Alloy Powders and Methods for Producing the Same

Abstract

The present invention relates to an alloy with formula of RE-M-B—Fe as defined herein and oxygen content less than 0.9 wt %, wherein said RE is in the range of 29.0 weight % to 33.0 weight %; M is in the range of 0.25 weight % to 1.0 weight %; B is in the range of 0.8 weight % to 1.1 weight %; and Fe makes up the balance. The present invention also relates to a method for preparing a RE-M-Fe—B magnetic powder, as defined herein comprising the steps of: (a) melt spinning a RE-M-Fe—B alloy composition to obtain a melt-spun powder; (b) pressing the melt-spun powder of step (a) to obtain a compact body; (c) hot deforming the compact body of step (b) to obtain a die-upset magnet; (d) crushing the die-upset magnet of step (c) to obtain a powder; (e) milling and sieving the powder of step (d); and (f) passivating the powder of step (e) to obtain a magnetic powder; wherein: each of steps (d) to (f) is performed under a low oxygen environment and transfer between each of steps (d) to (f) is a sealed transfer; and wherein the oxygen content of the low oxygen environment and during each sealed transfer is below 0.5 weight %.

Claims

1. An alloy powder with Formula (I) and oxygen content less than 0.9 wt %:
RE-M-B—Fe  Formula (I) wherein: RE is one or more rare earth metals selected from the group consisting of lanthanum (La), cerium (Ce), neodymium (Nd), praseodymium (Pr), yttrium (Y), gadolinium (Gd), terbium (Tb), dysoprium (Dy), holmium (Ho), and ytterbium (Yb); M is one or more metals selected from the group consisting of gallium (Ga), zirconium (Zr), niobium (Nb), molybdenum (Mo), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), hafnium (Hf), tantalum (Ta), tungsten (W), aluminum (Al), and cobalt (Co); B is boron (B); and Fe is iron (Fe); wherein: RE is in the range of 29.0 weight % to 33.0 weight %; M is in the range of 0.25 weight % to 1.0 weight %; B is in the range of 0.8 weight % to 1.1 weight %; and Fe makes up the balance, wherein the alloy powder is an anisotropic magnetic powder, and wherein the anisotropic magnetic powder exhibits a remanence (Br) value greater than 12 kG at a coercivity (Hci) value in the range of 14 kOe to 20 kOe.

2. The alloy powder of claim 1, wherein the oxygen content is in the range of 0.5 wt % to 0.6 wt %.

3. The alloy powder of claim 1, wherein at most 30% of the particles are −325 mesh; or wherein 30% of the particles are −325 mesh, and 70% of the particles are −80 to −325 mesh.

4. (canceled)

5. (canceled)

6. (canceled)

7. The alloy powder of claim 15, wherein the anisotropic magnetic powder exhibits a remanence (Br) value greater than 13 kG at a coercivity (Hci) value of 15 kOe, about 13 kG at 17 kOe, about 12.7 kG at 19 kOe, and about 12.5 kG at 19.5 kOe.

8. The alloy powder of claim 1, wherein RE is selected from the group consisting of: (i) Nd; (ii) Nd, Pr; (iii) Nd, Pr, La; (iv) Nd, Pr, Ce; (v) Nd, Pr, La, Ce; (vi) Nd, La; (vii) Nd, Ce; (viii) Nd, Ce, La; (ix) Pr; (x) Pr, La; (xi) Pr, Ce; and (xii) Pr, La, Ce.

9. The alloy powder of claim 1, wherein Formula (I) is selected from the group consisting of: (i) Nd—Ga—Fe—B; (ii) Pr—Ga—Fe—B; (iii) (NdPr)—Ga—Fe—B; (iv) Nd—Al—Fe—B; (v) Pr—Al—Fe—B; and (vi) (NdPr)—Al—Fe—B.

