Corrosion Behavior and Electrochemical Properties of As-cast Mg-2Zn-0.5Ca-Y Series Magnesium Alloys in Hank's Solution and NaCl Solution

Microstructure and bio-corrosion behavior of as-cast Mg-2Zn-0.5Ca-Y series alloys were investigated for biomedical application by optical microscopy, scanning electronic microscopy (SEM), immersion tests and electrochemical measurements in Hank's solution and NaCl solution (3.5wt%). The morphologies of the Mg-2Zn-0.5Ca-Y series magnesium alloys indicate that the corrosion is not uniform and a lot of cracks are formed on the surface of the corrosion layer after immersion tests. The corrosion resistance of as-cast Mg-2Zn-0.5Ca-Y series alloys increases owing to the addition of the rare earth element Y and that of Mg-2Zn-0.5Ca-1.0Y alloy is the best. All of the potentiodynamic polarization curves obtained in the tests in Hank's solution and NaCl solution show current plateaus which are due to the presence of a protective corrosion product film. The electrochemical impedance curves of the alloys in the test solutions have only one capacitive loop. The appearance of a capacitive loop at high frequency is caused by the stable double-layer capacitance. The capacitive loop at low frequency is attributed to diffusion control at film-free areas.