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PERMANENT MAGNETIC MATERIALS

At A Glance...

LITERATURE DOWNLOADS

Alnico

Alnico magnet material is made by alloying aluminum, nickel and cobalt with iron. Some grades also contain copper and/or titanium. The alloying process is casting or sintering. These constituents, the process and the heat treatment needed to optimize magnetic properties produces hard (Rc45) and brittle parts that are best shaped or finished by abrasive grinding. Cast parts are generally under 70 pounds and may be used as-is, but polar surfaces are usually ground flat and parallel. Sintering is confined to high volume parts in sizes under one cubic inch and an effective press length to diameter ratio under four.

To minimize the volume of magnet material required by an application, the entire magnetic circuit must be considered. An optimized circuit design results in a circuit permeance coefficient that causes the magnet to operate above the knee of its demagnetization curve by a margin large enough to offset anticipated operating demagnetizing effects. Optimized steel components result in an effective magnetic length greater than the magnet itself, but this is only effective if the magnet can be magnetized after assembly into the circuit. The alternate is to design the magnet shape to produce a load line, on its own, that intersects the BH curve above its knee, so minimal flux is lost due to the self demagnetizing factor upon removal from the magnetizing fixture. In either case, a magnetizing force of 3.0 kOe must be applied to Alnico 5 magnets and 7.0 kOe for Alnico 8. When magnetized in a magnetic circuit, the magnetizing pulse must be wide enough to allow eddy currents in the steel to decay before dropping below these values.

Grade Maximum
Energy
Product
BHmax
Residual
Induction
Br
Minimum
Intrinsic
Coercivity
Hci
Coercivity
Hc
Maximum
Operating
Temp
Tmo
Curie Temp
Tc
Coefficient
Induction
20-150 °C]
α
Coefficient
Coercivity
20-150 °C]
β
MGOe kG kOe kOe °C °C % / °C % / °C
Cast
AC200 1.3 7.2 0.60 0.58 450 810 -0.03 -0.03
AC300

1.35

7.0 0.50 0.48 450 760 -0.02 -0.02
AC400 1.4 5.5 0.72 0.68 450 760 -0.02 -0.02
AC500 5.5 12.7 0.64 0.64 525 860 -0.02 -0.02
AC570 7.5 13.5 0.74 0.73 525 860 -0.02 -0.02
AC5DG 6.5 13.3 0.67 0.67 525 860 -0.02 -0.02
AC600 3.9 10.5 0.80 0.78 525 860 -0.02 -0.02
AC800 5.5 8.5 1.70 1.62 550 860 -0.03 -0.03
AC8HC 5 7.2 2.17 2.00 550 860 -0.03 -0.03
AC900 10 10.6

1.50

1.48 550 860 -0.03 -0.03
Sintered
AS200 1.5 7.0 0.57 0.56 450 810 -0.03 -0.03
AS500 3.9 10.8 0.62 0.62 525 860 -0.02 -0.02
AS600 3 9.7 0.78 0.77 525 860 -0.02 -0.02
AS800 4.5 8.0 1.60 1.52 550 860 -0.03 -0.03
AS8HC 4.5 6.7 2.00 1.84 550 860 -0.03 -0.03

 

Typical Physical Properities - Cast

Curie Temperature

760 - 860 °C

Coefficient of Thermal Expansion

+11.0 - +13.0 x 10-6 °C-1

Electrical Resistivity

45 - 75 µΩ·cm

Density

6.9 - 7.3 g·cm-3

Rockwell C Hardness

45 - 55 HRC

Tensile Strength

0.02 - 0.15 kN·mm-2

Transverse Modulus of Rupture

0.05 - 0.30 kN·mm-2

Typical Physical Properities - Sintered

Curie Temperature

810 - 860 °C

Coefficient of Thermal Expansion

+11.0 - +12.4 x 10-6 °C-1

Electrical Resistivity

50 - 70 µΩ·cm

Density

6.8 - 7.0 g·cm-3

Rockwell C Hardness

45 HRC

Tensile Strength

0.35 - 0.45 kN·mm-2

Transverse Modulus of Rupture

0.35 - 0.76 kN·mm-2

ISO 9001:2000 Certified

RoHS Statements