New strategy for efficient manufacturing of bulk anisotropic nanocrystalline Nd-Fe-B permanent magnets.

• For the first time, fully dense Nd-Fe-B precursors were prepared by hot rolling. • The large-size hot-rolled Nd-Fe-B magnet has excellent homogeneity. The hot-rolled magnets undergo densification and deformation simultaneously. • The microstructural evolution of hot rolling and hot deformation was systematically investigated. • Dissolution-precipitation, anisotropic grain growth, and regular grain arrangement were the deformation mechanisms. • The hot rolling technology enables the industrial production of anisotropic nanocrystalline Nd-Fe-B magnets. The application of bulk nanocrystalline Nd-Fe-B permanent magnets manufactured by hot deformation methods was severely limited by production efficiency. Therefore, this work proposed an efficient preparation method combining hot rolling and deformation. Using the melt-spun Nd-Fe-B magnetic powders as original materials, dense, large-sized, and well-uniform precursors for deformation can be obtained through cold pressing and hot rolling. The large-sized hot-rolled magnet can be cut into small pieces and subjected to hot deformation. The deformed magnet exhibits obvious crystallographic anisotropy, and the optimal maximum energy product can reach 35.7 MGOe. Furthermore, the mechanism of deformation and texture formation has been systematically studied, according to the microstructure and texture characterization of different height reduction magnets. The results indicated that there was a typical heterogeneous structure in the hot-rolled and hot-deformed Nd-Fe-B magnets. Dissolution precipitation, grain growth, and regular grain arrangement were the main reasons for deformation and texture formation during the deformation process. Our strategy of replacing traditional hot-pressing with large-sized hot-rolling can produce massively deformed precursors at once, greatly improving production efficiency, which is crucial for promoting the application of bulk nanocrystalline anisotropic Nd-Fe-B permanent magnets. [Display omitted] [ABSTRACT FROM AUTHOR]