JP2558095B2 - Rare earth ferrous iron permanent magnet manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a rare earth-iron-based permanent magnet.

[Prior Art] Conventionally, the following three methods have been reported for producing an R-Fe-B magnet.

(1) Sintering method based on powder metallurgy (Reference 1).

(2) Using a quenching ribbon manufacturing apparatus used for producing an amorphous alloy, a quenching thin piece having a thickness of about 30 μm is formed, and the thin piece is made into a magnet by a resin bonding method (reference document 2).

(3) A method of mechanically orienting the same thin piece used in the method of (2) above by a two-step hot pressing method (Reference 2).

References 1. M. Sagawa, S. Fujimura, N. Togawa, H. Yamamot
o and Y. Matsuura; J.Appl.Phys.Vol.55 (6), 15 March
1984.P2083 Reference 2. RWLee; Appl.Phys.Lett.Vol.46 (8), 15
April 1985, P790 The above-mentioned prior art will be described along with the literature. First, in the sintering method (1), an alloy ingot is produced by melting and casting, and is crushed into magnet powder having a particle size of about 3 μm. The magnet powder is kneaded with a binder serving as a molding aid and press-molded in a magnetic field to form a molded body. The compact is sintered in argon at a temperature of around 1100 ° C. for 1 hour and then quenched to room temperature. After sintering, heat treatment at a temperature of around 600 ° C further improves the coercive force.

In the above (2), first, a quenched ribbon of an R-Fe-B alloy is produced at an optimum rotation speed of a quenching ribbon manufacturing apparatus. The obtained ribbon has a ribbon shape with a thickness of 30 μm, and polycrystals having a diameter of 1000 Å or less are aggregated. The ribbon is brittle and easily broken, and since the crystal grains are distributed isotropically, it is magnetically isotropic. If the ribbon is adjusted to an appropriate particle size, kneaded with a resin and press-molded, about 85% by volume can be filled with a pressure of about 7 ton / cm ² .

In the manufacturing method (3), first, the ribbon-shaped quenched ribbon or strip is put into graphite or another heat-resistant press die preheated at about 700 ° C. in a vacuum or an inert atmosphere. . Uniaxial pressure is applied when the ribbon reaches the desired temperature. Although the temperature and time are not specified, T = 725 ± 25 ° C. and pressure P = 1.4 ton / cm ² are suitable conditions for producing sufficient plasticity. At this stage the magnets are generally isotropic although they are slightly oriented in the pressing direction. The next hot pressing is performed with a mold having a large area. It is most commonly pressed at 700 ° C. at 0.7 ton for a few seconds. Then, the sample becomes 1/2 of the initial thickness, the easy axis of magnetization is oriented parallel to the pressing direction, and the alloy becomes anisotropic. These steps are called the two-stags hot-press procedure. By this method, a dense and anisotropic R-Fe-B magnet can be manufactured.

In addition, the crystal grains of the ribbon ribbon made by the first melt spinning method should be smaller than the grain size when it shows the maximum coercive force, and later the crystal grains become coarse during hot pressing. Make sure the particle size is optimal.

[Problems to be Solved by the Invention] Although the R-Fe-B magnets can be produced for some time by the above-mentioned conventional techniques, the production methods utilizing these techniques have the following drawbacks. There is.

In the sintering method of the above (1), it is essential to make the alloy into a powder, but since the R-Fe-B type alloy is very active with respect to oxygen, if it is made into a powder, excessive oxidation will occur, resulting in burning. The oxygen concentration in the body will inevitably increase. Also, when molding the powder, a molding aid, such as zinc stearate, must be used, which is removed beforehand during the sintering process, but a few tenths of the form of carbon in the magnet body. Will remain. This carbon significantly reduces the magnetic performance of R-Fe-B. The green body is the green body after press molding by adding a molding aid. This is very fragile and difficult to handle. Therefore, it is a great disadvantage that it takes a considerable amount of time to neatly arrange them in the sintering furnace. Generally speaking, because of these drawbacks, R
In order to manufacture a —Fe—B system sintered magnet, not only expensive equipment is required, but also the production efficiency is poor and the manufacturing cost of the magnet becomes high. Therefore, it cannot be said that the manufacturing method can sufficiently bring out the low raw material cost of the R-Fe-B magnet.

