Preparation and microstructure of La-containing R-Fe-B permanent magnets

The unfavorable effect of La on the magnetic properties of R-Fe-B permanent magnets is shown to be related closely to remarkable changes in microstructure due to excessive oxidation of La-containing R-rich phases in the alloys. Ce and Al are found to be effective in promoting the sintering process of La-containing alloys, resulting in improvements in both microstructure and magnetic properties. Al segregates into the fcc R-rich phase and improves the wetting ability of its liquid at high temperatures. It is suggested that the influence of Al on coercivities of R-Fe-B magnets is connected with a depression of magnetic interactions between hard magnetic grains.