The Relationship Between Magnetic Field Direction and Magnet Charging Direction in Magnetic Field Orientation Process, and the Performance Loss Rate of Non-Oriented AlNiCo Magnets
This paper delves into the core relationship between magnetic field direction and magnet charging direction in the magnetic field orientation process, taking sintered NdFeB and AlNiCo magnets as examples. It analyzes how different orientation processes and charging directions affect the magnetic properties of magnets. Furthermore, it explores the performance loss rate of non-oriented AlNiCo magnets, considering factors such as material composition, production process, and external environmental conditions. The research aims to provide a comprehensive understanding of the magnetic field orientation process and the performance characteristics of AlNiCo magnets, offering valuable references for related fields such as magnet production, motor design, and sensor manufacturing.
Keywords
Magnetic field orientation process; Magnet charging direction; Sintered NdFeB magnets; AlNiCo magnets; Performance loss rate
1. Introduction
Magnetic materials play a crucial role in modern industry and technology, widely used in motors, sensors, speakers, and other fields. Among them, permanent magnets are an important category, and their magnetic properties directly affect the performance of related equipment. The magnetic field orientation process is a key step in the production of permanent magnets, which determines the orientation of the easy magnetization axis of magnetic powder particles and thus has a significant impact on the magnetic properties of the final magnet products. AlNiCo magnets, as one of the early developed permanent magnet materials, have unique characteristics in terms of high-temperature stability and corrosion resistance. Understanding the relationship between the magnetic field direction in the orientation process and the magnet charging direction, as well as the performance loss rate of non-oriented AlNiCo magnets, is of great significance for optimizing magnet production processes and improving equipment performance.
2. Magnetic Field Orientation Process and Its Importance
2.1 Definition and Principle of Magnetic Field Orientation Process
The magnetic field orientation process is a method that utilizes the interaction between magnetic powder and an external magnetic field to arrange the easy magnetization directions of powder particles so that they are consistent with the final charging direction of the magnet. In the production of permanent magnets, especially anisotropic magnets, this process is essential. For example, in the production of sintered NdFeB magnets, the Nd₂Fe₁₄B crystal grains are uniaxially anisotropic, and each grain has only one easy magnetization axis—the c-axis of the main phase crystal cell. Through the magnetic field orientation process, these c-axes can be arranged in the same direction, thereby improving the magnetic properties of the magnet.
2.2 Significance of Magnetic Field Orientation Process for Magnet Performance
The magnetic field orientation process has a direct impact on the key magnetic properties of magnets, such as remanence (Br) and maximum magnetic energy product ((BH)max). When the easy magnetization directions of magnetic powder particles are well aligned, the magnet can achieve higher remanence and maximum magnetic energy product. Taking sintered NdFeB magnets as an example, a high orientation degree (≥95%) can ensure that the rectangularity of the magnet is ≥0.9. A magnet with high rectangularity can effectively reduce the generation of stray magnetic fields in practical applications, thereby improving the use efficiency and stability of the magnet.
3. Relationship Between Magnetic Field Direction and Magnet Charging Direction
3.1 Case Study of Sintered NdFeB Magnets
3.1.1 Orientation Process and Charging Direction Determination
In the production of sintered NdFeB magnets, the magnetic field orientation process is usually carried out during the molding stage. A strong magnetic field (1.5 - 2.5T) is applied to make the easy magnetization axes of the Nd₂Fe₁₄B crystal grains align along the target direction. This target direction is the future charging direction of the magnet. For example, in the production of square sintered NdFeB magnets, the magnetic field direction during orientation is set to be consistent with the expected charging direction, which is usually along the thickness or length direction of the magnet.
3.1.2 Influence of Charging Direction on Magnetic Properties
The charging direction has a crucial impact on the magnetic properties of sintered NdFeB magnets. When the charging direction is consistent with the easy magnetization direction obtained during the orientation process, the magnet can achieve higher remanence and coercivity. For instance, in a新能源汽车 (new energy vehicle) drive motor, the sintered NdFeB magnets are used as key components. If the charging direction is inaccurate, the motor may not operate efficiently or even malfunction. Accurate charging direction ensures that the magnet can provide a stable and strong magnetic field, thereby improving the torque output and operating efficiency of the motor.
3.1.3 Different Charging Directions for Different Shapes of Magnets
- Ring - shaped Magnets: Ring - shaped sintered NdFeB magnets can be charged axially or radially. Axial charging results in planar magnetic poles, which are suitable for coaxial magnetic field coupling in some coaxial rotating equipment. This charging method can achieve stable magnetic field coupling and ensure the synchronous operation of the equipment. Radial charging produces inner and outer ring magnetic poles, which are suitable for radial magnetic circuit closure design and can effectively improve the magnetic flux utilization rate of the magnetic circuit.
- Arc - shaped Magnets: Arc - shaped (瓦形) sintered NdFeB magnets commonly have four charging directions. In motor applications, the charging direction needs to be precisely matched with the arc of the motor stator/rotor to ensure the uniformity of the air - gap magnetic field. This can improve the motor efficiency, reduce energy loss, and extend the motor service life.
