Investigation of the Electrochemical Breakdown Response in Sensitised AA5083 Aluminium Alloy

The light-weight aluminium alloys play an important role in reducing emissions from the transport industry. However, to take full advantage of these, the corrosion mechanisms that govern their failure need to be properly understood. Hence, the electrochemical response, especially after passive film breakdown, of the aluminium alloy AA5083 was analysed via potentiodynamic polarisation. By starting the scans at the relatively negative potential of −1.4 V (vs. SCE), the reduction of water in the electrolyte causes a localised increase in pH, leading to a preferential attack on the susceptible regions in the (sensitised) microstructure; that is, the deleterious β-Al 3 Mg 2 along the grain boundaries. Subsequently, in the later stages of the potentiodynamic scan, these regions that have been degraded by the dissolution of β-Al 3 Mg 2 undergo imperfect repassivation, leading them to be vulnerable to localised breakdowns. These conditions allowed for the discovery of a discernible trend after breakdown, in which AA5083 microstructures with a more extensive β-Al 3 Mg 2 region (both in size and in amount) recorded a more rapid increase in the measured current density. In particular, the potential at which the anodic current density reached 1 × 10 −4 A cm −2 was correlated with the extent of β-Al 3 Mg 2 formed during isothermal heat-treatments. This work provides a possible pathway towards the development of an electrochemical quantification technique for the extent of β-Al 3 Mg 2 growth, degree of sensitisation, and, ultimately, the intergranular corrosion (IGC) susceptibility of the microstructure of AA5083 components used in industrial applications.