The manufacturing methods (2) and (3) use a vacuum melt spinning device. This device is currently very unproductive and expensive. In the above (2), since it is isotropic in principle, it is a low energy product, and the squareness of the hysteresis loop is not good, which is disadvantageous in terms of temperature characteristics as well as in the direction of use. The method of (3) above is
This is a unique method of using hot pressing in two steps, but it cannot be denied that it will be very inefficient when actually considering mass production.

Further, as a drawback of the magnets according to the methods (1) and (3), low mechanical strength can be mentioned.
These magnets are magnets that were originally in the state of powder or ribbon and are sintered or compression bonded at high temperature.
Therefore, chipping is likely to occur in handling and handling becomes very difficult.

The method for producing an R-Fe-B magnet according to the present invention solves these drawbacks, and its purpose is to:
It aims to provide high-performance magnets at low cost.

[Means for Solving Problems] The present invention relates to a method for producing a rare earth-iron-based permanent magnet, and specifically, contains iron as a main component and has an atomic percentage of R: 8 to 25% (however, R is at least one of rare earth elements including Y) and B: an alloy containing 2 to 8% is melted and cast so that the cast macrostructure becomes columnar crystals, and the cast ingot is heated to 500 ° C. or higher. The method for producing a rare earth-iron-based permanent magnet is characterized in that it is magnetically hardened by heat treatment at a temperature of, and further cut and ground into a magnet shape.

Further, the present invention contains iron as a main component, and in atomic percentage, R: 8 to 25% (however, R is at least one of rare earth elements including Y), B: 2 to 8% and Co to 40% ( (Excluding 0)
After melting the alloy containing, and casting so that the cast macrostructure becomes columnar crystals, the cast ingot is magnetically hardened by heat treatment at a temperature of 500 ° C or higher, and further cut and ground to obtain a magnet. It is a method for producing a rare earth-iron-based permanent magnet, which is characterized in that it has a shape.

As described above, the existing rare-earth-iron-based permanent magnet manufacturing method has a large drawback such as difficulty in powder management by pulverization, poor productivity, and low mechanical strength in the sintering method and the quenching method, respectively. Have In order to improve these drawbacks, the present inventors have started research on an alloy capable of obtaining a coercive force in the bulk state, and it is possible to obtain the coercive force in the bulk state in the above composition. Yes, coercive force is easily obtained by making the cast structure columnar crystals at this time, and since it becomes an anisotropic magnet by utilizing the in-plane anisotropy of columnar crystals, rather than using equiaxed crystals, The present invention has been accomplished by finding that a higher performance permanent magnet can be obtained.
In the present invention, since it is not necessary to crush the cast ingot, there is no need to perform strict atmosphere control as in the sintering method, and a furnace with high mass productivity such as a belt furnace can be used for heat treatment, and the equipment cost is large. Will be reduced. Further, by magnetizing the alloy in the as-cast state, it does not go through a powder state, and as a result, the bonds between the crystal grains become very strong and the mechanical strength increases.

In addition, research on the same system includes Hiroaki Miho et al. (The Japan Institute of Metals, Autumn 1994, Lecture No. (544)), but this research not only differs from the present invention in composition range. No mention is made of any change in performance due to the macrostructure, and the performance is greatly inferior to the present invention. In addition, the secondary processing for obtaining the desired shape after magnetically hardening is also extremely effective in this system because it has a large bending strength, compressive strength, etc. compared to conventional samarium-cobalt rare earth magnets. Cheap.

