# US 2019/0172637 A1 · Method for preparing rare-earth permanent magnet > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2019/0172637 A1 - Document ID: US20190172637A1 - Status: Published application - Kind: A1 - Application number: 16/120,865 - Filed: 2018-09-04 - Published: 2019-06-06 - Earliest claimed: 2017-12-01 - Assignees: Hyundai Motor Company; Kia Motors Corporation - Applicants: Hyundai Motor Company; Kia Motors Corporation - Inventors: Hyung Ju Lee - Web page: https://patentgrep.com/patent/US20190172637A1 ## CPC - H01F 41/0293: {diffusion of rare earth elements, e.g. Tb, Dy or Ho, into permanent magnets} - B22F 3/24: After-treatment of workpieces or articles {(B22F3/1146 takes precedence)} - B22F 9/04: starting from solid material, e.g. by crushing, grinding or milling ({C22C1/1084 takes precedence}; crushing, grinding or milling, in general, see the relevant subclasses, e.g. B02C) - C22C 38/005: {containing rare earths, i.e. Sc, Y, Lanthanides} - H01F 1/057: and IIIa elements, e.g. Nd2Fe14B - B22F 2003/241: {Chemical after-treatment on the surface} - B22F 2003/248: {Thermal after-treatment} - B22F 2201/10: Inert gases - B22F 2201/20: Use of vacuum - B22F 2202/05: Use of magnetic field - B22F 2301/355: Rare Earth - Fe intermetallic alloys - B22F 2998/10: Processes characterised by the sequence of their steps - C22C 2202/02: Magnetic - H01F 1/0577: {sintered} - H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES - B22F: WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER (making alloys by powder metallurgy C22C); APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER - C22C: ALLOYS (treatment of alloys C21D, C22F) ## Abstract Disclosed is a method for preparing a rare-earth permanent magnet. The method includes: preparing an R-T-B-based sintered magnet; applying a first mixture including a light rare-earth element onto the surface of the R-T-B-based sintered magnet and diffusing the first mixture under a vacuum atmosphere to prepare a light rare-earth permanent magnet having the light rare-earth element diffused into a grain boundary; and applying a second mixture including a heavy rare-earth element onto the surface of the light rare-earth permanent magnet and diffusing the second mixture into the grain-boundary under a vacuum atmosphere to prepare a rare-earth permanent magnet. ## Claims ### Claim 1 A method for preparing a rare-earth permanent magnet, comprising: preparing an R-T-B-based sintered magnet; applying a first mixture comprising a light rare-earth element onto the surface of the R-T-B-based sintered magnet and diffuses the first mixture into a grain boundary of the R-T-B sintered magnet to prepare a light rare-earth permanent magnet having the light rare-earth element; and applying a second mixture comprising a heavy rare-earth element onto the surface of the light rare-earth permanent magnet and diffuses heavy rare-earth element into a grain boundary of the light rare-earth permanent magnet to prepare the rare-earth permanent magnet. ### Claim 2 (depends on 1) The method of claim 1, wherein the R-T-B-based sintered magnet are prepared by steps comprising: preparing an R-T-B-based alloy ingot by melting an R-T-B-based alloy; preparing an R-T-B-based alloy powder having an average grain size of about 5.0 μm or less (excluding zero) by grinding the R-T-B-based alloy ingot; preparing an R-T-B-based green body by subjecting the R-T-B-based alloy powder to magnetic field forming under an inert atmosphere; and preparing the R-T-B-based sintered magnet by sintering the R-T-B-based green body. ### Claim 3 (depends on 1) The method of claim 1, wherein the light rare-earth permanent magnet is prepared by steps comprising: preparing the first mixture comprising the light rare-earth element by mixing a light rare-earth compound with a solvent; applying the first mixture onto the surface of the R-T-B-based sintered magnet; and inserting the R-T-B-based sintered magnet having the first mixture applied thereon into a heating furnace under a vacuum atmosphere such that the first mixture is diffused into the grain-boundary. ### Claim 4 (depends on 3) The method of claim 3, wherein the light rare-earth compound comprises NdF or NdH, and the solvent comprises alcohol. ### Claim 5 (depends on 3) The method of claim 3, wherein the light rare-earth permanent magnet is prepared by diffusing the first mixture under a vacuum atmosphere at a temperature of about 800 to 1,000° C. for about 1 to 30 hours. ### Claim 6 (depends on 3) The method of claim 3, further comprising, after the first mixture is diffused: cooling the light rare-earth permanent magnet under an inert atmosphere; and removing stress of the light rare-earth permanent magnet by heat-treating the light rare-earth permanent magnet at a temperature of about 400 to 600° C. under an inert atmosphere for about 1 to 3 hours. ### Claim 7 (depends on 1) The method of claim 1, wherein the rare-earth permanent magnet is prepared by steps comprising: preparing the second mixture comprising the heavy rare-earth element by mixing a rare-earth compound with a solvent; applying the second mixture onto the surface of the light rare-earth permanent magnet; and inserting the rare-earth permanent magnet having the second mixture applied thereon into a heating furnace under a vacuum atmosphere such that the second mixture is diffused into the grain-boundary. ### Claim 8 (depends on 7) The method of claim 7, wherein the heavy rare-earth compound comprises TbF or TbH, and the solvent comprises alcohol. ### Claim 9 (depends on 7) The method of claim 7, wherein the rare-earth permanent magnet is prepared by diffusing the second mixture under a vacuum atmosphere at a temperature of about 800 to 1,000° C. for about 1 to 30 hours. ### Claim 10 (depends on 7) The method of claim 7, further comprising, after the second mixture is diffused: cooling the rare-earth permanent magnet under an inert atmosphere; and removing stress of the rare-earth permanent magnet by heat-treating the rare-earth permanent magnet at a temperature of about 400 to 600° C. under an inert atmosphere for about 1 to 3 hours. ### Claim 11 (depends on 1) A vehicle comprising a rare-earth permanent magnet prepared by a method of claim 1.