Surface quality and material removal via viscosity-controlled Magnetorheological finishing Ti-6Al-4V using Fe₃O₄-SiO₂ abrasives and Halbach array

• A viscosity-controlled magnetorheological fluid with Fe₃O₄-SiO₂ abrasives and Halbach arrays for Ti-6Al-4V polishing. • The working distance increases the apparent viscosity and the separation ratio between the carrier fluid and the Fe 3 O 4 -SiO 2 abrasive particles decrease. • Improved Halbach array set via a slider crank mechanism employing magnetic particles (Fe 3 O 4 ), abrasive particles (SiO 2 ), oxidizer (H 2 O 2 ) and malic acid. • The dynamic viscosity of 52.8 (Pa·s) yields optimal MRF polishing performance. • The surface quality and material removal capacity with Ti-6Al-4V alloy workpieces decreased with decreasing dynamic viscosity of the MRF strip or vice versa. This study investigates the polishing performance of Ti-6Al-4V alloy using a magnetorheological fluid (MRF) composed of Fe₃O₄–SiO₂ abrasives, malic acid, and H₂O₂ as an oxidizing agent. The effects of key process parameters abrasive concentration, cutting velocity, polishing distance, and magnetic field strength were systematically examined. Their influence was assessed on the slurry’s apparent viscosity, cutting force, material removal rate and surface roughness. Experimental results show that increasing polishing distance and cutting velocity, while reducing abrasive concentration, decreases both the cutting force and material removal rate. These changes are accompanied by a reduction in the slurry’s apparent viscosity. A stronger magnetic field enhances the stability and flow characteristics of the MRF slurry, thereby improving both material removal efficiency and surface finish. To further clarify the underlying mechanism, X-ray Photoelectron Spectroscopy (XPS) analysis revealed the abrasive-assisted formation and removal of oxide layers on the Ti-6Al-4V surface, underscoring the critical role of surface chemical reactions during polishing. To support these findings, an improved polishing system was designed incorporating an innovative Halbach magnet array, which generates a strong and focused magnetic field. This array, integrated with a slider-crank mechanism, ensures uniform magnetic field distribution, thereby enhancing process stability and controllability. Under MRF polishing optimal conditions, the process achieved a dynamic viscosity of 52.8 Pa·s, a surface roughness of Ra = 1.0 nm, and a maximum material removal rate of 179.1 mg/h. These findings underscore the significance of controlling the rheological behaviour of MRF and magnetic field characteristics in achieving high-precision surface finishing and demonstrate the scientific contribution of the proposed polishing system.