JPS648454B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a precipitation type rare earth permanent magnet whose main components are rare earth elements and metals. A method for manufacturing a rare earth permanent magnet according to the present invention is shown in FIG. It has long been known that the magnetic performance of this magnet is influenced by alloy composition, heat treatment, powder particle size and shape, binder type, molding method, etc. We found that the performance changed significantly. Magnets using Sm-Y-Co-M alloys fall into the category of precipitation hardening type or two-phase separation type magnets.
This is because a different phase is precipitated in the matrix and magnetically hardened. This system of magnets was initially
It is an Sm-Co-Cu ternary alloy that has been widely developed since it was first made into a magnet with a composition mainly using Sm ₂ CO ₁₇ crystals. Instead of Cu, Mn, Cr, Mo,
W, Ni, Ag, Au, Al, Ti, Zr, Hf, V, Nb,
By combining one or more of Ta,
When used as Sm-Co-M, the alloy similarly hardens magnetically. If we replace part of Sm with Y, we get
Since Y ₂ Co ₁₇ has a higher saturation magnetization 4πIs than Sm ₂ Co ₁₇ , it becomes possible to obtain a magnet with a high energy product. Also, from the viewpoint of securing rare earth metal resources, it is convenient because both Sm and Y can be used. However, when a part of Sm is replaced by Y, 4πIs increases, but the anisotropic magnetic field Ha
decreases. If Ha decreases, coercive force iHc will also inevitably decrease. Therefore, one object of the present invention is to
The purpose is to prevent the decrease in iHc due to the addition of Y by forming the ingot into columnar crystals. Generally, when molten metal is poured from a crucible into a mold, solidification begins at the casting walls. This is explained by the fact that the energy barrier to stable nucleation of embryos (crystal buds) that come into contact with solid foreign matter is smaller than that of embryos that float in the melt without contact. Crystals formed on the casting wall grow into the molten metal while competing with neighboring crystals. The competitive growth region of crystals in the outermost layer of the ingot, as shown in FIG. 3, is called the chill crystal zone. Since crystals have anisotropy in growth rate, crystals whose direction of maximum growth rate is parallel to the direction of heat flow grow preferentially, suppressing the growth of adjacent crystals. During crystal growth, the closer the preferred orientation is to the heat flow, the longer the crystals survive, and other crystals are weeded out.As a result, the number of crystals decreases as they move inside the ingot, forming columnar crystal zones. When the conditions are right, the columnar crystal bands collide and solidification is completed, but as shown in FIG. 3, equiaxed crystals are usually formed inside the columnar crystals. Although the origin of equiaxed crystals was not well known before, it is now known that crystals formed on the casting wall or on the cooled surface of the liquid become free crystals, and these free crystals form equiaxed crystals. (A. Ohno, T. Motegi and H.
Soda: Trans.ISIJ.11 (1971) 18). Even in this alloy, as mentioned above, chill crystal bands,
It has become clear that among columnar crystal bands and equiaxed crystal bands, columnar crystal bands are the most suitable for making into magnets. Regarding chill crystals, between equiaxed chill crystals and columnar chill crystals, columnar chill crystals are superior. An example will now be explained using a resin bonded rare earth cobalt magnet. This magnet is made from a magnetic alloy by the method shown in FIG. If we make magnets using equiaxed crystal alloys, columnar crystal alloys, and chill crystal alloys using exactly the same manufacturing method, we find that the columnar crystal alloys have all the same characteristics in terms of saturation magnetization 4πIs, coercivity iHc, bHc, and hysteresis loop squareness. It was found that the performance was excellent across the board. vice versa,
Equiaxed crystal alloys and equiaxed chill crystal alloys have the poorest performance. Columnar chill crystal alloys produce magnets with values intermediate between these. This is thought to be because the columnar crystal structure acts effectively when the alloy is heat treated (solution treatment and aging treatment). That is, it is thought that the columnar crystals promote uniform distribution of different phase precipitates precipitated in the matrix, thereby improving the squareness of the hysteresis. At the same time, the crystal structure and morphology of the precipitates are thought to have the effect of forming in the direction of increasing iHc, and therefore, iHc
It also improves. In the production of this alloy, it is important to produce a good magnet by forming columnar chill crystals in the chill crystal zone near the casting wall and forming columnar crystals in other parts. Since the amount of chill crystal bands is small in the entire alloy, the most important thing in manufacturing is to prevent equiaxed crystal bands and increase the ratio of columnar crystal bands. In addition, in terms of composition, the most effective effect of columnar crystallization is expected when the composition using atomic ratio is Sm _1-x Y _x (Co _1-u M _u ) _z (where 0<x <0.5 0<u<0.2 6.5≦z<9.0 M is Mn, Cr, Mo, W, Ni, Ag, Au, Al,
Indicates an element consisting of at least one of Ti, Zr, Hf, V, Nb, and Ta. ) is an alloy represented by The reason for limiting the components and composition range will be explained below. In this alloy system and its composition range, Sm-
Co type is the basic type. Among them, Sm ₂ Co ₁₇ type crystals are the main type. M is added to obtain the coercive force of the Sm ₂ Co ₁₇ type alloy, and by adding M,
iHc improves, but 4πIs decreases. Therefore, as a practical magnetic material, the value of u in the composition formula is u<
0.2 is desirable. M is not only used alone, but also
Two or more types may be added in combination. The value of Z is 5
When between z8.5, the Sm-Co alloy is
Separates into SmCo type ₅ compound and Sm ₂ Co type ₁₇ compound.
The value of 4πIs is higher for Sm ₂ Co ₁₇ . It's expensive
In order to realize 4πIs, Z is preferably 6.5 or more. Furthermore, if Z is 9.0 or more, the amount of Co phase increases, which deteriorates the squareness of the hysteresis loop, which is not preferable. In addition, the Y ₂ Co ₁₇ compound has _a larger value of _4πIs than the Sm ₂ Co ₁₇ compound, but the magnetocrystalline anisotropy constant K ₁ is negative. You can't make magnets. Therefore, Sm ₂ Co ₁₇ type compounds with positive and large K ₁ and Y ₂ CO ₁₇ with large 4πIs
Combining type compounds to form a magnet is an effective method for obtaining a magnet with large saturation magnetization and a relatively high coercive force. For this purpose
In the composition of Sm _1-x Y _x (Co _1-u M _u ) _z , it is also desirable that x<0.5. If the value of x is larger than that, iHc becomes insufficient. As mentioned above, the macrostructure during casting improves the performance of the ingot, and the magnet manufacturing method that can best utilize this fact is the fine powder bonded magnet. This is because the steps shown in FIG. 1 are used to manufacture the magnet, so all the heat treatment is performed on the ingot as it is, magnetically hardened, and then crushed and bonded with a binder. Therefore, it can be magnetized in the ingot state, and in this respect it is no different from cast magnets. The purpose of binding with a binder is to align the crystals, improve moldability and reduce costs when making actual products.
The essence of magnetism is the same as that of cast magnets. Therefore, in the case of a sintered magnet, the performance of the magnet is not affected by the metal structure of the cast ingot, but in the case of a fine powder bonded magnet, it is greatly affected. In other words, this can be used to improve the performance of fine powder bonded magnets. Hereinafter, the present invention will be explained in detail according to examples. Example 1 Using a high frequency melting furnace, 1 kg of an alloy was melted in argon gas. The molten metal was cast into the cylindrical iron mold shown in FIG. The macrostructure of the cross section of the cast ingot was as shown in FIG. That is, part A shows a chill crystal zone, part B shows a columnar crystal band, and part C shows an equiaxed crystal band. The composition of the cast alloy is as shown in Table 1.

