Impact of magnetization state on the corrosion of sintered Nd-Fe-B magnets for e-motor applications

Abstract

We have created an accelerated corrosion environment for sintered Nd-Fe-B magnets in e-motor applications. E-motor working conditions are complex, and standard magnet corrosion tests only cover a small subset of possible parameters (e.g., samples are usually tested in the demagnetized state). In this work magnetized and demagnetized sintered Nd-Fe-B magnets were placed in gearbox oil, and exposed to temperature cycles (u max ¼ 130 8C) using an autoclave. Beforehand the magnets were pre-immersed in saturated waterbased salt solution to account for water and de-icing salt that might interfuse gearbox oil over time. The corrosive behavior was studied for two commercial magnet grades, ''high grade'' (8.9 wt% dysprosium) and ''low grade'' (3.1 wt% dysprosium); and monitored by weight loss, structural analysis (scanning electron microscopy and energy dispersive X-ray) as well as magnetic characterization. The magnetized samples corroded significantly faster than their demagnetized counterparts. Strong differences in the corrosion rates of the ''low grade'' and ''high grade'' material are discussed. We concluded that the magnetization state is one key parameter that needs to be considered in corrosion tests for e-motor applications.

Electrochemical behaviour in synthetic saliva of silane coated Ni/Cu/Ni Nd‐Fe‐B magnet for dentistry applications

“…However, the Nd-Fe-B magnets, produced by powder metallurgy, have a very relevant application limit in their low intrinsic corrosion resistance even in relatively mild corrosive environments [7]. Corrosion causes surface degradation and deteriorates magnetic performances [5,8,9]. This behavior is a direct consequence of the intrinsic porosity and complex microstructure of Nd-Fe-B magnets, in which can be identified a main matrix phase F (Nd 2 Fe 14 B), a h phase (Nd 1þe Fe 4 B 4 ) and a Nd-rich phase (Nd 5 Fe 2 B 6 ) at the grain boundary [10].…”

“…However, the Nd‐Fe‐B magnets, produced by powder metallurgy, have a very relevant application limit in their low intrinsic corrosion resistance even in relatively mild corrosive environments . Corrosion causes surface degradation and deteriorates magnetic performances .…”

Effect of DyF3 on the corrosion behavior of hot‐pressed Nd–Fe–B permanent magnets

“…The corrosion susceptibility increased with decreasing density and with refining the grain size . Recent studies revealed that magnetized Nd–Fe–B based specimens corroded significantly faster than their demagnetized counterparts . Various additives were investigated regarding their effect on the corrosion behavior.…”