DE811976C - Permanent magnet and method for making a magnetically anisotropic permanent magnet - Google Patents

Description

Permanent magnet and method of making a magnetically anisotropic Permanent Magnets The present invention relates to a permanent magnet and a method for producing a magnetically anisotropic permanent magnet from a magnetically hardenable iron-based alloy containing nickel, aluminum and cobalt as the most important alloy components.

It is known that the anisotropy of such magnets is thereby preserved can be that the: magnetic alloy during cooling for the purpose of magnetic Curing in a temperature range around the Curie point and a temperature around r @ o @ C below this point, is subjected to an X-1 magnetic field. By subsequent 'magnetization of the' magnetic body parallel to the direction of the during the magnetic field used for cooling, a permanent magnet can be obtained in this direction, the so-called preferred direction, a considerably lighter BH "" "value as if the cooling in a magnetic field is omitted. So far have been obtained best results with iron-based alloys ranging from 16 to Contained 30% cobalt, 12 to 20% nickel and 6 to r r 0l0 aluminum.

In the tests that led to the present invention, it was found that the energy product BH "",., in the preferred direction of alloys, which are the same or similar in composition to those mentioned above, and were subjected to a magnetic field during cooling by applying the inventive concept still essentially: dimensions can be improved. \ ach the invention are to this purpose the crystals of the magnet predominantly 'oriented in such a way, that the (ioo) direction is mainly parallel to the preferred magnetic direction, in which the magnet is magnetized. After the heat treatment in the magnetic field can the body has been subjected to an aging treatment.

With a composition that would otherwise be obtained by cooling in a magnetic field a BH, "" value of 5,000,000 in the preferred direction can be used of a material with the specified crystal orientation a BHmox - '# N'ert of deliver higher than 8oooooo. If instead of magnetizing the alloy body of the same composition in the direction of the predominant crystal orientation this body while cooling in a different direction, e.g. B. the transverse direction, is magnetized, the energy product of around 5,000,000 is the highest achievable Value. On the other hand, in the case of compositions, which otherwise by cooling in a Magnetic field BHmox values that do not exceed 25ooooo and for this reason So far, the use of materials has not been of interest in practice Crystal orientation BH "." Values give well above this limit lie. It is therefore evident that, in general, by applying the invention performed process obtained improvement in the energy product on the combination the predominant crystal orientation in the (ioo) direction and the magnetization parallel to this direction during the cooling of the alloy body for the purpose of magnetic Hardening is due.

In order to obtain a significant advantage, as mentioned above, from the selected crystal orientation, permanent magnets according to the present invention have a cobalt content of 10 to 400/0, preferably 16 to 30%, a nickel content of 10 to 28%, an aluminum content from 6 to ii% and a copper content of not more than 70/0. The higher BH .. "values are obtained with a cobalt content of 16 to 300/0, in particular higher than 20%, and also through a suitable choice of the other components. Titanium can be present in an amount of not more than 70/0 The alloy may also contain minor amounts, namely less than i # 4, of tungsten, chromium, molybdenum, vanadium, zirconium, calcium, cerium and silicon, the remainder being essentially iron and impurities found in engineering steels.

The alloy may be in the form of a single crystal or a complex of crystals. In the latter case, the best results are obtained when all the crystals are in the desired crystal direction, but useful results are obtained when practically more than 50 percent by volume, and preferably more than 70 percent by volume of the alloy consists of crystals oriented in the desired direction.

The crystal orientation can be achieved by casting the alloy under solidification conditions which heat the alloy in essentially only one direction is withdrawn. In parallel to this direction, the alloy body becomes more magnetic for the purpose of being more magnetic Hardening subjected to the magnetic field. Preferably, the alloy is mainly the heat withdrawn in the vertical direction, so that the crystal growth is not caused by convection currents and differences in specific gravity will be affected, as will be the case could if the direction of the crystal growth were horizontal.

The desired result can be achieved by using a mold, which is placed in an oven with a temperature of i2oo to i5oo ° C, the underside of the mold in contact with an artificially cooled metal plate brought or even by an air flow or other suitable coolant is cooled. By gradually reducing the heat input to the furnace, the alloy becomes solidified from the bottom of the mold in the upward direction. Large stem crystals emerge, which are perpendicular to the cooled side of the mold stand with a (ioo) direction that is parallel to the longitudinal axis of the columnar crystals is.

