JPS648452B2 - - 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 transition 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-Cu-Fe 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 series of magnets is a final Sm-Co-Cu three-element alloy, mainly
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 4πIs increases up to a certain amount. The reason why the crystal exhibits uniaxial anisotropy in the range where 4πIs increases is Sm ₂ (Co _1-X
Fe _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 a part of Sm is replaced with Y, since the Y _z Co ₁₇ crystal has a higher 4πIs than the Sm _z CO ₁₇ crystal, it becomes possible to obtain a magnet with a high energy product. Also,
From the perspective of securing rare earth element resources,
This is an advantage since both Sm and Y can be used. However, when a part of Sm is replaced with Y, although 4πIs increases, the crystal anisotropy decreases, so the anisotropic magnetic field Ha becomes smaller. Ha
If the coercive force iHc decreases, the coercive force iHc will also inevitably decrease.
Therefore, one of the objects of the present invention is to
The objective is to prevent the decrease in iHc caused by replacing Sm in Fe-based alloys with Y by converting 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 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. 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. It has become clear that the formation of
Soda: Trans.ISIJ.11 (1971) 18). In the case of this Sm-Y-Co-Cu-Fe alloy, as mentioned above, among the chilled crystalline zone, columnar crystalline band, and equiaxed crystalline band, the columnar crystalline zone is the most suitable for making into a magnet. It became clear. 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. The manufacturing method is exactly the same,
When using equiaxed crystal alloys, columnar crystal alloys, and chill crystal alloys as magnets, the columnar crystal alloys are superior in all performances, such as saturation magnetization 4πIs, coercivity iHc, bHc, and hysteresis loop squareness. I found out that there was. 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 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, it is thought that the crystal structure and morphology of precipitates 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 effect of columnar crystallization is expected when the composition using atomic ratio is Sm _1-X Y _X (Co _1-UV Cu _U Fe _V ) _Z (However, 0 <x<0.5 0<u<0.2 0<v<0.5 6.5≦z<9.0). 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, 4πIs decreases. Therefore, as a practical magnetic material, the value of u in the composition formula is preferably u<0.2. Also, adding Fe improves 4πIs, but if it increases too much, iHc decreases significantly, so v
It is desirable that the value of v<0.5. The value of z is 5z
8.5, the Sm-Co alloy separates into SmCo ₅ type compounds and Sm ₂ Co ₁₇ type compounds. The value of 4πIs is 20% higher for Sm ₂ Co ₁₇ . Therefore, in order to realize a high 4πIs, it is desirable that z be 6.5 or more. On the other hand, when z exceeds 9.0, 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. In addition, although the Y ₂ Co ₁₇ compound has a larger value of 4πIs than the Sm ₂ Co ₁₇ compound, the magnetocrystalline anisotropy constant K ₁ is negative, so if Y ₂ Co ₁₇ is used as it is, it is difficult to use uniaxial anisotropy. Magnets cannot be made, therefore, Sm ₂ Co ₁₇ type compounds with positive and large K ₁ and Y _z with large 4πIs
Combining CO ₁₇ type compounds to make a magnet is
This is an effective method for obtaining a magnet with a large 4πIs and a somewhat high iHc. For this Sm _1-X
Y _X (CoCuFe) In _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. 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 take advantage of this fact is a fine powder bonded magnet. This is because the steps shown in FIG. 1 are used to manufacture the magnet, 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. Conversely, in the magnetic 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 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 Sm _0.9 Y _0.1
(Co _0.8 Cu _0.1 Fe _0.1 ) _8.3 . Ingots were cut out from parts A, B, and C, respectively, and resin-bonded magnets were produced according to manufacturing method 1 shown in FIG. Solution treatment was performed at 1170°C for 4 hours, and aging was performed at 800°C for 20 hours in an argon atmosphere. 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 can be seen from the table, the values obtained from the columnar zone in section B are much better than those obtained from the equiaxed zone in section C. Although the chill crystal zone in part A has lower values of 4πIs and SQ than those in part B, it is considerably better than that in part C.

[Table] However, SQ is an index indicating the squareness of the hysteresis loop, and is given by SQ = Hk/iHc. Hk is 0.9Br on the 4πI-H demagnetization curve
is the magnitude of the magnetic field that gives . From these results, it was found that the columnar crystal 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, part A is very small in the whole ingot, so 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 4 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. (SmY) ₂ (CoCuFe) In alloy type ₁₇ , Cu
As the amount of Cu decreases, iHc decreases, but in columnar crystals, compared to equiaxed crystals, up to a low Cu composition,
It can be seen that a high value of iHc can be obtained. 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.

[Table] After the ingot was removed from the mold, it was heat-treated in its entirety, and all 1 kg of it was crushed. The heat treatment conditions are the same as in Example 2. The sufficiently finely divided powder was kneaded with epoxy resin. Through crushing and 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. It is also seen that even if Y is increased to a certain extent, the iHc required for a practical magnet can be obtained by forming columnar crystals. In this way, a fine powder bonded magnet using an alloy that increases the saturation magnetization by adding Y to the Sm-Co-Cu-Fe alloy and further improves the coercive force, squareness, and saturation magnetization by columnar crystallization is performance, formability,
It is excellent in terms of 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
In the composition of Sm _0.9 Y _0.1 (Co _0.88-v Cu _0.12 Fe _v ) _8.3 ,
The magnetic performance of the resin-bonded magnet is shown when v is changed. FIG. 5 shows the magnetic performance of the resin bonded magnet when u is varied in the composition of Sm _0.9 Y _0.1 (Co _0.9-u Cu _u Fe _0.1 ) _8.3 . FIG. 6 shows a rectangular iron mold. The unit of dimension is mm. Figure 7 shows
An alloy with a composition of Sm _1-x Y _x (Co _0.68 Cu _0.12 Fe _0.20 ) _8.3 was cast into a cylindrical mold and a square mold, and changes in magnetic performance were observed.

Claims (1)

[Claims] 1. A rare earth permanent magnet formed by kneading a binder into an alloy powder mainly composed of Sm ₂ CO ₁₇ type crystals and forming the alloy, wherein the alloy has a composition using an atomic ratio of Sm _{1-X Y _ _ _ _} A rare earth permanent magnet characterized by using an alloy with a certain structure.