Study On Electric Field Sintering And Corrosion Resistant Of NdFeB Alloys

This paper summarizes the latest development on methods of sintered NdFeB permanent magnets. Put forward the mostly problems are innovating of sinter technical and improving of magnet antisepsis capability. On the basis of that, NdFeB powders compact is rapidly sintered successfully by the method based on an electric field.The thermal simulation instrument Gleeble-1500D is mainly used in this experiment. Microstructure of the compact is researched with the help of Scanning Electronic Microscope(SEM) and Energy Diversity Spectrometer(EDS). The process of sintering densification and the influence of sintering parameter on it are studied deeply. Meanwhile, corrosion resistant of electric-field sintering magnet and tradition method magnet is comparatively studied.It is shown by the exploring study on the electric field sintering of NdFeB alloys that electric field can preferably control the practical sintering course of compact, it has good dependability to realize sintering process. When preset heating rate is 2000℃/s and pretreated compact of NdFeB alloys is sintered at 1000℃for 8min, densified magnet is obtained. Compared with the microstructures of traditionally sintered magnet, the Nd-rich phases in electric field sintering magnet are smaller, more dispersion and uniform. The phase microstructures are the same as those of traditionally sintered magnets, and no new phases appear.The researches show that the pretreat state of NdFeB alloy compact has important effects on electric field sintering densification and microstructures.When preset heating rate is 500℃/s and the non-pretreated NdFeB alloy compact is sintered at 600℃, relatively densified compact can obtain. The distribution of white Nd-rich phases in compact is uniform and dispersion, but more pores exist in compact, the density of compact is relatively lower, and weaker in magnetism capability , which is obviously different from electric field sintering of pretreated NdFeB alloy compacts.The study on electric field sintering process of NdFeB alloys indicates that the preset heating rate, sintering temperature and sintering time have some effects on compact densification. When preset heating rate and sintering temperature are low, there are many original grains in compact, and some sintering necks between grains haven't formed. With the increase of preset heating rate, the densification of compact gradually improves. Additionally, there exists an optimal sintering time in electric field sintering of NdFeB alloys.As pretreat state of NdFeB alloy compact sintered at 1050℃with preset heating rate of 2000℃/s,the optimal sintering time is 8min.Experiment on the corrosion resistant of electric-field sintering magnet and tradition method magnet. Heat analysis experiment indicates that oxidation rate of tradition method magnet is bigger than electric-field sintering magnet,as twice at most. Oxidation increase rates are different with sintering process,as the sintering heating rate increases, the oxidation rate being reduced. The electrochemistry experiment indicates that the corrosion rate of traditional method magnet is twice as electric-field sintering magnet in the same condition.