Detection of nanoscale η-MgZn2 phase dissolution from an Al-Zn-Mg-Cu alloy by electrochemical microtransients

In this article we demonstrate how the dissolution of nanosize intermetallic particles present in Al alloys can be detected using microelectrochemical techniques. The local electrochemical properties of a high-strength Al-Zn-Mg-Cu alloy, which contains nanoscale eta-MgZn2 phases, were investigated with a microcapillary cell. At the open-circuit potential (OCP) with the sample surface in the range of 1000 mu m(2), potential fluctuations (microtransients) can be observed. Under polarization of such small areas, current transients are detected in the passive range of the alloy. An estimation of the size of dissolution events from the charge passed during the current transient leads to the conclusion that the current transients could stem from the dissolution of eta-phase particles, with diameters in the order of 100 nm. This size scale corresponds well with the size of the grain-boundary MgZn2. Transmission electron microscopy (TEM) and high-resolution SEM images provide further insights for possible mechanisms leading either to potential or to current microtransients. Copyright (C) 2008 John Wiley & Sons, Ltd.