The Enhanced Oxidation Resistance of Zinc-Coated Nd-Fe-B Spherical Powders Using a Rotation Coating Technique

Abstract

A rotation coating technique was used to apply Zn layer onto MQP-S Nd-Fe-B spherical powders, aiming to enhance their anti-oxidation properties while maintaining their high magnetic performance. As the coating temperature increases and duration extends, the Zn layer thickness grows, subsequently leading to a reduction in powder magnetization primarily due to the introduction of nonmagnetic Zn. A certain level of degradation of the original Nd-Fe-B powders also occurs during coating, which appears to be relatively minor, as the powders' coercivity remains almost unchanged after coating. All powders coated under different conditions effectively prevent further oxidation, maintaining almost unaltered magnetization during high-temperature tests. It demonstrates that rotation coating using lower melting point metals is a simple yet effective method to enhance the anti-oxidation capability of Nd-Fe-B powders. Moreover, this approach is easily scalable, which is important for applications in fabricating metal injection molding or bonded magnets.

Keywords: Nd-Fe-B, rotation coating, oxidation resistance, spherical powders, permanent magnets