Development of Dy-LRE-Zn-Cu Low-Melting Diffusion Sources for Efficient Coercivity Enhancement in Nd-Fe-B Magnets

Abstract

Nd-Fe-B sintered magnets with high magnetic performance are ess ential components in a wide range of modern devices, particularly in electric vehicle (EV) drive motors. However, their coercivity significantly decreases at elevated temperatures, leading to reduced efficiency under operating conditions typical of EV applications. To address this limitation, the grain boundary diffusion process (GBDP) utilizing heavy rare earth (HRE) elements has been employed to enhance coercivity and thermal stability. Despite its effectiveness, the use of HREs presents several challenges, including limited availability, high and unstable prices, and inefficient diffusion due to their high melting points. In this study, Dysprosium (Dy) was partially substituted with transition metals (TM) such as zinc (Zn) and copper (Cu), along with light rare earth elements (LRE) such as praseodymium (Pr) and neodymium (Nd), to lower the melting point of the diffusion source and improve diffusion efficiency. Optimal GBDP temperatures for various Dy-LRE-Zn-Cu (LRE = Pr, Nd) compositions were determined, and the resulting magnetic properties of the diffused magnets were systematically investigated. The magnet produced using a low-melting Dy-Pr-Zn-Cu diffusion source (Fig. 1) with 20 wt.% Dy in composition demonstrated comparable magnetic properties at 25 °C and improved magnetic performance at 200 °C compared to the sample fabricated through Dy metal diffusion.