Effects Of Key Process Parameters And Alloying On Magnetic Properties And Mechanical Properties Of Sintered Magnets

Sintered NdFeB permanent magnetic material has outstanding magnetic properties. This material not only has great economic significance, but also has great academic value. As far, in China, only below 45MGOe NdFeB permanent magnets could be manufactured by home equipments. In this paper, we analysed the effects of process parameters and addition elements on properties and microstructure of sintered NdFeB. And we successfully manufactured energy product over 45MGOe of the magnets, based on home equipments by optimizing process parameters and compositions. The main progressing of this study is followed:The key process parameters of manufacturing sintered NdFeB magnets, such as strip casting, hydrogen decrepitation process, jet-milling process, orientation and pressing process, sintering and annealing process are investigated.Optimized process parameters of manufacturing sintered magnets are achieved: strip thickness of 0.45mm, hydrogen desorption at 590℃ for 10h, average jet-milling powder size of 3.3m, extra magnetic field strength 16.5kGs, and sintering and annealing heat treatments depends on the composition.Based on optimized process parameters, the effects of rare earth elements Nd and Dy, doped elements Nb and Zr on magnetic properties and microstructure are investigated. Results show that the NdFeB magnets have the best magnetic properties when the rare earth content is about 30.5wt%. When Nb addition, precipitation NbFeB exits in main phase grains and also distributes at boundary of main phase grains which can pin domain wall. And with 0.3wt% Nb addition, remanence Br, intrinsic coercivity Hci and the maximum energy product (BH)max are improved. When Zr addition, it refines main phase grains and improves the microstructure of sintered magnets, which results in the increase of Hcj. Also the effects of mechanical properties and microstructure on magnetic properties are investigated.Above all, high magnetic properties of sintered NdFeB permanent magnets are produced. The optimized composition is (NdDy)30.5Fe67.95(TM)0.6B0.95 (wt%) (TM:A1,Ga, Nb, Zr). It has the best magnetic properties, Br H.llkGs, Hci 12.36kOe and (BH)max 47.36MGOe, respectively.