According to a further feature of the present invention, the desired crystal orientation obtained by the fact that the magnet alloy in a Form is made to solidify, which consists of surfaces with different thermal conductivity exists or is provided with surfaces with the greatest thermal conductivity are perpendicular to the required direction of crystal growth. A type in which embodies this feature of the invention includes a sand mold or another refractory material with metal quenching surfaces or other material with corresponding high thermal conductivity. The quenching or cooling surfaces can be solid or hollow and driven by a fluid such as a water or air flow, be cooled.

To promote the directional crystallization, the shape can be attached to the Places of low thermal conductivity, e.g. B. by electric heater, which in Sand or the refractory material is embedded near the mold surface are to be supplied with heat. The crystal orientation is thus obtained by that of the molten alloy in the direction of the desired crystal orientation Heat is withdrawn, the heat losses in a direction perpendicular to it be limited as possible to a crystal growth from the walls of the mold in the transverse direction to avoid.

The cooling surfaces can be easily removed, if necessary, and the low thermal conductivity parts can be heated to a high temperature prior to the assembly of the mold and casting of the magnet alloys to avoid heating of the cooling surfaces. There is less effect if the entire mold, including the cooling surfaces, is heated shortly before casting. It was found that the presence of Titanium in large quantities the growth of the stalk crystals disturbs, so that when using the driving to (learn the last-mentioned characteristics of the finding, with (learn essentially differences in thermal conductivity to promote the Stetigel crystal offspring are used, it proved necessary no more than Compositions containing 0.7% titanium use, the composition otherwise by the in the presenting in connection with directional crystallization as favorable given area is conditional. Although the directive effect is not as complete as when using application of the other aforementioned procedures found that through the oriented crystal growth of the BHmaX- @ Vert ran alloys with no directional crystal growth an I @ H "" c value of 4oooooo to 5oooooo give, to be increased to 6,000,000 to 7,000,000 can. The cooling in the magnetic field can occur during the Cooling of the lagliet alloy in the mold occur. When the coolant of the mold is out Eiseil or another magnetically conductive Order factory version. I open them as pole pieces Head of the \ lagiietfeldes iai the desired direction tuni; er «en (let« -erden. The alloy can also after cooling down in the mold and after fenitinri from this subjected to a new heating \\ - ground, nin then the magnetic treatment perform. Talfelle 1 illustrates the wide, popular schr; inlaen and (partly preferred area for the ZilsainniensetztinZ (ler to ver «-en (lenden permanent magnetic alloys Talfelle 1 Wide-, r B:, schr2inkt (r Area B: rich Preferred b ° rich 6 to 1100 ff to iio; 'o 7.0 to 8.50; o Ni io to 2 S 11 to 210% 13.5 to 16.5o% Co 10 to 400% 16 to 3,> 0% 20, o to 25.00% Cli Abis 70-o (f to 70l0 less than 6.5o% Ti 0 to 7% o to 50% less than 2.8o% Fe remainder remainder remainder with norms with normal with normal \ 'erun- N-erun- @' erun- cleaning cleaning cleaning The invention becomes all hand of the drawings explained in more detail in (lead Fig. I shows a longitudinal section of a sand mold vain horror plate, as it is in suitable in any way bmiin (-, ellen a permanent magnet alloy according to your principle of the present invention finding used \\ - can ground; Fig. 2 is a larger-scale step through the form along the line 11-11 in Fig. i; Fig. 3 shows (read in the form according to Figs and 2 received castings with one of them separate part to hold a permanent magnet and with other dividing lines, which are shown in dashed lines; Fig. 4 is an enlarged front view of a portion of the casting illustrating the direction of crystal growth; Fig. 5 is a front view of a portion of the portion of Fig. 4 severed therefrom for the purpose of maintaining maximum orientation of crystal growth in a single direction, schematically illustrating the magnetization of the portion in the same direction; 6 is a graph of demagnetization curves of permanent magnets with the same composition of the alloy, but made under different conditions, to illustrate the better magnetic properties achieved according to the invention.

Casting an alloy within the aforementioned compositional ranges can be conveniently done in a sand mold as with the Reference symbol io in FIGS. I and 2 is indicated. The form io consists of one lower part i i and an upper part 12. The part i i is with a mold cavity 13 provided, which is shown rectangular in section. An opening 14 in the part 12 is connected to the cavity 13 by a in the lower part of the mold near the Top of the cavity attached channel 15 connected. Through channels 16 and 17 an overflow of the hollow space is provided in the molded parts i i and 12.

