Alnico Research Articles

Refining Alnico 8 magnets with composition optimization of matrix phase, directional solidification and magnetic field annealing

Optimized shape anisotropy of the Fe-Co rich ferromagnetic (α1) phase and the effective separation of the α1 and α2 phases with maximum magnetization difference—where α2 represents a paramagnetic magnetic phase—are the key parameters for maximizing the magnetic properties of Alnico magnets. In this manuscript, efforts have been undertaken to optimize the shape anisotropy of the α1 phase and increase the difference in magnetization and separation between α1 and α2 phases by fine tuning Al and Ni contents, directional solidification and magnetic field annealing methods. At first, Alnico magnets were fabricated by adjusting the content of α2 phase followed by homogenization, magnetic field annealing at high temperature, and low-temperature tempering. Intrinsic coercivity (Hcj) of ⁓146.0 kA/m, remanence (Br) of ⁓0.90 T and maximum energy density ((BH)max) of 46.02 kJ/m3 are achieved in the magnet with 8.2 wt% Al and 12.8 wt% Ni treated in field of 1.5 T for 10 minutes. At the second stage, the magnet with optimal magnetic properties is directionally solidified to develop columnar grains, and then the α1 phase is grown in the direction of the columnar grains by magnetic field annealing to enhance the (BH)max to 79.8 kJ/m3. The axial ratio of the α1 phase increased significantly with the increase of the grain size, particularly in the directionally solidified magnets. The Curie temperature of the α1 phase is noted near 1150 K, while the Curie temperature of the α2 phase is below 400 K. The magnets demonstrated excellent temperature stability, with magnetic properties decreasing by only 10–12 % at 800 K. These results may pave the way for further development of Alnico magnets specifically for high temperature applications.

Comparison of differential phase Contrast, Lorentz and non-Lorentz transmission electron microscopy for microstructural and magnetic imaging of alnico magnet

In this work, non-Lorentz, Lorentz transmission electron microscopy (LTEM) and differential phase contrast (DPC) methods were used to observe the phase and magnetic structure of the alnico magnet. All observations were performed on alnico-5 in transverse orientation. The results showed the magnetic contrast of the domain walls in the conventional TEM images despite the effects of the lens magnetic field, which was verified and explained using DPC. Experimental methodology and sample results are summarized with advice for further research.

High-performance Alnico magnets prepared by powder bed fusion

Fine-grained and anisotropic Alnico magnets were prepared by powder bed fusion using a laser beam. The as-built magnets were treated by solution treatment (ST) at 1250 °C, magnetic heat treatment (MHT) at 835 °C, and three-stage aging treatment (TSA) at 600 − 500 °C, respectively. The phase transition, microstructure evolution, and magnetic characteristics of the magnets were investigated. The findings demonstrate that as-built magnets are composed of equiaxed grains with a fine grain size of ∼1.5 µm and exhibit crystalline and magnetic anisotropy. After ST-MHT-TSA treatment, the magnets are composed of equiaxed grains with an average grain size of 12.1 − 15.5 µm, and every grain exhibits a spinodal structure consisting of the FeCo-type α1 phase and the Fe2NiAl-type α2 phase as well as enhanced < 211 > orientation. The orientation relation between α1 and α2 mainly forms {110}α1//{220}α2, {200}α1//{400}α2, and the atoms at the interface have a strong coherent matching. The spinodal structure in ST-MHT-TSA magnets mainly displays checkerboard-like. Both α1 and α2 phases exhibit a single domain structure; their interface is the magnetic domain wall. High α1 aspect ratio and anisotropy give Alnico magnet exceptional magnetic performance with Hc= 1363.1 Oe, Br= 9.0 kGs, and (BH)max= 6.2 MGOe. Furthermore, micro-magnetic simulations were used to disclose how some defect structures in the micro-regions affect the magnetic properties.