10. The alloy powder of claim 1, wherein cobalt (Co) or dysprosium (Dy) is absent.

11. The alloy powder of claim 1, wherein RE is in the range of 30.0 wt % to 32.5 wt %, M is in the range of 0.50 weight % to 0.75 weight %, B is in the range of 0.9 weight % to 1.0 weight %, and Fe makes up the balance or wherein RE is in the range of 30.40 weight % to 32.45 weight %, M is in the range of 0.45 weight % to 0.55 weight %, B is in the range of 0.885 weight % to 0.945 weight %, and Fe makes up the balance.

12. (canceled)

13. The alloy powder of claim 1, wherein the alloy composition is selected from the group consisting of: NdPr—Ga—B—Fe, wherein RE is 30.45 wt %, Ga is 0.53 wt %, B is 0.94 wt %, and Fe is 68.08 wt %; NdPr—Ga—B—Fe, wherein RE is 31.45 wt %, Ga is 0.53 wt %, B is 0.93 wt %, and Fe is 67.09 wt %; NdPr—Ga—B—Fe, wherein RE is 31.9 wt %, Ga is 0.63 wt %, B is 0.92 wt %, and Fe is 66.55 wt %; and NdPr—Ga—B—Fe, wherein RE is 32.4 wt %, Ga is 0.78 wt %, B is 0.91 wt %, and Fe is 65.91 wt %.

14. A bonded magnet comprising the alloy powder of claim 1 and at least one binder selected from the group consisting of epoxy, polyamide, and polyphenylene sulfide.

15. A method for preparing a RE-M-Fe—B magnetic powder, wherein: RE is one or more rare earth metals selected from the group consisting of lanthanum (La), cerium (Ce), neodymium (Nd), praseodymium (Pr), yttrium (Y), gadolinium (Gd), terbium (Tb), dysoprium (Dy), holmium (Ho), and ytterbium (Yb); M is one or more metals selected from the group consisting of gallium (Ga), zirconium (Zr), niobium (Nb), molybdenum (Mo), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), hafnium (Hf), tantalum (Ta), tungsten (W), copper (Cu), and aluminum (Al), and cobalt; B is boron (B); and Fe is iron (Fe); wherein the method comprises the steps of: (a) melt spinning a RE-M-Fe—B alloy composition to obtain a melt-spun powder; (b) pressing the melt-spun powder of step (a) to obtain a compact body; (c) hot deforming the compact body of step (b) to obtain a die-upset magnet; (d) crushing the die-upset magnet of step (c) to obtain a powder; (e) milling and sieving the powder of step (d); and (f) passivating the powder of step (e) to obtain a magnetic powder; wherein: each of steps (d) to (f) is performed under a low oxygen environment and transfer between each of steps (d) to (f) is a sealed transfer; wherein the oxygen content of the low oxygen environment and during each sealed transfer is below 0.5 weight %, and wherein the sealed transfer is carried out using a container comprising means for sealed connection with equipment used in steps (d) to (f), means for sealed collection and release from the container after each step; and means for supplying an inert gas into the container.

16. The method of claim 15, wherein each of steps (c) to (f) is performed under a low oxygen environment.

17. The method of claim 15, wherein the oxygen content of the low oxygen environment and during each sealed transfer is below 0.1 weight %.

18. The method of claim 15, wherein step (e) comprises sieving the powder on a sieve unit comprising means for prolonging the residence time of said powder on said sieve unit.

19. The method of claim 15, wherein step (f) comprises passivating the powder with phosphoric acid at a concentration of at least 0.25 wt % or at a concentration of at least 0.40 wt %.

20. (canceled)

21. (canceled)

22. The method of claim 15, wherein the inert gas may be selected from a group consisting of argon, nitrogen, helium, and mixtures thereof.

23. The method of claim 15, wherein step (b) comprises the steps of: (bi) cold pressing the melt-spun powder of step (a); and (bii) hot pressing the cold-pressed powder of step (bi) to form the compact body.

24. The method of claim 22, wherein step (bii) is performed in inert atmosphere comprising argon, nitrogen, helium, or mixtures thereof.

