A new eco-friendly magnetorheological chemical polishing system with an improved dual-layer Halbach magnet array for Ti-6Al-4V surface finishing

Ti-6Al-4V alloys are widely applied in aerospace and biomedical fields; however, achieving ultra-smooth surface finishes remains challenging due to their high strength, low thermal conductivity, and poor machinability. To address these limitations, this study proposes a novel chemical magnetorheological finishing (CMRF) approach integrating an optimized slurry system with a cost-efficient dual-layer Halbach magnetic array. Among five investigated slurries, the formulation containing 2-aminonicotinic acid (2-ANA) achieved the best performance, providing a material removal rate of 1.91 mg/min and a surface roughness of 1 nm. To reduce dependence on expensive rare-earth magnets, a hybrid ferrite/NdFeB Halbach array was developed, decreasing NdFeB consumption by approximately 30% while maintaining magnetic performance comparable to conventional designs. Finite element simulations and experiments verified the enhanced magnetic field characteristics and stable abrasive interactions. The proposed process reduced surface roughness from 503 nm to 1 nm within 90 min, demonstrating an efficient and economical ultra-precision finishing strategy for Ti-6Al-4V alloys.