Method for preparing R-Fe-B based sintered magnet

摘要

A method for preparing an R—Fe—B based sintered magnet, including: preparing a R1—Fe—B-M sintered magnet having a thickness of between 1 and 10 mm; spraying a layer of Tb or Dy having a thickness of between 10 and 200 μm on each surface of the sintered magnet in a sealed box under an Ar atmosphere by hot spraying method; and transferring the sintered magnet coated with the layer of Tb or Dy to a vacuum sintering furnace, heating the sintered magnet at the temperature of between 750 and 1000° C. in a vacuum condition or under the Ar atmosphere, and allowing heavy rare earth element Tb or Dy to enter an inner part of the sintered magnet via grain boundary diffusion.

主权项

1. A method for preparing an R—Fe—B based sintered magnet, the method comprising:
1) preparing an R1—Fe—B-M sintered magnet, wherein the R1—Fe—B-M sintered magnet comprises: between 26 and 33 wt. % of R1 being selected from the group consisting of Nd, Pr, Dy, Tb, Ho, Gd, and a combination thereof; between 0 and 5 wt. % of M being selected from the group consisting of Ti, V, Cr, Mn, Co, Ni, Ga, Ca, Cu, Zn, Si, Al, Mg, Zr, Nb, Hf, Ta, W, Mo, and a combination thereof; between 0.5 and 2 wt. % of B; and the rest being Fe; 2) degreasing, acid washing, activating, and washing by deionized water the R1—Fe—B-M sintered magnet obtained from step 1); 3) placing the sintered magnet obtained from step 2) in a sealed box comprising a hot spray gun under a circulating Ar protective atmosphere; employing Tb or Dy as a coating material, and coating a layer of the coating material having a thickness of between 10 and 200 μm on each surface of the sintered magnet by hot spraying, wherein the hot spraying is performed by feeding a metal wire comprising Tb or Dy into the hot spray gun, turning on the hot spray gun to produce electric arc inside the hot spray gun to heat and melt the metal wire comprising Tb or Dy into melted metal, and then supplying compressed Ar gas into the hot spray gun to atomize the melted metal into droplets and then spraying the droplets out of the hot spray gun toward each surface of the sintered magnet to form a coating layer on each surface of the sintered magnet; 4) placing the sintered magnet obtained from step 3) in a vacuum sintering furnace, heating the sintered magnet at a temperature of between 750 and 1000° C. for between 2 and 72 hrs; and controlling a vacuum degree of the vacuum sintering furnace at between 10−2 and 10−5 Pa or controlling an Ar pressure in the vacuum sintering furnace at between 5 and 20 kPa to allow Tb or Dy to enter an inner part of the sintered magnet via grain boundary diffusion; and 5) aging the sintered magnet obtained from step 4) at a temperature of between 450 and 600° C. for between 1 and 10 hrs to obtain the R—Fe—B based sintered magnet.