ALNICO MAGNETS  

Excellent Temperature Stability!

Alnico was the strongest permanent magnet available until rare earth magnets were developed.

Alnico magnets, composed of primarily Aluminium (Al), Nickel (Ni), Cobalt (Co), and also sometimes copper, titanium and iron, were developed in the 1940s. This class of magnet remains a preferred material because of its excellent temperature stability, high magnetic flux density, and corrosion resistance. There are plenty of trade names are used for different grades such as Columax, Alcomax 3SC, Alni etc.

The most commonly used grade names are; Alnico 5, Alnico 8, Alnico 9, Alnico 5DG, Alnico5-7, Alnico8HC, Alnico 6, Alnico 2, Alnico3, Alnico 500, Alnico 400, Alnico 600 and Alnico 700, etc.

Alnico magnets are widely used today in applications where strong permanent magnets are needed and/or high temperatures are present, in applications requiring low coercivities (the ability to demagnetize and re-magnetize easily). Also has good resistance to demagnetization from vibration and shock.

The advantages of alnico magnets are high magnetic flux density, low-temperature coefficient of magnetic properties, high mechanical strength, and very stable magnets. Alnico magnets are generally (approx. four times) stronger than regular ferrite (ceramic) magnets, but not as strong as rare-earth magnets, they are also electrically conductive, unlike ceramic/ferrite magnets. Alnico magnets are available in either isotropic or anisotropic versions.

On a cost per pound basis, this material is comparable to the cost of neodymium magnets. However, in most applications, alnico is much less powerful than Neodymium magnets.

However, the coercive force and maximum energy product are not high. They limit their applications in many cases.

There are two production processes used to manufacture Alnico Magnets: casting and sintering, magnetization is possible only in axial direction.

AlNiCo magnets have high remanence, but low coercivity – this fact determines the magnetization direction. Optimal ratio of diameter and length of the magnet is 1:4. Magnetic field of AlNiCo magnets can be weakened by demagnetizing. AlNiCo is a hard material, machining is possible by grinding. Working temparature is between -270°C and +500°C. AlNiCo magnets are resistant against acids and solvents.

The casting process allows the magnet to be manufactured into complex shapes. Sintered Alnico is made from a powdered mixture of ingredients that are pressed into a die under tons of pressure. The Sintering process allows for the magnets to be manufactured to tighter tolerances and higher mechanical strength.

Alnico magnets have high magnetic flux density, high resistance to corrosion and excellent temperature stability. Though the corrosion resistance of alnico is excellent and, in most cases, no surface treatments are required, alnico magnets can be plated for aesthetic applications.

Alnico magnets are widely used in industrial and consumer applications where strong permanent magnets are needed and/or high temperatures are present.

What makes Alnico a preferred magnet material for many manufacturers is its high induction levels with good resistance to demagnetization and stability. This occurs because industrial sintered alnico magnets have a low-temperature coefficient and are produced at an affordable cost.

Advantages of Alnico Magnets

• Excellent temperature stability up to 550°C and retain their magnetic properties up to high temperatures.
• High resistance to acids and other chemicals.
• High residual induction can produce powerful fields in certain configurations.
• Corrosion resident to most chemical and environment.
• When sintering and casting, Alnico magnets can also be manufactured in very complex ways.
• Low-cost Tooling for cast magnets, generally sand moulds are used for the casting process.

Disadvantages of Alnico Magnets

• Alnico materials have low coercivities, so they are easily demagnetized.
• They are relatively costly, as they contain both nickel and cobalt.
• Cast alnicos often have casting pores and voids within them, which can be problematic from an aesthetic point of view, and because large voids may lower expected magnetic flux.

Caution!
Special care should be taken to ensure that these magnets are not subject to adverse repelling fields since these could partially de-magnetize the magnets. If alnicos are partially de-magnetized however, they can be easily re-magnetized.

The lower coercive force of Alnico makes magnetizing a simple matter in most cases. To optimize the performance of Alnico magnets, it is advisable to magnetize the magnet after assembly with other circuit components.

MANUFACTURING PROCESS:

• Cast alnico is produced by conventional foundry methods using resin bonded sand moulds
• Sintered Alnico magnets are formed using powdered metal manufacturing methods. Sintering alnico is suitable for complex geometries.

