Design of synergistic polishing mechanism for hard magnetic phase–soft abrasive particles in strontium ferrite magnetorheological fluid

To address the structural instability of magnetic chains and uneven abrasive distribution inherent in traditional soft-magnetic magnetorheological polishing (MRP) fluids, this work proposes a novel MRF fluid based on SrFe 12 O 19 @SiO 2 core-shell structured magnetic composite abrasives, which are synergistically regulated by the hard magnetic phase SrFe 12 O 19 and the soft abrasive SiO 2 .The SrFe 12 O 19 @SiO 2 magnetic composite abrasives were prepared via the sol-gel method. Their composition and structure were characterized by XRD, SEM, and EDS, while the magnetic properties of both the composite abrasives and the polishing fluid were evaluated using VSM. Furthermore, friction, wear, and polishing experiments were conducted. The results show that a high-precision optical surface of K9 glass with a surface roughness of Ra = 1.73 nm was achieved at a spindle speed of 950 r/min and a polishing time of 30 min, which satisfies the standard optical polishing requirements for high-precision K9 components (typically Ra < 2 nm). Unlike traditional soft-magnetic CIP fluids, the high remanence of the strontium ferrite core is expected to enhance the structural stability under shear forces, thereby contributing to more stable polishing pressure and material removal efficiency. Meanwhile, the core-shell structure effectively mitigates phase separation. Compared to traditional methods, fine scratches were significantly ameliorated, and a highly stable, relatively consistent material removal process was achieved.