Local probing of the galvanic coupling between micrometer-sized Al2Cu phases and the surrounding aluminum-based matrix of a specially heat-treated 2011 alloy is investigated using a microcapillary electrochemical cell. The aging of an isolated Al2Cu particle, i.e., selective dissolution of aluminum, is controlled by the aeration condition at the tip of the capillary due to the nature of the silicon membrane used as a gasket. The local electrochemical behavior of an isolated particle after aging confirms the mass transport control of the oxygen reduction on the galvanic coupling of the particle with the surrounding matrix. (C) 2009 The Electrochemical Society. [DOI:10.1149/1.3224876] All rights reserved.