Cast vs. Sintered Alnico Magnets

Alnico is actually an acronym that refers to a family of iron alloys that are made mostly of aluminum,

nickel, and cobalt. Alnico magnets were first developed in the 1940s and this class of magnets is still a

desirable material because of its outstanding temperature stability, resistance to corrosion and high

magnetic flux density. Before rare-earth magnets were created, alnico magnets were the strongest type

of magnet available.

Alnico alloys can be magnetized in order to product strong magnetic fields. The magnetic field strength at

the poles of an alnico magnet can go as high as 1500 gauss (0.15 tesla), which is approximately 3000

times the strength of the magnetic field of Earth.

Alnico magnets are manufactured in one of two ways: through a casting process or through a sintering

process:

Cast Alnico

When they are made through a casting process, it allows for the magnet to be manufactured into very

complicated and complex shapes. Cast alnico is melted down and then poured into a mold. Once it has

become solid, it is rough ground and then heat-treated and cooled. This is sometimes done in a magnetic

field, and the end result is called anisotropic. If the cast magnet is not heat-treated in a magnetic field, it

is called isotropic. Once it has been heat-treated and cooled, it can then be ground for precise tolerances

and then magnetized. Attributes of cast alnico magnets are:

Will cast to many different shapes and sizes

Size parameters can range from 1 ounce to 70 pounds

Sintered Alnico

Sintered alnico is made from a powdered mixture of ingredients that are put into a die and placed under

incredible pressure. This allows for the magnets to be manufactured with higher mechanical strength and

to tighter tolerances. Attributes of sintered alnico magnets are:

They are the strongest type of alnicos

They are pressed to close tolerance/minimal grinding to complete

Size parameters can range from 1 ounce of material up to one cubic inch

Both cast and sintered alnico have the following attributes:

Can be ground to size

High residual induction and energy product when compared to ceramic material

Low coercive force when compared to rare earth and ceramic materials

Maximum working temperature of 975° - 1020° F

Not good for conventional machining

Stable temperatures

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