JPS648455B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a fine powder bonded rare earth permanent magnet. 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-Pr-Co-Cu-Fe-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 has been widely developed since it was first made into a magnet using a ternary alloy of Sm-Co-Cu, mainly using Sm ₂ Co ₁₇ crystals. CoFe
It is known that the saturation magnetization 4πIs increases up to a certain amount by replacing it with . In the range where 4πIs increases, the crystal exhibits uniaxial anisotropy because Sm ₂
(Co _1-x F _x ) ₁₇ , where X is in the range of 0 to 0.6. This fact does not change even if a certain amount of Cu is substituted for Co. When M is further added to Sm ₂ (CoCuFe) ₁₇ , the magnetic performance can be greatly improved even if the amount of M is very small. That is, when M is added, even if the amount of Cu is reduced or the amount of iron is increased, an iHc sufficient for a practical magnet can be obtained and a magnet with a high energy product can be manufactured. When a part of Sm is replaced with Pr, the Pr ₂ Co ₁₇ crystal becomes smaller than the Sm ₂ Co ₁₇ G crystal,
The high 4πIs makes it possible to obtain a magnet with a high energy product. Also, from the viewpoint of securing rare earth element resources, it is advantageous because both Sm and Pr can be used. however,
When a part of Sm is replaced with Pr, 4πIs increases but the crystal anisotropy decreases, so the anisotropic magnetic field
Ha becomes smaller. If Ha decreases, coercive force iHc
will also inevitably decline. Therefore, one of the objects of the present invention is to prevent the decrease in iHc caused by replacing Sm with Pr in a Sm-Co-Cu-Fe-M alloy by converting the ingot into columnar crystals. Another objective is to obtain enough iHc for a practical magnet by columnar crystallization, even if the Cu content is further reduced and the Fe content is further increased. 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 for stable nucleation of embryos (crystal buds) that have come into contact with a solid foreign material is smaller than that of embryos that are floating in solution 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 preferential 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 toward the inside of 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. The origin of equiaxed crystals was not well known in the past, but it is now known that crystals formed on the casting wall or on the cooled surface of the molten metal are liberated and become free crystals, and these free crystals form the equiaxed crystal zone. (A. Ohno, T. Motegi and H.
Soda: Trans.ISIJ.11 (1971) 18). Even with this Sm-Pr-Co-Cu-Fe-M alloy,
As mentioned above, it has become clear that among the chill crystal zone, columnar crystal zone, and equiaxed crystal zone, the columnar crystal zone is the most suitable for making into a magnet. 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 use exactly the same manufacturing method to make magnets from equiaxed crystal alloys, columnar crystal alloys, and chill crystal alloys, we find that the columnar crystal alloys exhibit saturation magnetization.
It was found that all performances were excellent, including 4πIs, coercive force iHc, bHc, and the squareness of the hysteresis loop. On the contrary, 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 composition acts effectively when the alloy is heat treated (solution treatment and aging treatment). In other words, it is thought that the columnar crystals promote uniform distribution of different phase precipitates precipitated in the matrix.
