Magnetic Applications

The use of warm compaction of P/M magnetic alloys effects higher sintered densities with corresponding higher saturation induction levels and higher permeabilities with no change in the coercive force (Ref 15). Sintered densities in excess of 7.4 g/cm3 are possible using warm compaction of iron-phosphorus alloys. At this density level, the magnetic and mechanical performances of this family of materials are equal to the properties of a low-carbon steel forging. Table 4 summarizes the mechanical and magnetic property data for a 0.45% P/M phosphorus steel processed to 7.4 g/cm3 and an AISI 1008 steel forging. From these data, the P/M material is a suitable replacement for the wrought steel.

Table 4 Magnetic and mechanical properties of a warm-compacted iron-phosphorus steel versus AISI 1008

Property

Fe-0.45 wt% P

AISI1008

Density, g/cm

7.35

N/A

Sintering temperature, °C (°F)

1120 (2050)

N/A

0.2% yield strength, MPa (ksi)

285 (42)

285 (42)

Tensile strength, MPa (ksi)

405 (59)

383 (56)

Elongation, %

12

37

Maximum permeability

2700

1900

Coercive force, Oe

1.9

3.0

Saturation at 15 Oe, G

15,000

14,400

N/A, not applicable

Warm-compaction processing enables the introduction of a new class of P/M materials for use in alternating current (ac) magnetic applications (Ref 15, 16, 17). These materials utilize a high-strength polymer and warm-compaction processing to produce components that do not require sintering. The polymer acts to both electrically insulate the powder particles and provide strength without the need for sintering. As-compacted green densities in excess of 7.2 g/cm3 are possible. Manufacturing flexibility can produce a variety of material options with unique magnetic performance. Applications for these materials include automotive ignition coils and stators for high-speed electric motors.

Table 5 summarizes these ac magnetic materials and their magnetic performance. These materials are ideally suited for applications with operating frequencies above 400 Hz. Optimizing the amount and type of insulation produces components that can operate at frequencies up to 50,000 Hz. The unique three-dimensional structure of these materials can be used to carry magnetic flux in any direction. The strength of these materials in the as-compacted condition is approximately 103 MPa (15 ksi) transverse rupture strength. Employing a 315 °C (600 °F) thermal treatment to the as-compacted part raises the transverse rupture strength to approximately 240 MPa (35 ksi).

Table 5 Magnetic performance of insulated iron powders

Material

Initial

Maximum

Coercive

Induction at

permeability

permeability

force, Oe

40 Oe, G

Iron powder with 0.6% plastic

120

425

4.7

11,200

Iron powder with 0.75% plastic

100

400

4.7

10,900

Iron powder with oxide coating and 0.75% plastic

80

210

4.7

7,700

0 0

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