Electrochemical Superfinishing of Cast and ALM 316L Stainless Steels in Deep Eutectic Solvents: Surface Microroughness Evolution and Corrosion Resistance

Significant weight and cost savings are provided by Additive Laser Manufacturing (ALM) compared to mechanical machining, particularly for complex shape parts. However, ALM as-printed parts are affected by surface defects and roughness and require a post-treatment, which can be done with an electrochemical polishing performed in harmful solutions, sometimes following another processes such as chemical etching. The same possibilities still exists for ALM parts in applications that require a mirror-like finishing which can be obtained after a mechanical polishing step. This paper focuses on ALM 316 L pre-polished parts, successfully electropolished in a Deep Eutectic Solvent composed of choline chloride + ethylene glycol mixture. A typical electropolishing behavior, characterized by the presence of a large current density plateau on polarization curves was observed. In situ Atomic Force Microscopy measurements allowed surface modifications and film formation during the polishing process to be followed. After electropolishing, both Cast and ALM samples exhibit bright and smooth aspects, revealing a high roughness reduction. The pitting corrosion resistance of both materials is also enhanced by this process.