Toughening Sm–Co Sintered Magnets Via Microstructure Modification with Additives

The mechanical properties of the brittle Sm–Co permanent magnets are of great practical significance. However, studies on the magnets have mostly focused on their magnetic properties. In this paper, we report the modified microstructure and refined unimodal grain size, enhanced flexural strength, and magnetic properties of Sm2(Co,Fe,Cu,Zr)17 sintered magnets doped with La2O3, MgO, and CaF2 fine particulates. The correlations between microstructure, phase composition, and mechanical and magnetic properties were studied. Doping of a small amount (e.g., 0.5–3 wt%) of La2O3, MgO, or CaF2 fine particulates could significantly refine the unimodal grain sizes of the Sm–Co magnets via the Zener pinning effect. Moreover, doping significantly improved the flexural strengths s of the magnets. For example, the s values of the magnets with 0.5 wt% MgO, 1 wt% La2O3, and 1 wt% CaF2 were approximately 65%, 63%, and 42% higher than that of the reference magnet, respectively. Micromechanical simulations revealed that the fine particles of La2O3 and Sm2O3 could deflect crack growth, while the CaF2 particles could attract or arrest cracks during the fracture process. The mechanical strengthening effect was mainly due to grain size refinement. The Sm–Co magnets with 0.5–1.5 wt% CaF2 and 0.5–1 wt% La2O3 exhibited excellent magnetic properties. The rational design of CaF2- or La2O3-doped microstructure can be an economical and effective method for producing toughened Sm–Co sintered magnets with high magnetic performance.