What are the main disadvantages of aluminium-nickel-cobalt(AlNiCo) magnet?

The main disadvantages of aluminium-nickel-cobalt (AlNiCo) magnets are as follows:

1. Low Coercivity and Susceptibility to Demagnetization

• Low Coercivity: AlNiCo magnets have a very low coercivity, typically less than 160 kA/m. Coercivity is a measure of a magnet's ability to resist demagnetization. A low coercivity means that AlNiCo magnets are easily demagnetized when exposed to external magnetic fields or reverse magnetic fields. This limits their use in applications where strong and stable magnetic fields are required.
• Nonlinear Demagnetization Curve: The demagnetization curve of AlNiCo magnets is nonlinear, which means that the relationship between the magnetic field strength and the magnetization is not straightforward. This nonlinearity can make it difficult to predict and control the magnetic behavior of AlNiCo magnets in practical applications.
• Vulnerability to External Factors: Due to their low coercivity, AlNiCo magnets are particularly vulnerable to demagnetization from external factors such as shock, vibration, and temperature fluctuations. This makes them less suitable for use in harsh environments or applications where mechanical stress is a concern.

2. High Cost and Raw Material Expenses

• Expensive Raw Materials: AlNiCo magnets are composed of rare metals such as aluminum, nickel, and cobalt, which are relatively expensive. The high cost of these raw materials contributes to the overall high manufacturing cost of AlNiCo magnets.
• Comparison with Other Magnets: Compared to other permanent magnet materials such as ferrite magnets, AlNiCo magnets have higher manufacturing costs. This can make them less competitive in price-sensitive applications.

3. Limited Magnetic Field Strength

• Weak Magnetic Force: Although AlNiCo magnets have relatively high remanence (up to 1.35 T), their overall magnetic force is relatively weak compared to other permanent magnetic materials such as neodymium iron boron (NdFeB) magnets. This limits their use in applications that require higher magnetic field strength.
• Application Limitations: Due to their limited magnetic field strength, AlNiCo magnets are not suitable for use in applications where a strong and concentrated magnetic field is required, such as in high-performance motors, generators, and magnetic separators.

4. Poor Mechanical Properties and Workability

• Low Mechanical Strength: AlNiCo magnets have low mechanical strength and are brittle. This makes them prone to cracking or breaking under mechanical stress, limiting their use in applications where mechanical durability is required.
• Poor Workability: AlNiCo magnets cannot be cold-worked and must be processed using casting or sintering methods. These methods have limitations in terms of the shapes and sizes that can be produced, and the resulting magnets may have rough surfaces that require additional machining.
• Design Constraints: Due to their poor mechanical properties and workability, AlNiCo magnets cannot be designed as structural parts and are typically used in applications where their magnetic properties are the primary consideration.

5. Heavy Weight

• Higher Density: AlNiCo magnets have a higher density (about 7.0-7.3 g/cm³) compared to some other types of magnets. This means that they are heavier for a given volume, which can be a disadvantage in applications where weight is a critical factor, such as in aerospace and automotive components.
• Impact on Performance: The heavy weight of AlNiCo magnets can affect the performance of devices in which they are used, particularly those that require lightweight and compact designs.