The shape io can be made from moist or dried sand or from a other suitable molding material can be made: To-1? Maintain one in one In the direction of predominant crystal growth in the casting, a chill plate 18 made of iron or other metal or another suitable material with good thermal conductivity attached at the bottom in cavity 13. The plate can also be attached to another Place as attached to the bottom of the mold, or rushed mold with an often ene The end can be clamped onto the metal base plate, which serves as a quenching plate or otherwise attached. It is also ni ;; ') like hurried the mold walls made of a material with higher thermal conductivity, such as zircon sand.

lin operation becomes a melted. permanent magnet alloy labeled i9 of the specified composition through the opening 14 and the extension piece i 5 brought through into the cavity 13 in order to fill it with the alloy. The mold is allowed to cool sufficiently to solidify the molten material 1_egiei-uiig to effect. The casting 20 thus obtained is then removed from the mold removed. The casting as a whole can be further described below Stages of the process are subjected to all of them, as shown in Fig. 3 is, parts 21 can be separated from the casting in order to earth several smaller magnets to obtain. The separation of the part 21 and smaller files can be best by N "er @ \ - ethic a circular one with a diamond Saw to be carried out.

In Fig. 4 it is shown how a characteristic crystal growth can be obtained by using a cooling plate as described. 4 shows an enlarged vertical surface of the section 21 with a lower edge 22 which corresponds to the lower surface of the casting which was in contact with the cooling plate 18. While, as shown in Fig. 4, the solidification and crystal growth naturally begin at the surfaces of the molten metal which are near the wall of the cavity and continue inwardly perpendicular to the aforementioned walls, is by far that fastest crystal growth perpendicular to the surface of the plate 18, as indicated by the surface A above the bottom 22. This is because the cold plate extracts heat from the molten metal faster than the walls of the cavity. Consequently, the surface A represents a crystal growth region in one direction which is largely predominant compared to the side surfaces B and B ' and the surface A'. In the smaller surfaces B and B ' , the direction of crystal growth is perpendicular to the direction of crystal growth in surfaces A and A'.

The entire section 21 can be implemented according to the invention Process to be edited, or if an even higher energy product is desired is, a with 23 (Fig. 5) designated smaller part from the section 21 along the dashed line 23 ° (Fig. 4) are cut so that this part is practically completely within the surface A. In the smaller part 23 are all lines indicating the crystal growth or the main features of the crystals practically parallel to each other.

During the subsequent processing of the casting 20 or its section 21 or the smaller part 23, the alloy body is subjected to a heat treatment which is necessary in alloys of this type in order to maintain what is known as magnetic hardening. For this purpose, the alloy body is heated to a temperature of approximately 1200 ° C. or higher and then cooled. During this cooling and while the alloy body cools below the Curie point, the body is subjected to a magnetic field, the direction of which is parallel to the direction of the predominant crystal growth. This is indicated by the two-headed arrow M in FIG. 5. Since the Curie point of an alloy in the above-mentioned composition range is in the vicinity of around 750 to 900 ° C, the alloy body must be heated to at least above the given upper limit and then subjected to the magnetic field. The body cools down below the Curie point, preferably until a temperature of about 150 ° C. below the Curie point is reached. The magnetic treatment can take place while the piece is cooling in the mold, or the casting can be removed from the mold after cooling and then reheated and cooled in the magnetic field. In general, in the latter case, the alloy body is heated again to a temperature of around 130 ° C. and cooled to a temperature of around 60 ° C. at a rate of 0.5 to 5 ° C. per second. The slower cooling rate is best used while the alloy body cools from about the Curie point to a temperature of about 150 ° C. below the Curie point.

The temperature range between the Curie temperature and about 150 ° C. below the Curie point is part of the temperature range which is passed through during cooling of the alloy for the purpose of magnetic hardening. The length of time during which the temperature of the alloy remains in this range between the Curie point and the temperature 150 ° C. below the Curie point must be at least 30 seconds, but about ten times or 300 seconds in order to obtain the most favorable magnetic properties. Since it is known that a suitable tempering results in an improvement in the magnetic properties of nickel-aluminum-cobalt-iron alloys, the alloy is preferably then tempered. This treatment consists e.g. B. in that the alloy is held at a temperature of about 60o ° C for 6 to 12 hours.

After the alloy body is subjected to the complete heat treatment has been, it is usually demagnetized to facilitate its processing will. With each subsequent magnetization, however, the alloy body must be in the same direction as first, that is parallel to the direction of the prevailing Crystal growth to be magnetized.

