High Resolution SEM Investigation of Intercrystalline Corrosion on 6000-Series Aluminum Alloy with Low Copper Content

This work investigates the role of Al-base intermetallics in intercrystalline corrosion (ICC) of a 6000-series alloy, containing 0.2% Cu. In the underaged condition, ICC was initiated at the alpha-Al(Fe,Mn)Si precipitates. These phases corroded rapidly in the acidified NaCl solution, while ICC still propagated. The AlMgSiCu (Q-phase) precipitates were relatively inert. The material became resistant to ICC in the maximum hardness T6 condition, despite increase in the density of the Q-phase by coarsening of a Cu-rich film along the grain boundaries. These results throw light on the nature of the local grain-boundary cathodes on the mechanism of ICC on this material. (C) 2014 The Electrochemical Society. All rights reserved.