In Situ Characterization of Corrosion Processes of As-Extruded Pure Magnesium Using X-Ray Computed Microtomography

X-ray computed microtomography was used to investigate the corrosion process of the extruded pure magnesium (Mg). The microscopic corrosion morphologies on the extruded pure Mg surface with corrosion time were observed by three-dimensional reconstruction technology. The effects of grain size and grain orientation of the extruded pure Mg on the corrosion rate were studied by the electron backscattered diffraction and first-principles calculations. It is found that the corrosion on the extruded pure Mg surface prefers to form on the grain boundary and the corrosion morphology is mainly the corrosion cracks distributed in a dendritic bifurcation state along the extrusion direction. Interestingly, these dendritic corrosion cracks are connected with the corrosion pits within the surface. The corrosion resistance of extruded pure Mg is improved slightly due to the presence of many high-energy sites at the grain boundaries that promote corrosion.