Abstract: In this work, a small amount of Al₂ O₃ powders (≤ 0.3 wt%) were incorporated into the Sm₂ Co₁₇-type sin-tered magnets, obtaining both high mechanical and magnetic properties. It is found that 0.1 % weight percentage of Al₂ O₃ doping is enough to enhance the flexural strength by about 20 % (～180 MPa for the case of the c-axis parallel to height). Meanwhile, the (BH)_max remains around 219 kJ/m³, and H_cj is 2052 kA/m, which is over 95 % of that of the original magnets without doping. The promising improvement in flexural strength is mainly attributed to the grain size effective refinement caused by Sm₂ O₃ particles including newly-formed ones from the reaction of the Al₂ O₃ powder and Sm in the matrix. Furthermore, the grain size of the magnets decreases significantly with increasing of Al₂ O₃ doping up to 0.3 wt%. Espe-cially, the grain size of 0.3 wt% Al₂ O₃ doped magnets is refined by 37 %. However, the flexural strengths (for the c-axis parallel to height and the c-axis parallel to width cases) of the magnets decrease sequen-tially and are even lower than that of the original magnet. The microstructure investigations indicate that the decrease in flexural strength may closely be correlated to the larger cell size and the incomplete cell boundaries phase. The obtained results infer that the flexural strength is susceptible to not only grain size but also the cellular structure of the magnets.

Key words: Sm₂ Co₁₇-type permanent magnets, Al₂ O₃ powder, Grain refinement, Microstructure, Flexural strength