Most alnico produced is anisotropic, meaning that the magnetic direction of the grains is oriented in one direction.  This orientation is achieved via heat treatment after casting or sintering.  The process involves heating the cast or sintered part above its Curie temperature and then cooling it at a controlled rate in the presence of a strong directional magnetic field.  Final shaping of the alnico materials is achieved by abrasive grinding and cutting where close tolerances are required.

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Cast alnico, magnets are produced by conventional foundry methods using resin bonded sand moulds.

Max Working Temperature of AlNiCo ranges from 450°C to 550°C. There are two kinds of AlNiCo, Sintered AlNiCo and Cast AlNiCo. Cast magnets may be manufactured in complex shapes and the mould charge (sand mould) is cheap. But due to the sand mould edges, cast alnico has darkened edges with a slightly rough texture. To get a smooth surface, grounding is needed. Sintered AlNiCo offer slightly lower magnetic properties but better mechanical characteristics.

Most AlNiCo magnet grades are anisotropic (they can only be magnetized in a single axis /direction – they are the more powerful magnet grades of AlNiCo.

The others are isotropic (Lower grade, they can be magnetized in any direction or directions) – but for these types of alnico magnets, magnetic strength is very low but offer more design and performance flexibility.

Available Shapes: blocks, bars, discs, rings, horseshoes, etc.

Sintered Alnico magnets are formed using powdered metal manufacturing methods. Sintering alnico is suitable for complex geometries

Most Alnico magnet grades are anisotropic (they can only be magnetised in a single axis/direction – they are the more powerful magnet grades of Alnico. The others are isotropic (they can be magnetised in any direction or directions) – they are weaker but offer more design and performance flexibility.

There are 29 grades of Alnico (17 cast grades, 10 sintered grades, 2 bonded grades).

Typical composition of Alnico alloy

Alnico Magnets Demagnetisation Curve

Anisotropic Alnico Magnets:

Isotropic Alnico Magnets:

Surface Treatments

Alnico magnets do not usually require a surface finish to prevent corrosion. However, this does depend on the grade of Alnico and the chemicals in the environment. Some grades of Alnico contain iron, so may corrode if it is exposed to water or acids.

They can, however, be easily plated using a variety of metals, such as nickel, zinc, chrome or paint

Cast Alnico materials commonly contain casting voids and hairline cracks within the material. Finish machining can expose these voids and hairline cracks.

DESIGN CONSIDERATIONS

Alnico Magnets can be made by both cast and sintered processes. Alnico Magnets have distinct advantages over other varieties of permanent magnets in terms of moderate prices & widest temperature stability. Alnico magnets are coarse-grained and very hard and brittle, therefore they cannot be drilled or machined with conventional methods.  Holes are usually cored in at the foundry. Magnets are cast or sintered as closely as possible to required size so that abrasive grinding to finish dimensions and tolerances are minimized.

Alnico parts are not normally used as structural parts. Where a choice exists, select simple shapes. Slots are preferred over holes. Cross-sections of less than 0.125″ (3.18 mm) should be avoided. Finished surfaces, when required, may be produced by grinding; however, for many applications, the “as cast” or “as sintered” surface yields a satisfactory result at a significantly lower cost. To facilitate mounting and give adequate protection to the magnet, special assemblies such as rotors and magnetron magnets may be supplied with an aluminium jacket. Additionally, low carbon steel pole pieces may be attached to magnet pole faces by adhesive bonding or with studs or bolts. Plastisol or paint can be applied for an improved appearance.

Available Shapes: blocks, bars, discs, rings, horseshoes, etc.

OPERATING TEMPRERATURES OF MAGNETS 

WORKING AND CURIE TEMPRETURES OF MAGNETS

Typical Applications:

Alnico magnets are widely used in industrial and consumer applications where strong permanent magnets are needed and/or high temperatures are present.

Today Alnico magnets are used many applications; most commonly; sensors, position, level, angle and acceleration sensors, instruments, meters, actuators, various types of electric motors, hi-fi/loudspeakers, lock mechanism etc.

We are equipped to manufacture these materials as per customers specifications.

If you would like to know more about our extensive range of magnets products please contact us.