Corrosion of structural constituents of 2017 aluminium alloy in acidic solutions containing inhibitors

Abstract

The objective of this study is to establish the corrosion behaviour of the most important structural constituents of the aluminium alloy 2017 in orthophosphoric acid solutions containing heteropolyoxomolybdate, tungstate and vanadate. These are potential candidates for replacing toxic hexavalent chromium species in stripping solution for anodic coatings. The corrosion rate of the alloy is estimated with linear polarisation method. It decreases from 0.58 mA cm−2 in uninhibited solution to 0.10 mA cm−2 in a solution containing heteropolyoxomolybdate species. Microscopic studies reveal that heteropolyoxomolybdate species inhibit corrosion of the matrix and intermetallic Al15(Fe,Mn)3(Si,Cu)2 but not Mg2Si. Intermetallic Al2Cu remains not corroded. Heteropolyoxotungstate species virtually do not inhibit the corrosion of the alloy. The solution containing vanadium species is not stable with time and the corrosion rate is not determined. Nevertheless, corrosion of the matrix is inhibited, but intermetallics Al15(Fe,Mn)3(Si,Cu)2 together with Mg2Si are dissolved. X‐ray photoelectron spectroscopy is used for examination of a corrosion product precipitated on the surface.