Technical Information About AlNiCo 

For short explanations of technical terms see our Dictionary Of Magnetism

AlNiCo-Magnets

... are permanent magnets. 

Ferromagnetic metal pieces are magnetized by a strong external magnetic field during the production process and then remain permanently magnetized. If handled properly, they will not lose their magnetic power even after decades.

... mainly remain of aluminium, nickel and cobalt. 

AlNiCo magnets are metallic permanent magnets based on AlNiCo alloys. Depending on the material composition, in addition to aluminum (Al), nickel (Ni) and cobalt (Co), iron (Fe), copper (Cu) and titanium (Ti), and the manufacturing process, isotropic and anisotropic magnets with different magnetic properties ​​can be produced.

... are described using a hysteresis curve. 

This magnetization curve contains information about the strength of the magnetization (remanence [Br]) as well as the required external magnetic force that leads to demagnetization (coercive field strength). However, the flux density in the entire space, i.e. the strength of the magnetic flux that flows through its surface, cannot be calculated analytically without complex finite element software. For cuboids and axially magnetized cylinders, the flux density can be approximately estimated using a formula along the magnetization axis.

... can be heated to extremely high temperatures.

To put it simply, magnetization means that the external magnetic field and the atomic magnetic moments located inside the workpiece are all aligned parallel in the north-south direction. This means the workpiece is magnetic. However, this common alignment disappears if the temperature increases too much. However, AlNiCo magnets have by far the highest temperature stability of all magnetic materials; Operating temperatures of up to 500°C are possible.

... can be produced isotropically or anisotropically.

This means: with or without a clear preferred direction. To put it simply, anisotropic magnets are magnetic, but without a clearly definable north and south pole (this is the case with most magnetic tapes, for example). With isotropic magnets, on the other hand, the direction of magnetization is clearly determined during magnetization, resulting in a clear preferred direction and a clearly defined north-south direction with a clear polar expression.

... are regularly offered with and without pole marks. 

AlNiCo magnets are often used as “school magnets”; then they are usually painted red and green (in German speaking countries, in . However, pure raw magnets without marking of the poles are also offered, so the poles must be determined in these cases. The easiest way to do this is to use a red-green “school magnet” or a compass. The following applies: equal poles repel each other. The north pole of a magnet is where it is attracted to the south pole of the test magnet.

... can be produced in different ways.

Permanent magnets made of AlNiCo can be manufactured using different processes: As part of the casting process, the raw materials are melted and then poured into sand or investment casting molds. In the sintering process, the powders of the raw materials are first mixed, filled into the cavity of a pressing tool and then pressed into its shape. The parts are then sintered under protective gas or in a vacuum at temperatures of around 1300 °C. This process creates the desired alloy and the compression of the shape. Depending on the press density and sintering temperature, a sintering shrinkage of approx. 10% can be expected. The magnets are then subjected to various heat treatments to further align and strengthen the elementary structure.

... are resistant to solvents and limited acid resistant.

AlNiCo magnets are partially resistant to acetic acid and organic acids at concentrations below 10%. They are not resistant to inorganic acids, sea water, citric acid and strongly alkaline solvents. They also have high remanence, extremely high corrosion resistance and are resistant to oil, organic solvents, gasoline and alcohols. Magnets made of AlNiCo are inert due to their manufacturing process and can be disposed of in an environmentally friendly manner. For certain areas of application, e.g. in direct contact with food, a plastic coating is recommended due to the cobalt content of the alloy.

... are difficultly to be edited mechanically.

Permanent magnets made of AlNiCo are very hard and brittle and can only be processed with diamond tools or by eroding.

... can be magnetized to different degrees.

The specification LN, LNG or LNGT, followed by a one- or two-digit number, indicates how strongly magnetized a permanent magnet made of AlNiCo is. The number indicates the energy density, i.e. the magnetic energy stored in the magnet: (WxH) max in MegaGaußOerstedt. However, when it comes to AlNiCo magnets, it should be noted that even the base material can be different due to the different manufacturing options; this is the initially more important note, which is indicated with the abbreviation Al and a subsequent single-digit number. Magnets made of Al2 or Al3 are usually isotropic. However, a holding force specification is not common for AlNiCo magnets, as this plays a secondary role in the classic areas of application of AlNiCo.

... are the “Methuselahs” among magnets and have been tried and tested for a long time.

AlNiCo magnets have been available since the 1930s; Japanese metallurgist Tokushichi Mishima discovered that adding aluminum to alloys of iron and nickel gave these alloys permanent magnetic properties. Through further refinements and expansions of the alloy ratio to include cobalt, copper and titanium, AlNiCo magnets quickly reached market maturity. Due to the development of ferrite and especially neodymium magnets, AlNiCo is no longer used very frequently.

... are most sensitive to disturbances in the magnetic function.

The disadvantage of AlNiCo magnets is their magnetic instability; they can be demagnetized relatively easily by an external magnetic field. In addition, magnets made of AlNiCo must be stored carefully: On the one hand, AlNiCo magnets should not be stored together with other magnetic materials and, on the other hand, they should be stored in an orderly manner. Horseshoe magnets made of AlNiCo require a back plate (or yoke) that connects the two legs together during storage.

Overview about magnetic properties of AlNiCo-magnets: