Alnico magnets are a type of permanent magnet primarily composed of the metals aluminum (Al), nickel (Ni), and cobalt (Co). The combination of these three elements is the origin of the name “alnico.” Before rare earth magnets began being widely developed in the 1970s and 1980s, the strongest permanent magnets available were alnico magnets. While rare earth magnets are more powerful, alnicos have unique advantages that still make them a highly desirable magnetic material today. Alnico magnets continue to be utilized today in many different applications because of their magnetic properties, strength, and temperature stability.
Temperature stability is one of the most unique characteristics of alnicos. Alnico magnets are the only magnets capable of performing at high temperatures up to 1000°F (about 535°C). The superior temperature stability of these magnets means they are frequently the magnet of choice for certain sensors, electric motors, military and aerospace applications, and other demanding applications. While samarium cobalt magnets also boast comparatively high temperature stability for rare earth magnets, alnico magnets perform at the highest operating temperatures out of all magnetic materials.
Compared to ceramic magnets, alnicos have another unique benefit. Unlike ceramic magnets, alnicos are electrically conductive. Additionally, alnico magnets maintain consistently greater strength than ceramic magnets.
Alnico magnets are not as strong as rare earth magnets in terms of magnetic performance, but they do have greater mechanical strength. Alnicos are less brittle than rare earth magnets, making them better suited for more harsh applications. Alnico magnets are also highly resistant to corrosion, and do not require surface treatments before use. As a note, however, it is still easy to plate alnicos if so desired.
Types of Alnico Magnets
The two most common available grades of alnico magnet are grades 5 and 8, However, other grades are available if a different characteristic is required for a certain application. The most common type of cast alnico material is Grade 5. Grade 5 cast alnico material can be found in applications ranging from complex rotating machinery to the most basic of holding applications. Grade 8 cast alnico material has a typical (BH)max 6.0 MGO, and excellent resistance to demagnetization. Out of any magnetic material available, grade 8 cast alnico has the highest temperature stability. Grade 8 cast alnico material can be found in transducers, generators, motors, computer components, and more.
In addition to the aforementioned types of alnico magnets, variations such as sintered alnico are available as well. Compared to cast alnico, sintered alnico has slightly lower magnetic properties, but boasts much higher mechanical properties. Sintered alnico has a fine grain structure which results in highly uniform flux distribution and mechanical strength. Additionally, sintered alnico is capable of being manufactured to exceptionally close tolerances. Sintered alnico is commonly used in applications that require a shorter magnetic length or involve high-speed motion. Examples of applications sintered alnico is used in include traveling wave tube stacks, reed switches, torque transmitting devices, and sandwich-type holding assemblies.
The engineers at Bunting-DuBois are magnet experts. Contact us today to learn more about different types of magnetic materials and select the perfect magnetic material for your unique application.