Simulation Study of Critical Aspects of MIAB Welding for Analysis of Potential Factors Governing the Performance of Weld Formation

Magnetically Impelled Arc Butt (MIAB) welding, is a solid-state welding technique. The magnetic system of this technique is pivotal for the generation of the Lorentz force, which impels an arc to rotate along the periphery of the weld tubes and thus facilitates the heating of faying surfaces. The magnetic arrangement and the arc dynamics significantly impact the effectiveness of the welding process, eventually dictating the efficiency. This study case investigates the impact of the magnetic arrangement on the arc rotation and possible factors that cause irregularities in the (MIAB) welding through COMSOL simulation. The COMSOL simulation has served as a powerful tool to comprehensively analyse various arc dynamics and magnetic systems and extrapolate the observations to analyse the arc dynamics and magnetic systems involved in MIAB welding. By employing simulation studies, the research aims to unravel critical insights for an efficient design of the MIAB welding system. This work includes a study of the effect of magnetic forces on arc dynamics using various models and attempts to develop an analogy to the MIAB welding process. This is further utilized to explain the process variations in the form of arc displacement, electric potential distribution, and the possibility of self-demagnetization of AlNiCo magnets. Thus, it provides a foundation for advancing the technological aspects of MIAB welding to overcome the limitations and irregularities. This research is instrumental in enhancing the understanding of magnetic interactions involved in the MIAB process, which can further pave the way for improved welding machine designs and consequently, enable research on these lines that can help in establishing an optimized parametric window.

Remnant Magnetisation State Control for Positioning of a Hybrid Tunable Magnet Actuator

The recent development of a hybrid tunable magnet actuator proposes to eliminate Joule heating when maintaining a force or position offset. By controlling the remnant magnetic flux in an AlNiCo magnet within the actuator, the actuation force can be linearly varied and maintained. While a method for tuning the magnetisation state of the magnet with minimal magnetic field changes has been demonstrated previously, the method is inefficient due to its slow tuning rate, which hinders its use in controlling the actuator’s position. This paper presents a novel method of magnetisation state tuning with a fast tuning rate and validates its effectiveness for controlling the position of a short-stroke linear actuator. This tuning method is implemented and verified for changing the flux density of an AlNiCo magnet in the range of ±1.2 T, with a root-mean-square error (RMSE) of 7.2 mT. An accurate estimation of the magnetisation state is furthermore achieved during positioning, guided by the design and experimental validation of a lumped parameter model, allowing the position to be controlled with an RMSE of 4.0 µm in a range of −157 to 320 µm.

Deformation mechanism of highly textured Alnico magnets

Deformed Alnico magnets were prepared by hot isostatic pressing (HIP) spherical powders and hot rolling (HR), and the hot-rolled magnets were solution-treated at 1250 ℃, magnetic heat treated at 835 ℃, and three-stage aged at 600 – 500 ℃, respectively. The results show that Alnico spherical powder comprises 77.5% α phase, 8.6% α1 phase, and 13.9% α2 phase. The HIP magnet has spinodal decomposed during the preparation, and HR improved α content. The magnet has spinodal decomposed thoroughly after magnetic heat treatment (MHT) and aging heat treatment (AHT), composed of 62.1% α1 phase with a B2 structure and 37.9% Fe2NiAl-type α2 phase with the L21 structure. Moreover, the HIP and HR magnet preferentially produces the< 100 > texture, which is also enhanced along the< 211 > directions. The preferred deformation of the α1 phase is carried out under the synergistic action of the α2 phase. The HIP deformation mechanism is that composition diffusion and structural transformation are carried out in different stages, resulting in four kinds of two-phase structures. The rolling deformation mechanism is that the grains parallel or nearly parallel to the rolling direction are directly rolled into lath-like ones, and four kinds of microstructures are formed in the grains. Compared to the HIP magnet, the MHT and AHT promote the formation of the fibrous structure, and the maximum aspect ratio of α1 phase reaches ∼35:1. The coercivity of the heat-treated magnet increased by 160.9%, and the remanence and magnetic energy product also increased simultaneously.

