AlNiCo Ring Magnets

AlNiCo ring magnets can be produced by either casting or sintering. Sintered AlNiCo allows the rings to be made close to their final (near net) shape, so only limited finishing work is needed. However, sintered AlNiCo has stricter size constraints and is mainly used for smaller rings or thin-walled ring magnets.

Cast AlNiCo magnets have a coarse-grained, hard, and brittle structure, which makes conventional machining—especially drilling—difficult and risky. For holes with lower accuracy requirements, the basic openings are usually formed directly during casting, with the parts cast close to final dimensions and then lightly machined to reach tolerance. When higher precision is required, or when working with grain-oriented ring magnets (such as those with columnar or semi-columnar crystal structures), more advanced methods like wire cutting or grinding are used to achieve the specified hole size and accuracy.

Some AlNiCo magnets are isotropic, meaning they can be magnetized in any direction. However, most commercial AlNiCo magnets are anisotropic and have a built-in preferred magnetization direction. This preferred direction is established during the heat treatment of cast or sintered AlNiCo, after the parts have been formed. In this step, the magnets are heated to a specific temperature and then cooled while exposed to an external magnetic field that sets the orientation.

After this process, anisotropic AlNiCo magnets can only be magnetized effectively along their preferred orientation and not in arbitrary directions. Even so, different pole patterns and configurations can still be created, as long as they are consistent with the established alignment direction.