Detection and analysis of anodic current transients associated with nanoscale β-phase precipitates on an Al–Mg microelectrode

The metastable pitting of Al–5 wt%Mg microelectrode (diameter 50 μm) after aging at 150 °C for 10 h has been investigated under a constant potential in deaerated 0.6 M NaCl solution (pH 3.5). Current transients (pA size) associated with the dissolution of nanoscale β-phase precipitates have been detected. Taking the cathodic current of H2 evolution inside the pit into account, the average volume determined from a charge associated with individual current transients is about 39% of those measured by TEM. This result implies that the selective dissolution of Mg in β-phase precipitates (Al3Mg2) may occur during the metastable pitting process.