Recent Developments in High-Energy Alnico Alloys

A brief review of the ``state of the art'' with emphasis on developments of the past several years is given. It is shown that with but two major exceptions, all significant advancements in energy product enhancement have been achieved by special foundry techniques to promote crystal anisotropy, and not by alloy composition variations. The exceptions are found in the advent of the family of high-coercive-force alloys using increased amounts of cobalt and titanium known today as Alnico 8, and in secondary recrystallizing techniques on special forms of Alnico 5 to produce a single large crystal from a polycrystalline aggregate. The latter technique was described in an earlier paper at this conference [E. Steinort et al., J. Appl. Phys. Suppl. 33, 1310 (1962)]. Work on producing crystalline anisotropy in a modified form of Alnico 8 has produced energy products as high as 10.5 MG·Oe and magnets are commercially available as Alnico 9 with energy products averaging 9.0 MG·Oe. Further work is described which shows that it is possible to apply the techniques of secondary recrystallization to a columnar aggregate of Alnico 9 and achieve further energy product enhancement to 12.5 MG·Oe for a large single crystal.