New Alnico Magnets Fabricated From Pre-Alloyed Gas-Atomized Powder Through Diverse Consolidation Techniques

Tang, Wei; Zhou, Lin; Kassen, Aaron G.; Palasyuk, Andriy; White, Emma; Dennis, K. W.; Kramer, M. J.; McCallum, R. W.; Anderson, Iver E.

doi:10.1109/tmag.2015.2437355

Cited by 10 publications

(11 citation statements)

References 7 publications

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“…Initial grain size varied, but ranged between 15-30µm in size, which is what might be expected for grain growth during sintering from the starting bimodal powder size. After straining and full magnetic heat treatment of samples, magnetic measurements for the selected stress levels were performed using a hysteresigraph for comparison to previously described sintered samples in Anderson et al 13,14 The magnetic measurement data, for example the remanence ratio (M r /M s ), also was compared over the full range of applied stress to look for trends, as seen in Fig. 4.…”

Section: Resultsmentioning

confidence: 99%

“…11 The key to improving mass produced alnico for drive motors will be not only the ability to improve coercivity, but also the ability to refine its non-square hysteresis loop shape, without resorting to complex directional solidification methods and extensive machining to final shape, like practiced for alnico 5-7 and 9. 8,[13][14][15] Our recent work (described in another paper of this volume) revealed that coercivity improvements can be approached through alloy changes, and nano-structure refinement during the magneto-thermal heat treating process. However, the loop shape problem must be taken on by radical processing and microstructure changes, especially if this technology is to be brought to mass production scales.…”

Section: Introductionmentioning

confidence: 99%

“…12 Thus, a more scalable powder metallurgy (P/M) processing approach with compression molding of pre-alloyed gas atomized powder was developed and used to successfully produce fully dense magnets of near-final shape in previous work. 13,14,16 Also, an alloy centered on alnico "8H" based alloys was chosen because of its notably higher coercivity in a non-aligned anisotropic magnet. 16 If the higher coercivity of 8H can be maintained in this test of the concept while controlled microstructure alignment is achieved, the energy product of the final magnet will be amplified considerably.…”

Section: Introductionmentioning

confidence: 99%

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Development of controlled solid-state alignment for alnico permanent magnets in near-final shape

et al. 2017

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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 TC, 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 produce 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. 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.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Development of controlled solid-state alignment for alnico permanent magnets in near-final shape

et al. 2017

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“…Batch of pre-alloyed powder was made by gas-atomization in Ames Laboratory. Details on magnet alloy consolidation to full density by hot isostatic pressing have been reported elsewhere [15]. The resultant alloy was polycrystalline with randomly oriented grains.…”

Section: Sample Preparation and Property Measurementmentioning

confidence: 99%

“…Some samples were then annealed at 840 • C with an external applied field of 1 T for 0.5, 1.5, 5, and 10 min, with corresponding samples labeled as 2 thru 5, respectively. This MA temperature was determined from our previous study which gives optimum alloy magnetic properties [15]. Some samples also underwent an additional low temperature drawing process at 650 • C for 1, 3, and 5 h (labeled 6 thru 8), respectively.…”

Section: Sample Preparation and Property Measurementmentioning

confidence: 99%

On spinodal decomposition in alnico - A transmission electron microscopy and atom probe tomography study

et al. 2018

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Alnico is a prime example of a finely tuned nanostructure whose magnetic properties are intimately connected to magnetic annealing (MA) during spinodal transformation and subsequent lower temperature annealing (draw) cycles. Using a combination of transmission electron microscopy and atom probe tomography, we show how these critical processing steps affect the local composition and nanostructure evolution with impact on magnetic properties. The nearly 2fold increase of intrinsic coercivity (H ci ) during the draw cycle is not adequately explained by chemical refinement of the spinodal phases. Instead, increased Fe-Co phase (α 1 ) isolation, development of Cu-rich spheres/rods/blades and additional α 1 rod precipitation that occurs during the MA and draw, likely play a key role in H ci enhancement. Chemical ordering of the Al-Ni-phase (α 2 ) and formation of Ni-rich (α 3 ) may also contribute. Unraveling of the subtle effect of these nano-scaled features is crucial to understanding on how to improve shape anisotropy in alnico magnets.

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Manufacturing Processes for Permanent Magnets: Part I—Sintering and Casting

Cui

Ormerod²,

Parker

et al. 2022

JOM

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Permanent magnets (PMs) produce magnetic fields and maintain the field even in the presence of an opposing magnetic field. Electrical machines using permanent magnets are more efficient than those without. Currently, all known strong magnets contain rare earth (RE) elements, and they are core components of a wide range of applications including electric vehicles and wind turbines. RE elements such as Nd and Dy have become critical materials due to the growing demand and constrained supply. Improving the manufacturing process is effective in mitigating the RE criticality issue by reducing waste and improving parts consistency. In this article, the state of the industry for PM is reviewed in detail considering both the technical and economic drivers. The importance of RE elements is discussed along with their economic importance to green energy. The conventional sintering and casting manufacturing processes for commercial magnets, including Nd-Fe-B, Sm-Co, Alnico, and ferrite, are described in detail.

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New Alnico Magnets Fabricated From Pre-Alloyed Gas-Atomized Powder Through Diverse Consolidation Techniques

Cited by 10 publications

References 7 publications

Development of controlled solid-state alignment for alnico permanent magnets in near-final shape

Development of controlled solid-state alignment for alnico permanent magnets in near-final shape

On spinodal decomposition in alnico - A transmission electron microscopy and atom probe tomography study

Manufacturing Processes for Permanent Magnets: Part I—Sintering and Casting

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