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.

Characteristics

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

Detailed product description

AlNiCo magnets are made of aluminium, nickel and cobalt. Most AlNiCo magnets are cast, whereby the alloy is cast in a sand form in liquid state at very high temperatures. This can take place in complex forms, such as for example the form of a horseshoe.

Some versions are pressed and sintered. The magnetic properties are slightly diminished, but the mechanical properties improve.
To prevent demagnetisation the correct length/diameter proportion must be maintained.


AlNiCo OVERVIEW

Once the strongest type of permanent magnetic material available, Alnico magnets were developed in the 1930’s. Regardless of being largely replaced by cheaper and stronger alternatives, Alnico magnets continue to receive widespread interest from many engineers and manufactures for the simple reason that they do not corrode and are chemically inert.
Alnico is primarily composed from a family of iron alloys, which in addition to iron are:
• Aluminium (Al)
• Nickel (Ni)
• Cobalt (Co)
They also include copper, and sometimes titanium. It’s the acronym of these chemical elements that give alnico its name, and it’s often referred to as AlNiCo.

AlNiCo APPLICATIONS

Despite the non-linear demagnetisation cures in the second quadrant, their excellent thermal performance and ability to be demagnetised in a controlled manner makes them an invaluable asset to various applications, such as:
• Anti-lock braking systems (ABS) in cars
• Reed switch based products such as fuel cut off sensors 
• Rotating Machinery
• Guitar pick-ups


KEY BENEFITS OF AlNiCo

There are many advantages associated with this magnetic material that make it a great choice for design engineers. Some key benefits include:
• Tooling for cast magnets is relatively low as sand moulds are generally used for the casting process.
• Alnico’s high remaining induction means Alnico magnets can produce powerful fields in certain shapes.
• Temperature stability ranging up to 1,000° F; where 90% of room temperature magnetisation is retained up to this
   temperature.
• Alnico material does not disintegrate.
• Complex and custom shapes can be produced from cast Alnico magnets.


KEY CHALLENGES OF AlNiCo

As with all materials, there are some disadvantages with Alnico for industrial applications. Careful consideration of
your application will help you decide if Alnico is the right choice for your product. Things to carefully consider are:
• Casting pores and voids within Alnico materials may be problematic from an aesthetic point of view, and large
   voids may lower expected magnetic flux.
• Can be easily demagnetised as Alnico materials have low coercivities.
• Since it contains both Nickel and Cobalt, Alnico material can be quite costly.


TECHNICAL DETAILS OF ALNICO MAGNETS

Here are a few facts:
• Its density is 0.265 lbs. per cubic inch.
• The magnetising field required for saturation is approximately 5kOe.
• Available grades of Alnico range from about 0105 to 0519, where the first 2 digits represent BHmax; and the
  second two digits represent intrinsic coercivity (Hci).


MANUFACTURING METHODS AND PROCESSES

There are two key manufacturing processes that are used to produce Alnico magnets:
• Casting is the most common process carried out to produce an Alnico magnet. The molten liquid material is
   poured into a mould that contains a hollow cavity of the desired shape, and then allowed to solidify. The
   solidified part, or casting, is then ejected or broken out of the mould to complete the process.
• Sintering involves forming a solid mass of magnetic material through compacting the powder form of the material
   with both pressure and heat.  


MACHINING ALNICO MAGNETS

Ideally, the Alnico casting will be designed in such a way that minimal processing is required. However, there are some things to consider when working with Alnico:
• Special machining techniques must be used to machine Alnico material as its fragility makes it prone to chipping
   and/or cracking.
• The final form of the Alnico material is most commonly created by abrasive grinding and cutting, where close
   tolerances are required.
• Generally, EDM methods must be used when creating holes.
• Here at Goudsmit we are fully equipped to machine these materials to your design specifications.


SURFACE TREATMENTS FOR AlNiCo Magnets

• Alnico is considered excellent in terms of corrosion resistance; thus, no surface treatments are required.
• If required for a specific application however, Alnico magnets can be easily plated for cosmetic reasons.


PRECAUTIONS WHEN WORKING WITH AlNiCo

• To fully ensure that Alnico magnets are not subject to adverse repelling fields and do not become de-magnetised,
   special care should be taken when handling these magnets.

 

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