Electric Field-Assisted Chemical Pretreatment for Enhancing Liquid Metal-Driven Abrasive Slurry Polishing of Ti-6Al-4V Internal Flow Channels

Ti-6Al-4V internal flow channels are difficult to finish because direct liquid metal-driven abrasive slurry polishing is constrained by both the limited driving capability of the liquid metal and the continuous formation of a dense surface reaction layer in alkaline electrolytes. In this study, the direct polishing behavior of Ti-6Al-4V flow channels was first investigated, and a distinct polishing capability boundary was identified through the evolution of surface morphology and areal roughness Sa. Although Sa decreased with polishing time, the reduction rate gradually diminished and eventually approached a plateau, indicating pronounced attenuation in effective material removal. Mechanistic analysis revealed that this limitation was governed by the dynamic formation and disruption of the oxide/reaction layer, which progressively shields the metallic substrate from direct abrasive action. To address this issue, an electric-field-assisted chemical pretreatment was introduced prior to the liquid metal-driven abrasive polishing stage, forming a two-step route (AB + P). Comparative experiments among direct polishing (P), chemical pretreatment followed by polishing (B + P), and electric-field-assisted chemical pretreatment followed by polishing (AB + P) showed that AB + P produced more homogeneous surface morphologies, lower Sa, and a significantly weaker plateauing tendency than direct polishing. In addition, the attainable limiting surface quality was shifted to a lower level, indicating an extension of the polishing capability boundary. The influence of pretreatment electrification time further revealed the existence of an effective time window, beyond which the polishing improvement gradually saturated. These results demonstrate that electric-field-assisted chemical pretreatment is an effective strategy for mitigating polishing attenuation and enhancing the finishing capability of liquid metal-driven abrasive slurry polishing for Ti-6Al-4V internal flow channels.