Investigating Rare-Earth Free Permanent Magnetic Materials for Applications in Electric Motors
- Research carried out by Elizabeth Davis-Fowell, AMS CDT PhD Researcher, seeks to address the shortfalls in the electrification of the automotive sector, in a bid to lower the geopolitical implications of production and development of electric vehicles [EVs].
- This project focusses on an alternative to current rare-earth permanent magnetic materials currently in play as the primary magnetic material used in vehicles powered by electric engines. Multiple issues have been identified in the current use of these rare-earth elements, including supply and demand; environmental concerns; and geopolitical impact.
- At present, electric motors utilise a NdFeB magnet within the motor system to provide torque and drive the system. The thermal behaviour of this material at engine operating temperatures, however, is poor and does not meet magnetic specifications for designs. To overcome this, the system needs to be doped with dysprosium [Dy], a heavy rare-earth metal.
- Current reliance on rare-earth elements such as dysprosium [Dy] for this application has been found to be unsustainable, due to the significant associated supply risk, therefore alternative materials are being explored in a bid to combat this issue.
- The MnAlGa alloy combination has been selected as the focus of this study, for use in electric motors. In theory, this combination will have the potential to reduce the production cost and thus increase the economic accessibility of electric transport at a personal and commercial level. This would also allow global society to reduce the steps in energy-for-transport production for electrical generation and storage.
A project led by Elizabeth Davis-Fowell, PhD Researcher in the Advanced Metallic Systems Centre for Doctoral Training at The University of Sheffield, seeks to address the shortfalls in the electrification of the automotive sector, in a bid to lower the geopolitical implications of production and development of electric vehicles [EVs].
This project focusses on an alternative to current rare-earth permanent magnetic materials currently in play as the primary magnetic material used in vehicles powered by electric engines. Multiple issues have been identified in the current use of these rare-earth elements. Concerns with supply are pressing due to the increased demand generated by ‘clean’ energy and modern electronics. Additionally, there are significant overarching environmental and geopolitical disputes associated with rare-earth elemental use in need of address which the outcome of this material will seek to circumnavigate.
The challenge moving forward [which forms the basis of this research] is to develop a novel alloy to replace existing materials in specifications where as such no appropriate material currently exists - within a reasonable price frame - whilst also aiming to address the issues detailed above.
The project is sponsored by Volkswagen Materials Group, and research development has been supported by Prof. Russell Goodall, AMS CDT UK Director, and Prof. Nicola Morley, Professor in Materials Physics, The University of Sheffield.
Understanding the Use of Rare-Earth Magnetic Materials in Electric Motors
There are two key components in an electric vehicle that feature rare-earth magnets - motors and sensors. Electric motors are often constructed to use alternating electromagnetic fields to provide axial rotary forces on a central drive shaft to generate propulsion. The most important element in this motor is the magnet, which in many current designs is a permanent magnet. In magnetic technology, permanent magnets can refer to a magnetic material that can maintain its field under opposing induced magnetic fields, allowing the system to be rotated without magnetic field switching occurring.
At present, this is achieved using NdFeB doped with rare-earth elements. The properties in this material makes it ideal for use as the primary magnetic alloy, due to their increased coercivity at higher operating temperatures as found in commercial EV motors. However, industry analysts foresee and have experienced pressure on the supply comparative to the demand of this raw material, due to upscaled EV production and the development of green energy technologies. Current reliance on rare-earth elements such as dysprosium [Dy] for this application has been found to be unsustainable, due to the significant associated supply risk, as these materials are mostly imported from monodominant sources.
Why is this Important?
At present, electric motors utilise a NdFeB magnet within the motor system to provide torque and drive the system. The thermal behaviour of this material at engine operating temperatures, however, is poor and does not meet magnetic specifications for designs. To overcome this, the system needs to be doped with dysprosium [Dy], a heavy rare-earth metal.
The most pressing issue with the addition of Dy to NdFeB for motor applications is availability. The UK and Europe are home to non-economically viable natural deposits of rare-earth elements, highlighting the need to either: address the instability of the supply chain; develop a strategy to recycle rare-earth elements after use; or continue research and development of high-temperature permanent magnetic materials that are not reliant on rare-earth elements.
With approximately 90% of the global supply of rare-earth elements dominated by China, most nations and industries of the world are dependent upon Chinese exports, resulting in a globally vulnerable supply. Furthermore, with Dy being a heavy rare-earth metal, the mining and refinement is difficult. No ore contains a majority of this element and the extraction involves the use of dangerous chemicals, releasing radioactive materials and hazardous waste through the process. With these factors in mind, there is an industrial motivation to move away from this system, where possible.
Alternatives are currently on the market, but they rely on cobalt (Co), which has similar environmental and political implications in its wide-scale use. The objective of this project is to develop a novel alloy to replace existing materials in specifications where no appropriate material exists - within a reasonable price frame - which hopes to improve environmental and geopolitical conditions.
This project is fundamentally driven by a paper published in 2012 by J.M.D Coey, titled, ‘Permanent Magnets: Plugging the Gap’. In this paper, existing limitations in materials for permanent magnet applications were identified - i.e., hard ferrites being low cost but low field, to NdFeB being very high field but high cost - with the suggestion made that three categories of material [Gap Magnets A-C] could be developed to bridge the gap in both capability and cost per kilo.