25. The method of claim 15, wherein the oxygen content of the RE-M-Fe—B magnetic powder is less than 0.9 weight %; or wherein the oxygen content of the RE-M-Fe—B magnetic powder is in the range of 0.5 weight % to 0.6 weight %.

26. (canceled)

27. The method of claim 15, wherein the RE-M-Fe—B magnetic powder is an alloy powder with Formula (I) and oxygen content less than 0.9 wt %:
RE-M-B—Fe  Formula (I) wherein: RE is one or more rare earth metals selected from the group consisting of lanthanum (La), cerium (Ce), neodymium (Nd), praseodymium (Pr), yttrium (Y), gadolinium (Gd), terbium (Tb), dysoprium (Dy), holmium (Ho), and ytterbium (Yb); M is one or more metals selected from the group consisting of gallium (Ga), zirconium (Zr), niobium (Nb), molybdenum (Mo), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), hafnium (Hf), tantalum (Ta), tungsten (W), aluminum (Al), and cobalt (Co); B is boron (B); and Fe is iron (Fe): wherein: RE is in the range of 29.0 weight % to 33.0 weight %; M is in the range of 0.25 weight % to 1.0 weight %; B is in the range of 0.8 weight % to 1.1 weight %; and Fe makes up the balance, wherein the alloy powder is an anisotropic magnetic powder, and wherein the anisotropic magnetic powder exhibits a remanence (Br) value greater than 12 kG at a coercivity (Hci) value in the range of 14 kOe to 20 kOe.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0140] The accompanying drawings illustrate disclosed embodiments and serves to explain the principles of the disclosed embodiments. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

[0141] FIG. 1 shows a process flow chart of the steps involved in the disclosed method for preparing a magnetic powder.

[0142] FIG. 2 shows the schematics of connection of the sealed transfer container to (a) crushing equipment, (b) milling and sieving equipment and (c) passivating equipment.

[0143] FIG. 3 shows a comparison between the Br of comparative magnetic powders (1a, 1b, 1c, 1d) and magnetic powder prepared using the method disclosed in Example 1 (2a, 2b, 2c, 2d).

[0144] FIGS. 4a and 4b show a schematic of embodiments of a sieve bar.

DETAILED DESCRIPTION OF DRAWINGS

[0145] Referring to FIG. 1, FIG. 1(a) illustrates step (a) of the disclosed method. FIG. 1(a) shows a melt spinning process to obtain melt spun powder from alloy composition, depicting the flow of a melt of alloy composition (2) through a nozzle (3) onto a rotating wheel (3a) to form ribbons which are ejected from the wheel (3b) and then crushed to form powder. FIG. 1(b) illustrates step (bi) of the disclosed method, wherein the melt spun powder of step (a) is subjected to cold-pressing (4) to form a pressed powder (9). FIG. 1(c) illustrates step (bii) of the disclosed method, wherein the pressed powder of step (bi) (9) is heated and subjected to hot-pressing to form a compact body (10) by first loading (6) the pressed powder from step b(i) (9), hot pressing the powder (7) and unloading the compacted powder (8). FIG. 1(d) illustrates step (c) of the disclosed method, wherein the compact body of step (bii) (10) is subjected to hot-deforming by first loading (12) the compact body of step b(ii), hot deforming the compact body (13), to obtain a die-upset magnet (15) and unloading it (14). FIG. 1(e) illustrates step (d) of the disclosed method, wherein crushing of die-upset magnet of step (d) (15) results in a powder (16). FIG. 1(f) illustrates step (e) of the disclosed method, milling and sieving of the powder of step (d) (16) resulting in a milled and sieved powder (17). FIG. 1(g) illustrates step (f) of the disclosed method, passivating the powder of step (e) (17) to obtain a magnetic powder (18).

[0146] FIG. 2 shows a schematic of connection of the sealed transfer container to (a) crushing equipment, (b) milling and sieving equipment and (c) passivating equipment.

