and H compared to the composition R1, -tFea*, aB*-*, which is the atomic percentage of the main phase Rt Feta B compound. This is explained from the point that in order to obtain a coercive force, not only the main phase but also non-magnetic phases such as an R-rich phase and a B-rich phase are required.

However, in the composition according to the present invention, on the contrary, the peak value of the coercive force exists where the B content shifts to the side where there is less B. In this composition range, the coercive force is drastically reduced in the case of the sintering method, so it has not been much of a problem so far. However, in the casting method, a high coercive force can be obtained in this composition range, and an even higher coercive force can be obtained by hot working.

These points can be considered as follows. First of all, whether a sintering method or a casting method is used, the coercive force mechanism itself is nuc.
It follows the leation model. This can be seen from the fact that both truncation curves show a steep rise like SmC0. The coercive force of this type of magnet is basically based on a single domain model. That is, in this case,
If the R,Fe+ a B compound, which has large crystal magnetic anisotropy, is too thick, it will have domain walls within the grains, so the reversal of magnetization will easily occur due to movement of the domain walls, and the coercive force will be small.

On the other hand, as particles become smaller and become smaller than a certain size, there is no domain wall within the particles, and reversal of magnetization proceeds only by rotation, so the coercive force increases. It is necessary that the R9F e +□B phase has an appropriate particle size.This particle size is 10μ
A suitable value is around m, and in the case of a sintered type, the particle size can be adjusted by adjusting the powder particle size before sintering.

However, when the casting method and hot working method are combined, Rt
The crystal size of the FesaB compound is first determined at the stage of solidification from the molten metal, but since the crystals are made finer by hot working, the final crystal size of the magnet depends on the hot working conditions. Depending on the selection, the rA node can be established and sufficient coercive force can be generated.

Moreover, the macrostructure at the time of casting is preferably a columnar crystal structure. By using this columnar crystal structure, it is possible to achieve in-plane anisotropy during casting and further improve performance during hot working.

Next, regarding resin bonding, resin bonded magnets can certainly be created using the quenching method described in Document 4.

However, the powder created by the rapid cooling method has a diameter of 1000λ.
Since the following polycrystals are gathered in the same direction, it is magnetically isotropic, and it is not possible to create an anisotropic magnet.
-The characteristics of low cost and high performance of the B series cannot be utilized. In the case of this system, if pulverization is performed with small mechanical strain, the holding force can be maintained considerably, so resin bonding can be performed. The biggest advantage of this method is that, unlike Document 4, it is possible to create an anisotropic magnet.

The preferred composition range of the permanent magnet according to the present invention will be explained below.

Rare earths include Y, La, Ce, Pr, Nd, Sm
, Eu, Gd, Tb, Dy, Ho, Er, Tm, Y
b, Lu are listed as candidates, and one of these! l
Or 1! Used in combination of l or more. The highest magnetic performance is obtained with Pr. Therefore, practically Pr,
Pr-Nd alloy, Ce-Pr-Nd alloy, etc. are used. Also, a small amount of additive elements, such as heavy rare earth elements DY, Tb
etc., AI, Mo, St, etc. are effective in improving coercive force.

The main phase of the R-Fe-B magnet is R*Fe+aB. Therefore, if R is less than 8 at %, the above compound is no longer formed and a cubic crystal structure having the same structure as α-iron is formed, so that high magnetic properties cannot be obtained. On the other hand, if R exceeds 30 atomic %, the nonmagnetic R-rich phase increases and the magnetic properties deteriorate significantly. Therefore, a suitable range for R is 8 to 30 atomic %. However, since it is a cast magnet, preferably R8~258~25
It is an atom.

B is an essential element for forming the RzFerraB phase, and if 2 atomic % is not grooved, it becomes a rhombohedral R-Fe system, so a high coercive force cannot be expected. Moreover, if it exceeds 28 at%, the non-magnetic phase rich in B increases, and the residual magnetic flux density decreases significantly (However, as a cast magnet, it is preferable to use B.
The number of atoms is preferably 88 atoms or less; if the number is more than 88 atoms, a fine Rt Fe+ a B phase cannot be obtained unless special cooling is performed, and the coercive force is small.

Co is an element that increases the Curie point of this magnet, and basically replaces Fe sites to create Rt Fe+
a B is formed, but this compound has a small crystal anisotropy magnetic field, and as the amount increases, the coercive force of the magnet as a whole decreases. Therefore, in order to provide a coercive force greater than IKOe, which can be considered as a permanent magnet, it is preferable that the content be within 50 atomic %.

