Multi-Scale Monitoring the First Stages of Electrochemical Behavior of AZ31B Magnesium Alloy in Simulated Body Fluid

Abstract

This work applies electrochemical noise technique (EN) and scanning electrochemical microscopy (SECM) to investigate the initial stages of degradation of AZ31B magnesium alloy in simulated body fluid (SBF). The fluctuations in potential and current, caused by the alloy's spontaneous degradation, were analyzed in both time and frequency domains to determine the type of attack and the fractal nature of the degradation. Substrate-generation/tip-collection mode SECM mapped the hydrogen evolution activity at the Mg surface during the initial corrosion process. This electrochemical information was correlated with pH changes of the solution, Mg ion concentration, mass loss, SEM-EDS and XPS analysis. The Mg matrix dissolution was promoted by Al-Mn intermetallic particles, which acted as cathodic sites. The corrosion products film was mainly composed by Mg(OH)2 and Ca10(PO4)6(OH)2, and its fast formation allowed a slower degradation and H2 evolution rates. Combining EN and SECM methods allowed the description of the early degradation processes of AZ31B in SBF as a persistent stationary process, related to fractional Gaussian noise, which was characterized by the quasi-uniform corrosion of the alloy.