[0147] FIG. 2(a) shows a schematic of the sealed transfer from step (c) to step (d). A magnet feed (19) is connected to a crushing equipment (22) via an isolation valve (21a). The magnet feed (19) is purged with inert gas through an inert gas inlet (20) and out through a gas outlet (24a). The die-upset magnet of step (c) is released into the crushing equipment (22) without exposing to the outside environment by opening the isolation valve (21a). After the transfer, the crushing equipment (22) is disconnected from the magnet feed (1) by closing the isolation valve (21a). The crushing equipment (22) is further purged under inert gas by flowing inert gas throughout the equipment using a gas inlet (23) and gas outlet (24b). When the crushing step is completed, a second isolation valve (21b) is opened to release the crushed powder into a container (25). The container is purged with inert gas through an inert gas inlet (26) and out through a gas outlet (24c). The purged gas from the gas outlets (24a, 24b, 24c) flows to water tank (27a).

[0148] FIG. 2(b) shows a schematic of the sealed transfer from step (d) to step (e). The powder container (25) containing the crushed powder from step (d) is connected to a milling and sieving equipment (30) via an isolation valve (21c). The powder container (25) is purged with inert gas through an inert gas inlet (29) and out through a gas outlet (24d). The crushed powder of step (d) is released into the milling and sieving equipment (30) without exposing to the outside environment by opening the isolation valve (21c). After the transfer, the milling and sieving equipment (30) is disconnected from the powder container (25) by closing the isolation valve (21c). The milling and sieving equipment (30) is further purged under inert gas by flowing inert gas throughout the equipment using a gas inlet (31) and gas outlet (24e). When the milling and sieving step is completed, a second isolation valve (21d) is opened to release the crushed powder into a container (32). The container is purged with inert gas through an inert gas inlet (33) and out through a gas outlet (24f). The purged gas from the gas outlets (24d, 24e, 24f) flows to water tank (27b).

[0149] FIG. 2(c) shows a schematic of the sealed transfer from step (e) to step (f). The powder container (32) containing the sieved powder from step (e) is connected to passivating equipment (36) via an isolation valve (21e). A container containing passivating agent (35) is connected to the passivating equipment (36) via another isolation valve (21f). The sieved powder of step (e) (32) and the passivating agent (35) is released into the passivating equipment (36) without exposing to the outside environment by opening the isolation valves (21e, 21f). After the transfer, the passivating equipment (36) is disconnected from the powder and passivating agent containers (32, 35) by closing the isolation valves (21e, 21f). The passivating equipment (36) is further purged under inert gas by flowing inert gas throughout the equipment using a gas inlet (37) and gas outlet (24g) by a vacuum pump (38). When the passivating step is completed, the magnetic powder is released into a container (39).

EXAMPLES

[0150] Non-limiting examples of the invention and a comparative example will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

Materials

[0151] NdPr obtained from Ganzhou Rare Earth Metals Ltd.

[0152] FeB obtained from Lioyang International Penghejin Limited Company.

[0153] Fe and Ga obtained from Alfa Aesar.

[0154] Li-St obtained from Valtris Specialty Chemicals Limited.

Example 1: Preparation of Alloy Magnetic Powder

[0155] Melt-Spun Powder (Step (a))

[0156] A rapidly solidified alloy composition is prepared by weighing an appropriate amount of raw material (Nd, Fe, Ga, Fe—B) according to formula (I) as disclosed herein. The raw material is placed into a melter for melting under argon atmosphere and subsequently cooled to obtain ingots. After which, the ingots are broken into pieces and loaded into a melt-spinner. The ingots are heated up and re-melted under argon atmosphere before ejecting onto a rotating metal wheel to form ribbons. Following which, the melt-spun ribbons are crushed to powder form.

[0157] Cold Press (Step Bi))

[0158] Before cold pressing, a lubricant (LiSt) is mixed with melt-spun powder.

[0159] Internal lubed melt-spun powder is pressed into a cold-pressed powder using a hydraulic cold press. Cold pressing is performed at room temperature and under normal atmosphere.