[Table] Parts A, B, and C were cut out from the cast ingot, and resin-bonded magnets were manufactured according to the magnet manufacturing process shown in FIG. Containment processing is 1100
The aging treatment was carried out for 10 hours at a temperature suitable for each composition between ~1200°C and 24 hours at 800°C. The results are shown in Table 2. Among the squares in the table, the numbers in the upper row are those obtained using the columnar crystal zone of section B, and those in the lower row are those obtained using the equiaxed crystal zone of section C. This shows that both iHc and 4πIs are larger in the columnar crystal zone.

[Table] Example 2 A resin-bonded magnet was manufactured in the same manner as in Example 1 using an alloy having the composition shown in Table 3.

[Table] The results are shown in Table 4. Among the squares in the table, the numbers in the upper row are those obtained using the columnar crystal zone of section B, and those in the lower row are those obtained using the equiaxed crystal zone of section C.

[Table] It can be seen from Table 4 that the squareness (Hk/iHc) is greatly increased by columnar crystallization. However, Hk is the magnitude of the magnetic field that gives 0.9×Br on the 4πI-H demagnetization curve. Also,
Even in these alloy compositions, the columnar crystals have a better iHc than the equiaxed crystals, and together with their superior squareness, the columnar crystals have a much larger maximum energy product. Example 3 A resin-bonded magnet was manufactured in the same manner as in Example 1 using alloys having the compositions shown in Tables 5 and 6.

【table】

[Table] The results are shown in Figures 4 and 5. From this result,
It can be seen that even when Sm is replaced with Y, the magnetic performance is improved due to columnar crystallization. Furthermore, from FIG. 5, it can be seen that columnar crystals have better magnetic performance for any value of z. In this way, resin-bonded magnets using an alloy that increases saturation magnetization by adding Y to the Sm-Co-M alloy, and further improves coercive force, squareness, and saturation magnetization by columnar crystallization, have excellent magnetic performance and moldability. properties, processability,
It is superior in terms of cost and has great benefits not only to the precision industry but to other industries as well.

[Brief explanation of drawings]

FIG. 1 shows the manufacturing process of a resin-bonded magnet.
FIG. 2 shows a cylindrical iron mold. FIG. 3, whose dimensions are in mm, shows the macrostructure of the ingot when it is cast into the mold shown in FIG.
A is a chill crystal zone, B is a columnar crystal zone, and D is a cross section of the side surface of the mold. Figure 4 shows Sm _1-x Y _x (Co _0.95 Zr _0.05 ) _8.3
The magnetic performance of the resin-bonded magnet is shown when x is varied in the composition. Figure 5 shows Sm _0.8 Y _0.2
(Co _0.95 Ti _0.05 ) In the composition of _z , the magnetic performance of the resin bonded magnet is shown when changing z.

Claims (1)

[Claims] 1. A rare earth permanent magnet formed by kneading a binder into powder of an alloy mainly composed of Sm ₂ Co ₁₇ type crystals and molding the alloy, wherein the alloy has a composition using an atomic ratio of Sm _1-x Y _x (Co _1-u M _u ) _z (However, 0<x<0.5 0<u<0.2 6.5≦z<9.0 M is Mn, Cr, Mo, W, Ni, Ag, Au, Al,
Indicates an element consisting of at least one of Ti, Zr, Hf, V, Nb, and Ta. ) and is characterized by using an alloy whose macrostructure is mainly a columnar crystal structure.