AlNiCo Magnets | 1st Modern Permanent Magnet
The discovery of AlNiCo magnets
AlNiCo permanent magnets are the first modern permanent magnets developed in 1930s by Japanese metallurgist Tokushichi Mishima. It’s mainly composed of Aluminum (12%), Nickel (30%), Cobalt, and Iron (58%). At the time AlNiCo permanent magnet was developed, it was characterized by high magnetic remanence and low temperature coefficient. Therefore, it’s widely used in permanent magnet motors. Before the development of rare earth magnets in 1970s, AlNiCo is the strongest permanent magnets commercially available.
Characteristics of AlNICo Magnets
Compared to other modern permanent magnets, AlNiCo alloys have low coercivity and high curie temperature. They are prone to demagnetization and therefore must be used with a high L/D ratio or in a closed magnetic circuit. AlNiCo alloy is hard but brittle, which is not suitable for cold working. They are either cast or sintered.
One of the advantages of AlNiCo permanent magnets are high remanence (up to 1.35T) and low temperature coefficient. When the temperature coefficient is -0.02%/℃, the maximum operating temperature can reach about 520℃. The disadvantage is that the coercivity is very low (usually less than 160kA/m) and the demagnetization curve is nonlinear. Therefore, AlNiCo magnets are easily demagnetized.
Classification: Sintered and Cast AlNiCo Magnets
According to different production methods, AlNiCo alloys are divided into sintered AlNiCo and cast AlNiCo. The shapes of the AlNiCo products are mostly cylindrical and square. Different sizes and shapes are possible using casting process. In comparison, sintered AlNiCo magnets are limited to small size. The dimensional tolerance of the sintered blank is better than that of the cast ones, though the magnetic properties are slightly lower than the cast AlNiCo.
Sintered AlNiCo also has better machinability. Among all permanent magnet materials, cast AlNiCo permanent magnets have the lowest reversible temperature coefficient, and the working temperature can be as high as 600 degree Celsius. AlNiCo permanent magnets are widely used in various instrumentation and other applications.
Application of AlNiCo permanent magnets
Many industrial and consumer products require strong permanent magnets, such as electric motors, electric guitar pickups, microphones, sensors, speakers, traveling wave tubes, cow magnets, etc., all use AlNiCo magnets. Nowadays, however, many products have turned to use rare earth magnets because these materials can offer a stronger magnetic field (Br) and a higher maximum energy product (BHmax), allowing the product to be reduced in size. In general, AlNiCo cylinder magnets, AlNiCo bar magnets and AlNiCo block magnets are most common shapes in modern applications. AlNiCo 5 magnets and LNG37 is the most common AlNiCo grades in the market.
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