Miniature DC electromagnetic pumps of molten lead and sodium to support development of Gen-IV nuclear reactors

This work developed designs of submerged, dual-regions, miniature DC-EM pumps for circulating molten lead and liquid sodium at ≤500 °C without active cooling for use in ex-pile and in-pile test loops to support of materials and fuel developments for Gen-IV sodium and molten lead fast nuclear reactor. These pumps with two pumping regions are 57 mm, 66.8 mm, 95.4 mm, and 133.5 mm in diameter and have two Alnico 5 permanent magnets with Hiperco-50 pole pieces for focusing the magnetic field lines in the flow duct. The Equivalent Circuit Model (ECM) linked to the Finite Element Method Magnetics (FEMM) software in MATLAB platform calculated the pumps characteristics for a wide range of parameters. Also determined are the pumps dimensions for the highest cumulative pumping power and peak efficiency. These dimensions are the height, width, and length of the flow duct, the thickness of the Alnico magnets, the length of current electrodes, and the separation distance between the two pumping regions. For molten lead, the pumping power increases from 368 W to 728 W, and the peak efficiency from 14.7% to 31.6% with increased pump diameter from 57 mm to 133.5 mm. For liquid sodium, both the pumping power and peak efficiency are higher, increasing from 392 W to 767 W and from 44.3 to 51.2%, respectively, with increased pump diameter from 57 mm to 133.5 mm.

Design and Performance Analysis of a Novel Hybrid PM Five-Phase Fault- Tolerant Switched-Flux Memory Motor

Background: The existing literature depicts that since the advent of the hybrid permanent magnet switched-flux memory motor (HPMSF-MM), comprehensive research is focused on the design of three (3)-phase HPMSF-MM topologies, which limits their practical safety crucial design application range or scope, namely, in electric vehicle (EV). Objective: This research work aims to design a novel five (5)-phase fault-tolerant HPMFS-MM using the synergy of two key PMs, namely, a neodymium magnet (NdFeB) and Alnico magnet, also known as low coercive force (LCF) with an intrinsic overload fault detection capacity and excellent flux-regulation capacity to extend it practical application scope. Methods: This research paper employs finite element analysis (FEA) via ANSYS Maxwell electromagnetic software in designing, simulation, and analyzing the proposed fault-tolerant HPMSF-MM. Results: The key merit of the Proposed HPMSF-MM is the exhibition of an overload fault protection mechanism via an injection of a reversed temporary control pulse current into the field winding (FW) in the event of an overload fault condition to demagnetize the Alnico PM configuration to ensure that, almost all the generated flux are short-circuited via the design stator-core without linking the designed rotor as in the case of normal operation is effectively verified via the flux-linkage analysis in this paper. Conclusion: The proposed HPMFS-MM can effectively demonstrate its intrinsic overload fault detection mechanism, due to its tremendous flux-regulating or weakening capacity, in addition to its fault-tolerant teeth implementation merit of ensuring physical motor winding phase isolation in an event of a fault.

An Active Magnetic Bearing With Controllable Permanent-Magnet Bias Field

Permanent-magnet (PM) biased magnetic bearings use a magnet to produce the bias field rather than applying a bias current, thereby eliminating the associated electrical power losses and heat generation. In the existing PM-biased magnetic bearings, the PM materials NdFeB or SmCo are generally employed due to their superior properties. However, these PMs should be pre-magnetized, and the generated bias magnetic field cannot be adjusted, limiting the flexibility of the magnetic bearings. This article proposes a new type of PM-biased magnetic bearing that uses a low-coercivity AlNiCo magnet and equips a magnetization coil to magnetize the magnet <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> . As a result, the magnet can be post-magnetized to make the assembly process of the machines easier without the disturbance of magnetic force, and the bias field generated by the magnet can be actively controlled to improve the rotor iron losses and force characteristics of the magnetic bearing. Experiments on a prototype successfully verify the advantages of the presented magnetic bearing.

