Performance enhancement of Nd-Fe-B sintered magnets through grain boundary diffusion using Pr-LRE-Tb-Cu-Al alloys in dry-coating

Abstract

The Nd-Fe-B sintered magnets are widely used in various applications, including hard disk drives, magnetic sensors, wind power generators, high-efficiency air-conditioner compressors, and electric vehicle motors. Nd-Fe-B magnets exhibit high maximum energy product at room temperature, but in high-temperature environments, the coercivity decreases and performance deteriorates. To achieve high coercivity and remanence at high temperatures, heavy rare-earth (HRE) based grain boundary diffusion process (GBDP) is widely used. However, the limited supply and price surge of the HRE elements caused by the recent trade war inhibit the wide application of HRE. In this study, we investigated the variation in magnetic properties according to the coating method for the optimization of GBDP. We explored optimized coating methods using both dip coating and dry coating techniques. Moreover, light rare-earth (LRE) elements and low-melting point metals were selected to substitute Tb and minimize the usage of HRE elements. The addition of LRE and low-melting point metals significantly reduced the amount of Tb required in GBDP for coercivity enhancement. Dry-coating has a significant impact on simplifying the process, reducing the use of diffusion sources and enhancing magnetic properties. The magnetic properties and microstructure of Pr-LRE-Tb-Cu-Al (LRE= La, Nd, Ce and None) diffusion magnets with various compositions are discussed.