Quantifying of the Effects of Secondary Phases on Corrosion in Mg-RE Alloys by X-Ray Computed Tomography

The secondary phases of Mg alloys are closely related to corrosion. In this work, the correlation between secondary phases and corrosion in a Mg-6Gd-Y-Al alloy was identified by x-ray computed tomography technology. The influence of aging treatment on secondary phases of Mg alloys during corrosion was studied. The corrosion morphology of Mg alloy was examined in situ using three-dimensional reconstruction techniques. To quantify the effects of secondary phases on the corrosion of Mg alloys, the variation of average number density, average equivalent diameter, and average distance were investigated. The corrosion rate of Mg alloys was measured by electrochemical tests. It was found that after low temperature aging at 95°C, the corrosion rate of Mg alloys decreased by approximately 50%. This is due to the uniform distribution of secondary phases which increases the local overall potential and improves the protection of surface films.