Permeating treatment method for radially oriented sintered magnet, magnet, and composition for magnet permeation

A method for improving coercivity of an oriented sintered magnet, comprising following steps:

• step a:
• preparing magnetic powder to be molded according to given components and ratios, followed by oriented molding, and then sintering to obtain an oriented sintered magnet, wherein an oriented magnetic field and the magnetic powder have relative rotation therebetween in the molding;
• the magnetic powder has following components and ratios (percentage by weight):
• rare-earth Pr and Nd in a total content of 28-31%, Dy+Tb+Ho in a total content of 2-5%, Co in a content of 0.2-0.8%, B in a content of 0.95-1.15%, Nb in a content of 0.2-1%, Cu in a content of <0.20%, Al in a content of 0.2-1.0%, a balance of Fe and impurities;
• step b:
• pre-treatment:
• removing pollutants, and rust from a surface of the magnet, wherein an inner surface and an outer surface of the magnet are first subjected to a rough processing before the pre-treatment;
• step c:
• preparing a composition as a target permeation source:
• performing high temperature baking above 1050° C. for the composition comprising any one or more selected from the group consisting of zirconium oxide, magnesium oxide, aluminum oxide or titanium oxide, then heating and melting metal gallium and adding the melted metal gallium to the baked raw material powder to form a pre-mixture, afterwards, adding terbium fluoride, carbonyl cobalt powder, and niobium powder (or zirconium powder) having baked at temperatures 120° C. sequentially to the pre-mixture to obtain the target permeation source after mixing them;
• and the target permeation source contains 0.1-5 wt % of metal Ga having a melting point of 29.8° C.;
• step d:
• permeating treatment:
• the magnet having undergone the pre-treatment in step b and the target permeation source prepared in step c are disposed into a vacuum container that is configured to be heated and rotated according to a volume ratio of 1:1-1:100 to be subjected to the permeating treatment during moving;
• in a permeating process, the magnet and the target permeation source have relative movement therebetween all the time at a rotational velocity of 1-100 rpm, in the movement permeation, the container is first vacuumized to below 6 Pa, afterwards, a vacuum or inert-gas atmosphere is maintained throughout rotational permeation;
• further, the permeation is conducted at a temperature of 500-950° C. for less than 30 h, and wherein a system of heat preservation in sections is used in the permeation:
• heating the magnet at a first heating rate of 3-8° C./min to 700° C. and keeping the temperature at 700° C. for 1.5 h in a first section, then heating the magnet at a second heating rate of 1-3° C./min to 870° C. and keeping the temperature at 870° C. for 3-10 h in a second section, afterwards cooling the magnet to 40-100° C.;
• and then heated at a third rate of 0.5-2° C./min to 880-950° C. and the temperature is kept at 880-950° C. for 15-40 h, afterwards cooling the magnet to 40-80° C., wherein in the cooling, vacuum or an inert-gas protective atmosphere is kept, and the magnet still maintains relative rotational movement with respect to the target permeation source;
• step ed:
• separating the magnet from a target permeation source substance after the permeating treatment is finished, and subjecting the magnet to a tempering treatment;
• the tempering treatment is conducted at 400-600° C. for 1-20 h;
• and
• step f:
• obtaining a product after the tempering treatment.