Semi-solid reforming of Nd–Fe–B magnets: A two-step recycling-oriented process with a design framework

We demonstrate a novel two-step fabrication process consisting of casting followed by semi-solid-assisted deformation for the direct production of anisotropic Nd–Fe–B permanent magnets, distinguishing the present approach from conventional powder-processing routes. Starting from a cast Nd2Fe14B-based feedstock containing a Nd–Cu grain-boundary phase, semi-solid-assisted deformation simultaneously promotes grain fragmentation, liquid-phase squeeze-out and redistribution, and crystallographic alignment, thereby producing a dense bulk anisotropic magnet through a single deformation event. Differential scanning calorimetry (DSC) measurements reveal that the Nd–Cu phase content decreases from 36 mass% in the starting material to 15 mass% in the central region after deformation, indicating substantial liquid-phase exudation during processing. Correlation analysis across approximately 40 Nd–Fe–B specimens, sampled from a processing space comprising 625 possible parameter combinations, indicates that temperature shows the strongest relative association with the maximum energy product, (BH)max, within the investigated conditions. Using the optimized processing conditions, an anisotropic magnet exhibiting Hc = 0.832 MA/m, Br = 1.36 T, and (BH)max = 217 kJ/m3 was successfully produced from an as-cast alloy with negligible magnetic performance (Hc = 0.007 MA/m, Br = 0.01 T). The simplicity of this cast–deform route, enabled by establishing a semi-solid state through the addition of a low-melting-point phase, and its ability to repeatedly reconstruct anisotropy through deformation suggest its potential not only as a magnet fabrication process but also as a future platform for reforming-based magnet reuse and recycling.