In Situ and Operando AFM and EIS Studies of Anodization of Al 6060: Influence of Intermetallic Particles

In this study, anodization of an Al 6060 alloy has been investigated by in-situ electrochemical atomic force microscopy (EC-AFM) and electrochemical impedance spectroscopy (EIS) under operando conditions, to elucidate the role of intermetallic particles (IMPs) in the alloy. The Volta potential maps measured by scanning Kelvin probe force microscopy (SKPFM) reveal that the relative nobility is higher for AlFeSi type and lower for Mg 2 Si type of particles as compared with the alloy matrix. The EIS results obtained at anodizing potentials show that the thickness of the barrier oxide layer increases linearly with the applied potential, but the oxide growth rate is lower than that of single crystal samples reported previously. Moreover, the EIS spectra show an inductive loop at low frequencies indicating an anodic dissolution process. The EC-AFM images display detailed morphological changes related to the IMPs during the anodization, which reveal certain localized dissolution in parallel to anodic Al oxide (AAO) formation on the alloy. The combined AFM and EIS measurements demonstrate that the IMPs in the alloy cause localized dissolution during anodization, resulting in a reduced AAO growth rate. The corrosion resistance of as-produced AAO film is low unless anodized at sufficiently high potential.