Effects of surface alloying on electrochemical corrosion behavior of oxygen-plasma-modified biomedical magnesium alloy

Mg–3Nd–0.2Zn–0.4Zr alloy with good mechanical properties is a new type of biodegradable magnesium alloy. In order to improve the surface stability in the initial healing stage and foster tissue growth on biomedical implants made of this Mg alloy, oxygen plasma immersion ion implantation (O-PIII) is conducted to modify the alloy surface. Although O-PIII increases the thickness of the surface oxide, no significant improvement in the surface corrosion resistance is observed. Hence, surface alloying with Al and Cr by means of high-energy ion implantation is conducted prior to O-PIII. The electrochemical data obtained in simulated body fluids, including polarization curves and electrochemical impedance spectra (EIS), reveal that the surface corrosion resistance is improved after surface alloying. Our results show that surface alloying with Cr produces the best result in this study. The improvement stems from the formation of Al or Cr-containing oxide films in the implanted layer.