Producing high coercivity alnico magnets requires extremely high precision in process parameters, and the process parameters need to be matched and tuned according to the customer’s specific requirements.
Advantages of High Coercivity Alnico Magnets
| Demagnetization Resistance: Through composition optimization, the high coercivity version enhances its resistance to external magnetic field interference and reverse magnetic fields. Compared with ordinary low coercivity alnico magnet, it is less prone to irreversible demagnetization and offers greater tolerance to operating environments (such as localized reverse magnetic fields).
| High-Temperature Performance: Its magnetic properties vary extremely little with temperature, remaining highly stable across a wide temperature range, making it suitable for applications that demand high magnetic field stability.
| Remanence: High coercivity alnico magnets still retain a high remanence (up to 1.35 T), capable of generating strong magnetic fields to meet application scenarios that require a certain level of magnetic flux density.
Although high coercivity alnico magnets offer improved demagnetization resistance, it still cannot fully match the coercivity level of samarium-cobalt or neodymium-iron-boron magnets. Moreover, the material is highly brittle, so care must be taken to prevent fracture and demagnetization under strong impact or severe vibration conditions.
How to Obtain High Coercivity Alnico Magnets
| Composition Optimization: High coercivity alnico magnets (such as high-titanium cobalt magnet steel) typically use a high-cobalt, high-titanium ratio, which helps promote the growth of acicular phases and enhance magnetic anisotropy, thereby increasing coercivity.
Appropriately adding trace amounts of elements such as niobium (Nb), zirconium (Zr), or samarium (Sm) to the base alloy helps refine grain size and increase the shape anisotropy of the magnetic phase after spinodal decomposition, contributing to improved coercivity.
| Process Optimization: Solution treatment at a set temperature eliminates the γ phase that impairs magnetic performance in the alloy, forming a single α solid solution in preparation for subsequent spinodal decomposition.
Cooling under a strong magnetic field causes the α phase to undergo spinodal decomposition under the strong field, enhancing anisotropy and thereby increasing coercivity.
In addition, isothermal treatment under a strong magnetic field—commonly understood as holding for 10–20 minutes—can further optimize the magnetic domain structure and enhance coercivity.
Vacuum melting combined with rapid cooling in a water-cooled crucible forms a directionally oriented columnar grain structure, which helps increase coercivity; however, the cooling rate must be controlled to avoid excessively fast cooling that would make the material overly brittle and prone to cracking.
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Image Source: Albmagnets & Couragemagnet & Hsmagnet & Sciencedirect & Springer
