The enhanced oxidation resistance of zinc-coated Nd-Fe-B spherical powders using a rotation coating technique

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.