Optimization of the electropolishing process of titanium using Taguchi robust design and surface analysis in an eco-friendly electrolyte

In this investigation, the electropolishing process of titanium in an eco-friendly electrolyte was optimized using Taguchi robust design and surface analysis. The parameters included voltage, process time, electrolyte ratio, added distilled water concentration and temperature. The eco-friendly electrolyte used deep eutectic solvents (DES) composed of choline chloride (hydrogen bond donor, HBD) and ethylene glycol (hydrogen bond acceptor, HBA). Additionally, the effect of adding distilled water at various concentrations to the DES was investigated to promote ion diffusion. Increasing the distilled water content shortened the time required for the current density to reach a steady state during electropolishing. Distilled water, a highly polar molecule, likely weakened hydrogen bonding between the HBD and HBA, reducing electrolyte viscosity and stabilizing the dissolution reaction. Voltage had the most significant effect on surface roughness, directly influencing the thickness and microstructure of the oxide layer. Excessive voltage caused surface damage. The optimal electropolishing conditions finally determined through Taguchi robust design were 16 V voltage, 25 min process time, 35 °C temperature, an ethylene glycol ratio of 2 and a 30 % added distilled water concentration.