Modelling the anodizing behaviour of aluminium alloys in sulphuric acid through alloy analogues

Anodic film morphologies on aluminium aerospace alloys are strongly influenced by alloying elements. The present study uses model alloys to interpret the early stages of anodizing of AA2024-T3 and AA7075-T6 aluminium alloys in 0.4 M sulphuric acid electrolyte. Further, coupled model alloys, representative of matrix and second phase regions, are employed as alloy analogues. The findings enable assignment of transient anodic currents during potentiodynamic polarization of the commercial alloys to oxidation of Al₂CuMg phase at 0 V SCE and of Al₂Cu, Al₇Cu₂Fe and Al–Cu–Fe phases at 5–6 V SCE. The phases that oxidize at the latter potential also cause voltage arrests during galvanostatic anodizing.