Development of Bonded (La,Ce,Y)-Fe-B Permanent Magnets with Higher Performance/Cost Ratio than Nd-Fe-B and (Nd,La,Ce)-Fe-B Magnets

Abstract

Aiming at developing cost-effective bonded permanent magnets, the microstructure, magnetic properties, thermal stability, corrosion resistance, and mechanical properties of bonded (La,Ce,Y)-Fe-B magnet were investigated and compared with Nd-Fe-B and (Nd,La,Ce)-Fe-B magnets. Only RE2Fe14B and Ce(La) grain boundary phases were found in the melt-spun (La,Ce,Y)-Fe-B alloy with a composition of [(Ce0.7La0.3)0.8Y0.2]17Fe78B6, and no paramagnetic CeFe2 phase was detected, which is beneficial to hard magnetic properties. Bonded (La,Ce,Y)-Fe-B magnet exhibits a combination of magnetic properties with intrinsic coercivity Hcj = 330 kA/m, remanence Jr = 0.40 T, and maximum energy product (BH)max = 21.7 kJ/m3 , compared to Hcj = 519 kA/m, Jr = 0.52 T, and (BH)max = 43.8 kJ/m3 for (Nd,La,Ce)-Fe-B magnet, and Hcj = 751 kA/m, Jr = 0.66 T, and (BH)max = 75.3 kJ/m3 for Nd-Fe-B magnet. Despite its low hard magnetic properties, (La,Ce,Y)-Fe-B magnet exhibits the highest performance/ cost ratio of 7.97 kJ∙m-3∙kg/$. In the temperature range of 300~400K, (La,Ce,Y)-Fe-B magnet shows better thermal stability than those of Nd-containing magnets, demonstrated by the high temperature coefficient of coercivity (-0.181 %/K). The corrosion process of bonded magnets includes two reactions related to the corrosion of the surface double layer oxide film. The (La,Ce,Y)-Fe-B magnet exhibits better corrosion resistance than other magnets. The mechanical properties of various bonded magnets were also investigated and the highest compressive strength was obtained in (La,Ce,Y)-Fe-B magnet, possibly due to its higher density and the less brittleness of (La,Ce,Y)-Fe-B alloy. This work is beneficial for accelerating the industrialization of high abundance RE magnets.

Keywords: Nd-Fe-B permanent magnets, High abundance rare earths, Bonded magnets, Performance/cost ratio, magnetic properties, Corrosion resistance