[0160] Hot Press (Step b(ii))

[0161] The cold-pressed powder is lubricated with an alcohol mixture before putting into a hot press die cavity. The alcohol mixture is prepared from graphite, boron nitride and alcohol. The alcohol mixture is sprayed onto the cold-pressed powder and the alcohol is evaporated by exposing the powder to a ventilation cabinet.

[0162] Hot pressing is performed under argon protection (i.e. inert atmosphere) to achieve a full dense magnet. The hot pressing stage is purged by argon gas to minimize oxidation amid the hot-pressing process.

[0163] Hot Deformation (Step (c))

[0164] After hot-pressing, the hot-pressed compact body is immediately feed into a hot deformation feeder for about 60% to about 80% die-upset hot deformation. The hot deformation step is performed under inert atmosphere.

[0165] Sandblasting

[0166] Die-upset magnets are first sandblasted to remove the surface dirt and lubricant before crushing.

[0167] Sealed Transfer

[0168] Each of the steps from crushing to passivating (steps (d) to step (f)) are conducted under low oxygen environment (below 0.5 weight % oxygen) and the transfer between each of steps (d) to (f) is a sealed transfer. The inert gas used is nitrogen. The oxygen content of the low oxygen environment and during each sealed transfer is below 0.5 weight %.

[0169] Crushing (Step (d))

[0170] During the jaw crushing step, big pieces of die-upset magnets are broken down into smaller pieces under nitrogen protection. The smaller pieces of magnets are better feed for the milling step.

[0171] Sieving and Milling (Step (e))

[0172] The crushed die-upset magnets are milled and then sieved to the desired particle size through the use of means for prolonging the residence time of the particles on the sieve unit (for example, by using a sieve bar as depicted in FIG. 4a or 4b) under nitrogen purging and sealed transfer, with oxygen content below 0.5%.

[0173] Passivating (Step (f))

[0174] The magnetic powder is treated with phosphoric acid in a mixer for anti-aging and passivating effect. The passivating mixer is subjected to vacuum and nitrogen purging repeatedly to decrease the oxygen level. Next, the powder and phosphoric acid are fed into the mixer chamber for mixing and heating.

Example 2: Properties of Magnetic Alloy Powders

[0175] Alloy powders formed by the method of Example 1 and their magnetic properties are shown in Table 1:

TABLE-US-00001 TABLE 1 Sample Br Hci (BH)max Oxygen name NdPr Dy Ga Co B Fe (kG) (kOe) (MGOe) (wt %) Magnetic powder of 2a 30.45 — 0.53 — 0.94 68.08 13.3 14.5 38.9 ~0.5-0.6 present invention 2b 31.45 — 0.53 — 0.93 67.09 13.0 16.9 38.2 (Example 1) 2c 31.90 — 0.63 — 0.92 66.55 12.7 18.9 36.8 2d 32.40 — 0.78 — 0.91 65.91 12.5 19.5 36.2

Example 3: Effect of Phosphating on Hazard Rating of Magnetic Powder

[0176] In step (f), the powder of step (e) may be subjected to passivating with phosphoric acid.

[0177] The inventors have surprising found that at least 0.25 wt % of phosphoric acid is effective and sufficient in protecting the magnetic powder from oxidation. Metal oxidation is undesirable as metal oxides, unlike metals, do not exhibit magnetic properties. Conventionally, the phosphating step prevents the oxidation of iron in the magnetic powder to iron oxide. Using 0.25 wt % of phosphoric acid for passivation not only prevents magnetic powder from forming undesired iron oxide but also prevents magnetic powder from forming neodymium oxide. Reducing oxidation of both neodymium and iron is beneficial as it improves magnetic performance of the magnetic powder. Also advantageously, using at least 0.25 wt % of phosphoric acid allows a phosphate protective layer to be formed around each metal particle without such corroding the particles.

[0178] The disclosed method may also comprise passivating the powder with phosphoric acid at a concentration of 0.4 wt %. The inventors have surprisingly found that by passivating the magnetic powder in 0.4 wt % of phosphoric acid, the resultant magnetic powder may be non-hazardous which allows it to be safely handled and transported (Table 2).

