Manufacturing of Die-Upset Rare Earth-Iron-Boron Magnets With (Ce,La)-Mischmetal

Utilization of the relatively abundant and inexpensive (Ce,La)-mischmetal in manufacturing die-upset R-Fe-B magnets (R = rare earth) from melt-spun nanocrystalline alloys was attempted via: 1) the standard single-alloy process; 2) the diffusion of Nd and Pr from low-melting-temperature alloys blended into the magnet; and 3) the diffusion of Nd and Pr by infiltrating the magnet through its surface. No practically viable magnetic properties could be obtained without the introduction of Nd(Pr). Blending with the (Nd,Pr)-rich alloys was found to be less efficient for the development of coercivity than the single-alloy process; so was the infiltration of those precursors which had been alloyed with 0.5 at.% Ga. More efficient than the single-alloy process was infiltration of those precursors which had been alloyed with 2 at.% Si or with 1 at.% Zn. Coercivities of 7-10 kOe and energy products of 17-20 MGOe were obtained for magnets having 43%-55% of the R elements represented by Ce0.65La0.35 and containing overall 7.5-9.7 at.% Nd(Pr). The coercivity of the significantly hyper-stoichiometric (17-19 at.% R) (Ce,La)-containing alloys was found to decline 80% or more as a result of the deformation process, but partially recover after subsequent annealing. The latter improvement is likely to be caused by redistribution of the R-rich phases.