This improves the squareness of the hysteresis. At the same time, it is thought that the crystal structure and morphology of the precipitate also act to increase iHc, and therefore iHc also improves. Therefore, in order to obtain a good magnet, it is important to manufacture this alloy in such a way that the chill crystals near the casting wall are made into columnar chill crystals, and the other parts are made into columnar crystals. Since the amount of chill crystal bands is small in the overall 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 columnar crystallization is expected to be the composition using the atomic ratio, Sm _1-x Pr _x (Co _1-uvw Cu _u Fe _v M _w ) _z (However, , 0<x<0.5 0<u<0.2 0<v<0.5 0<w<0.1 6.5≦z<9.0 M represents 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. Cu is added to the Sm ₂ Co ₁₇ type alloy to obtain coercive force, and adding Cu improves iHc. However, 4πI decreases. Therefore, as a practical magnetic material, the value of u in the composition formula is preferably u<0.2. Although 4πIs is improved by adding Fe, if the amount is too large, iHc decreases significantly, so the value of v in the composition formula is preferably v<0.5. When the value of z is between 5z8.5, the Sm-Co alloy separates into SmCo ₅ type compounds and Sm ₂ Co ₁₇ type compounds. The value of 4πIs is
Sm ₂ Co ₁₇ is 20% more expensive. Therefore, in order to realize a high 4πIs, it is desirable that z be 6.5 or more. On the other hand z
If it becomes 9.0 or more, iHc decreases significantly and a large amount of Co--Fe phase comes out, which impairs the squareness of the hysteresis loop, which is not preferable.
Also, the Pr ₂ Co ₁₇ compound is more effective than the Sm ₂ Co ₁₇ compound.
Although the value of 4πIs is large, the magnetocrystalline anisotropy constant
K ₁ is negative, and a magnet utilizing uniaxial anisotropy cannot be produced using Pr ₂ Co ₁₇ as it is. Therefore, Sm ₂ Co ₁₇ type compounds with positive and large K ₁ and large 4πIs
Making a magnet by combining Pr ₂ Co ₁₇ type compound is
This is an effective method for obtaining a magnet with a large 4πIs and a somewhat high iHc. For this Sm _1-x
Pr _x (CoCuFe) In _{the z} composition, x < 0.5 is desirable as a practical material. If the value of x is larger than that,
I don't have enough iHc. What made w less than 0.1 was M
This is because if 0.1 or more is added, there is no point in increasing 4πIs by increasing Fe, reducing Cu, or adding Pr, as it significantly lowers the 4πIs of the alloy. M may be used not only alone, but also in combination of two or more. As mentioned above, the magnetic performance of the ingot changes significantly depending on the crystalline state at the time of casting. The magnet manufacturing method that can best utilize this fact is a fine powder bonded magnet. This is because manufacturing the magnet involves the steps shown in FIG. 1, so all heat treatment is performed in the ingot state, and after magnetic hardening, it is crushed and bonded with a binder. Therefore,
A magnet of a desired shape can also be produced by cutting out the ingot after magnetic hardening. The process before crushing is the same as for cast magnets. Because such a manufacturing process is used, the crystalline state of the ingot has a greater effect on magnetic performance than in the sintering method. Therefore, in contrast, with the resin bonding method, it is possible to produce a magnet with excellent magnetic performance by controlling the crystalline state during casting. Hereinafter, the present invention will be explained in detail according to examples. Example 1 Using a high frequency melting furnace, 1 kg of alloy was melted in argon gas, and the molten metal was cast into a 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 Sm _0.9 Pr _0.1
(Co _0.6 Cu _0.08 Fe _0.3 Zr _0.02 ) _8.3 . A part, B part,
Cut out an ingot from part C, and
A resin-bonded magnet was manufactured according to Manufacturing Method 1 shown in the figure.
Solution treatment is at 1150℃ for 10 hours and aging is at 800℃.
The test was carried out in an argon atmosphere for 20 hours. Epoxy resin was used as the resin, and was mixed at 2.0 wt% with respect to the magnetic powder. The results are shown in Table 1. As you can see from the table,
The values obtained from the columnar zones in section B are much better than those obtained from the equiaxed zones in section C. Although the chill crystal zone of part A has lower values of 4πIs and SQ than those of part B, it is considerably better than that of part C.

