Research progress on structural refinement process of sintered NdFeB

Refining grain size can effectively enhance the coercivity of bulk sintered NdFeB permanent magnets while ensuring high uniformity in magnetic properties. Key steps for grain refinement in sintered NdFeB magnets and current industrial equipment status had been described. During rapid solidification, high cooling rates effectively suppress α-Fe phase formation and reduce fragmentation difficulty. For cerium-rich magnets, trace additions of co-associated rare earth elements like La and Y help decrease the growth width of rapidly solidified flakes. Quantification of liquid volume per unit time during production proves crucial for structural consistency in rapid-solidified products. In powder preparation, regulation and adaptive control of hydrogen decrepitation process achieve preliminary powder refinement. Different jet mill configurations exhibit distinct characteristics, with fluidized bed jet mills being the most prevalent equipment, where airflow velocity at nozzle intersections in grinding chambers determines powder refinement efficiency. Regarding sintering, beyond conventional processes, spark plasma sintering emerges as an effective approach for achieving densification and suppressing abnormal grain growth. For powders with particle sizes below 2 μm, pressureless forming technology successfully resolves the forming challenges inherent to ultrafine powders.