Surface chemistry, film morphology, local electrochemical behavior and cytotoxic response of anodized AZ31B magnesium alloy

Abstract

This work investigates the effect of current density on the surface chemistry, film morphology, cytotoxic response, global and local electrochemical behaviors of AZ31B alloy anodized in 1.0 M NaOH + 0.5 M Na2SiO3 solution. Three different current densities, namely 5, 10 and 20 mA cm−2 were tested. The surface morphology and thickness of the anodized layers were examined by scanning electron microscopy. The surface chemical states were assessed by X-ray photoelectron spectroscopy. The corrosion resistance was evaluated in phosphate-buffered saline (PBS) based on electrochemical impedance spectroscopy and potentiodynamic polarization measurements. The use of scanning probe techniques with physicochemical resolution, the scanning electrochemical microscopy (SECM) and the scanning Kelvin probe (SKP), allowed the best corrosion behavior to be assigned to the sample anodized using a current density of 20 mA cm−2. Altogether, these methods allowed to establish that the anodizing current density imposed to the magnesium alloy had a major effect on the morphology and composition of the surface layers, and produced changes in their electrochemical behavior. In vitro cytotoxicity tests using the MTS assay demonstrated that the good biocompatibility of the AZ31B magnesium alloy was not damaged by the surface layers formed during the anodization treatment.