JPS6111447B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a precipitation-hardened rare earth cobalt magnet with Sm ₂ Co ₁₇ type crystals. An object of the present invention is to improve the magnetic performance of a permanent magnet by making the macrostructure of an alloy ingot during casting mainly a columnar crystal structure. In our patent application No. 55-3226, we previously proposed that Sm
- By changing the macrostructure of a cast ingot of a Co-Cu-Fe-Zr alloy into a columnar crystal, we have found that the magnetic performance is much better than that of equiaxed or chill crystal alloys, even if they have the same composition. However, it has been discovered that columnar crystallization is further promoted by adding an element consisting of at least one of S, Se, Te, and Bi to the above alloy, leading to the present invention. The present invention heat-treats a cast ingot lump as it is, crushes it, mixes it with a binder, molds it in a magnetic field,
It is extremely effective in improving the performance of resin, metal, or ceramic bonded magnets, which are produced by strengthening the binding of binders. In other words, the process before pulverization is the same as for cast magnets, and the crystalline state of the cast ingot is used as is, so the special element M added in a small amount to the cast ingot can be used to add the columnar crystals that provide the above-mentioned high-performance magnetic properties. Due to its effect, it is possible to obtain a high-performance magnet by producing as much as possible. 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 engrios (crystal buds) in contact with a solid foreign material have a smaller energy barrier to stable nucleation than those floating in the melt without contact. Crystals formed on the casting wall grow during melting while competing with neighboring crystals. The competitive growth region of crystals in the outermost layer of the ingot, as shown in FIG. 1, is called the chill layer. 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 toward the inside of the ingot, forming columnar crystal bands. When the conditions are right, the columnar crystal bands collide and solidification is completed, but as shown in FIG. 1, equiaxed crystals are usually formed inside the columnar crystals. The origin of equiaxed crystals was not well known in the past, but now crystals formed on the casting wall or on the cooled surface of the molten metal are liberated and become free crystals.
It has become clear that these free crystals form equiaxed crystals (A. Ohno, T. Motegi and H. Soda:
Trans.IBIJ.11 (1971) 18). Magnets using the Sm-Co-Cu-Fe-Zr-M six-element alloy are called precipitation hardening type or two-phase separation type magnets. This is because a different phase is precipitated in the matrix and magnetically hardened. This series of magnets was initially made of a ternary Sm-Co-Cu alloy.
Since it was magnetized with a composition using Sm ₂ Co ₁₇ crystals,
It has been widely developed today. It is known that when Co is replaced with Fe, the saturation magnetization 4xIs increases up to a certain amount. In the range where 4xIs increases, the crystal exhibits uniaxial easiness when X is 0 to 0.6, expressed as Sm ₂ (Co ₁ - _x Fex) ₁₇ .
is within the range of This fact does not change even if a certain amount of Cu is substituted for Co. Sm ₂ (CoCuFe) ₁₇ ,
Furthermore, by adding Zr, the magnetic performance can be greatly improved even if the amount of Zr is minute. In other words, if Zr is added, even if the amount of Cu is small or the amount of iron is large, the coercive force will be sufficient for a practical magnet.
iHc was obtained, making it possible to create a magnet with a high energy product. As mentioned above, in this alloy, 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. Furthermore, an ingot in which a small amount of special element M is added to the alloy to increase the columnar crystal zone in the ingot is superior to an ingot cast under the same conditions. An example will now be explained using a resin bonded rare earth cobalt magnet. This magnet is made from a magnetic alloy using 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 advantages of saturation magnetization 4xIs, coercive forces iHc, bHc, and squareness of the hysteresis loop. It was found that the performance was excellent across the board. On the contrary, equiaxed crystal alloys and chill crystal alloys are the worst in terms of performance. In addition, ingots cast under the same conditions but with a small amount of special element M added to increase the columnar crystal zone, and ingots without special element M added, the columnar crystal zone was increased by adding special element M. The performance is better. Since the crystals of columnar crystal alloys are aligned, they have good orientation in the uniaxial direction when made into a magnet. In addition, it is thought that in this alloy, precipitates formed by heat treatment are more uniform than in other alloys. This improves the squareness of the hysteresis. It is also believed that the crystal structure and morphology of the precipitates are formed in a direction that increases iHc better than that of equiaxed crystals. 