[Table] However, SQ is an index indicating the squareness of the hysteresis loop, and is given by SQ = Hk/iHc. Hk is on the 4πI-H demagnetization curve
This is the magnitude of the magnetic field that gives 0.9Br. From these results, it was found that the columnar crystal part of part B had the best performance. The chill crystal zone in part A is generated only in the very vicinity of the casting wall, and in the ingot of this example, it is 1 mm or less. Therefore, it seems that the ingot of Part A used to obtain the results in Table 1 contains a considerable proportion of columnar crystals of Part B. In this way, since part A is very small in the whole ingot, it can be ignored. The important point in producing ingots is how to suppress equiaxed crystals in the C portion and develop columnar crystals. Example 2 A resin-bonded magnet was manufactured from an alloy having the composition shown in Table 2 in the same manner as in Example 1. However, the solution treatment was performed at the most optimal temperature between 1150 and 1180°C for 10 hours.

[Table] This example was also carried out mainly on ingots of only parts B and C. The results are shown in Figure 4. It can be seen that columnar crystals provide better magnetic performance even as the amount of Fe increases. This revealed that iHc can be obtained even if the amount of Fe is increased to some extent. Example 3 In exactly the same manner as in Example 2, resin-bonded magnets were manufactured from alloys having the compositions shown in Table 3. The results are shown in Figure 5. (SmPr) _z (CoCuFeM) For alloy type ₁₇ ,
As the amount of Cu decreases, iHc decreases, but it can be seen that in columnar crystals, higher iHc values can be obtained up to low Cu compositions than in equiaxed crystals. Columnar crystals also have better squareness.

[Table] Example 4 1 kg of the alloy having the composition shown in Table 4 was added to the second
In order to obtain a large number of columnar crystal portions, casting was performed in the mold shown in the figure and in a rectangular mold shown in FIG. 6. The proportion of columnar crystal portions was approximately 40% in the former mold and approximately 80% in the latter mold. After the ingot was removed from the mold, it was heat-treated in its entirety and pulverized to 1 kg. The heat treatment conditions are the same as in Example 2. The sufficiently finely divided powder was kneaded with epoxy resin. crushing,
Through kneading, the magnetic powder becomes uniform throughout. A 10g sample was taken from the whole sample and molded in a magnetic field to form a magnet. Therefore, the manufacturing process is Manufacturing Method 1 shown in FIG. The results are shown in FIG. It can be seen that the performance of the magnet cast in a square mold is superior. Furthermore, even if the Pr content is increased to a certain extent, the iHc required for a practical magnet can be obtained by forming columnar crystals.

[Table] Example 5 An alloy having the composition shown in Table 5 was cast into the mold shown in FIG. The temperature of the molten metal during casting was 1600°C. Conventionally, molten metal temperature was around 1450℃. At this temperature, the cast ingot has a large proportion of equiaxed crystals, as shown in FIG. In order to obtain a large amount of columnar crystals, it is important to raise the water temperature. Therefore, in the casting performed in this example, approximately 90%
A columnar crystal structure was obtained.

[Table] The magnet manufacturing method was carried out in the same manner as in Example 5. The results are shown in Table 6. It can be seen that high performance values are obtained for each M as a resin bonded magnet.

[Table] Example 6 A resin-bonded magnet was produced using the alloy having the composition shown in Table 7 using the same process as in Example 5. The results are shown in Table 8.

【table】

[Table] As shown above, it was possible to produce a magnet with sufficiently high performance even if the value of z was changed. In this way, a fine powder bonded magnet using an alloy that increases saturation magnetization by adding Pr to the Sm-Co-Cu-Fe-M alloy, and further improves coercive force, squareness, and saturation magnetization by columnar crystallization. It has excellent magnetic performance, moldability, workability, and cost, and has great utility not only in the precision industry but in 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. The unit of dimension is mm. FIG. 3 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, C is an equiaxed crystal zone, and D is a cross section of the side surface of the mold. Figure 4 shows
The magnetic performance of the resin-bonded magnet is shown when V is varied at a composition of Sm _0.9 Pr _0.1 (Co _0.9-v Cu _0.08 Fe _v Zr _0.02 ) _8.3 . Figure 5 shows Sm _0.8 Pr _0.2 (Co _0.676-u Cu _u Fe _0.3
Zr _0.024 ) Magnetic performance of the resin bonded magnet when u is changed in the composition _8.1 is shown. FIG. 6 shows a rectangular iron mold. The unit of dimension is mm.
Figure 7 shows the changes in magnetic performance when an alloy with a composition of Sm _1-x Pr _x (Co _0.6 Cu _0.08 Fe _0.3 Ti _0.02 ) _8.3 was cast into a cylindrical mold and a square mold. .

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 Pr _x (Co _1-uvw Cu _u Fe _v M _w ) _z (0<x<0.5 0<u<0.2 0<v<0.5 0<w<0.1 6.5≦z<9.0 M is Ti, Zr, Hf , V, Nb, and Ta), and is characterized by using an alloy whose macrostructure is mainly a columnar crystal structure.