[0179] The testing basis of the Hazardous Test performed on the magnetic powders was based on the UN Recommendations on the Transport of Dangerous Goods (19.sup.th revised edition), UN Globally Harmonized System of Classification and Labelling of Chemicals (6.sup.th revised edition) and China's Catalogue of Hazardous Chemicals (CHC), published by the State Administration of Work Safety (SAWS) on 9 Mar. 2015 and entered into force on 1 May 2015.

[0180] The results of the Hazardous Test may be found in Table 2 below.

TABLE-US-00002 TABLE 2 Phosphoric Acid on MQA (wt. %) MQA Br Loss (%) Hazardous Test 0.00 0.0 Hazardous 0.20 −0.4 Hazardous 0.25 −0.5 Hazardous 0.30 −0.7 Hazardous 0.40 −0.8 Non-hazardous 0.50 −0.9 Non-hazardous

Comparative Examples

Comparative Example 1: Method of Preparing Comparative Magnetic Powders

[0181] Comparative Samples 1a, 1b, 1c and 1d were prepared according to the steps set out in Table 3 below. The differences between the method for preparing Samples 1a, 1b, 1c and 1d and the method for preparing Samples 2a, 2b, 2c and 2d are also set out in Table 3.

TABLE-US-00003 TABLE 3 Method of Example 1 Comparative Method Steps (Samples 2a, 2b, 2c, 2d) (Samples 1a, 1b, 1c, 1d) Difference Melt-spun A rapidly solidified alloy A rapidly solidified alloy powder composition is prepared composition is prepared by (Step (a)) by weighing an weighing an appropriate appropriate amount of raw amount of raw material material (Nd, Fe, Ga, Fe—B) (Nd, Fe, Ga, Fe—B) according to formula according to formula (I) as (I) as disclosed herein. disclosed herein. The raw The raw material is placed material is placed into a into a melter for melting melter for melting under under argon atmosphere argon atmosphere and and subsequently cooled subsequently cooled to to obtain ingots. After obtain ingots. After which, which, the ingots are the ingots are broken into broken into pieces and pieces and loaded into a loaded into a melt-spinner. melt-spinner. The ingots The ingots are heated up are heated up and re- and re-melted under argon melted under argon atmosphere before ejecting atmosphere before ejecting onto a rotating metal onto a rotating metal wheel wheel to form ribbons. to form ribbons. Following Following which, the which, the melt-spun melt-spun ribbons are ribbons are crushed to crushed to powder form. powder form. Cold press Before cold pressing, a Before cold pressing, a (Step bi)) lubricant (LiSt) is mixed lubricant (LiSt) is mixed with melt-spun powder. with melt-spun powder. Hot press The cold-pressed powder The cold-pressed powder Example 1 is (Step b(ii)) is lubricated with an is lubricated with an performed under alcohol mixture before alcohol mixture before inert atmosphere, putting into a hot press putting into a hot press while the die cavity. The alcohol die cavity. The alcohol Comparative mixture is prepared from mixture is prepared from Method is graphite, boron nitride graphite, boron nitride performed under and alcohol. The alcohol and alcohol. The alcohol partial inert mixture is sprayed onto mixture is sprayed onto atmosphere. the cold-pressed powder the cold-pressed powder and the alcohol is and the alcohol is evaporated by exposing evaporated by exposing the powder to a the powder to a ventilation cabinet. ventilation cabinet. Hot pressing is Hot pressing is performed performed under argon only under argon purging protection (i.e. inert to achieve a full dense atmosphere) to achieve a magnet. The hot pressing full dense magnet. The stage is performed under hot pressing stage is partial inert atmosphere. purged by argon gas to minimize oxidation amid the hot-pressing process. Hot After hot-pressing, the After hot-pressing, the Example 1 is deformation hot-pressed compact hot-pressed compact body performed under (Step (c)) body is immediately feed is immediately feed into a inert atmosphere, into a hot deformation hot deformation feeder while the feeder for about 60% to for about 60% to about Comparative about 80% die-upset hot 80% die-upset hot Method is deformation. The hot deformation. The hot performed in air. deformation step is deformation step is performed under inert performed in air. atmosphere. Sandblasting Die-upset magnets are Die-upset magnets are first sandblasted to first sandblasted to remove the surface dirt remove the surface dirt and lubricant before and lubricant before crushing. crushing. Sealed The transfer between No sealed transfer. The transfer transfer each of the steps from between each of crushing to passivating steps (d) to (f) of (steps (d) to step (f) is a Example 1 is a sealed transfer where the sealed transfer, oxygen content during while the transfer each sealed transfer is between steps (d) below 0.5 weight %. to (f) of the Comparative Method is not a sealed transfer and the contents are exposed to air. Crushing During the jaw crushing During the jaw crushing (Step (d)) step, big pieces of die- step, big pieces of die- upset magnets are broken upset magnets are broken down into smaller pieces down into smaller pieces under nitrogen under nitrogen protection. protection. The smaller The smaller pieces of pieces of magnets are magnets are better feed better feed for the milling for the milling step. step. Sieving and The crushed die-upset The crushed die-upset Example 1 uses a milling magnets are milled and magnets are milled and means for (Step (e)) then sieved to the desired then sieved. prolonging the particle size through the residence time of use of means for the particles on the prolonging the residence sieve unit, whereas time of the particles on the Comparative the sieve unit (for Method does not example, by using a sieve use such means bar as depicted in FIGS. (i.e. normal sieving 4a or 4b). process). Passivating The magnetic powder is The magnetic powder is (Step (f)) treated with phosphoric treated with phosphoric acid in a mixer for anti- acid in a mixer for anti- aging and passivating aging and passivating effect. The passivating effect. The passivating mixer is subjected to mixer is subjected to vacuum and nitrogen vacuum and nitrogen purging repeatedly to purging repeatedly to decrease the oxygen decrease the oxygen level. level. Next, the powder Next, the powder and and phosphoric acid are phosphoric acid are fed fed into the mixer into the mixer chamber chamber for mixing and for mixing and heating. heating.

