Research On The Corrosion Behavior Of The Low-cost Sintered NdFeB Magnets With Ce

NdFeB sintered magnets are widely used in various fields such as information technology, communication electronic and wind mill power generation technology due to excellent magnetic properties. However, its application scopes are restricted by the defects of its poor corrosion resistance. With the increasing applications of NdFeB sintered magnets, the demand and the price of rare earth metal neodymium both increased much more in recent years. Therefore, it is significant to develop the low-cost sintered Nd-Fe-B magnets and investgate its corrosion resistance. According to this background, this paper successfully prepared low-cost magnets by introducing Ce. The corrosion behavior of N33, N45and the magnet with Ce in different corrosion environments and electrolyte solution were studied, and the corrosion mechanism and microstructure were analyzed and compared. It’s expected to establish a theoretical foundation for the fabrication and application of low-cost sintered NdFeB magnets with high corrosion resistance. The main research results are showed as below:(1) The corrosion behaviors and corrosion mechanism of different magnets in130℃,2atm and100%relative humid atmosphere were studied by high pressure accelerated test (HAST). It was found that under these conditions the mass loss of N33, N45and the magnet with Ce were83.192%,0.3846%and0.08813%, respectively. The result indicated that the corrosion resistance of the magnet with Ce is better than N45and N33magnets.(2) The corrosion behaviors and mechanism of different magnets in neutral salt spray atmosphere were studied by salt spray test (NSS). It was found that under these conditions, the corrosion reaction of sintered NdFeB magnets is mainly oxidation. The mass loss of N33、N45and the magnet with Ce were1.6357%,2.2636%and2.9873% for168h in neutral salt spray atmosphere. The result also indicated that the corrosion resistance of the magnet with Ce was better than N45and N33magnet.The reasons are as follow:fistly, the main phase grain size of the magnet with Ce was the smallest, which lead to the smallest mass loss when the magnet occured surface peeling; secondly, the rare earth-rich phase was evenly distributed around the main phase,which reduced the activity of the rich rare earth phase.In addition.it is also found that the corrosion resistant of substrate played a vital role after electroplating Ni/Cu/Ni. The magnet with Ce has the lowest mass loss. Therefore, the Ce magnet with Ni/Cu/Ni coating performs the best corrosion resistant.(3) By measuring the polarization curves and electrochemical impedance spectroscopy, it found that the magnet with Ce showed the highest corrosion potential, the minmum corrosion current and the maximum impedance in different solution (3.5%NaOH,3.5%NaCl and tap water), which further explained the fundamental cause of the best corrosion resistance of the magnet with Ce; At the same time, the corrosion behavior of magnets in the three kinds of solution showed that, when they were in3.5%wt NaOH solution, they showed the best corrosion resistance; The magnets showed the worst corrosion resistance when they were in3.5%wt NaCl solution.