The production of rare-earth permanent magnet materials, which are dominated by rare-earth resources, is increasing day by day, but the contradiction between limited rare-earth resources and huge market demand is becoming more prominent. Currently, researchers both domestically and abroad are seeking new high-performance permanent magnet materials that do not contain rare-earth elements or expensive rare metals. Research has found that the low-temperature phase of manganese-bismuth has strong magnetic crystal anisotropy and a positive temperature coefficient of coercivity, making it a highly potential new high-temperature, rare-earth-free permanent magnet material. Vietnam is rich in mineral resources, with confirmed manganese ore reserves exceeding tens of millions of tons, but the utilization of manganese resources is seriously insufficient. Research teams from both China and Vietnam have been conducting long-term research on manganese-bismuth permanent magnet alloys. The Vietnamese side focuses on the preparation of manganese-bismuth master alloys, optimization of rapid quenching processes, anisotropy suppression techniques, and the development of composite magnets. The Chinese side has been conducting systematic research on the composition control of rare-earth-free manganese-based alloys, phase transitions, optimization of microstructure and magnetic properties, and ball milling preparation of alloy powders. Both sides complement each other's strengths, and in this project, they will collaborate closely to enhance exchanges between scholars from China and Vietnam, promote the development and application of high-performance manganese-based permanent magnet materials, increase the high value-added utilization of manganese resources in Vietnam, and address the relative shortage of manganese resources in China.
The project involves the following key scientific issues:
- Low-temperature phase transformation mechanism of MnBi alloy: Achieving complete low-temperature phase transformation structurally is the basis for excellent magnetic properties of MnBi alloys. Detailed understanding of the low-temperature phase transformation mechanism of MnBi alloys is essential to achieve the complete low-temperature phase transformation structurally. Thus, interpreting the low-temperature phase transformation mechanism of MnBi alloys is the first key scientific issue that needs to be addressed in this project. By clarifying the behavior and intrinsic mechanisms of low-temperature phase transformation of MnBi alloys under different preparation processes and element doping, the foundation for studying the microstructure and magnetic properties of the alloy can be laid.
- Control mechanism of microstructure of low-temperature phase MnBi alloy: The microstructure of materials, such as phase composition, structure, atomic local structure, grain size, composition distribution, and boundary phase thickness, directly influences the magnetic properties of the material. In order to improve the permanent magnetic properties of MnBi alloys, it is necessary to study the impact of preparation processes and element doping on the microstructure of low-temperature phase MnBi alloys. Elucidating the control mechanism of microstructure of low-temperature phase MnBi alloys by preparation processes and element doping is an important foundation for further optimizing the alloy's magnetic properties, which is the second key scientific issue that needs to be addressed in this project.
- Intrinsic mechanism of preparation processes and element doping controlling the magnetic properties of MnBi alloys through microstructure regulation: Improving the permanent magnetic properties of the alloy is one of the ultimate goals of MnBi alloy research. Clarifying the intrinsic mechanism of preparation processes and element doping in controlling the magnetic properties of MnBi alloys through microstructure regulation provides possible avenues for enhancing the permanent magnetic properties of MnBi alloys, and this is the third key scientific issue that the project aims to address.
The project also includes the following key technologies:
- Key preparation technology for high-purity low-temperature phase MnBi alloy materials: In the process of smelting MnBi master alloys, manganese is easily volatile and segregates, while bismuth atoms are heavy and tend to deposit during smelting. In addition, during the inclusion reaction process of MnBi low-temperature phase transformation, manganese easily segregates from the MnBi phase, and there are also high-temperature phases with crystal structures similar to the low-temperature phase and elemental bismuth, making it difficult to obtain high-purity low-temperature phase LTP. Controlling the atomic ratios of manganese, bismuth, and doping elements in the alloy, as well as selecting appropriate smelting processes and subsequent heat treatment processes, are crucial to obtaining high-purity low-temperature phase MnBi alloy materials.
- Key preparation technology for high energy product MnBi permanent magnetic alloy: High energy product is one of the key indicators of the performance of MnBi permanent magnet materials, and it is closely related to the purity of the low-temperature phase of MnBi, internal defects/stresses, magnetic orientation, magnetic domain structure, etc. The optimization and selection of preparation processes such as powder magnetic selection, magnetic field heat treatment, and magnetic orientation suppression are crucial for obtaining high energy product MnBi permanent magnetic alloys.
The project will reveal possible pathways to regulate the phase transformation, microstructure, and magnetic properties of MnBi permanent magnetic alloys; develop 1-2 manganese-bismuth permanent magnetic alloys (with magnetic energy product >13 MGOe) and carry out small-scale production demonstrations; promote advanced material technology innovation cooperation and technology transfer between China and Vietnam, enhance the international influence of China's research on rare-earth-free permanent magnetic materials, advance the construction of the "Belt and Road" Initiative; publish 8 high-quality papers, apply for 3 invention patents, and train 3 graduate students. The project will organize 3-5 exchanges and participate in 3 international conferences.
The project results will effectively promote the development and application of high-performance rare-earth-free MnBi permanent magnetic materials, enhance the high value-added utilization of manganese resources in Vietnam, and address the relative shortage of manganese resources in China. It will also strengthen exchanges between scholars from both countries, enhance the international influence of China's research on rare-earth-free permanent magnetic materials, promote advanced material technology innovation cooperation and technology transfer between China and Vietnam, serve the science and technology diplomacy between China and Vietnam, and advance the construction of the "Belt and Road" Initiative.
Considering the characteristics of this project, the main sources of data generation in the research and development process are the study of the low-temperature phase transformation mechanism of MnBi alloys, the investigation of the control mechanism of microstructure of low-temperature phase MnBi alloys, the research on the intrinsic mechanism of preparation processes and element doping controlling the magnetic properties of MnBi alloys through microstructure regulation, and the study of key preparation technologies for high-purity low-temperature phase MnBi alloy materials and high energy product MnBi permanent magnetic alloys.
