Open Access

Although magnesium and its alloys are promising candidates as biodegradable implant materials, the tendency for localized corrosion mechanism in physiological environment limit their biomedical application. Electropolishing is an attractive strategy for improving the corrosion behaviour of metals, but it is still largely unexplored in magnesium materials. In this study, the characterization of electropolished surfaces of AM50 and pure magnesium was performed, focussing on their in vitro degradation behaviour in cell medium. Corrosion rates were evaluated using potentiodynamic polarisation. The surface morphology before and after the onset of corrosion was investigated by scanning electron microscopy and confocal laser scanning microscopy. The presented electropolishing process led to improved surface performances, observable by significantly lower corrosion rates (0.08 mm·year-1 in Dulbecco's modified Eagle's medium), lower arithmetical mean height (0.05 µm), lower water contact angle (25-35°) and lower micro hardness (35-50 HV 0.1) compared to mechanically and chemically treated surfaces. MgO/Mg(OH)2 could be detected on electropolished surfaces. The localized corrosion mode could be reduced, but not entirely prevented. Electropolishing shows great potential as post-treatment of magnesium-based components, but detailed tests of the long-term corrosion behaviour are an important area of future research.

Electropolishing magnesium materials is challenging due to the strong susceptibility of magnesium to corrosion in aqueous electrolytes. Deep eutectic solvents (DES) represent a less aggressive alternative, but their electrochemical behavior toward magnesium is not well understood. In this study, Ethaline, Glyceline and Reline were systematically investigated as electrolytes for the electropolishing of a magnesium material. The process parameters from traditional phosphoric acid systems were adapted and optimized to DES regarding electrolyte temperature and agitation as well as specimen position and orientation. Electropolishing was conducted at 1700 mV vs Ag/AgCl (3 M) and 18 C cm −2, employing elevated temperature (80 °C), rapid stirring of the electrolyte and positioning the sample surface perpendicular to the electrolyte flow with repeated 180° specimen rotation. The optimized DES systems produced smooth, mirror-like, nearly defect-free and corrosion-resistant surfaces comparable to those obtained with acidic electrolytes. Additionally, DES enabled high-purity surfaces, reduced polishing times, and excellent reproducibility. Ethaline achieved the best surface quality despite strong driving forces for anodic film formation, whereas Glyceline and Reline showed promising results for further optimization. The findings reveal new insights into the anodic behavior of magnesium in DES and establish them as viable electrolytes for sustainable and high-performance electropolishing of magnesium materials.