In this paper, MnAl was identified as a potential candidate, however, there were concerns raised relating to the metastability of the alloy and its workability. Research carried out by Elizabeth Davis-Fowell aims to investigate the viability of the MnAl alloy combination.
To address the issues highlighted previously, Elizabeth’s research aims to develop an alloy of MnAlGa using readily available materials to combat increased conflicts already in play and likely to escalate over the next 30 years.
The low-cost and availability of manganese makes the element an attractive option to explore, due to its lack of primary alloying applications comparative to alternative elements available in similar quantities. This also applies to aluminium, which is currently also available in large quantities. The gallium content of these elements are also relatively low weight, which would mitigate the cost of the most expensive element of the ternary alloy.
Current findings of this on-going research relate to:
- The refinement of MnAlGa composition to balance magnetic properties against metastability in the low Ga at.% regime.
- The discovery of increased ductility in MnAl with added Ga, which will open novel deformation processing routes.
- The optimisation of the transformation temperature of MnAlGa for practical engineering applications.
Additional benefits of this research relate to the lack of geopolitical concerns linked to the above elements, comparative to those found with Co or Dy extraction. With the potential for greater economic investment following the successful competition of this research, the results of this study could inform MnAlGa electric motors. In theory, this combination will have the potential to reduce the production cost and thus increase the economic accessibility of electric transport at a personal and commercial level. This would also allow global society to reduce the steps in energy-for-transport production for electrical generation and storage.
Long Term Impact
The outcome of this research aims to reduce the global dependence on rare-earth element mining activities in China and East Africa by providing a more sustainable alternative.
Reflecting on developments in global politics over time, it can be interpreted that the centralisation of critical resources for industrial applications leads to economic risk and restricted supply. This is demonstrated somewhat through the export ban placed on Dy which occurred in the last decade, which led to a significant market cost increase for the material. The outcome of this should it be left untouched could be comparable to the Middle East crises as observed in the 20th and 21st centuries when considering oil deposits as an analogous resource. With the three combined elements proposed in this study readily available worldwide [only Ga is somewhat scarce but can be found as a minority element with Bauxite, coal, and zinc ores], this study has the potential to decentralise the critical technology, which is also supported by the global abundance of refineries for each material, resulting in minimised global conflicts.
Additional impact refers to the mass production of electric vehicles. By minimising the demand for Dy-doped NdFeB, accessibility of EVs will increase while cost decreases. This allows for a more centralised framework in energy-for-transport production when compared to hybrid systems involving bio-fuels for internal combustion, resulting in the decarbonisation efforts for the sector becoming more streamlined as fewer power generation mechanisms will need to shift to net-zero production. Whilst electric vehicles are not currently carbon neutral, by removing rare-earth elements from the drive magnet, the environmental impact of EV production will be significantly reduced and the increased availability will lead to the ability to restructure the transport network to a carbon-neutral model.
In terms of timescales to realise the benefits of this material, it is harder to speculate. The project will be moving to trials for deformation processing in order to improve the magnetic properties of this alloy, which if successful, pushes progress towards near-net-shape manufacture.
However, with the outcome of these trials unpredictable at present, the material could be a decade away from industrial implementation, as the processing element takes centre-stage in the development of the alloy properties to engine specifications. In contrast, if the trials are successful, the next steps are to attempt to recreate the process using industrial, rather than lab grade equipment, to investigate the production viability of the alloy. The results of a successful trial will move the project one step closer to mass production and application, thus shaving years off the target.
The two stages to be completed within the next 18 months are:
- Thermo-Mechanical characterisation of an undisclosable grade of MnAlGa (referred to as MAG-E) from RT to 500°C in order to prepare the system for deformation processing. This shall be conducted for both the epsilon (precursor) and tau (magnetic) phase in order to determine the best states for processing.
- Deformation processing of MAG-E in order to determine the best conditions to improve the BHMax (the working point of a permanent magnet in a motor and thus how ‘good’ it is) from the as-annealed state. This will be tied to the texture and parameters of the crystal lattice in order to model the system and interpolate optimum conditions using the Malvern Panalytical Empyrean situated at the Royce Discovery Centre, Royce at the University of Sheffield.
The stretch goal is to repeat this process using industrial or simulated industrial grades in order to look at performance and properties changes. This will allow for a sensitivity analysis of the material. By determining the level of purity required in the material reagents for effective properties, it will become possible to begin to pitch the material to both manufacturers for production and designers for application once a cost has been set.
The outcomes of this research hope to not only develop a novel alloy to replace existing materials, but also to improve the environmental and geopolitical concerns surrounding the sector.
Malvern Panalytical Empyrean, X-Ray Laboratory, Royce Discovery Centre, Royce at the University of Sheffield
Quantum Design MPM3 SQUID, Advanced Characterisation Laboratory, Royce Discovery Centre, Royce at the University of Sheffield
Arcast Arc 200 Melter, Royce Discovery Centre, Royce at the University of Sheffield
Elite TSH18/75/300 Tube furnace, Quarrell Laboratory, Sir Robert Hadfield Building, Department of Materials Science and Engineering
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