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Alnico

Alnico is an term referring to a series of permanent magnet alloys which in addition to iron are composed primarily of aluminium (Al), nickel (Ni) and cobalt (Co).
(stock 9999 piece)

Introduction

AlNio is an term referring to a series of permanent magnet alloys which in addition to iron are composed primarily of aluminium (Al), nickel (Ni) and cobalt (Co). The development of alnico began in 1931, when T. Mishima in Japan discovered that an alloy of iron, nickel, and aluminum had a much higher coercivity than the best steel magnets of the time. The composition of alnico alloys is typically 8–12% Al, 15–26% Ni, 5–24% Co, up to 6% Cu, up to 1% Ti, and the balance is Fe.

Various Alnico grades with differing magnetic properties are achieved by modifying the chemistry and manufacturing process.  For example, specialized casting techniques are used to achieve the unique crystalline grain orientation found in the Alnico 5-7 grade.

Before the development of rare earth magnets in the 1970s, Alnico was the strongest type of permanent magnet. In many applications Alnico has been replaced by other type of magnets. However, the temperature stability of Alnico magnets, and the fact that they can be used in very high temperatures, up to 500C, make them indispensable in certain applications.

Manufacturing 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. 


Cast AlNiCo Manufacturing Process