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Abstract: The influence of yttrium on the corrosion residual strength of an AZ91D magnesium alloy was investigated detailedly. Scanning electron microscope was employed to analyze the microstructure and the fractography of the studied alloys. The microstructure of AZ91D magnesium alloy is remarkably refined due to the addition of yttrium. The electrochemical potentiodynamic polarization curve of the studied alloy was performed with a CHI 660b electrochemical station in the three-electrode system. The result reveals that yttrium significantly promotes the overall corrosion resistance of AZ91D magnesium alloy by suppressing the cathodic reaction in corrosion process. However, the nucleation and propagation of corrosion pits on the surface of the 1.0wt.% Y modified AZ91D magnesium alloy indicate that pitting corrosion still emerges after the addition of yttrium. Furthermore, stress concentration caused by corrosion pits should be responsible for the drop of corrosion residual strength although the addition of yttrium remarkably weakens the effect of stress concentration at the tip of corrosion pits in loading process. [Copyright &y& Elsevier]

Abstract: The corrosion behavior of AZ91Ce alloy in the presence of sulfate-reducing bacteria (SRB) was investigated using a specially designed in-situ corrosion method. For comparison, AZ91 alloy was also studied under the same corrosion condition. It seemed that AZ91Ce alloy was susceptible to crystal boundary corrosion under SRB condition to some extent. A possible mechanism for the crystal boundary corrosion was proposed. The microstructure and corrosion morphologies of alloys were analyzed by optical microscope and SEM, and the corrosion products were detected by X-ray photoelectron spectrometer (XPS). The analysis results showed that Ce in AZ91 alloy can reduce the grain size, and impede the formation of oxide, and thereby improved the corrosion performance. The electrochemical test revealed that the formation of Ce compound can restrict the cathodic reaction, and thus improve the corrosion resistance significantly as observed under the sterile condition. However, it appeared that the improvement was unconspicuous in the presence of SRB. [Copyright &y& Elsevier]