| Nd-Fe-B magnet is widely used in all fields of modern science and technology, such as computer technology,information technology,communication and transportation technology,aviation and space technology,office automatization,civil appliances and health care technology etc.Based on the different producing processes, the Nd-Fe-B magnet can be classified as sintered magnet and bonded magnet.The investigation and development status of Nd-Fe-B bonded magnet have been synthetically commented in this paper.We adopted new SC-HDDR preparing procedure,regulated process parameters,and greatly improved the hard magnetic property of magnets.Our main studying works are as follows:1.Effect of preparing processes of Strip Casting(SC ) technique on the alignment degree and microstructure of casting flakes.1) The flakes produced by SC technique are mainly composed of 2:14:1 strip grains and exist apparent alignment along[00L].Both the cooling surface and the free surface of flakes prepared at different wheel speeds were analyzed by XRD.The alignment degree changes with the wheel speed.The alignment degree reached maximum when the wheel speed V is 3-4m/s.2) The microstructure of the flakes was investigated by backscattered scanning microscope.The influence of solidification rate(wheel speed) on the microstmcture of flakes was studied.The experimental results show that when the wheel speed is too low,the soft magnetic phaseα-Fe will be appeared in the flakes and apparently decrease the hard magnetic properties.When the wheel speed is too high,the over-small isometric grains are formed on the cooling surface,and the Nd-rich phase distribution are un-homogenous,and also decrease the hard magnetic properties.The best wheel speed is about 3m/s.The Nd2Fe14B main phase strip grains are about 3～5μm in mean width,and Nd-rich phase with thickness of 0.1～0.2μm distributed uniformly along the boundaries of fine strip grains of matrix phase.The grain distributions of main phase and Nd-rich phase are homogeneous.This flake is the ideal starting material for preparing bonded magnet with high hard magnetic:property.2.Effect of HDDR processe parameters on the magnetic properties of magnetic powders.1) The effects of time,temperature and pressure of HD stage on the properties of Nd-Fe-B magnetic powders.HD treatment is the procedure of hydrogenation and decomposition of Nd-Fe-B based phase compounds.HD stage influences hydrogenation and decomposition condition of the main phase and the rich-Nd phase.The different values of time, temperature and pressure in HD stage are carried on.The experiment shows that the optimal HD technology parameters are 40min,820℃and 0.8bar,respectively.The corresponding magnetic properties are as follows,Hcj=645.5 KA/m,Br=1.18T,(BH) max=165 KJ/m3,Br/Bs =0.8022) The effects of time,temperature and pressure of DR stages on the properties of Nd-Fe-B magnetic powders.DR treatment is the procedure of desorption and recombination of materials.The treatment conditions have great impact on the magnetic properties of materials.The different values of time,temperature and pressure in DR stage were carried on.The experiment shows that the optimal DR technology parameters are 1.5h,840℃and (0.3bar + 5×10-3pa),respectively.The corresponding magnetic properties are as follows,Hcj=810kA/m,Br=1.24T,(BH)max= 195 kJ/m3,Br/Bs=0.841. |
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