Hot workability of R-Fe-B alloys and their magnetic properties

The hot workability of R-Fe-B alloys and their magnetic properties were extensively investigated. Modified hot pressing employing a ring which constrains an alloy ingot enabled hot working without cracking at high strain rates up to ε̇ = 1 × 10−1/s. Excessive discharging of the liquid R-rich phase was controlled and the refinement of crystal grains occurred at high strain rate hot pressing. Through these effects the maximum Hci reached 18 kOe, and a (BH)max of 33.3 MGOe with a moderate Hci of 15 kOe was obtained in a composition of the Pr-Fe-B-Cu system. Post-heat treatment at 475–525 °C was effective for enhancing Hci. It was found that even in Nd-based alloys, a (BH)max of more than 30 MGOe was achieved by hot pressing at a high strain rate, because the change in composition during pressing is minimized.