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. For this reason, the alloy of the present invention contains an element M consisting of at least one of S, Se, Te, and Bi in order to minimize the formation of equiaxed crystal bands in cast ingots. By adding these elements, oxides and nitrides that promote crystallization nucleation from the melt can be wrapped up and inactivated, and these elements M can be combined with oxygen and nitrogen in the melt. It is possible to reduce the generation of oxides and nitrides that serve as nuclei for crystal formation, and to suppress the formation of equiaxed crystals. In this case, although the effect is not necessarily the same depending on the added element, the effect of promoting columnar crystallization is the same. In addition, the most suitable composition for obtaining the effect of columnar crystallization is the composition using the atomic ratio: Sm(Co ₁ ― _u ― _v ― _w ― _x Cu _u Fe _v Zr _w M _x )z (However, 0 <u<0.2 0<v<0.5 0<w<0.1 0<x<0.1 6.5z9.0). Each component and the reason for limiting its composition range will be described 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, 4xI decreases. Therefore, as a practical magnetic material, Sm
The u value in (Co ₁ - uCuu)z is limited to 0.2. When the value of Z is between 5Z8.5,
The Sm-Co alloy is separated into SmCo ₅ type compound and Sm ₂ Co ₁₇ type compound. The value of 4xIs is 20% higher for Sm ₂ Co ₁₇
expensive. Therefore, in order to achieve high 4xIs, Z is
6.5 or higher is desirable. On the other hand, when Z becomes 9.0 or more,
This is not preferable because iHc is significantly lowered and a large amount of Co--Fe phase comes out, which impairs the squareness of the hysteresis loop. Since Zr significantly reduces the 4xIs of the alloy, 0.1
If more than 4xIs is added, Fe is increased and Cu is decreased.
There is no point in increasing the value. The effect of M varies somewhat depending on the added element, but when it exceeds a certain amount,
Since 4xIs and iHc decrease, the upper limit was set at 0.1 in consideration of this limit. Note that these indicate the total amount of composite addition, and the ratio is not particularly specified. The binder can be a variety of polymers, such as epoxy, phenol, rubber, polyester, etc.
The metal binder is preferably a low melting point alloy with a melting point of 400°C or less. The present invention will be explained below with reference to Examples. Example 1. Sm after casting (Co0.6Cu0.07Fe0.3Zr0.02S0.01)
Mix raw materials to have the composition of 8.2, total 1Kg
The alloy was melted in an Ar gas atmosphere using a high frequency furnace and cast into an iron mold as shown in Figure 3 at a hot water temperature of 1600°C. The molten metal was cooled mainly from the side walls, and had the structure shown in FIG. 1st
The figure shows the structure when the ingot is cut at the center. In these parts, A is the chill layer, B is the columnar structure, and C is the tread axis structure. Cast ingots were cut from parts A, B, and C of the alloy ingot, and resin-bonded magnets were produced according to manufacturing method 1 shown in FIG. Solution treatment was performed at 1150°C for 24 hours, and aging treatment was performed at 800°C for 20 hours in an argon atmosphere.
Epoxy resin as a binder is added to fine magnetic powder that has been ground to an average particle size of 10μ using a ball mill method.
1.6wt% was kneaded. 16kg of this kneaded mixture
The magnet was completed by press molding in a magnetic field and applying appropriate heat to the molded body to harden the resin (cure treatment). The results are shown in Table 1. As can be seen from the table, the magnetic performance obtained from the columnar crystal zone in section B is much better than that obtained from the equiaxed crystal zone in section C. Although the chill crystal band of part A is lower than that of part B, it is superior to 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 4xI-H demagnetization curve
This is the magnitude of the magnetic field given by 0.9Br. From these results, it became clear that the columnar crystal portion of part B had excellent performance. The chill crystal zone in part A is generated only in the vicinity of the casting wall, and is very small in the whole ingot, so the most important thing in ingot production is how to suppress the formation of equiaxed crystals and form columnar crystals. The key is to develop crystals. Incidentally, it seems that part A used in this example contains a certain amount of columnar crystal B, judging from the occurrence of part A. Example 2. Resin-bonded magnets were manufactured from alloys having the compositions shown in Table 2 in the same manner as in Example 1. However, the solution treatment was carried out at the most appropriate temperature between 1130 and 1180°C for 20 hours.