Recent Developments in 3D Printing of Rare-Earth-Free Permanent Magnets

This article reviews the advances in additive manufacturing of magnetic ceramics and alloys without rare-earth elements. Near-net-shaped permanent magnets with varying shapes and dimensions overcome traditional limitations of the cast, sintered, and bonded magnets. The published articles are categorized based on material types and 3D printing techniques. Selective laser melting and electron beam melting were predominantly used to produce alnico magnets. In addition to the electron beam melting, manganese aluminium-based alloys were successfully printed by fuse filament fabrication. By incorporating magnetic powders in polymers and then printing via extrusion, the fuse filament fabrication was also used to produce strontium ferrite magnets. Moreover, hard ferrites were printed by stereolithography and extrusion free-forming, without drawing composites into filaments. Magnetic properties in some cases are comparable to those of conventional magnets with the same compositions. Currently, available software packages can simulate magnetic fields for designing magnets and optimize the integration in electrical machines. These developments open up opportunities for next-generation permanent magnet applications.

Influence of Low-Coercive-Force Magnet Property on Electromagnetic Performance of Variable Flux Memory Machine

The magnetization properties of low-coercive-force (LCF) permanent magnets (PMs), i.e., remanent flux density, coercivity, and hysteresis curve slopes, are closely related to the magnetization characteristics of variable flux memory machine (VFMM). Therefore, this article investigates the inherent relationship between the properties of LCF PMs and electromagnetic characteristics of VFMM using a combined solution integrated with magnetic equivalent circuit (MEC) and graphical methods. First, the hysteresis curve of the LCF PM is analytically modeled by a simplified piecewise linear hysteresis model to characterize the mathematical relationships among the key parameters of the hysteresis model. Then, a simplified MEC method is used to obtain the permeability curves of VFMM, thereby further determining the intrinsic relationship between the dimensional parameters of the LCF PM and the electromagnetic characteristics of VFMM. Afterward, the flux regulation characteristics and on-load magnetization state (MS) stabilization capability of VFMM are qualitatively analyzed using a newly developed coupled approach. Furthermore, the electromagnetic characteristics of three VFMMs equipped with different version LCF PM materials are comprehensively compared using the finite-element (FE) method. Finally, a VFMM prototype using the selected AlNiCo magnet is manufactured and tested to verify the correctness of the theoretical and FE analyses.

Tailoring the magnetic properties and microstructure of Alnico 8 magnets by various Ti contents and processing conditions

Shape anisotropy, developed as a result of spinodal decomposition (SD) is the basis for the hysteresis behavior of Alnico magnets. The SD process is sensitive to processing conditions and constituent elements. In this paper, the development of spinodal structure and its effects on magnetic properties and serviceability of Alnico 8 alloys are investigated. The Ti-content is varied between 2.5 and 7.5 wt%. The magnets are fabricated by conventional casting, homogenization, magnetic field annealing and tempering treatments. The magnetic properties of intrinsic coercivity, Hcj = 30 kA/m, remanence, Br = 0.53 T and maximum energy density, (BH)max = 6.03 kJ/m3 for 2.5 wt% Ti are increased to Hcj = 150 kA/m, Br = 0.0.88 T and (BH)max = 29.3 kJ/m3 for 6.5 wt% Ti alloy. These magnetic properties are 100% reversible up to 800 K. Furthermore, an alloy with 5.5 wt% Ti is directionally solidified and magnetic properties of Br = 1.01 T and (BH)max = 58.9 kJ/m3 are obtained. The evolution of mosaic nano structure, the mechanism of magnetic hardening and the interactions of various phases have been investigated.