The composition of the conventional R-Fe-B magnet is R ₁₅ Fe ₇₇ B ₈ represented by the reference 1. This composition is the composition R in which the main phase R ₂ Fe ₁₄ B compound of the R-Fe-B magnet is expressed in atomic percentage.
Compared to _11.7 Fe _82.4 B _5.9 , it shifts to the side rich in both R and B elements. This is explained by the fact that not only the main phase but also non-magnetic phases called Rrich phase and Brich phase are necessary to obtain the coercive force. On the contrary, in the composition according to the present invention, on the contrary, a peak value is present when the composition shifts to the side with less B.

This is a feature of the present alloy. Firstly, when the amount of B is reduced, the crystal grains become finer, and secondly, when the molten metal is rapidly cooled to form good columnar crystals, the crystal grains become finer. It is considered that the composition range is peculiar to the magnet according to the present invention having a nucleation type coercive force mechanism.

The use of columnar crystals in the permanent magnet material has been performed in rare earth magnet-based samarium-cobalt magnets as well as in Alnico magnets. Announced (T. Shimoda et al., Proceedings of the fifth Inte
rnational Workshop on Rare Earth-Cobalt Permanent
Magnets, 1981, P595).

In the present invention, obtaining columnar crystals in a cast state is an important point for high performance magnetization. That is, the process of obtaining coercive force by heat treatment is due to diffusion, and columnar crystals are easier to obtain coercive force, as in samarium-cobalt. Further, the present magnet has a property that the easy axis of magnetization is oriented in a plane perpendicular to the columnar crystals, so that an in-plane anisotropic magnet can be produced by using the columnar crystals.

The reasons for limiting the composition of the permanent magnet according to the present invention will be described below. Rare earth elements include Y, La, Ce, Pr, Nd, Sm, F
u, Gd, Tb, Dy, Ho, En, Tm, Yb, and Lu are listed as candidates, and one or more of these may be used in combination. The highest magnetic properties are obtained with Pr. Therefore, practically, Pr, Pr-Nd alloy, Ce-Pr-Nd alloy, etc. are used. In addition, a small amount of additional elements, such as heavy rare earth elements such as Dy-Tb, Al, Mo, and Si, are effective for improving the coercive force. Main phase of R-Fe-B magnet is R ₂ Fe ₁₄ B. Therefore, if R is less than 8 atomic%, the above compound is no longer formed and a cubic crystal structure having the same structure as α-iron is obtained, so that high magnetic properties cannot be obtained. On the other hand, if R exceeds 25 atom%, it is non-magnetic.
The Rrich phase is increased and the magnetic properties are significantly reduced. Therefore, the range of R is appropriately 8 to 25% atomic%.

B is an essential element for forming the R ₂ Fe ₁₄ B phase,
If the content is less than 2 atomic%, a high coercive force cannot be expected because of the rhombohedral R-Fe system. However, if it is added in excess of 8 atomic% as in the case of a magnet produced by the conventional sintering method, the coercive force in the cast state cannot be obtained. Therefore, the amount of B is preferably in the range of 2 to 8 atomic%.

Co is an element useful for increasing the Curie point and improving the temperature characteristics, but it tends to decrease the coercive force as the amount of addition increases. Further, if Co is increased, the low cost and the ease of processing, which are the features of this magnet, are lost. From these points, the range of Co content is preferably 0 to 40 atomic%.

Example 1 A manufacturing process diagram according to the present invention is shown in FIG. First, an alloy having a desired composition is melted in an induction furnace and cast in an iron mold to form columnar crystals. Next, in order to magnetically harden the ingot, annealing treatment is performed in a temperature range of 500 to 1050 ° C. The casting type magnet according to the present invention becomes an in-plane anisotropic magnet utilizing the anisotropy of columnar crystals by cutting or grinding at this stage.