AI shows the effect of increasing coercive force. (Reference 7: Zhan
g Maocai et al., Proceedingsoft
he 8th International
Works, hop on Rare-F
arth Magnets, 1985. p
54 This document 7 shows the effect on sintered magnets, but the same effect also exists on cast magnets. However, since AI is a non-magnetic element, if the amount added is increased, the residual magnetic flux density will decrease, and if it exceeds 15 at %, the residual magnetic flux density will be lower than that of hard ferrite, so it cannot fulfill its purpose as a rare earth magnet. do not have. Therefore, the amount of AI added is preferably 15 atomic % or less.

Furthermore, in the present invention, hot working is a concept with respect to cold working, and refers to high-temperature wave working in which processing is performed while removing most of the working strain caused by plastic working. Therefore, during hot working, crystal grain refinement due to recrystallization and subsequent growth of crystal grains also occur, and it is clear that these phenomena are also included in hot working.

This is because the hot press described in the above-mentioned document (4) aims at bulking the flakes and orienting the crystal axes, and does not like the reduction in coercive force due to grain growth at high temperatures, so the temperature is kept as low as possible (near 700°C).
This is very different from the case where short-time processing (within 5 minutes) was optimized. That is, in the method for manufacturing a permanent magnet of the present invention, hot working at a temperature exceeding 1050°C causes the coarsening of the crystal grains, which causes a large decrease in the coercive force; Coercive force increases with miniaturization. And its workability is good. That is, in order to enable processing at a strain rate of 10-'/sec or more, a processing temperature of 800° C. or higher is required.

Next, examples of the present invention will be described.

[Example 1] A process diagram of the manufacturing method according to the present invention is shown in FIG.

First, as shown in FIG. 1, an alloy having a desired composition is melted in an induction furnace and cast into a mold.

Next, various types of hot working are performed to impart anisotropy to the magnet.

As various hot workings, Fig. 2 shows an explanatory diagram of extrusion processing, Fig. 3 shows an explanatory diagram of rolling processing, and Fig. 4 shows an explanatory diagram of stamping processing.

In the figure, 1: Hydraulic press; 2: Die; 3: Magnetic alloy; 4: Magnetized molten metal direction; 5HIJ-R; 6: Stamp: 7
: Indicates a board.

Regarding the extrusion process, we devised a way to apply force from the die 2 side so that the force was applied in the same direction.

Regarding rolling and stamping, the speeds of the rolls 5 and stamps 6 were adjusted so that the strain rate was as low as possible.

In either method, the axis of easy magnetization of the crystal is oriented parallel to the direction in which the alloy is pressed, as shown by the arrow, in the high temperature range (500 to 1100°C).

After melting and casting an alloy whose basic components are rare earth elements, iron, and boron, the present inventors conducted a wide range of rational processing experiments and obtained the following experimental results.

(1) When assisted processing is performed at a low temperature between room temperature and 500° C. and a high strain rate, alloy ingots of most compositions will crack.

Coercive force iHc when magnetically measured using a small piece that is not broken
increases in proportion to the processing rate, but almost no crystal orientation occurs, so the residual magnetic flux density Br hardly increases. For this reason, the maximum energy product (BH)m-x hardly increases in plastic working within this range.

(2) On the other hand, when plastic working is performed at a high temperature exceeding 200° C., no cracking occurs even at a high strain rate, and workability becomes good and good crystal orientation occurs. However, coercive force i
Hc is decreasing.

(3) Hot working between 500 and 1100°C increases the strain rate, increases the residual magnetic flux density Br and coercive force iHc, and increases the maximum energy product (BH) m-x. Among them, the preservative temperature is 800 to 1050℃.
is good.

(4) Even when an ingot made of the alloy composition of the present invention is heated to near its melting point, coarsening of crystal grains occurs only slightly.

(5) When the processing temperature and strain rate are optimal, the relationship between processing rate, average C-axis, and orientation is as follows: processing rate is 20% and C-axis orientation rate is 6.
0-70%, processing rate is 40% and C-axis orientation rate is 65-75
%, at a working rate of 60%, the C-axis orientation rate is 75-85%, at a working rate of 80%, the C-axis orientation rate is 85-95%, and at a working rate of 90%, the C-axis orientation rate is 85-98%.

An alloy having the composition shown in Table 1 was melted, and a magnet was produced by the steps shown in FIG. However, the hot working method used is also listed in Table 1.

For alloys with compositions shown in Table 1, hot working was carried out under various combinations of working temperatures of 500 to 1100°C and strain rates of 10-4 to 17 seconds. Table 2 shows the magnetic properties when the annealing treatment was performed at 1000°C for 24 hours. The characteristics of a sample without hot working are also shown as reference data.

The optimum conditions for annealing, namely temperature and time, vary depending on the composition of the alloy and processing conditions. 500-8 depending on composition
00°C, and 5oo-iooo°C depending on the hot working conditions.

From Table 2, it can be seen that the residual magnetic flux density increased and magnetic anisotropy was achieved by all hot processing methods such as extrusion, rolling, and stamping. Among these, the extrusion method is superior.

