PM2014 World Congress: Enhancement of properties of Soft Magnetic Composites through material and process developments – Part One

July 2, 2014

The 2014 World Congress on Powder Metallurgy and Particulate Materials, organised by the Metal Powder Industries Federation (MPIF), took place May 18-22 in Orlando, Florida, USA. In the first of a series of reports highlighting key presentations at the event Dr David Whittaker takes a look at developments in Soft Magnetic Composite (SMC) materials.

Emerging markets, including green energy and electric vehicles, are generating new opportunities for soft magnetic components. Soft magnetic composite materials, processed by Powder Metallurgy compaction and curing of the inter-particle insulants, have potential advantages in terms of offering isotropic magnetic properties and 3-dimensional product design capabilities, but require the enhancement of certain properties (magnetic and mechanical) in order to respond to these new opportunities.

A number of groups have therefore been focussing on material or process developments, aimed at generating these property enhancements, and these developments were the subject of a series of papers at PM 2014.

Development of new Soft Magnetic Composite material possessing higher levels of magnetic and mechanical performance

In the first of these papers, Francis Hanejko, Hoeganaes Corporation, USA, described developments aimed at increasing the compacted densities of soft magnetic composite components, in order to attain higher magnetic permeability, higher induction and greater mechanical strength.

These developments involved the application of the Ancormax 225 pressing lubricant concepts, previously applied to PM structural parts and described in previous conference reports on ipmd.net.

This recently developed lubricant can be used at addition levels as low as 0.25 wt%, in combination with warm die compaction with a part ejection temperature of 107°C (225°F), hence the suffix “225”.

Fig. 1 Strip and slide pressure of various lubricants (courtesy

Hoeganaes Corporation)

Use of this lubricant concept, together with a compaction pressure of 830 MPa (60 tsi), offers green density levels in excess of 7.5 g/cm³.

As shown in Fig. 1, this advanced lubricant system offers nearly identical ejection characteristics to the use of a conventional 0.75 wt% EBS lubricant addition, while providing 0.2-0.25 g/cm³ higher green density.

Two different soft magnetic composite grades were processed using these lubricant/compaction concepts in the reported study:-

AncorLam HD, a material aimed at achieving high levels of density, permeability and induction.
AncorLam HR-HD, a material aimed at attaining a moderate density but with high resistivity. High resistivity helps to limit eddy current losses and therefore total core losses in higher frequency operation.

Fig. 2 Compressibility data for AncorLam and Anchorlam HD

(courtesy Hoeganaes Corporation)

Fig. 2 compares the compressibility of AncorLam HD with the existing AncorLam lubricant system. Reducing the lubricant level from 0.4 wt% to 0.25 wt% results in higher green density over the range of compaction pressures evaluated.

Table 1 shows the green and cured densities attained with these two materials. Higher cured densities are achieved with the lower lubricant addition AncorLam HD. This table also shows that AncorLam HD has a higher resistivity despite having higher cured density and that Ancorlam HD offers an increase of “cured” TRS strength to 130 MPa, around 20% higher than AncorLam.

Table 1 Compacted and cured densities of AncorLam and AncorLam HD (courtesy Hoeganaes Corporation)

The attained magnetic data for AncorLam HD and AncorLam HR-HD are shown in Table 2.

Table 2 Magnetic Properties of AncorLam HD and AncorLam HR – HD Tested at 1 Tesla (courtesy Hoeganaes Corporation)

AncorLam HD maintains constant permeability up to approximately 1000 Hz in AC operation. Above that frequency, permeability decreases as eddy current losses increase. Despite the higher cured density achieved with AncorLam HD, resistivity and core losses are equivalent to existing materials.

AncorLam HR-HD has lower core losses than AncorLam HD at frequencies above 1 kHz and this enables constant permeability up to 10 KHz.

The full paper is available to download from the Hoeganaes website (PDF)

Author

Dr David Whittaker is a consultant to the Powder Metallurgy and associated industries. Contact +44 1902 338498 email: [email protected]