A METHOD FOR PREPARATION OF A SINTERED TYPE NDFEB PERMANENT MAGNET WITH AN ADJUSTED GRAIN BOUNDARY

摘要

The invention relates to a method for preparing sintered type NdFeB permanent magnet. The NdFeB magnet is covered with a diffusion source to form a NdFeB magnet intermediate. The chemical composition of NdFeB magnet intermediate is expressed in weight percentage as [R1xR2yR31-x-y]aMbBcFe100-a-b-c, 0.8≤x≤1, 0≤y ≤0.08, 32≤a≤38, 0.5≤b≤7, and 0.9≤c≤1.2. R1 refers to one or more of Nd, Pr, and Ce, R2 refers to one or two of La and Sm, R3 refers to one or more of Tb, Dy, and Ho, and M refers one or more of Al, Cu, Ga, Ti, Co, Mg, Zn, Nb, Mo, and Sn. The diffusion source refers to an alloy, the alloying elements include one or more of Nd, Pr, Ce, La, Ho, Tb, Dy, Ga, Al, Cu, and Mg. The NdFeB magnet intermediate is then put into a furnace and a diffusion treatment and subsequently an aging treatment is performed. The aging treatment is divided into a heating step and a cooling step. The cooling step is carried out by means of argon gas positive pressure circulation cooling such that NdFeB magnets with a thickness of grain boundaries in the range of 10nm to 1µm are formed. A structure of the grain boundaries includes a main phase, grain boundary (a), grain boundary (b), and grain boundary (c). Grain boundary (a) meets the following conditions: R≥55wt% or 35wt%≤R≤40wt%, 10wt%≤M≤28wt%, where 3:1≤Nd/(Pr or Ce or La)≤2:1, and (Cu+Al+Ga)/M≥0.8; grain boundary (b) meets the following conditions: 40wt%≤R≤55wt%, 10wt%≤M≤20wt%, 9:10≤Nd/(Pr or Ce or La)≤2, and (Cu+Co+Al)/M≥ 0.9; and grain boundary (c) meets the following conditions: 25wt%≤R≤50wt% or R≥60%, 0≤M≤10wt%, where R in the grain boundaries (a) to (c) refers to the total amount of rare earths, and M refers to the total amount of Al, Cu, Ga, Ti, Co, Mg, Zn, Nb, Mo, and Sn.