Impact of the anodizing duration on the surface morphology and performance of A2024-T3 in a model corrosive medium

Abstract

Since the preliminary surface treatment is of crucial importance for the anticorrosion coating deposition, the duration of the anodization was investigated because it is directly related to the total electric charge passed (in Coulombs) and the respective electrochemical conversion rate. This process parameter predetermines the surface roughness, surface structure and the elemental distribution. Thus, a systematic comparative evaluation was performed on AA2024-T3 samples, after anodization for 12, 24 and 48 min in 15% wt. H2SO4 at a constant current density of 15 mA cm−2. The treated samples were submitted to observations by Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray spectroscopy (EDX) analysis. Additional electrochemical measurements by means of Electrochemical Impedance Spectroscopy (EIS) and Linear Voltammetry (LVA) were performed after defined periods of exposure (24 and 168 h) to a 3.5% NaCl model corrosive medium, in order to establish the barrier ability of the respective specimens. The further analysis of the obtained results enabled the development of a concept for gradual sulfur containing porous oxide layer growth with high permeability for corrosive species.