Initially designed for meters and instruments, AlNiCo (Aluminum Nickel Cobalt) magnets are well known for excellent temperature stability, high residual induction, and relatively high magnetic energy products since the 1930s. AlNiCo can be divided into cast AlNiCo and sintered AlNiCo.
When compared to cast AlNiCo, sintered AlNiCo performance with lower magnetic properties but has better mechanical properties. AlNiCo is brittle and hard, not suitable for traditional machining processes except grinding process.
Alnico magnets are manufactured either by casting or sintering. Alnico is produced by conventional foundry methods using resin bonded sand molds or powder metal manufacturing methods. Sintering Alnico is suitable for complex geometries.
Most Alnico produced is anisotropic meaning that the magnetic axle of the grains is oriented in one direction. The orientation is achieved by a heat treatment process after casting or sintering. The process involves heating the casting or sintered part above its Curie temperature and then cooling it at a controlled rate in the presence of a directionalized magnetic field. Final shaping of the Alnico materials is achieved by abrasive grinding and cutting where close tolerances are required.
Note:
Curie temperature, The Temperature Coefficient Is Only for Reference, Not as judgment Basis.
As the coercivity of Alnico magnets is low, it’s important to design the magnet system in such a way that the performance coefficient is high enough to quarantee the stability of the magnet in all temperatures (the working point is above the knee of the J-H-curve). For example, the length of an Alnico 5 rod should be > 5 times the diameter.
As Alnico magnets are easily demagnetized by careless handling, it is recommended to make the magnetizing after assembly.
Alnico magnets offer outstanding temperature stability. The output from Alnico magnets varies the least with changes in temperature, making it an ideal choice for temperature sensitive applications. The reversible temperature coefficient of induction is -0.02%/℃ from ambient and the reversible temperature coefficient of Intrinsic Coercivity is +0.01%/℃ from ambient. This makes Alnico a perfect choice in performance critical applications such as medical and military. Alnico magnets can actually be used up to 530 C, without irreversible losses in magnetizing.