Safe Electropolishing Process for Aluminum and Its Alloys Using Sodium Chloride Glycol Solutions Without Perchloric Acid

A safe and straightforward process was developed for electropolishing aluminum surfaces using a nonhazardous electrolyte solution, specifically ethylene glycol (EG) or propylene glycol (PG) with NaCl, instead of perchloric acid. High-purity aluminum specimens were immersed in a slowly stirred electrolyte solution of EG or PG with NaCl and anodically polarized at 20–140 V for 2–30 min. At an optimal voltage of 40–60 V, the current density reached a constant value after an initial transition, resulting in uniform dissolution of the specimen’s surface and successful electropolishing. The surface reflectance exceeded 80% across the visible light spectrum, nearly matching that of an ideal specular plate. The surface showed numerous bumpy structures with a height of 10 nm and a roughness of 3.0 nm. This electropolishing method is also applicable to aluminum alloys (e.g., A1050, A5052, A6063, and A7075), improving the reflectance of these alloys by more than 20% compared to those of untreated surfaces.