Preparation of Alnico magnet with high magnetization by thermal deformation

Fe-Co-rich α1 and Al-Ni-rich α2 ribbons were compounded by hot isostatic pressing and hot rolling in a ratio of 2:1, subsequently, the Alnico alloys were subjected to traditional heat treatment. This new composite method solved the problem of the uncontrollable ratio of α1 to α2 phase in Alnico alloy and can form a two-phase embedded microstructure, especially the saturation magnetization of the alloy can be significantly improved. However, the coercivity decreases due to the small aspect ratio of α1 phase and coarse phase size, this needs further improvement. Besides, the effects of temperature, pressure and magnetic field on the diffusion direction of elements are disclosed.

Analysis of a Hybrid Permanent Magnet Variable-Flux Machine for Electric Vehicle Tractions Considering Magnetizing and Demagnetizing Current

The overall driving cycle efficiency of conventional permanent magnet synchronous machines (PMSMs) for electric vehicle tractions in a wide speed range is constrained due to the large field weakening current and high iron loss in high speed. The series hybrid permanent magnet variable flux machines (HPM-VFMs) which employ both low coercive force (LCF) magnets and high coercive force magnets are proposed to obtain high torque density and flexible air-gap flux density simultaneously. The key of HPM-VFMs design is the accuracy of hysteresis model of LCF magnets and operating principle analysis. This article contributes to clarify operating principle based on hysteresis model of AlNiCo magnets and propose a novel design consideration to reduce magnetizing and demagnetizing current. Based on the theoretical analysis, this article proposes a novel series HPM-VFM, in which the NdFeB and AlNiCo magnets are arranged separately. Furthermore, flux paths are designed to achieve appropriate interaction between two kinds of magnets. The proposed machine has features of wide magnetization state (MS) variation range, low magnetizing and demagnetizing current, and low risk of unintentional demagnetization. By manipulating the MS of the proposed machine, the losses of a wide speed range operation could be reduced. The comparison of efficiency maps and the worldwide-harmonized light vehicles test cycle driving cycle losses between the proposed machine and a conventional interior PMSM proves that the proposed machine achieves higher efficiency for electric vehicle.

TriBeam tomography and microstructure evolution in additively manufactured Alnico magnets

The Alnico 8 alloy has been printed using the selective laser melting additive manufacturing approach, resulting in material with magnetic properties in the as-printed state comparable to properties produced by conventional casting or powder metallurgy routes. Microstructural characterization in 3D, via electron backscattered diffraction (EBSD) in a TriBeam microscope, simultaneously reveals a fine-scale grain structure, grain orientations and sub-grain misorientation gradients as a function of proximity to spherical pores that form during the print process. The nanostructure of the 3D printed part has the same highly coherent spinodal α1//α2 structure observed in conventionally fabricated Alnico 8, which gives rise to a coercivity (Hc) of 51.2 kA m-1. Further investigation of the phase constituents by TEM analysis provides an understanding of the microstructure evolution during the additive manufacturing process. Modified processing pathways for improved microstructure and properties are discussed.

Analysis of a Novel Surface-Mounted Permanent Magnet Motor With Hybrid Magnets for Low Cost and Low Torque Pulsation

This article presents a novel surface-mounted permanent magnet motor (SPMM) with hybrid NdFeB-Alnico magnets to achieve low cost and low torque pulsation. Based on the analysis of the effects of stator magnetomotive force (MMF) on rotor magnets, the Alnico magnets can be properly configured to avoid demagnetization. To reduce torque pulsation, three models with different slot-pole combinations are proposed and compared, with the aid of the finite element method (FEM), and the results show that the torque pulsation of the 27-slot/4-pole model is the lowest, which is selected for further optimization. The multi-objective genetic algorithm (MOGA) is adopted to optimize the usage of Alnico and NdFeB magnets, thereby improving torque performance and reducing the cost. To verify the effectiveness of the optimization, the optimized model with hybrid NdFeB-Alnico magnets is compared with other models with only NdFeB magnets under the same operating conditions. As a result, it shows that the optimized model can significantly reduce the cost of magnets while maintaining excellent torque performance.

