Alnico Magnet

Alnico was developed in the early 1930’s. During World War II it was used in military electronic applications. After the war, it quickly spread into civilian versions of those applications and replaced magnet steel in many applications. High induction levels with good resistance to demagnetization and stability, due to its low-temperature coefficient (0.02% / °C), at a reasonable cost made Alnico the magnet material of choice.

Alnico magnets offer the best temperature characteristics of any standard production magnet material available. Alnico magnets can be used for continuous duty applications where temperature extremes up to 930°F (500°C) can be expected. Temperatures above 1000°F will result in permanent metallurgical changes which can only be recovered by reheat treating.

A high working temperature limit (550 °C / 1020 °F) makes Alnico especially well suited for sensitive automotive and aircraft sensor applications. Alnico is produced in many grades to fit the requirements of these applications, from Alnico 1 to Alnico 12, but the most popular grades are 2, 5 and 8. By comparison to newer materials, the coercivity of Alnico is low.

Alnico magnets resist corrosion very well and are usually employed in applications with no coatings or plating. Alnico magnets can be plated or coated with a variety of materials if an application so requires. Some applications which may require Alnico surface treatment include cosmetic necessity, bonding, internal use, or to increase the surface hardness.

Alnico magnet material is made by alloying aluminum, nickel and cobalt with iron. Some grades also contain copper and/or titanium. The alloying process is casting or sintering. The process and the heat treatment needed to optimize magnetic properties produce hard (Rc45) and brittle parts that are best shaped or finished by abrasive grinding. Cast parts are generally under 70 pounds and may be used as-is, but polar surfaces are usually ground flat and parallel. Sintering is confined to high volume parts in sizes under one cubic inch and an effective press length to diameter ratio under four.