Electrochimica Acta 56 (2011) 7038–7044 Contents lists available at ScienceDirect Electrochimica Acta j ourna l ho me pag e: www.elsevier.com/locate/electacta Simulation of pH-controlled dissolution of aluminium based on a modified Scanning Electrochemical Microscope experiment to mimic localized trenching on aluminium alloys Roland Oltra a,∗,1 , Alexandre Zimmer a,1 , Claire Sorriano a , Fabien Rechou a , Céline Borkowski a , Olivier Néel b a Interfacial Electrochemistry Corrosion group, Laboratoire ICB UMR 5209, CNRS-Université de Bourgogne, 9 avenue Alain Savary, 21078 Dijon, France b Constellium – Centre de Recherches Voreppe Parc Economique Centr’Alp, 38341 Voreppe, France a r t i c l e i n f o Article history: Received 1 February 2011 Received in revised form 1 June 2011 Accepted 2 June 2011 Available online 13 June 2011 Keywords: Aluminium Localized corrosion Trenching Modelling SECM a b s t r a c t Some constituent intermetallic (IMPs) particles at the surface of aluminium alloys are considered as pref- erential sites for the initiation of structural corrosion resulting in localized trenching around the particles and the surrounding Al matrix. In this work, a modified scanning electrochemical microscope (SECM) experiment was used to induce such phenomena via a local alcalinisation on 200 nm thick aluminium coatings promoting their local dissolution in an aerated 0.1 M NaCl electrolyte. The local alcalinisation was induced by the oxygen reduction reaction on the tip of a SECM which mimics the surface of an iso- lated IMP. From a phenomenological point of view, reproducible cylindrical damage develops in front of the platinum ultramicroelectrode (UME). Using a 2D finite element modelling to simulate the SECM experiments, the role of the local alcalinisation was validated and the calculated Al dissolution rate was found in agreement with the experimental evaluation. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction Coarse intermetallic particles (IMPs), namely; Al 2 Cu (“ phase”), Al 2 CuMg (“S phase”) and AlCuFeMnSi (“2nd phase”) exhibiting dif- ferent behaviours, can be found at the surface of aluminium alloys (AA). In open circuit potential conditions, it is usually accepted that S phase IMP act as anodes and both 2nd and  phases act as cathodes. However, the S and  phases suffer dealloying which is accompanied by Cu-enrichment and in fact they behave as cath- odes promoting the oxygen reduction reaction (ORR). These IMPs are preferential sites for the initiation of structural corrosion which give rise to the formation of a trench around the IMP [1] and its surrounding matrix. For a specific heat treated 2011 AA, the mor- phology of such grooving at the interface “ phase-matrix” has been related to both the contribution of galvanic coupling and the local alcalinisation due to the ORR on the IMPs enhancing the dissolution of the surrounding Al matrix [2,3]. Whilst the trenching phenomenon has been largely reviewed from a phenomenological point of view [4], only a few papers deal with quantification of the local grooving rate. This is probably due ∗ Corresponding author. E-mail address: roland.oltra@u-bourgogne.fr (R. Oltra). 1 ISE member. to the fact that it is rather difficult to performed measurements on isolated IMPs. On the surface of an industrial alloy, over long time the individual diffusion fields around individual IMPs on which ORR is occurring, expand and the diffusion field is entirely homoge- neous, i.e. the diffusion layer is thicker than the distances between the active IMPs [5]. It renders impossible local investigation of pH changes which can be used to validate some models proposed in the literature [1]. In this work, the local alcalinisation is generated at the same scale as the microstructural scale (for coarse IMPs) using a plat- inum (Pt) ultramicroelectrode (UME). It was expected that the local alcalinisation due to the imposed ORR on the UME will be sufficient to trigger the local dissolution of the aluminium oxide followed by the dissolution of the bulk aluminium (a thin film in this case). The objective is to validate a simulation based on a finite element method (FEM) modelling which could be applied to real IMPs (sin- gle particle and IMPs array). Of particular relevance to this modified UME approach, pioneering works [6,7] employed Scanning elec- trochemical microscopy (SECM) to induce localised corrosion of passivated metallic electrodes using an UME. In these latter studies the UME generated Cl - ions initiating pitting on the sample surface whereas in our case the UME will generate OH - ions to promote the dissolution of the native oxide and the bulk aluminium. Previous FEM simulations showed [3] that although the depth of the groove is in good agreement with the experiments, its lateral 0013-4686/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2011.06.002