To enhance the reusability of nickel slag， a novel approach is proposed to modify nickel slag and utilize it in the precision polishing of magnetic compound fluids （MCF）， leveraging the magnetic elements inherent in nickel slag. This study investigates the relationship between the modified slag content and the polishing performance of MCF. The methodology involves several steps： first， nickel slag is processed through melting， oxidation， crushing， and magnetic separation to produce modified slag， whose composition and magnetic properties are subsequently analyzed. Next， the influence of MCF containing varying mass fractions of modified slag on surface roughness （R_a） and material removal rate is evaluated by examining the surface morphology of polymethyl methacrylate after polishing. The effect of modified slag on MCF formation is further explored by observing the morphology of MCF magnetic clusters before and after polishing under an external magnetic field. The intrinsic relationship between MCF morphology and polishing forces is analyzed by measuring the polishing forces of different slurries. Finally， the polishing mechanism of MCF containing modified slag is constructed by integrating observations of MCF polishing cluster microstructures， morphology， and polishing force characteristics. The experimental results indicate that the saturation magnetization of the modified slag is 5.64 times higher than that of unmodified nickel slag. As the mass fraction of modified slag increases， the polishing performance of MCF decreases. When the modified slag content reaches 10%， the surface roughness of the workpiece is significantly reduced from 0.502 μm to 0.010 μm within 10 minutes， corresponding to a surface roughness reduction rate of 97.966%. This reduction rate is only 0.482% lower than that achieved with MCF without modified slag but is 3.603% higher than the rate obtained with 15% modified slag content. In addition， the material removal rate reaches 1.237×10⁸ μm³/min. As the modified slag content increases， the curvature of the chain-like structures formed by magnetic particles during polishing increases， leading to a decrease in polishing force and， consequently， polishing performance. The proposed polishing mechanism reveals that modified slag occupies the middle and rear segments of the magnetic cluster and exhibits strong shear resistance. These findings demonstrate that modified nickel slag is suitable for MCF polishing applications， with optimal polishing performance achieved when the modified slag content in the MCF remains below 10%.

magnetic compound fluids;nickel slag;polishing;surface roughness