Abstract:

Simultaneously achieving high energy product and high coercivity in the 2:17-type Sm-Co-Fe-Cu-Zr high temperature magnets has been closely relied on long-term isothermal aging to develop complete cellular nanostructure. In this work, we report a novel stress-aging approach that can substantially shorten the aging time to fabricate high-performance Sm-Co-Fe-Cu-Zr magnets. As exhibited by a model magnet Sm₂₅Co_50.2Fe_16.2Cu_5.6Zr_3.0 (wt.%), applying 90 MPa compressive stress can shorten the aging time from 20 h for conventional isothermal aging to 10 h at the same aging temperature for achieving nearly equivalent magnetic performance. Further comparative study between the 10 h-aged samples under stress-containing and stress-free conditions revealed that the stress not only promotes the precipitation of the cell boundary phase that are essential for enhancing the coercivity but also accelerates the dissociation of the cell edge defects that are detrimental to squareness factor, without destroying the [001] crystallographic texture. Such microstructural improvements enable the achievement of high-performance with maximum energy product of -30 MGOe and coercivity above 35 kOe at reduced aging time.

Key words: Permanent magnets, Sm-Co magnets, Precipitation, Stress-aging