Electro-permanent magnetic weight release mechanism for buoyancy control of an autonomous well-logging tool

We present the design and test of a magnetic actuator that is used to hold and release a ballast and switch buoyancy of a miniaturized autonomous well-logging tool from negative to positive. The actuator makes use of a low coercivity aluminum-nickel-cobalt (AlNiCo) magnet paired with a high coercivity neodymium-iron-boron (NIB) magnet to create and cancel a magnetic pull force on a steel plate by changing the polarization direction of the former magnet. Brief current pulses sent through a solenoid wrapped around the AlNiCo magnet by charging and discharging a capacitor. The resulting resistor-inductor-capacitor (RLC) circuit is analyzed to understand the polarization process of the AlNiCo magnet and state change of the actuator’s pull force. Our numerical solution using a nonlinear inductor model and test results showed that the repolarization can be achieved in steps using a relatively small 0.1 mF capacitor thanks to stored remnant field at each step. This made it possible to save space and energy for the miniaturized autonomous logging tool. Effects of NIB and steel weight piece on the AlNiCo polarization are experimentally analyzed. Magnetic circuit geometry is optimized using finite element analysis to maximize the pull force on the weight. The actuator occupies less than 2 cm3 and provides more than 2 kg-f to carry a ballast that weighs about 60 grams.

Micromagnetic Simulation of Coercivity of Alnico Magnets

A branch connecting two neighboring ferromagnetic α <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> -phase rods is one of the geometric factors that contributes to degradation of alnico's normally high coercivity. This letter investigates the effects of various branch geometries and dimensions on the coercivity of alnico comprehensively by using a micromagnetic simulator when the branch is assumed to be connected in either H- or U-shaped alnico structure and the magnetization reversal of the ferromagnetic α <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> -phase rod occurs by quasi-coherent rotation or curling. For the H-shaped structure, high coercivity is realized by adopting the middle-branch-connected (MBC) structure with a long branch length and width for quasi-coherent rotation, regardless of the branch thickness. For curling, the same geometric parameters are suggested except for a thick branch thickness. For the U-shaped structure with quasi-coherent rotation, a short branch thickness, width, and length, and MBC position lead a high coercivity. For curling, a short branch width but long length and edge-bridge-connected position result in a high coercivity, regardless of the branch thickness.

The Effect of Using Various Magnetic Materials on Diesel Engines using Biodiesel Fuel

One of method to improve engine performance and reduce fuel consumption is to use exposure to magnetic fields in the fuel lines. Several studies have proven that magnetic field exposure can improve diesel engine performance. This research aims to test the performance of a diesel engine using fuels that are given a magnetic field from 3 types of permanent magnets, namely magnets made from Neodymium Iron Boron (NdFeB), Aluminum Nickel Cobalt (AlNiCo), and Ferrite (Fe). Performance tests on the Yanmar TF85MH diesel engine include power and torque. The fuel used in this research is Biodiesel B20. The results showed that neodymium magnets (NdFeB) are the best magnets of the 3 types of magnets tested with an average increase in power of 2.30%, an average increase in torque of 2.35%.

Low‐Cost Permanent Magnet‐Assisted Switched Reluctance Motor for Adjustable Speed Drive Applications

AbstractPermanent Magnet (PM) motors have been attracting great attention in recent technology because of providing higher efficiency as well as power/volume as compared to conventional wound‐rotor type machines. Recently, it has been demonstrated that NdFeB magnets, which are one of the expensive magnets, can be replaced by Alnico magnets in the case of Switched Reluctance Motor (SRM) without any performance degradation. However, the performance of this machine has not been analyzed so far under a proper torque control strategy. The main objective of this work is to investigate the performance of DITC‐controlled PM‐SRM under various conditions. The possible demagnetization effect of the Alnico magnets on motor performance has also been considered. Compared to same size SRM, 3% efficiency increase has been obtained at rated operation. Overall results demonstrate that PM‐SRM drive shows valuable performance and may have potential to be used in near future motor drive technology. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.