Nanocontrolled thinning of the barrier layer thickness of porous anodic films using galvanodynamic polarization of aluminum alloys

Thinning the barrier layer thickness of anodic films prepared on refined aluminum substrates (4 N or 5 N) was usually performed to elaborate -after the usual two-step anodizing method- anodic aluminum oxide (AAO) templates with pores opened at both sides, allowing the subsequent nanodevices synthesis. By contrast, there is a lack of studies concerning similar barrier layer thinning for anodic films grown -by a single-step anodizing - on commercial low alloyed aluminum substrates (1XXX series) or other more complex aluminum alloys (AA 2XXX-8XXX). Yet such a need is now emerging, particularly for future applications requiring transverse electrical conductivity of usual anodic films toward the aluminum alloy substrate. This work aims to study and to master a simple and cheap method for thinning the barrier layer thickness of such anodic films on commercial aluminum alloys. Here, the thinning is studied using a current density decrease (at a constant rate) after the anodic film growth in phosphoric acid-based electrolyte, using the conjunction of in-situ accurate electrochemical follow-up and ex-situ FE-SEM morphological observations. Variation of current density scan rate highlights that fast processes lead to no barrier layer thinning, and slow ones to the detachment of the whole oxide film. However, by choosing the right scan rate range, it is possible to successfully obtain, in a straightforward manner, anodic films still supported on aluminum alloy substrates, but with barrier layer thickness tuned at the nanoscale.