The effect of anodic polarization parameters of 316L steel in a propylene glycol: Choline chloride eutectic solvent on surface finishing, chemistry and corrosion resistance

Abstract

AISI 316 alloy steel was polarized anodically in a deep eutectic solvent based on choline chloride and propylene glycol (1:2 M ratio) at the temperature range of 35–75 °C and the current density range of 10–60 mA cm−2. At certain parameters (i.e., 65 °C, 40 mA cm−2), a significant increase in corrosion resistance and surface gloss were found compared to the “raw” steel, but without a spectacular reduction in the roughness of the samples after the polarization process. The SEM analysis carried out allowed us to determine that despite the increase in roughness, micro-irregularities on the steel surface were reduced. Thanks to the ICP-AES tests, it was found that the increase in the overall roughness of the samples could be caused by the excessive leaching of iron from the surface in selected variable process parameters. XPS showed that the anodic polarization process increased the content of chromium and molybdenum compounds on the steel surface. In conclusion, this liquid may be a future replacement for the standard acid baths used for the AISI 316L electrochemical polishing process, but the optimal process conditions (as well as the use of appropriate bath additives) have yet to be determined.