| Nd-Fe-B permanent magnetic materials have been widely used in modern industrial and electronic technology due to its extremely high magnetic energy product and coercivity.With the rapid development of the economy,the consumption of rare earth permanent magnet materials is getting larger and more imbalance.At present,the demand for rare earth for permanent magnet materials is mainly concentrated on heavy rare earths.Therefore,balanced utilization of rare earth resources and breakthrough of material properties are the main directions for the development of Nd-Fe-B permanent magnet materials,and have very important significance.(1)In order to further improve the balanced utilization of rare earth resources,the effect of Ce addition on the properties of melt-spun Nd-Fe-B alloys were investigated.XRD results show that when the Ce content is low,the Nd-Ce-Fe-B alloys maintains a single hard magnetic phase,but phase separation occurs in the alloy,which has a high Ce content,and a CeFe2 phase is formed.As the Ce content increases,both coercivity and remanence show a tendency to decrease,due to the intrinsic magnetic properties of Ce2Fe14B are lower than those of Nd2Fe14B.However,when the Ce addition amount x=0.45,the coercivity still maintains a high level,from 894 kA/m at x=0 to 830 kA/m at x=0.45,which is only reduced by 64 kA/m.Therefore,the cost-performance ratio of materials has been significantly improved Since the Curie temperature of Ce2Fe14B is lower than that of Nd2Fe14B,the addition of Ce reduces the temperature stability of the Nd-Fe-B alloys.The remanence temperature coefficient α decreases from-0.215%/K to-0.556%/K,and the coercivity temperature coefficient β reduced from-0.461%/K to-0.556%/K.(2)In order to further improve the coercivity of Nd-Ce-Fe-B alloy and its temperature stability,the effect of Ga addition on the properties of[Nd0.55Ce0.45]12.5Fe81.5-zGazB6 alloys were also investigated.The results show that proper addition of Ga can significantly improve the coercivity and its high temperature stability.The remanence,coercivity and magnetic energy product of alloys first increased and then decreased with the increase of Ga content.The comprehensive magnetic properties are best when the content of Ga is about 1.2,The remanence temperature coefficient of alloys after Ga doping is improved,which indicatied that the Curie temperature and room temperature magnetic properties act simultaneously on the remanence temperature coefficient.The coercivity temperature coefficient also first decreases and then increases,indicating that the influence of the coercivity at room temperature is relatively large,and the influence of Curie temperature is relatively small.In addition,the study of the coercivity mechanism of the alloys found that it is basically a pinning mechanism,and the pinning effect of the alloys after the addition of Ga is gradually enhanced during the demagnetization process.(3)Finally,the low-melting Nd-Zn alloys were used to refine the grain boundary of Nd-Fe-B melt spun Alloys.The Nd70Zn30 alloy powder was added to the Nd15Fe79B6 alloy powder in a certain ratio for the diffusion source,and then subjected to different diffusion heat treatments.The research results are as follows:The optimal diffusion heat treatment process is 700 0C for 1 h and then annealed at 500 0C for 4 h.Under the heat treatment process,the coercivity Compared with 7288 Oe of the Nd15Fe79B6 powder after simple heat treatment(x=0),The coercivity of diffused powders have been greatly improved,and reached a maximum value of about 12532 Oe.while,the remanence decreased from 61.8 emu/g for simple heat treatment to 56.28 emu/g during the content of the diffusion source Nd70Zn30 is 15wt.%.In the temperature range of 300-480 K,the temperature coefficient of coercivity was increased from-0.466%/K to-0.462%/K,and the temperature coefficient of remanence was also increased from-0.337%/K to-0.296%/K.It is shown that the grain boundary diffusion using Nd-Zn alloys can effectively improve the temperature stability of Nd15Fe79B6 alloy. |
PDF Full Text Request