The Abnormal Corrosion Behavior of the (Nd,Ce)-Fe-B Magnet with Dual Main Phases in Nd 2 SO 4 and NaCI Solutions

Sintered NdFeB magnets are widely used in various fields in that NdFeB magnets have the most excellent magnetic properties at room temperature. As Ce element is the most abundant rare earth element, a lot of research on the substitution of Ce for Nd has been conducted[1] But the corrosion resistance of the Ce-riched magnet is questioned as Ce element has stronger chemical activity than Nd element. In this paper, the abnormal corrosion behavior of the (Nd,Ce)-Fe-B magnet with dual main phases in Na 2 S0 4 and NaCl solutions has been investigated, in which (Ce 3 Nd 17 )FebalBI and (Ce 9 Nd 21 )Fe ba1 B 1 were prepared by the mixed powder sintering preparation technology. The maximum magnetic energy product $(\text{BH})_{\max}$ of Ce 3 Nd 17 Fe ba1 B 1 and (Ce 9 Nd 21 )FebalBI are 44.8 MGsOe and 33 MGsOe respectively, which were measured by using a NIM-2000H closed-circuit hysteresigraph and the scanning electron microscope (SEM) was used to measure the distribution of the matrix and the rare earth-riched phase. The corrosion behavior of the Ce 3 Nd 17 Fe ba1 B 1 and (Ce 9 Nd 21 )Fe bal B 1 samples have been studied in 3.5 wt.% NaCl and 0.5 mo1/1 Na 2 S0 4 solutions, separately. To be specific, the polished samples were immersed in different electrolytes aqueous solution for 33 days in order to get weight loss and corrosion morphology and the polarization curves were measured with a CHI660D electrochemistry analyzer to characterize the electrochemical stability. The conclusions are as follows: