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AlNiCo magnets

Short description

AlNiCo magnets are made of Aluminium, Nickel and Cobalt. Most AlNiCo magnets are cast. This can take place in complex forms.

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Characteristics

  • Magnets are overmoulded
  • Complex shapes possible
  • High temperature resistance
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Alnico magnets

Detailed product description

Aluminium-nickel-cobalt

Aluminium-nickel-cobalt, or AlNiCo magnets, are made of aluminium, nickel, cobalt and iron. These magnets were developed around 1930. Despite the fact that this material has been largely replaced by cheaper and more powerful alternatives, AlNiCo magnets are still widely used, mainly because they do not corrode and are chemically inert.
AlNiCo is an alloy; the following metals are added to iron:

  • aluminium (Al)
  • nickel (Ni)
  • cobalt (Co)

The material also contains copper and sometimes titanium. The name AlNiCo is formed from the symbols of the chemical elements it is made of.

Applications

Thanks to its excellent thermal performance and property of being easily demagnetizable in a controlled manner, this material can be found in a variety of applications, including:

  • ABS brake systems in cars;
  • products based on reed switches, such as fuel supply sensors;
  • guitar pickups.

Advantages

  • relatively low mould costs because sand moulds are generally used;
  • due to the high residual induction value, AlNiCo magnets with particular shapes can produce exceptionally strong magnetic fields;
  • maximum application temperature up to 450 °C, with the magnet retaining 90% of the magnetic power it has at room temperature;
  • AlNiCo material does not disintegrate;
  • AlNiCo magnets can be cast to produce complex shapes.

Disadvantages

  • moulding cavities and pores can be an aesthetic problem;
  • larger cavities may affect the magnetic field;
  • AlNiCo can easily demagnetize due to the low coercivity;
  • because the material contains nickel and cobalt, AlNiCo is a relatively expensive material.

Technical details of AlNiCo

  • density: 7300 kg/m³ (0.265 lbs./in³);
  • magnetic field required for saturation: ±5 kOe;
  • BHmax value of the available range of neodymium grades: 28-80 kJ/m³.

Production methods

  • Casting is the most widely used production process for an AlNiCo magnet. The liquefied alloy is poured into a sand mould at very high temperature. This makes it possible to create complex shapes, such as a horseshoe.
  • Some versions are pressed and sintered. The magnetic properties are somewhat degraded, but the mechanical properties are improved. To avoid demagnetization, it is important to maintain the correct length/diameter ratio.

Processing of AlNiCo magnets

Ideally, the casting process of an AlNiCo magnet is such that no finishing is required. In practice, one must consider several things:

  • due to their fragility, AlNiCo magnets must be processed with special machining techniques;
  • where accurate tolerances are required, the final shape of the AlNiCo material is usually created by grinding or cutting;
  • EDM methods are usually used to create holes.

Surface treatment for AlNiCo magnets

AlNiCo is highly resistant to corrosion and thus there is no need for surface treatments. But AlNiCo magnets are easy to coat, when this is desirable for cosmetic reasons.

Precautions when working with AlNiCo

When machining AlNiCo magnets special care must be taken to ensure that the magnets are not demagnetized.

AlNiCo permanent magnets - table

Grade Remanence Normal coercivity Intrinsic coercivity Max.
Energy product
Max.
operating
Temp.
  Br
mT
min
Hcb
kA/m
min
Hcj
kA/m
min
BH(max)
kJ/m3
min
°C
Cast AlNiCo
GSA-5A 1200  50 52 40 525 
GSA-5B 1250 52 54 44 525
GSA-6 1300 56 58 52 525
GSA-7 1350 58 60 60 525
GSA-8A 800 110 112 38 550
GSA-8B 900 115 117 44 550
GSA-9A 1000 110 112 60 550
GSA-9B 1080 120 122 80 550
Sintered AlNiCo
GSAS-5 1150 48 50 34 525
GSAS-6 1100 58 60 28 525
GSAS-8 800 110 112 38 550