Comparative analysis of material removal rate and surface roughness in electrochemical machining of AISI 304 steel using complexing and reducing agent mixed electrolytes

Electrochemical machining (ECM) of AISI 304 stainless steel is often limited by passivation and chromium-containing surface films, which reduce material removal efficiency and surface quality. This study investigates the effect of two electrolyte additives, ethylenediaminetetraacetic acid (EDTA) as a complexing agent and nano zero valent iron (nZVI) as a reducing agent. ECM characteristics of AISI 304 stainless steel were evaluated using NaCl, EDTA + NaCl, and nZVI + NaCl electrolytes. EDTA + NaCl increased the material removal rate (MRR) at low current densities (5–20 A/cm 2 ); however, above 20 A/cm², MRR decreased and surface roughness (Ra) increased due to excessive oxygen evolution and rapid reformation of passivating oxide films. Although local rupture of the film occurred at higher current densities, it rapidly reformed thereby hindering efficient dissolution. In contrast, nZVI + NaCl suppressed passivation and promoted active dissolution, resulting in improved MRR and surface quality. A maximum MRR of 0.6311 g/min and a minimum Ra of 0.53 µm were achieved, corresponding to an increase in MRR of 33.4% and a reduction in Ra of 19.6%, respectively, compared with NaCl. Cyclic voltammetry, electrochemical impedance spectroscopy, ultraviolet-visible spectrophotometry, field-emission scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy were employed to investigate dissolution behavior and characterize machining products and surface morphology. The results demonstrate the potential of nZVI-assisted electrolytes to suppress passivation and improve ECM performance of AISI 304 stainless steel.