Electropolishing of Magnesium and Its Alloys Using a Safe Glycol Solution Containing Sodium Chloride

The electropolishing behavior of pure magnesium and its alloys in ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol (TrEG), and tetraethylene glycol (TeEG) solutions containing sodium chloride was investigated using electrochemical measurements, microscopic observations, and reflectance measurements. Large light-grayish cloudy areas with micrometer-scale linear irregularities were formed on the magnesium surface via constant-voltage electrolysis in the EG solution, whereas mirror-finished magnesium surfaces were successfully obtained in the DEG and TeEG solutions. Among these, the DEG solution is considered appropriate for electropolishing because of its lower viscosity and market price. The reflectance of the entire visible wavelength region gradually increased with time during electrolysis in the DEG solution at 308 K. We found that short-term electrolysis for 3 min at the higher voltage of 75 V should be selected if a moderately polished surface is to be rapidly obtained, whereas long-term electrolysis for 60–300 min at 50 V should be performed if a highly polished surface with an extremely high reflectivity measuring more than 80% can be obtained. Three-dimensional magnesium specimens with curved and spiral shapes and an LZ91 magnesium alloy consisting of a simple solid-solution matrix can also be electropolished via electrolysis in a DEG solution.