Surface morphology evolution and corrosion resistance enhancement mechanism of 15-5PH stainless steel electropolished using environmentally friendly neutral electrolyte

This study employed an environmentally friendly neutral alcohol-salt electrolyte, consisting of ethylene glycol, sodium chloride, and ethanol, for electrochemical polishing (ECP) of 15-5PH martensitic precipitation-hardening (MPH) stainless steel, achieving improved surface finish and corrosion resistance. A systematic investigation examined the effects of processing time, rotational speed, temperature, ethanol content, and NaCl concentration on post-polishing surface quality, and obtained the optimized parameter combination of 35 min, 80 rpm, 60 °C, 10 vol% ethanol content, and 1.0 mol/L NaCl concentration to reduce surface roughness from 387.40 nm to 32.76 nm. Energy-dispersive X-ray spectroscopy and transmission electron microscopy characterization revealed that the ECP process generated a uniform, dense, and impurity-free oxide layer on the surface, with a thickness of approximately 5 nm. Specifically, the oxide layer exhibits a bilayer structure with ion-selective permeability, which enhances corrosion resistance by inhibiting both the penetration of external ions and the leaching of internal ions. Notably, the denser inner layer plays a critical role in this improved corrosion resistance. In summary, this study investigated the surface treatment of MPH stainless steel using environmentally friendly neutral electrolytes and systematically optimized the corresponding processing parameters. The findings demonstrate a promising approach to enhancing the surface quality and corrosion resistance of MPH, contributing to its long-term performance and sustainability.