JPH031801B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a rare earth permanent magnet whose main components are rare earth elements and transition metals. More specifically, in an alloy mainly composed of Sm ₂ Co ₁₇ type crystals, C and M (M represents at least one of S, Se, Te, Ce, Pb, Cd, Bi, and Si). This invention relates to a permanent magnet that promotes columnar crystallization of the macrostructure of a cast ingot of this alloy due to the effects of C and special element M during melting and casting of this alloy. We have previously shown in Japanese Patent Application No. 3226/1987 that by making the macrostructure of a cast ingot of a rare earth alloy into a columnar crystal, the magnetic performance is significantly improved compared to equiaxed crystals and chill crystals. The present invention shows that when C and special element M are added to such an alloy, columnar crystallization is promoted, and magnetic performance is further improved even when such elements are added. 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 columnar crystals that provide the above-mentioned high-performance magnetic properties are combined with a small amount of carbon C added to the cast ingot. Due to the effect of element M, 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 the energy barrier for stable nucleation of crystal buds that are in contact with a solid foreign material is smaller than that of crystal buds that are floating 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. 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 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. 1, 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). Magnets using a Sm-Co-Cu-Fe-Nb-C-M based seven-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.
It has been widely developed since it was first made into a magnet with a composition 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 ease because Sm ₂
(Co ₁ −xFex) ₁₇ , where x is in the range of 0 to 0.6. This fact does not change even if a certain amount of Co and Cu are replaced. When Nb is further added to Sm ₂ (Co Cu Fe) ₁₇ ,
Even a small amount of Nb can significantly improve magnetic performance. In other words, by adding Nb, even if the amount of Cu is small or the amount of iron is large, a coercive force iHc sufficient for a practical magnet can be 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. In addition, by adding trace amounts of carbon C and special element M to the alloy,
An ingot with an increased columnar crystal zone 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. When 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 saturated magnetization.
It was found that all performances, such as 4πIs.bHc or the squareness of the hysteresis loop, were excellent. On the contrary, equiaxed crystal alloys and chill crystal alloys are inferior in performance. In addition, ingots cast under the same conditions but with a small amount of carbon C and special element M added to increase the columnar crystal zone, and ingots without carbon C and special element M added. The performance is better when the columnar crystal zone is increased by compound addition of . 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 compared to those 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, Sm−Co−Cu
-Fe-Nb alloy with carbon C and S, Se, Te, Ce,
By casting with trace amounts of Pb, Cd, Bi, Si, etc. added, oxides and nitrides that promote crystallization nucleation from the melt are wrapped in carbides, sulfides, etc. to prevent nucleation. Activation, carbon C, special element M, and oxygen, nitrogen, etc. in the melt combine to reduce the generation of oxides, nitrides, etc. that become nuclei for crystal formation, and form equiaxed crystals. is suppressed as much as possible. In this case, although the effects are not necessarily the same depending on the added elements, they play the same role in promoting columnar crystals. A particularly preferable alloy composition in the present invention is a composition formula using atomic ratios, and when expressed as Sm (Co _-uvwxy Cu _u Fe _v Nb _w C _{v My} )z, 0<u<0.2 0<v <0.5 0<w<0.1 0<x<0.05 0<y<0.1 6.5≦z≦9.0. The reason for limiting the composition range of each component 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, 4πIs decreases. Therefore, as a practical magnetic material, Sm
The value of u in (Co1-uCuu)z is limited to 0.2. When the value of z is between 5z8.5,
Sm-Co alloys are separated into SmCo ₅ type compounds and Sm ₂ Co ₁₇ type compounds. The value of 4πIs is 20% higher for Sm ₂ Co ₁₇
expensive. Therefore, in order to realize high 4πIs, z should be
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. Nb is significantly alloyed
Since it lowers 4πIs, if more than 0.1 is added, there is no point in increasing Fe and reducing Cu to increase 4πIs. As C increases, 4πIs and iHc decrease, so the upper limit was set at 0.05 in consideration of this limit. The effect of M varies somewhat depending on the added element, but if it exceeds a certain amount, 4πIs and iHc decrease, so taking this limit into consideration, the upper limit was set at 0.1. 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 (Co _0.6 Cu _0.07 Fe _0.28 Nb _0.02 C _0.02 S _0.01 ) _8.2
A total of 1 kg of the alloy was melted in an Ar gas atmosphere using a high frequency furnace, and the hot water was poured into an iron mold as shown in Figure 3.
It was cast at 1550℃. 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, chill layer A, columnar structure B,
And let C be the equiaxed 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 810°C for 16 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. This kneaded mixture
The magnet was completed by press molding in a 16KG 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 part B is
It is much better than that obtained from the equiaxed crystal zone. 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 4πI-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 part of part B had the best performance. The chill crystal zone in part A is
It forms 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 develop columnar crystals. In addition, the A part used in this example contains, considering the occurrence situation of the A part,
It seems that a certain amount of columnar crystal B is included. Example 2 In the same manner as in Example 1, resin-bonded magnets were manufactured from alloys having the compositions shown in Table 2. However, the solution treatment was carried out at the most appropriate temperature between 1120 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. Even as 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 the Sm (Co Cu Fe Nb CM) type ₁₇ alloy,
It can be seen that as the amount of Cu decreases, iHc decreases, but in columnar crystals, higher iHc values can be obtained up to low Cu compositions than in equiaxed crystals. Also,
The columnar crystal part also 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 1600℃. The cast ingot has a cross-sectional macrostructure as shown in FIG. The proportion of columnar structure in B is approximately 60% in alloy No. 1, and in alloy No. 2 ~
It was 78-87% for Alloy No. 4, and 68-76% for Alloy No. 5-6. 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 carbon C and S,
Special elements M such as Se, Te, Ce, Pb, Cd, Bi, Si, etc.
It can be seen that the magnetic performance is improved by adding a combination of to promote the columnar structure as much as possible.

【table】

[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 the Sm-Co-Cu-Fe-Nb alloy,
By adding carbon C and S, Se, Te, Pb, Cd, Bi, Si, etc. in combination, the columnar crystallization of the alloy ingot is further promoted, and the formation of Sm ₂ Co ₁₇ type magnets bonded with resin, metal, or ceramic Performance has been improved.
The high performance magnet of the present invention has wide industrial applications such as step motors for watches, micro speakers, coreless motors, and magnetic sensors.

[Brief explanation of the drawing]

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(Co _0.88-v Cu _0.07 FevNb _0.02
C _0.02 S _0.01 ) _8.1 shows the magnetic performance of the resin-bonded magnet when V is varied. Figure 5 shows
The magnetic performance of the resin bonded magnet is shown when u is varied in the composition of Sm(Co _0.725-u Cu _u F _0.22 Nb _0.02 S _0.01 ) _8.3 .

Claims (1)

[Claims] ₁ C and M (however, M is _at least one of S, Se, Te, Bi 1. A rare earth permanent magnet characterized by using an alloy in which the macrostructure of the ingot at the time of casting is made into columnar crystals by adding a certain number of seeds or more.