Corrosion performance of {MAO} coatings on {AZ31} Mg alloy in simulated body fluid vs. Earle's Balance Salt Solution
By Wilke, Benjamin M.; Zhang, Lei; Li, Weiping; Ning, Chengyun; Chen, Cheng-fu; Gu, Yanhong
Published in Applied Surface Science
2016
Abstract
Abstract Earle's Balance Salt Solution (EBSS) provides an alternative to the conventional simulated body fluids (c-SBF) and has been shown to better simulate the corrosion conditions in vivo. In this work, a series of tests were conducted to explore the corrosion performance of MAO-coated {AZ31} samples in {EBSS} vs. c-SBF. Samples were produced by varying {MAO} process parameters and then immersed up to 21 days in both {EBSS} and c-SBF. The corrosion rates were evaluated by the electrochemical impedance spectroscopy and potentiodynamic scanning. Scanning electron microscope (SEM) was used to compare the progression of microcracks across the surface of the coatings. The evaluation of cross-sectional thickness showed an increase in {MAO} coating thickness with the process voltage. {MAO} samples with a thicker coating generally have higher impedance and lower current density at the initial immersion time point of 0.5 h. Samples in {EBSS} showed higher initial impedance and lower current density values as compared to c-SBF counterparts for all process groups. Samples in {EBSS} demonstrated a much slower corrosion rate than c-SBF samples because of the decreased chloride content and {CO2} buffering mechanism of the EBSS.