Stability Analysis of the Mg2Si Phase in AA 6061 Aluminum Alloy

The spent MTR fuel elements, manufactured with the aluminum-based alloy AA 6061, are stored under water in interim storage basins. In such conditions the AA 6061 is susceptible to degradation by localized corrosion processes which might be related to the behavior of second-phase particles present in the alloy.According to its electrochemical behavior, the second-phase particles present in AA 6061 can be classified into cathodic or anodic in relation to the aluminum matrix.In order to investigate the stability of the Mg2Si phase, which dissolves in high purity water, immersion and polarization tests were carried out in alkaline solutions. SEM and EDS were used to analyze the second-phase particles after the tests.It was determined that Mg2Si phase particles are stable in solutions of pH 8 to 14, and undergo selective magnesium dissolution from pH 7 to lower values.