Some specific examples of how the invention can be practiced are as follows: Example 1 Rectangular coupons of 22mm2 and 35mm high are cast in a two-part sand mold which is set up so that one half of the vertically running, associated channels in each Molded part are closed on the sides facing away from each other with sand and the remaining channels are correspondingly closed with steel quenching plates, which form the upper and lower surfaces of the mold cavities. After the alloy has solidified, the castings are heated to 130 ° C and at the same time cooled in a magnetic field of 3,000 Gauss directed parallel to the longitudinal axis of the test pieces, whereupon the castings are subjected to an aging treatment at 585 ° C for 72 hours. The magnetic properties are determined after 0.5 mm has been separated from each side of the sample blocks and are shown in Table 1I, which enables a comparison between the normal sand castings and the castings with oriented crystals produced by the action of the cooling plates Table 1I composition Al% N i 0/0 Co 0/0 Cu 0/0 Ti 0/0 @, i i3.3 24.3 2.9 - 7.6 14.3 25 0 3.2 0.5 6.8 11.4 26.7 4.9 - 8.9 16.o 35, o 4.7 - 9, o 15.0 15.3 4.5 - 9.5 2 0 .3 19.9 2.2 - Sand castings Remanence BHM "X coercive force 12.85O 5.50 X1o6 63 0 12.400 4.80X l 06 655 11.400 2.35X106 32 0 10.150 2, IOX l 06 345 9.60o 2.50X 106 565 8.75 0 1.90 X 1 0 6 6o5 Examples with oriented crystals 1Zemanence BHmax coercive force 13,050 6, o5Xios 700 12.80o 5.80X 1 0 6 715 13,500 3.90X 1 0 8 495 11.400 3.45 X 108 490 11.65o 4.20X 1 0 8 685 8.95 0 2.50X I06 715 Example 11 Cylinder magnets with a diameter of 22 mm and a height of 19 minutes are cast in a mold which consists of vertical sand walls and horizontally attached water-cooled steel quenching plates on the top and bottom of the mold cavity. The vertical sand walls are heated to about 100 ° C. by means of an electrical resistance heater embedded in the sand at a distance of 3 mm from the mold surface. The magnets are cast from an alloy consisting of 7.9% aluminum, 13.10 / 0 nickel, 25.6% cobalt, 4.0% copper and the remaining part iron and are heated to 1300 ° C after the melt has solidified and cooled at a rate of i, i ° C per second in a magnetic field of 3000 Oersted parallel to the cylinder axis. The magnets are also subjected to an aging treatment at 585 ° C. for 72 hours. Investigations on the magnetic body result in a BH "",., - value of 61,000,000 Gauss-Oersteds, a remanence of 13,40 Gauss and a coercive force of 72,000 Oersteds. Investigations with magnetic bodies of the same alloy, which are made according to the normal casting process in a sand mold, result in a BH. "" Value of 5,200,000 with a remanence of 12,700 Gauss and a coercive force of 66o Oersteds. Example III A molten magnetic alloy is introduced into a sand mold, the cavity of which is 100 mm 2 in cross-section and 120 mm in depth, and which contains a heavy steel quenching plate 15 mm thick, which is mounted horizontally along the bottom of the cavity. After the alloy has solidified, rectangular sample blocks measuring 35X 35X 10 mm are cut from the central portion of the casting so that one of the 35X 10 mm sides is formed from the horizontal cooled side of the casting. The sample blocks are heated to 1300 ° C. and cooled at a rate between i, o and 1.5 ° C. per second in a magnetic field of 3,000 Gauss, in such a way that the direction of the field is perpendicular to the cooling surface of the original casting. After cooling, the sample blocks are subjected to an aging treatment at 585 ° C. for 72 hours. The magnetic test results for various compositions are given in Table III. Table 111 composition A1 0 / e Ni 0 / e Co 8 / e Cu 0/0 Ti 0 / e 8.4 13.8 24.3 3.2 - 9.2 14.2 28.8 2.9 - 8.1 15.3 25.6 3.6 0.5 7.5 14.7 28.8 - - Magnetic properties Remanence B ,. BH ... coercive force H, 13,550 8.05X-106 725 12.350 7.65 X 1o6 800 11.950 7.25 X 1 0 6 645 13.750 6.70X 1 06 645 In Fig. 6, the three curves C, D and E are demagnetization curves for permanent magnet alloys of the same chemical analysis. This analysis is as follows: A1 8.21%, Ni 14.3%, CO 24.35%, Cu 3.18%, C 0.03%, Fe remainder.