[0182] Samples 2a to 2d were prepared as shown in Example 1 which is under a low oxygen environment, using sealed transfer between steps (d) to (f) and using means for prolonging the residence time of the particles on the sieve unit in step (e). As a result, Samples 2a to 2d have a lower oxygen content than Comparative Samples 1a to 1d.

[0183] Advantageously, Dy and Co are absent from the magnetic powder of Samples 2a to 2d, yet they achieve comparable or even better Hci when compared to Comparative Samples 1a to 1d (Table 4). For example, Sample 2d exhibits high Hci exceeding 19 kOe without using dysprosium, which is higher when compared to Comparative Samples 1b and 1c.

[0184] In addition, Sample 2c shows an improvement of Br magnetic performance by about 0.4 kG when compared to Comparative Sample 1c. Sample 2b also surprisingly shows an improvement of Br magnetic performance by about 0.5 kG when compared to Comparative Sample 1d, even though Sample 2b and Comparative Sample 1d share the same composition.

TABLE-US-00004 TABLE 4 Br Hci (BH)max Oxygen Sample name NdPr Dy Ga Co B Fe (kG) (kOe) (MGOe) (wt %) Comparative magnetic Comparative 30.4 — 0.61 4.00 0.92 64.07 12.9 13.7 36.1 ~0.9 powder Sample 1a Comparative 29.50 1.60 0.61 2.00 0.92 65.37 12.5 16.0 34.5 Sample 1b Comparative 27.50 3.60 0.61 2.00 0.92 65.37 12.3 18.9 33.5 Sample 1c Comparative 31.45 0.53 0.93 67.09 12.5 16.7 34.6 Sample 1d Magnetic powder of 2a 30.45 — 0.53 — 0.94 68.08 13.3 14.5 38.9 ~0.5-0.6 present invention 2b 31.45 — 0.53 — 0.93 67.09 13.0 16.9 38.2 (Example 1) 2c 31.90 — 0.63 — 0.92 66.55 12.7 18.9 36.8 2d 32.40 — 0.78 — 0.91 65.91 12.5 19.5 36.2

Comparative Example 2: Low Oxygen Sealed Transfer Process

[0185] Sample 2b was prepared by low oxygen sealed transfer during milling step, while Comparative Sample 1d of the same composition was prepared under standard transfer process which exposes the powder to air during milling.

