Development of Low Cost Rare-earth Permanent Magnets With High Energy Products

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The purpose of the present investigation is to develop the low cost R-Fe-B permanent magnets in selectiing the low cost R elements among available various rare-earth elements. Good candidate rare-earth elements for this purpose is the family of so called "didymium" which is the mixture of Nd, Pr, and Ce. The didymium is then abundant and inexpensive. One might say that a mischmetal will be also abundant and inexpensive, and is the good candidate for low cost R-Fe-B magnets. But it is reported that La, which is the main constituent of mishmetal, does not form the R Fe B compounds. Thus, didymium will be better candidate.The best magnetic properties obtained in present studies are Br=13.2kG, Hc=10.2kOe, and (BH)max=320kJ/m(40MGOe) with Fe33.5%-(5%Ce-didymium)-1%B alloy. Temperature dependence of iHc of5%Ce-didymium and didymium alloys arealmost same as that of the Fe-33.5% Nd-1%B alloy.Ce play an important role in densification of the alloy as sintering aid, and in lowering the melting point of (NdPr) Fe B compounds and making it possible to sinter at relatively low temperatures of 104'C. Economically, 40%Ce-didymium alloys are most inexpensive, and give the energy products of 27MGOe, but have the high temperature coefficient. The iHc of 40%Ce- didymium alloy decrease rapidly, by about 65% of iHc of the room temperature, at 100'C. Alternatively, 5%Ce-didymium-Fe-B sin ter-ed magnets with (BH)max=320kJ/m, are most promising among the present studied low cost alloys.Didymium-Fe-B magnet alloys are also available magnetic powders for bonded magnets.