Fabrication of High-Density Zn-Bonded Sm–Fe–N Bulk Magnets via High-Velocity Compaction

Abstract

High-velocity compaction (HVC) using a die was investigated as a compaction technique for the fabrication of high-density isotropic Zn-bonded Sm–Fe–N bulk magnets. The compaction characteristics of Zn-mixed Sm–Fe–N powders obtained by HVC were investigated while varying the Zn content. Moreover, the magnetic properties, flexural strengths (σ), and microstructures of the resulting magnets were studied. The relative density (d_r) steadily increased with the piston velocity during compaction and reached approximately 90% at a piston velocity of 11.2 m·s⁻¹ (equivalent to a compaction pressure of 3.45 GPa), regardless of the Zn content. Because the magnets were fabricated using a die, they also had a high dimensional precision. The resulting magnet, with 5 wt% Zn and d_r of 89.1%, exhibited a maximum energy product ((BH)_Max) of 54.4 kJ·m⁻³, remanence (B_r) of 0.56 T, and coercivity (H_cJ) of 965 kA·m⁻¹. σ exceeded 100 MPa when d_r was above 88%, which satisfies the required mechanical strength for applications such as permanent magnet motors.

Fig. 4 Dependences of d_r and magnetic properties (B_r, H_cJ, and (BH)_Max) on the piston velocity for the isotropic Zn-bonded Sm–Fe–N magnets with various Zn contents fabricated using HVC and subsequently annealed at 450°C. The inset shows a photograph of the green compact (5 wt% Zn) immediately after compaction.