[0186] Table 5 and FIG. 3 shows that Sample 2b exhibits 0.4 wt % lower oxygen content and 0.5 kG higher Br as compared to Sample 1d. This may be attributed to the low oxygen sealed transfer process with reduces oxidation of magnetic powder and therefore improves Br.

[0187] The oxygen reduction in magnetic powder of the present invention (Example 1) is mainly attributed to oxygen-free sealed transfer during milling. As shown in Table 5, the total oxygen content in the magnetic powder is reduced from 0.92 wt % to 0.45 wt % by using low oxygen sealed transfer.

TABLE-US-00005 TABLE 5 Method MQA Br (kG) Oxygen (wt. %) Sample 1d 12.5 0.92 Sample 2b 13.0 0.45

Comparative Example 3: Particle Size of Magnetic Powder

[0188] Table 6 shows the difference in magnetic properties between different particle sizes of magnetic powders of −80 mesh and −80 mesh to −325 mesh. A wider particle size is observed for −80 mesh. Table 6 shows that fine powders (−325 mesh, <45 um) exhibits poorer magnetic performance and higher oxygen content.

TABLE-US-00006 TABLE 6 Sample Br Hci (BH)max Oxygen no. Particle size (kG) (kOe) (MGOe) (wt. %) Comparative 1d −80 to −325 mesh 12.7 16.9 36.5 0.75 magnetic powders 1d −80 mesh 12.5 16.7 34.6 0.92 1d −325 mesh 12.0 15.9 29.3 1.52 Magnetic powder 2b −80 to −325 mesh 13.0 17.0 39.0 0.37 of present 2b −80 mesh 13.0 16.8 38.4 0.45 invention 2b −325 mesh 12.4 16.1 32.4 0.98

[0189] The range of particle sizes obtained may be achieved by controlling the extent of sieving. In particular, this by including means for prolonging the residence time of the particles on the sieve unit, less fine particles (i.e. −325 mesh) particles can be obtained.

[0190] One such means for prolonging the residence time of the particles on the sieve unit is by utilizing an elongated flexible member which coils around the top of the sieving platform to extend the journey path of the particles. Embodiments of such a member are shown in FIGS. 4a and 4b (sieve bar).

[0191] Through the use of such means, a reduction from 35% to 30% in the portion of fine particles (i.e. −325 mesh) can be achieved as shown in Table 7. Reducing the portion of fine particles in the magnetic powder helps to improve the overall magnetic properties of magnetic powder as shown above in Table 7.

TABLE-US-00007 TABLE 7 Weight % Sample 1d Sample 2b −325 mesh 35% 30% −80 to −325 mesh 65% 70%

INDUSTRIAL APPLICABILITY

[0192] The disclosed alloy powder may advantageously exhibit improved magnetic properties, for example, high B.sub.r and H.sub.ci values. The alloy powder may be used for high performance bonded magnets.

[0193] Advantageously, the disclosed alloy powder may not require the use of expensive rare earth metals, for example, Dy or Co, which translates to cost-savings.

[0194] Advantageously, the methods for making the disclosed alloys of the present disclosure may produce alloys with lower oxygen content and improved magnetic properties such as high Hci and Br.

[0195] More advantageously, the method of the present disclosure may produce alloys with reduced portion of fines and improved magnetic properties.

[0196] Further advantageously, the method of the present disclosure may allow more effective phosphate treatment of alloys without degradation, leading to better anti-oxidation and non-hazardous properties.

[0197] The disclosed alloys, magnetic materials or bonded magnets with superior magnetic properties may be used in numerous applications, including computer hardware, automobiles, consumer electronics, motors and household appliances.

[0198] It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.