AINiCo magnets are a special type of magnet mainly composed of aluminum, nickel, and cobalt. These magnets can also include titanium, iron, and copper. They come in two forms; the isotropic, non-directional form, or the anisotropic, mono-directional form. Once they’re magnetized, they typically have 5 to 17 times the magnetic force of magnetite or lodestone. These are naturally occurring magnets that attract iron. In this post, we’ll talk about the properties, production, and common uses of Alnico magnets.
What is an AlNiCo Magnet?
Before the discovery of rare-earth magnets, AlNiCo magnets were the mainstay of the world of magnets. They used to be the strongest magnets ever known. Even today, they’re still instrumental in several industrial and everyday life applications. AlNiCo magnets are used widely in electric motors, microphones, engineering applications, the aerospace industry, military, sensors, etc. In some cases, they even perform better than the stronger rare-earth magnets.
Generally, they can be produced by either casting or sintering processes. These will be explained in further detail later. They are a combination of three essential elements (Al, Ni, and Co), and have excellent temperature stability, high residual induction, and relatively high energies.
Properties of AlNiCo Magnets
The isotropic form of AlNiCo magnets can be magnetized in any direction, while anisotropic Alnico magnets can only be magnetized in one pre-defined direction.
Anisotropic magnets have a higher magnetic performance than isotropic AlNiCo magnets.
AlNico magnets are generally stronger than the more common ferrite (ceramic) magnets
They are electrically conductive, unlike ferrite magnets.
AlNico magnets are not as brittle as most rare-earth magnets, and because of this, they produce a strong magnetic field.
They retain their magnetic properties even at very high temperatures. (AlNico magnets still exhibit magnetism at unbelievably high temperatures, even when they are glowing red-hot. They have excellent temperature stability up to 1,000F.
These magnets are more easily demagnetized than ceramic or rare-earth magnets.
They exhibit high residual induction
AlNiCo magnets hardly corrode
An AlNiCo magnet can generate a magnetic field up to 0.15 Tesla.
The composition of a typical AlNico alloy is 8–12% Aluminum (Al), 15–26% Nickel Ni, 5–24% Cobalt Co, 6% Copper Cu, 1% Titanium Ti. The rest is a small amount of Iron Fe. For an intermediate anisotropic cast aluminum-nickel-cobalt alloy, AlNiCo-6, the composition is 8% Aluminum Al, 16% Nickel Ni, 24% Cobalt Co, 3% Copper Cu, 1% Titanium Ti, while the rest are all Fe.
Production of AlNiCo Magnets: Sintering & Casting
As mentioned earlier in the post, AlNiCo magnets are manufactured in two ways; by sintering or using a casting process. Casting is the more common method because it yields AlNico magnets that are greater in density and mass, and, subsequently, have better magnetic properties and performance. However, sintered AlNico magnets are more economical to produce.
The casting process involves pouring a molten metal alloy into a mold and then further processing it through various heat cycles, which gives a magnet with a dark gray exterior and rough surface. The surface of the magnet can be machined to give a shiny appearance.
In the sintering method, the raw elements are first finely ground by milling them into tiny particles. The powdered magnetic material is pressed under tonnes of pressure in a die that closely resembles the desired magnet shape. After the powder has been pressed, the material is sintered in a furnace in a hydrogen atmosphere at over 1200 degrees Celsius. This process fuses all the pressed particles together to form a single magnet.
The red hot single magnet material is then cooled. If it is cooled in the presence of an external magnetic field, it will have anisotropic properties and a specific magnetic direction. But if it is not cooled in an external magnetic field, the resulting magnet will be isotropic in nature, and without a preferred direction of magnetism.
Although AlNiCo magnets have been largely replaced by rare-earth magnets, they are still used for important applications requiring high operating temperatures. This is because they are much more resistant to high temperatures than ferrite or rare-earth magnets.
AlNiCo magnets are often used in the following applications:
Traveling wave tubes
AlNiCo magnets are mainly made up of aluminum, nickel, cobalt, and smaller amounts of iron, titanium, and copper. They are one of the strongest known magnets, which can either have a specific direction of magnetic effect or none at all. AlNiCo magnets are often used in high-temperature applications due to their ability to retain their magnetism under high temperatures. If you want to find more about permanent magnets, we would like to recommend you to visit Stanford Magents for more information.