Alnico (AlNiCo): Technical Information
| Isotropic | Anisotropic | ||||
| Magnetic Characteristics | 2 | 5 | 5-7 | 8 | |
| Residual Induction Br |
(G) | 7750 | 12800 | 13500 | 8200 |
| (mT) | 775 | 1280 | 1350 | 820 | |
| Coercive Force Hc | (Oe) | 580 | 640 | 740 | 1650 |
| (kA/m) | 46 | 51 | 58.5 | 131 | |
| Intrinsic Coercive Force Hcl | (Oe) | 595 | 640 | 740 | 1800 |
| (kA/m) | 47 | 51 | 58.5 | 143 | |
| Maximum Energy Product BHmax | (MGOe) | 1.65 | 5.50 | 7.50 | 5.30 |
| (kJ/m³) | 13.0 | 43.7 | 59.5 | 42 | |
| Magnetic Characteristics | 2 | 5 | 5-7 | 8 | |
| Density | (lbs/in³) | .256 | .265 | .265 | .263 |
| (g/cm³) | 7.1 | 7.3 | 7.3 | 7.2 | |
| Curie Temperature | °F | 1500 | 1630 | 1630 | 1580 |
| °C | 815 | 890 | 890 | 860 | |
| Maximum Operating Temperature | °F | 840 | 930 | 930 | 930 |
| °C | 450 | 500 | 500 | 500 | |
Alnico Manufacturing Processes
A cast alloy consisting primarily of iron, aluminum, nickel, cobalt, with minor amounts of other elements including copper and titanium. Produced by conventional foundry methods using resin bonded sand molds, Alnico is suitable for complex geometries and configurations not achievable with other magnet materials. These alloys can be tailored easily to obtain a variety of magnetic properties and characteristics. Specialized casting techniques are used to achieve the unique crystalline grain orientation found in the Alnico 5-7 grade. Properties are optimized during a heat treatment process which is unique to Alnico. The direction of orientation for most Alnico material is determined during this process which involves heating the casting above its Curie temperature then cooling at a controlled rate in the presence of a directionalized electromagnetic field. The actual shape of the magnetic field as well as its intensity can be optimized during this process. Magnets which have been processed in this fashion are anisotropic in nature and exhibit a preferred direction of orientation. Unoriented materials (Alnico 2) are available for those applications which require the specialized magnetizing capabilities of a non-aligned material. Final shaping of the Alnico materials is achieved by abrasive grinding and cutting where close tolerances are required, otherwise it is desirable to use the part with as cast features.
Magnetizing Requirements and Recommendations
The lower coercivity of Alnico makes magnetizing a simple matter in most cases. In order to optimize the performance of an Alnico magnet, it is advisable to magnetize the part after assembly with the other circuit components. This also helps control particle contamination, simplifies assembly operations, and allows for automation of the assembly process. Calibration of the magnet to achieve very precise levels of performance can also be accomplished after the magnetizing process is complete. Caution: Alnico magnets can be adversely effected by exposure to the repulsive forces generated by another magnetized magnet or by stray AC fields. (Care must be exercised when either of these conditions exists.)
Temperature Characteristics of Alnico Materials
Alnico offers the best temperature characteristics of any standard production magnet material available. It can be used for continuous duty applications where temperature extremes up to 930°F can be expected. Temperatures above 1022°F will result in permanent metallurgical changes which can only be recovered by reheat treating. Excursions to lower temperatures pose less of a problem for most Alnico applications, however each individual circuit should be examined carefully to determine the effects which may occur as a result of operating at those extremes. Duramag's Application Engineering staff can provide specific guidelines concerning the temperature characteristics for a given Alnico grade and make recommendations for their proper use.
Physical Characteristics of Alnico
Alnico materials are hard and brittle and are not suited to common drilling, tapping, or machining operations. Tolerances closer than as cast are achieved only by abrasive grinding and cutting.
Due to its brittle nature, Alnico should not be used as a structural component in any device. Pole pieces or other components can be attached by using a structural adhesive for assembly purposes. In addition, Alnico lends itself to silver soldering operations in certain circumstances. Specific recommendations can be made by our Application and Engineering staff.