New Alnico Magnets Fabricated From Pre-Alloyed Gas-Atomized Powder Through Diverse Consolidation Techniques

Fine Alnico 8 spherical powder produced by gas atomization was consolidated through hot pressing (HP), hot isostatic pressing (HIP), and compression molding and subsequent sintering (CMS) techniques. The effects of different fabrication techniques and processing parameters on microstructure and magnetic properties were analyzed and compared. The HP, HIP, and CMS magnets exhibited different features in microstructures and magnetic properties. Magnetically annealed at 840 °C for 10 min and subsequently tempered at 650 °C for 5 h and 580 °C for 15 h, the HIP sample achieved the best coercivity (H_cj =1845$ Oe) due to spinodally decomposed (SD) phases with uniform and well-faceted mosaic morphology. The CMS sample had a lower H_cj than HIP and HP samples, but a higher remanence and thus the best energy product (6.5 MGOe) due to preferential grain alignment induced by abnormal grain growth.