In this study, the effects of the length-to-width ratio on the magnetic and microstructural properties of die-upset Nd-Fe-B magnets were examined. A die-upset magnet with a uniform shape and no significant cracking was successfully developed. During the die-upset process, the applied pressure was not uniform across the magnet and varied depending on its shape and position. In the case of the magnet with a 4:1 ratio, which had the largest length-to-width ratio, there was a higher concentration of stress at the edges compared to the center, resulting in easier grain deformation and growth at the edges, which led to the lowest remanence and (BH)max. As the length-to-width ratio approached 1:1, the grain size increased slightly, reducing the coercivity; however, the magnets maintained a uniform grain-size distribution. The change from a rectangular to a square pressing surface resulted in a more uniform stress distribution, particularly at the center and corners, which improved the consistency of the magnetic properties across different regions of the magnet. Consequently, an 11.9% enhancement in (BH)max, reaching 285.6 kJ/m3, was achieved in the 1:1 ratio die-upset magnet, which is attributed to the uniform grain size and improved grain alignment.
Keywords: Nd–Fe–B magnet; die-upset magnet; grain refinement; net-shaped magnet.