Dependence of Degradation Mechanisms in Magnesium Alloys on Grain Orientation and Interfaces in 3D

Abstract: Magnesium alloys are promising candidates as biomedical implants. However, a good understanding of their degradation processes is lacking. In this work, degradation in two magnesium alloys were studied in a simple physiological-fluid electrolyte of H2O+0.9wt%NaCl, Mg-5wt%Zn (Z5) & Mg-5wt%Zn-0.3wt%Ca (ZX50). Z5 alloy was studied in two microstructural states, as-cast and as a supersaturated solid solution. Degradation rate and enthalpy were determined using hydrogen gas evolution and isothermal calorimetry, respectively. Diffraction contrast tomography was then used to assess the dependence of grain orientation during degradation of the Z5 material in both the microstructural states by immersion tests in the same electrolyte. Corrosion was observed over the entire samples. Specific regions were identified where the samples were more corroded. These regions showed affinity for both local microstructural properties as well as certain crystallographic orientations.