Abstract:
The present study aims at understanding the electrochemical impedance and biocorrosion characteristics of AZ91 Mg-alloy in Ringer’s
solution. As-cast AZ91 Mg-alloy was subjected to T4 heat treatment in a way to homogenize its microstructure by dissolving most of the
β-Mg17Al12 phase at the vicinity of grain boundaries. The electrochemical impedance and biocorrosion performances of these two different
microstructures (as-cast and T4 heat treated AZ91 Mg-alloys) in Ringer solution were evaluated by electrochemical impendence spectroscopy,
potentiodynamic polarization and weight loss method. EIS spectra showed that both microstructures exhibit similar dynamic response as a
function of the immersion time; however, the value of impedance and maximum phase angle are about 50% higher in as-cast AZ91 Mg-alloy
as compared to that of homogenized AZ91 Mg-alloy. Weight loss measurement indicated that corrosion resistance of as-cast AZ91 was
significantly better than that of homogenized AZ91. Microstructural and XRD analysis revealed that as-cast AZ91 contains a passive film of
MgCO3 and CaCO3 precipitates with near spherical morphologies, whereas homogenized AZ91 comprised mainly unstable Mg(OH)2 film
featured by irregular plate-like morphologies
