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An estimated 750,000 new hybrid electric and plug-in battery vehicles, most with permanent magnet synchronous alternating current (PMAC) drive motors, took to the road in 2016 alone. Accompanied by 40% year over year growth in the EV market significant challenges exist in producing large quantities of permanent magnets (on the order of tens of millions) for reliable, low-cost traction motors [IE Agency, Energy Technology Perspectives (2017)]. Since the rare earth permanent magnet (REPM) market is essentially 100% net import reliant in the United States and has proven to have an unstable cost and supply structure in recent years, a replacementmore » RE-free PM material must be designed or selected, fully developed, and implemented. Alnico, with its high saturation magnetization and excellent thermal stability, appears to be uniquely suited for this task. Further, while alnico typically has been considered a relatively low coercivity hard magnet, strides have been made to increase the coercivity to levels suitable for traction drive motors [W Tang, IEEE Trans. Magn., 51 (2015)]. If a simple non-cast approach for achieving near [001] easy axis grain aligned permanent magnets can be found, this would allow massproduced final-shape anisotropic high energy product magnets suitable for usage in compact high RPM rotor designs. Therefore, a powder metallurgical approach is being explored that uses classic compression molding with “de-bind and sinter” methods, where a novel applied uniaxial loading, and an applied magnetic field may create final-shape magnets with highly textured resulting microstructures by two different mechanisms. Results indicate a positive correlation between applied uniaxial load and resulting texture (Fig. 1), along with benefits from using an applied magnetic field for improved texture, as well. Lastly, the apparent mechanisms and resulting properties will be described using closed loop hysteresisgraph measurements, EBSD orientation mapping, and high-resolution SEM.« less

We present economic uncertainty in the rare earth (RE) permanent magnet marketplace, as well as in an expanding electric drive vehicle market that favors permanent magnet alternating current synchronous drive motors, motivated renewed research in RE-free permanent magnets like “alnico,” an Al-Ni-Co-Fe alloy. Thus, high-pressure, gas-atomized isotropic type-8H pre-alloyed alnico powder was compression molded with a clean burn-out binder to near-final shape and sintered to density >99% of cast alnico 8 (full density of 7.3 g/cm³). To produce aligned sintered alnico magnets for improved energy product and magnetic remanence, uniaxial stress was attempted to promote controlled grain growth, avoiding directionalmore » solidification that provides alignment in alnico 9. Lastly, successful development of solid-state powder processing may enable anisotropically aligned alnico magnets with enhanced energy density to be mass-produced.« less

The 2011 price shock in the rare earth (RE) permanent magnet (PM) marketplace precipitated realization of extremely poor RE supply diversity and drove renewed research in RE-free permanent magnets such as “alnico.” Essentially, alnico is an Al-Ni-Co-Fe alloy with high magnetic saturation and T_C, but low coercivity. It also was last researched extensively in the 1970’s. Currently alnico “9” magnets with the highest energy product (10MGOe) are manufactured by directional solidification to make highly aligned anisotropic magnets. This work developed novel powder processing techniques to improve on unaligned anisotropic alnico “8H” with elevated coercivity. Gas atomization was used to producemore » pre-alloyed powder for binder-assisted compression molding of near-final shape magnets that were vacuum sintered to full density (<1% porosity). Biased grain growth with resulting grain alignment was achieved during a second solution annealing step, during which a uni-axial stress was applied along the axis parallel to the magnetization direction. Lastly, evaluation of heavily stressed samples (>250g) showed reduced overall loop squareness compared to unaligned (equiaxed) 8H due to grain rotation-induced misalignment, while low stresses improved squareness and greatly improved alignment compared to equiaxed magnets, with squareness approaching 0.30 and remanence ratio as high as 0.79.« less

Progress is reviewed on development of an improved near-final bulk magnet fabrication process for alnico 8, as a non-rare earth permanent magnet with promise for sufficient energy density and coercivity for electric drive motors. This study showed that alnico bulk magnets in near-final shape can be made by simple compression molding from spherical high purity gas atomized pre-alloyed powder. Dwell time at peak sintering temperature (1250°C) greatly affected grain size of the resulting magnet alloys. This microstructure transformation was demonstrated to be useful for gaining partially aligned magnetic properties and boosting energy product. Furthermore, while a route to increased coercivitymore » was not identified by these experiments, manufacturability of bulk alnico magnet alloys in near-final shapes was demonstrated, permitting further processing and alloy modification experiments that can target higher coercivity and better control of grain anisotropy during grain growth.« less