How long do Alnico magnets last?

Alnico magnets were invented in the 1920s and are the product of the combination of aluminum, nickel and cobalt. They last as long as neodymium magnets and are used today in high-temperature applications, applications requiring low coercitivity, mass production instruments and legacy applications in which the material has been designed.

In fact, alnico magnets, for many years, were the strongest permanent magnets available until rare earth magnets developed, so before the appearance of neodymium magnets, for example, alnico magnets ruled the world.

While eclipsed and largely replaced by these stronger rare earth magnets, alnico magnets are still commonly used in various industries for specific jobs such as high temperature control equipment and sensor manufacturing, to name a few.

If they are durable, why have they been displaced?

They have been displaced because in most applications, alnico is much less powerful than neodymium magnets. Alnico magnets are manufactured by casting or sintering, i.e. they are molded, so they have the advantage of being made in quite complex shapes, such as a 4-pole round horseshoe magnet.

The durability of alnico magnets is precisely one of the reasons why they are still used today. In addition, it has important benefits such as:

  • Excellent temperature stability up to 537°C. 90% of the magnetization at room temperature is maintained up to this temperature.

  • High residual induction. Alnico magnets can produce powerful fields in certain configurations.

  • Alnico material does not corrode.

  • Fused alnico magnets can be produced in relatively complex shapes.

  • The tooling for molten magnets is relatively low, as sand moulds are generally used for the casting process.

But as we have mentioned before, alnico magnets are not the most commonly used in the modern era, precisely because, beyond their duration, they have some handicap that leaves them behind rare earth magnets, such as:

  • Alnico materials have a low coercitivity, so they are easily demagnetized.

  • They are relatively expensive, as they contain nickel and cobalt.

  • Fused alnicos often have pores and cast holes inside them, which can be problematic from an aesthetic point of view, and because large voids can decrease the expected magnetic flux.

Other interesting facts about Alnico magnets

  • Density: 0.265 lbs. per cubic inch

  • Required saturation magnetization field: around 5kOe.

  • Manufacturing methods: casting (most common), or sintering.

  • They are available in blocks, bars, discs, rings, horseshoes, etc.

  • They are available in grades from approximately 0105 to 0519. (The first 2 digits represent BHmax, and the other two digits represent Intrinsic Coercivity, or Hci).

  • Sizes: Outside of the tool, very large alnico magnets can be molded (horseshoe magnets weighing 225 kilos); smaller magnets are usually sintered (sintered disks, 1/16" in diameter).

Can Alnico's magnets be re-magnetized?

Although special care must be taken to ensure that alnico magnets are not subjected to adverse repulsion fields, as these could partially demagnetize the magnets, they can certainly be easily re-magnetized as they are partially demagnetized by their coercitivity (the ability to demagnetize and re-magnetize easily).

At IMA we have a wide variety of alnico magnets and help you choose the right model for your needs. If you have any doubt, ask us.

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