Alnico

Alnico is an alloy of iron, aluminum, nickel, copper and cobalt. Permanent magnets are made by casting or sintering techniques from them. Such magnets are then referred to as steel magnets.

History

The material was first produced in 1931 by the Japanese metallurgists Tokushichi Mishima. Mishima discovered when working with iron -nickel alloys ( " silver plate ", or " nickel steel " ), that the addition of aluminum alloy set in the permanent magnetic properties. He scored a coercivity of 32 kA / m, which was very much for that time and under the trademark English MK Magnetic Steel, Steel MKM has been sold.

In the magnetic properties improved alnico alloys are obtained by additions of copper, cobalt, and titanium, and there are in percent by volume of 8-12 % aluminum, 15-26 % nickel, 5-24 % cobalt, up to 6% copper and up to 1 % titanium. The main content of the alloy is iron represents the actual proportions vary depending on the requirements of the material.

Properties

The residual flux density is conventional Alnico about 0.6 T to 1.3 T ( from 6000 to 13000 Gauss ), and is relatively high in comparison to ferrite magnets. As for the other permanent magnet and the flux density at the surface of the magnets, is usually much smaller. AlNiCo magnets have a Curie temperature of 700-850 ° C and an upper use temperature of 450-500 ° C.

The material loses more and more important and is replaced by Seltenerdmagnetwerkstoffe such as neodymium -iron-boron. One reason is that Alnico has a low magnetic stability. This means that the coercivity of Alnico is relatively small in comparison with rare earth magnets with around 50-100 kA / m and the risk of demagnetization by an external field is relatively large. Accordingly, permanent magnets have AlNiCo an elongated or horseshoe shape.

One benefit of AlNiCo is that it after artificial aging has a stable magnetization. Of all known materials, it has the lowest temperature coefficient of the remanence. Therefore, AlNiCo magnets are still used in sensors, speakers and Gitarrentonabnehmern while they were ousted in electric motors with permanent excitation of rare earth magnets.