3.2 Case Study of AlNiCo Magnets
3.2.1 Production Process and Orientation of AlNiCo Magnets
AlNiCo magnets are mainly produced by casting and sintering processes. The casting process can produce complex - shaped magnets with good high - temperature resistance, while the sintering process has higher dimensional accuracy but slightly lower magnetic properties. During the production of AlNiCo magnets, although the orientation process is not as critical as that of sintered NdFeB magnets, proper magnetic field application during molding can still improve the magnetic properties to a certain extent. For example, in the casting process, a weak magnetic field can be applied to align the magnetic domains of the alloy during solidification, thereby improving the remanence of the magnet.
3.2.2 Relationship Between Charging Direction and Magnetic Properties of AlNiCo Magnets
AlNiCo magnets have relatively stable magnetic properties, and their charging direction also affects their performance in specific applications. In some sensor applications, the charging direction of AlNiCo magnets needs to be precisely controlled to ensure the accuracy of the sensor. For example, in a position sensor, the magnetic field generated by the AlNiCo magnet interacts with the sensing element. If the charging direction is not accurate, it will lead to inaccurate position detection.
4. Performance Loss Rate of Non - Oriented AlNiCo Magnets
4.1 Factors Affecting the Performance Loss Rate
4.1.1 Material Composition
The composition of AlNiCo magnets has a significant impact on their performance loss rate. AlNiCo magnets are composed of aluminum (Al), nickel (Ni), cobalt (Co), iron (Fe), and other trace metal elements. Different proportions of these elements will affect the magnetic properties and stability of the magnets. For example, increasing the cobalt content can improve the coercivity of the magnet, but may also increase the cost. At the same time, improper composition may lead to a higher performance loss rate of the magnet under certain environmental conditions.
4.1.2 Production Process
- Casting Process: The casting process of AlNiCo magnets involves melting the alloy and then pouring it into a mold for solidification. During this process, factors such as cooling rate and solidification structure will affect the magnetic properties of the magnet. If the cooling rate is too fast, it may lead to the formation of internal stresses in the magnet, which will increase the performance loss rate over time.
- Sintering Process: In the sintering process, the powder is pressed and then sintered at high temperatures. The sintering temperature, time, and pressure all have an impact on the density and magnetic properties of the magnet. Improper sintering parameters may result in a low - density magnet with poor magnetic properties and a high performance loss rate.
4.1.3 External Environmental Conditions
- Temperature: AlNiCo magnets have good high - temperature stability, but extreme temperatures can still affect their magnetic properties. At high temperatures, the thermal agitation of magnetic domains will increase, leading to a decrease in remanence and coercivity. For example, when an AlNiCo magnet is used in a high - temperature environment above 500°C for a long time, its performance loss rate will be significantly higher than that at room temperature.
- External Magnetic Field: Exposure to a strong reverse magnetic field can cause demagnetization of AlNiCo magnets, resulting in a performance loss. In some applications where there are strong alternating magnetic fields, the performance loss rate of AlNiCo magnets may be relatively high.
4.2 Measurement Methods of Performance Loss Rate
4.2.1 Magnetic Property Testing
The performance loss rate of AlNiCo magnets can be measured by testing their magnetic properties before and after a certain period of use or under specific environmental conditions. Common magnetic property testing methods include using a vibrating sample magnetometer (VSM) to measure the remanence, coercivity, and maximum magnetic energy product of the magnet. By comparing the changes in these parameters, the performance loss rate can be calculated.
4.2.2 Long - term Stability Testing
Long - term stability testing involves placing the AlNiCo magnet in a specific environment (such as a high - temperature oven or a magnetic field generator) for a long time and regularly testing its magnetic properties. This method can more accurately reflect the performance loss rate of the magnet under actual use conditions. For example, in a study on the high - temperature stability of AlNiCo magnets, the magnets were placed in a 300°C oven for 1000 hours, and their magnetic properties were tested every 100 hours to calculate the performance loss rate.
4.3 Research Progress on Reducing the Performance Loss Rate of Non - Oriented AlNiCo Magnets
4.4.1 Material Optimization
Researchers are constantly exploring new material compositions to improve the performance and stability of AlNiCo magnets. For example, by adding rare - earth elements or other trace elements to the AlNiCo alloy, the coercivity and temperature stability of the magnet can be improved, thereby reducing the performance loss rate.
4.4.2 Process Improvement
Improving the production process is also an important way to reduce the performance loss rate. In the casting process, optimizing the cooling system can reduce the internal stresses of the magnet. In the sintering process, precise control of sintering parameters can improve the density and magnetic properties of the magnet.
4.4.3 Surface Treatment
Surface treatment methods such as coating can protect the AlNiCo magnet from the external environment, reducing the impact of factors such as corrosion and oxidation on its magnetic properties. For example, applying a nickel - plated layer on the surface of the AlNiCo magnet can improve its corrosion resistance and reduce the performance loss rate in humid environments.
5. Conclusion
The magnetic field orientation process is crucial for determining the magnetic properties of permanent magnets, and the relationship between the magnetic field direction and the magnet charging direction directly affects the performance of the magnets in practical applications. For sintered NdFeB magnets, accurate control of the charging direction is essential for achieving high - performance motors and other equipment. Although AlNiCo magnets have relatively stable magnetic properties, non - oriented AlNiCo magnets still have a certain performance loss rate under the influence of factors such as material composition, production process, and external environmental conditions. By optimizing the material composition, improving the production process, and adopting surface treatment methods, the performance loss rate of non - oriented AlNiCo magnets can be effectively reduced, thereby expanding their application range in high - temperature and other special environments. Future research can further explore new materials and processes to improve the overall performance of magnetic materials and meet the growing demands of modern industry and technology.