Table 3 shows the composition of Prt t Few I Ba,
Nds o Feas B+ 6 and Ces Nd
r @ Pr+ o Fea @ Cot t Zrx
Taking Be as a representative example, short column processing temperature and workability/1Hc
- The relationship with the C-axis orientation rate is shown. Processing rate is 8
The target is 0%, and Δ marks are those where cracks occurred during breath processing, and X
The mark indicates those that could not be processed with U-character.

A suitable processing temperature ranges from 500 to 1100°C, but 800 to 1050°C is optimal when both magnetic properties and processability are evaluated together. The strain rate can be increased as the temperature increases and as the rare earth element boron content *i decreases.

The strain rate in this experiment was in the range of 10-4 to 1/sec.

Among these, a strain rate of 10-3 to 10-'/sec was better. It has been found that it is possible to set the strain rate to 1 to 10'/sec at around 1000 DEG C. because the processing stress is mainly compressive stress and small tensile stress in the processing method, particularly in extrusion molding.

Furthermore, as the C-axis orientation rate increases, both the residual magnetic flux density Br and the coercive force iHc increase, and (BH)rn-8 increases rapidly.

Table 4 shows the composition of P r+ o Ndt Few
IB4 and Ce @ Prz @ Ndm e Feb
*Cot.

After melting and casting B, the temperature was changed until the strain rate was 10.
The magnetic properties are shown when hot pressing is performed at a processing rate of 75% so that the time is within the range of −1 to 17 seconds.

Table 1 Table 2 Table 4 × mark: Cracking occurred.

[Example 2] First, an alloy having the composition shown in Table 5 was melted in an induction furnace, cast in an iron mold, hot pressed at 1000°C, and then annealed at 1000°C for 24 hours to magnetically harden the ingot. was applied.

At this time, the average grain size after annealing was about 15 μm.

If this step is used to cut and grind the material, it will become an anisotropic magnet.

For resin-bonded type magnets, 18-8 at room temperature.
In a stainless steel container, hydrogen was absorbed in a hydrogen gas atmosphere of about 10 atm and dehydrogenated at 10-'torr. After pulverization, 4% by weight of epoxy resin was kneaded. Transverse magnetic field forming was performed using a magnetic field.

The above results are shown in Table 6.

Table 5 Table 6 [Effects of the Invention] As described above, according to the method for producing a permanent magnet of the present invention, after casting rare earth elements, etc., the temperature is 800 to 1050°C.
By performing hot working at a processing rate of 50% or more and at a low strain rate, the following effects can be achieved.

(1) The C-axis orientation rate can be increased, and the residual magnetic flux density is 1
It was possible to significantly improve fBr.

(2) Furthermore, by making the crystal grains finer, the coercive force iHc could be significantly increased.

(3) The synergistic effect of (1) and (2) made it possible to significantly increase the maximum energy product (BH) rn-x.

(4) Compared to conventional sintering methods, processing man-hours and production equipment investment can be significantly reduced.

(5) Compared to the conventional melt spinning method, it was possible to produce magnets with high performance and at low cost.

[Brief explanation of drawings]

Fig. 1 is a manufacturing process diagram of the R-Fe-B magnet of the present invention, Fig. 2 is an explanatory diagram of the orientation treatment of the magnet alloy by hot extrusion,
FIG. 3 is an explanatory diagram of orientation treatment of magnetic alloy by hot rolling;
FIG. 4 is an explanatory diagram of orientation processing of a magnetic alloy by hot stamping. In the figure, 1: hydraulic press, 2: die (mold), 3: magnet alloy, 4: direction of magnetized molten metal, 5: roll, 6: stamp, 7: substrate. Note that the reference numerals in the drawings indicate the same or equivalent parts. Applicant Seiko Epson Co., Ltd. Agent, Patent Attorney Tsutomu Mogami and 1 other person, // 1 11. Figure 1 Figure 2 Figure 3 Figure 4

Claims (3)

[Claims] (1) In a method for manufacturing a magnet whose basic components are a rare earth element (including Y), a transition metal, and boron, at least a step of melting and casting an alloy consisting of the basic components, and a temperature of 800°C or higher after casting. A method for producing a permanent magnet, comprising the steps of hot working. (2) A method for manufacturing a magnet whose basic components are a rare earth element (including Y), a transition metal, and boron, at least a step of melting and casting an alloy consisting of the basic components, at a temperature of 800°C or more after casting. 1. A method for producing a permanent magnet, comprising the steps of hot working and then heat treatment. (3) In a method for manufacturing a magnet whose basic components are a rare earth element (including Y), a transition metal, and boron, at least a step of melting and casting an alloy consisting of the basic components, and a temperature of 800°C or higher after casting. A method for producing a permanent magnet, comprising the steps of hot working, heat-treating and pulverizing the cast alloy, and then kneading the pulverized alloy powder with an organic binder and press-molding.