Alnico is a family of permanent magnets that have been widely used for decades. It is a powerful alloy, a mixture of metals, and was one of the first high-strength permanent magnets developed, replacing older, less efficient magnetized steel. These magnets are prized for their unique combination of magnetic strength and remarkable stability across wide temperature ranges.
Core Elements and Different Grades
The name Alnico is a mnemonic derived from its primary elements: Aluminum (Al), Nickel (Ni), and Cobalt (Co). These three metals are alloyed with Iron (Fe) to form the base material. Other elements, such as Copper (Cu) and Titanium (Ti), are often included to refine the alloy’s characteristics; adding Titanium helps to increase the material’s resistance to demagnetization. These varying percentages lead to different classifications, known as grades. The most commonly used grades are Alnico 5 and Alnico 8, each offering a different balance of magnetic performance and physical characteristics.
Unique Magnetic Performance
Alnico magnets exhibit high residual induction (remanence), meaning they retain a strong magnetic field after the external magnetizing force is removed. This allows them to generate a powerful magnetic field strength relative to their size. Their magnetic output changes minimally with temperature fluctuation, defined by a low-temperature coefficient of about 0.02% per degree Celsius. This excellent thermal stability is Alnico’s most defining trait, allowing it to maintain its magnetic strength at temperatures as high as 550°C, a capability few other magnet types can match. The final performance also depends on the internal alignment; anisotropic Alnico (like Alnico 5) is magnetized in one preferred direction and offers superior strength over isotropic Alnico, which can be magnetized in any direction.
Production Methods
Alnico magnets are manufactured using two distinct methods: casting and sintering, which yield materials with differing properties. The casting process involves melting the constituent metals at high temperatures and then pouring the molten alloy into a mold. This method is best suited for producing large magnets and allows for the creation of complex shapes, such as the classic horseshoe magnet. Cast Alnico generally achieves better magnetic performance, especially when a specialized heat treatment is applied to create an anisotropic structure.
The alternative production route is sintering, which uses powder metallurgy techniques. Fine metal powders are mixed, compacted under high pressure into a die, and then heated near the melting point to fuse the particles. Sintered Alnico magnets are typically smaller and have better mechanical strength compared to cast magnets. While they offer slightly lower magnetic properties, the sintering process is more economical for high-volume production of small parts and achieves higher dimensional accuracy.
Common Uses
The unique characteristics of Alnico magnets make them indispensable in several specialized applications. They are widely used in industrial motors and generators, where their magnetic stability ensures consistent performance over long periods. Their ability to withstand high heat also makes them a preferred choice for various sensors used in aerospace and automotive systems for measuring speed or fluid flow in challenging thermal environments.
Alnico also retains a strong presence in the audio industry, notably in microphone transducers and electric guitar pickups. Musicians often favor Alnico magnets in pickups for the tone they impart. Furthermore, their capability to focus electron beams under high temperatures makes them suitable for specialized electronic devices, such as traveling wave tubes used in radio frequency amplification.