Ferroalnico

Ferroalnico, commonly called alnico magnets, refers to a family of permanent magnets based on iron with aluminum, nickel, and cobalt, sometimes with copper and titanium. The name comes from the principal alloying elements—aluminum, nickel, cobalt—and these magnets have long been valued for their temperature stability and corrosion resistance.

Composition and microstructure: The alloys are engineered with iron as the base and additions of aluminum, nickel, cobalt, and small amounts of copper and titanium. Variations produce cast (isotropic) or anisotropic grades. The magnetic properties arise from a complex microstructure formed during controlled casting or powder metallurgy followed by heat treatment that develops magnetic anisotropy.

Manufacturing: Cast Alnico magnets are produced by pouring the molten alloy into molds and, for anisotropic grades, applying a strong magnetic field during solidification. After solidification, a two-step aging heat treatment creates the microstructure that aligns with the magnetization direction. Isotropic grades are machined into shapes and magnetized in a single direction.

Properties: Alnico magnets offer high remanence and good coercivity with exceptional temperature stability and resistance to demagnetization. They provide good corrosion resistance and can operate at high temperatures. Their energy product (BHmax) is lower than that of modern rare-earth magnets, reflecting a trade-off for stability and temperature performance.

Grades and forms: Common grades include Alnico 2, 5, and 8, with different Ni, Co, and Al contents and the addition of Cu and Ti. They may be produced by casting into complex shapes or as isotropic powders for pressing.

Applications: Used in loudspeakers, guitar pickups, sensors, and certain motors and magnetic assemblies where thermal stability and robustness are prioritized and extremely high magnetic strength is not required. They remain a niche option alongside NdFeB and SmCo magnets.