In this example, first, in order to show the effect of columnar crystallization, Pr ₁₄ Fe ₈₂ B ₄ composition was taken as a typical composition, and changes in coercive force iHc due to heat treatment temperature, time and macrostructure were captured. As shown in Fig. 2, iHc increases as the temperature and time increase from 800 to 1000 ° C. This means that the increase in iHc is not due to the precipitation of the specific phase,
It shows that it is diffusion-dominant. Furthermore, the sample of the equiaxed crystal given as a comparative example has a small coercive force even though it is heat-treated at 1000 ° C. The main phase Pr ₂ Fe ₁₄ B of the present magnet is generated by the peritectic reaction Fe + L → R ₂ Fe ₁₄ B in which the iron phase is the primary crystal from the molten metal, and the primary crystal size largely depends on the cooling rate. Therefore, it is considered that the equiaxed crystal with a slow cooling rate has a large primary crystal and is coarsened, and it takes a long time to diffuse into the main phase.

The alloy with the composition shown in Table 1 was melted, and the cast in-plane anisotropic magnet of the present invention was melted by the method shown in FIG. 1 and, as a reference, a resin-bonded magnet obtained by kneading 4 wt% of an epoxy resin after pulverizing with hydrogen. And were made.

The annealing was all performed at 1000 ° C. for 24 hours. The results obtained are shown in Table 2.

As shown in Table 2, the casting type magnet according to the present invention has a higher holding force than the resin-bonded type magnet.

[Example 2] Next, using the alloys of Sample Nos. 2 and 7 of Example 1, a sintered magnet was produced based on the above-mentioned reference document 1, and JIS
Based on R1601, a sample having a length of 36 mm, a width of 4 mm and a thickness of 3 mm was cut out and the bending strength was compared with that of the product of the present invention. The results are shown in Table 3. No. 2 is a representative composition according to the present invention, No. 7 is a composition near the optimum composition of the sintering method according to Reference 1, and
No. 6 is an intermediate composition. It can be seen from Table 3 that the mechanical strength of the present invention is excellent regardless of the composition.

Example 3 Next, an alloy having the composition shown in Table 4 was melted in the same manner as in Example 1 to obtain a columnar crystal ingot. Then, after heat treatment at 1000 ° C. for 20 hours, JIS R1
Based on 601, a sample with a length of 36 mm, a width of 4 mm and a thickness of 3 mm was cut out and the bending strength was measured. The results are shown in Table 4.

From this Table 4 and Table 3 of Example 2, the low B of the present invention is shown.
It can be seen that excellent mechanical strength can be obtained in the quantitative composition (B = 2 to 6 at%).

[Effects of the Invention] As described above, according to the present invention, it is possible to obtain a coercive force in a bulk state in a composition range where it is difficult to obtain a coercive force by a conventional sintering method, which is excellent in mechanical strength, It is possible to obtain a simplified cast rare earth iron-based magnet.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram of the R—Fe—B magnets of the present invention and the reference example. FIG. 2 is a diagram showing changes in coercive force of Pr ₁₄ Fe ₈₂ B ₄ alloy by heat treatment.

Front page continuation (72) Inventor Rin Kobayashi 3-5 Yamato, Suwa-shi Seiko Epson Corp. (56) Reference JP-A-62-177101 (JP, A)

Claims (2)

(57) [Claims] 1. Iron as a main component, R: 8 in atomic percentage.
-25% (where R is at least one of rare earth elements including Y) and B: 2-8% is melted and cast so that the cast macrostructure becomes columnar crystals, A method for producing a rare earth-iron-based permanent magnet, which comprises magnetically hardening an ingot by heat-treating it at a temperature of 500 ° C. or higher, and further cutting and grinding it into a magnet shape. 2. Iron as a main component and R: 8 in atomic percentage.
~ 25% (where R is at least one of rare earth elements including Y), B: 2 to 8% and Co to 40% (excluding 0) are melted, and the cast macrostructure is columnar crystals. After being cast so that the cast ingot will be magnetically hardened by heat treatment at a temperature of 500 ° C. or higher, further cutting and
Rare earth characterized by being ground into a magnet-
Manufacturing method of iron-based permanent magnet.