Optimization Process Of Fabricating (PrNd,MM) FeB Magnets By Double Main Phase Method And The Study On Thermal Stability

As the development of rare earth permanent magnet materials preparation with high abundance elements La and Ce,the environmental pollution and costs during La,Ce,Pr,Nd separation process reqiured higher standards.Therefore,the development of baiyun obo Misch-Metal mine for efficiency and balance utilization have attracted great attention.In this paper,Pr?Nd?₂Fe₁₄B/MM₂Fe₁₄B composite magnets with different MM contents were prepared by double main phase method,and the strip casting process and hydrogen crushing process of MM₂Fe₁₄B in the preparation process were optimized.The thermal stability of the composite magnets with different MM content prepared by the optimized process was also analyzed.The main conclusions are as follows:MM-Fe-B is hard to form well columnar crystal structure with"island"morphology appears on the surface of the casting.By optimizing the MM-Fe-B rstrip casting process,the MM-Fe-B strip casting with good microstructure and surface morphology was obtained when the casting temperature,copper roller speed and the refining time was 1380?,42r/min and 15 min,respectively.The problem that the MM-Fe-B strip casting was hard to form columnar crystal structure and a large number of"island"morphologies appeared on the surface was solved.In the process of hydrogen crushing,it was found that with the increase of the proportion of Misch-Metal in the alloy casting piece,the time of both hydrogen crushing and surface activation time were shorter,and the particle size of the powder after hydrogen crushing was smaller for the alloy casting piece containing MM.Besides,the quadripartite main phase structure of 2:14:1 in the quick-condensed gold plate with Misch-Metal elements could still exist stably during the hydrogen crushing process,and the paramagnetic phase of REFe₂ in MM-Fe-B alloy was decomposed and reduced.The hydrogen crushing time of MM-Fe-B alloy was 40%shorter than that of Nd-Fe-B.?PrNd,MM?-Fe-B sintered magnet was prepared by double main phase method.The?BH?_maxax can still reach 39.51 MGOe and the coercive force H_cj=10.30 kOe when the Misch-Metal content is 30 wt.%of the total rare earth,while the?BH?_maxand H_cjj reached 39.52MGOe and 10.84 kOe after optimization with additional 10wt.%Misch-Metal introduced.The?BH?_maxax still reached 39.52 MGOe and coercive force H_cj=4.674 kOe when the Misch-Metal content was 70 wt.%of the total rare earth content.Besides,the?BH?_maxax and H_cjreached17.54 MGOe and 2.028 kOe with 90wt.%Misch-Metal content.The magnetic properties of?PrNd,MM?-Fe-B magnets at high temperature were studied at the same time.For magnets with a mixed rare earth content below 50 wt.%,the temperature coefficient of remanence remained within the range of-0.11%/?^-0.125%/?when the temperature was 100?,and the temperature coefficient of force remained within the range of-0.65^-0.675%/?.The irreversible flux loss of the magnet was 0.644%¹.974%when the service temperature rises from 20?to 100?,and the irreversible flux loss of the magnet was 21.619%³5.382%.when the service temperature rises to 180?.There is no deterioration of thermal stability caused by the addition of Misch-Metal elements,which fills the magnetic energy gap between ferrite and NdFeB.