Alnico magnets are made primarily from aluminum, nickel, cobalt, copper, iron and sometimes titanium. They can be either cast or sintered. Not sure if alnico is the best material for your application? Review our Permanent Magnet Materials comparison for more information.
Cast Alnico - Cast alnico is melted and poured into a mold. Once solidified, the material is rough ground, then heat-treated and cooled, sometimes within a magnetic field. When treated in the presence of a magnetic field, the magnet is called anisotropic (oriented). This orients the material to take on maximum magnetization and allows a higher gauss level.
A cast magnet that is not heat-treated in a magnetic field is called isotropic (non-oriented). After heat treatment and cooling, alnico can be ground to specific tolerances, then magnetized.
Sintered Alnico - Sintered alnico is made from a powdered mixture of ingredients that are pressed into a die under tons of pressure, sintered in a hydrogen atmosphere and then cooled either within or without a magnetic field (anisotropic vs. isotropic).
Tolerances - Unless otherwise specified, our tolerances on alnico material meet and often exceed International Magnetics Association (IMA) standards.
For unfinished surfaces (as cast) the following tolerances apply:
0-1”: +/- .016” 1-3”: +/- .031” 3-5”: +/- .047”
5-7”: +/- .062” 7-9”: +/-.078” 9-12”: +/- .094”
Finished surfaces are normally ground to +/- .005".
Magnetizing and Handling - Magnetizing is done after the magnet has been machined to the correct tolerances. Care should be taken when handling alnico material since it is brittle and can chip or break if dropped on a hard surface. Also, because it has a low resistance to demagnetization, it will lose power if it is stored improperly (poles repelling each other). For best results, store magnetized alnico so that pieces are attracting each other, or with a steel keeper.
Machining - Alnico is a very hard and brittle material and does not lend itself to conventional machining. Master Magnetics offers grinding and cutting services for alnico material.
Typical Magnetic and Physical Properties of Alnico
|Alnico Material||Density||Max. Energy Product
|Typical Residual Induction Br (max)||Coercive Force Hc (min)||Intrinsic Coercive Force (Hci)||Maximum Operating Temperature||Curie Temperature|
|Alnico 5 (cast)||0.264||7.3||5.5||12500||≥650||≥640||1022||550||1562||850|
|Alnico 8 (cast)||0.262||7.3||5.3||8200||≥1450||≥1860||1022||550||1562||850|
|Alnico 5 (sintered)||0.250||6.9||4.2||12000||≥600||≥630||842||450||1580||860|
|Alnico 8 (sintered)||0.252||7.0||4.0||8200||≥1500||≥1690||842||450||1580||860|
Applications of Alnico Magnets
- Electron tubes
- Traveling wave tubes
- Holding magnets
- Coin acceptors
- Clutches and bearings
- Bell ringers
- Guitar pickups
- Security systems
- Cow magnets
Attributes of Cast Alnico
- Size parameters range from one ounce to about 70 pounds
- Will cast to a variety of shapes and sizes
Attributes of Sintered Alnico
- Size parameters range from about one ounce of material up to one cubic inch
- Pressed to close tolerance/minimal grinding to finish
- Mechanically strongest of alnicos
Attributes of Both Cast and Sintered Alnico
- Very temperature stable, great for high heat applications
- Maximum working temperature 975° - 1020° F
- May be ground to size
- Does not lend itself to conventional machining (hard and brittle)
- High residual induction and energy product compared to ceramic material
- Low coercive force compared to ceramic and rare earth materials (more subject to demagnetization)
- Most common grades are 5 and 8