Alnico magnets are cast when the alloy compound is in molten form. The resulting metal is then heat treated in the presence of a magnetic field. The rate at which it is cooled during this process determines the direction and strength of the magnet.
Temperatures Below 1000-Degrees Farenheit
Alnico magnets are the magnets of choice because of their high heat tolerance. The magnet loses less than 5 percent of its magnetism at temperatures up to 1000 degrees Fahrenheit. Remagnetization procedures may even reverse this marginal change.
Temperatures Above 1000-Degrees Farenheit
While Alnico magnets retain above 90 percent of their room temperature magnetism up to temperatures around 1000 degrees Farenheit, irreversible loss of magnetism will occur once they are exposed to temperatures beyond that point. It is at this stage that changes at the metallurgic level permanently alter the magnet itself and the magnet undergoes a rapid loss of magnetism.