Corrosion behaviour of an Mg-Y-RE alloy used in biomedical applications studied by electrochemical techniques

Magnesium, due to its biocompatibility, a necessity in metabolic processes, and better mechanical properties than polymer, is an ideal candidate for biodegradable implants. The main actual limitation for the use of magnesium alloys is its too fast degradation rate in the physiological environment. The corrosion behaviour of an Mg-Y-RE magnesium alloy in two different physiological solutions (artificial plasma (AP) and simulated body fluid (SBF)) was investigated, using electrochemical impedance spectroscopy (EIS). The investigation showed that SBF is significantly more aggressive than AP with regard to the polished surface. A large difference in the corrosion rate and mechanisms (uniform or localized corrosion) is observed as a function of the buffer capacity of the media, but also of the carbonate and chloride content. For temporary surface protection, the formation of an approximately 350400 nm dense hydroxide layer is obtained by electrochemical anodising. An increase of the corrosion resistance of the treated alloy for both physiological solutions is obtained, and this is especially noticeable for a long immersion time in AP.