[Table] This example was carried out on ingots of sections B and C. The results are shown in Figure 4. Whenever the amount of Fe increases, better magnetic performance is obtained in columnar zone B. This revealed that even if the amount of Fe is increased to a certain extent, a certain level of iHc can be obtained. 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. In Sm(CoCuFeZrM) type ₁₇ alloy, the iHc decreases as the amount of Cu decreases, but it can be seen that in the case of columnar crystal, a higher value of iHc can be obtained up to a low Cu composition compared to that of equiaxed crystal. . In addition, the columnar crystal portion has better squareness.

[Table] Example 4. In exactly the same manner as in Example 2, resin-bonded magnets were manufactured from alloys having the compositions shown in Table 4. The temperature of the hot water during alloy casting is 1650℃. The cast ingot has a cross-sectional macroscopic composition as shown in FIG. The proportion of columnar structure in B is 45 to 60% in alloy No. 1, and in alloy No. 2.
-4, it was 75-85%, and alloy No.5-6, it was 60-65%. The proportion of columnar structure was estimated by observing the cross section of the ingot under a microscope and using the mesh method.

[Table] The results are shown in Table 5. As can be seen from Table 5,
The one with the most columnar structures has the best magnetic performance. In this way, the alloy composition includes S, Se,
It can be seen that the magnetic performance is improved by adding a trace amount of the element M consisting of at least one of Te and Bi to promote the columnar structure as much as possible.

[Table] Example 5. A resin-bonded magnet was manufactured using the alloy having the composition shown in Table 6 in exactly the same manner as in Example 2. The results are shown in Table 7.

【table】

[Table] As shown above, it was possible to obtain a magnet with sufficiently high magnetic performance even when the value of Z was changed. In this way, in Sm-Co-Cu-Fe-Zr alloy,
By adding a small amount of an element consisting of at least one of S, Se, Te, and Bi, the columnar crystallization of the alloy ingot is further promoted, and the performance of Sm ₂ Co ₁₇ type magnets bonded with resin, metal, or ceramic is improved. It was done. The high performance magnet of the present invention can be used in step motors for watches, micro speakers, coreless motors,
It has a wide range of industrial applications such as magnetic sensors.

[Brief explanation of drawings]

FIG. 1 is a cross section of an ingot cast into a mold, taken along the center of the mold. A, B, C
represent the chilled layer, columnar layer, and equiaxed layer, respectively. D is a cross section of the mold. FIG. 2 shows the manufacturing process of the resin-bonded magnet. Figure 3 shows an iron mold. All walls are 15mm thick. Unit of length is mm
It is. Figure 4 shows Sm(Co0.9−
In the composition of VCu0.007FevZr0.02S0.01) 8.2,
The magnetic performance of the resin bonded magnet is shown when V is changed. Figure 5 shows Sm(Co0.75-
In the composition of VCuFe0.22Zr0.02S0.01)8.3, u
This figure shows the magnetic performance of resin-bonded magnets when changing .

Claims (1)

[Claims] 1. A rare earth cobalt permanent magnet made by kneading a binder into powder of an alloy mainly composed of Sm ₂ Co ₁₇ type crystals and compacting the resultant powder, wherein the composition using atoms as the alloy is Sm ( Co ₁ ― _u ― _v ― _w ― _x Cu _u Fe _v Zr _w Mx)z (However, 0<u<0.2 0<v<0.5 0<w<0.1 0<x<0.1 6.5z9.0 M is S, A rare earth cobalt permanent alloy, which is represented by an element consisting of at least one of Se, Te, and Bi, and is characterized by using an alloy in which the macrostructure of the ingot at the time of casting is mainly a columnar crystal structure. magnet.