In the case of the permanent magnet alloy according to curve C, the method described and carried out according to the invention is used, but with the difference that the magnetic field during cooling is perpendicular to the prevailing direction of crystal growth. The result is a bra "energy product." from 5 050 ooo. Curves D and E are curves of two examples of permanent magnet alloys machined according to the preferred processes described above and give energy products of 7400000 and 7875ooo. The magnetic values obtained with these examples are given in the table below. Table IV Examples CDE B, 13000 13450 13400 H, 595 735 738 BH "" X 1 0 6 5.05 7.4 7.875 Compared to Example C, Examples D and E give an energy product that is at least 50% greater. This clearly shows the better magnetic properties which are obtained by using the method according to the invention.

Claims (15)

PATENT CLAIM: i. Magnetically anisotropic permanent magnet based on iron with nickel, aluminum and cobalt as the most important elements, characterized that the crystals of the magnet are predominantly oriented in such a way that the (ioo) Direction is mainly parallel to the preferred magnetic direction in which the magnet is magnetized. 2. Permanent magnet according to claim i, characterized in that that it is 10 to 40% cobalt, 10 to 28% nickel, 6 to 10% aluminum, 0 to 70./0 Contains copper and o to 7% titanium. 3. Permanent magnet according to claim i or 2, characterized characterized in that it contains 6 to i i% aluminum, ii to 21% nickel, 16 to 30% cobalt, up to 7% copper, up to 5% titanium and otherwise mainly iron with impurities contains that the magnet is magnetically anisotropic with a BH, R value in the preferred direction of at least 7,000,000, with the crystals of the magnet also predominant are oriented in the preferred direction. 4. Permanent magnet according to claim i or 2, characterized characterized in that it contains 7 to 8.50% aluminum, 13.5 to 16.5% nickel, 2o to 25% Cobalt, less than 6.5% copper, less than 2.8% titanium and otherwise mainly Contains iron with impurities and that the magnet is magnetically anisotropic with a BH. "., value in the preferred direction of at least 7,000,000, the crystals of the magnet are also predominantly oriented in the preferred direction. 5. Permanent magnet according to claim 1 or 2, characterized in that it contains 8% aluminum, i4 @ io nickel, 24% cobalt, up to 3% copper and otherwise mainly iron with impurities and that the magnet is magnetically anisotropic with a BH ",." value in the Preferred direction of at least 7000000, the crystals of the magnet also are predominantly oriented in the preferred direction. 6. Method of manufacture a magnetically anisotropic permanent magnet according to claim i or one of the following, characterized in that an alloy with a predominant crystal orientation in the (ioo) direction parallel to this direction that used for magnetic hardening Magnetic field is subjected, whereupon the magnetic body is finally affected by a field is magnetized parallel to the same direction. Method according to claim 6, characterized characterized in that an alloy is used which contains io to 40% cobalt, io to 280%, preferably between i i and 20% nickel, 6 to i i% aluminum, o to 70% Copper, 0 to 70/0 titanium and otherwise mainly iron and impurities contains. B. Method according to claim 7, characterized in that an alloy is used, which contains 16 to 30% cobalt. G. Method according to claim 6, 7 or 8, characterized in that the alloy is cast under solidification conditions through which the heat is extracted from the alloy in practically only one direction and the alloy body parallel to this direction is that for magnetic hardening used magnetic field is subjected. ok Method according to claim g, characterized in that characterized in that the alloy heats mainly in the vertical direction is withdrawn. i i. Method according to claim g or io, characterized in that the alloy is solidified in a form which consists of surfaces of different There is thermal conductivity or is provided with areas which have the highest Thermal conductivity are perpendicular to the required direction of crystal growth. 12. The method according to claim i i, characterized in that the alloy in a Sand mold or the like with quenching surfaces made of metal or other metal Thermal conductivity is made to solidify. . 13. The method according to claim i i or 12, characterized in that the shape on the surfaces of low thermal conductivity Heat is supplied in a direction perpendicular to the direction in which Heat is withdrawn. 14. The method according to claim 7, 11 and 12, characterized in that that an alloy is used which contains up to 0.7% titanium. 15. Procedure according to one of the preceding claims, characterized in that after casting of the alloy body is a part in which the crystals are mainly in the same Direction are oriented, separated from the casting and used to manufacture the magnet is used.