Pulsed current effect on hard anodizing process of 7075-T6 aluminium alloy

The aim of this work is to study the influence of pulsed current on hard anodizing process (in sulphuric acid bath) of AA 7075-T6, a commercial heat treated aluminium alloy widely used in several innovative and strategic mechanical sectors (military, automotive, aerospace, etc).Exploiting different pulsed current procedures (slow square pulse mode), combining different duty cycles and current levels it was possible to obtain thick and hard anodic oxides with a good interfacial adhesion. The optical microscopy characterization shows that the use of pulsed current minimizes the growth of defects at the oxide/alloy interface caused by the presence of intermetallic precipitates characteristic of AA 7075-T6. Moreover nano-indentation profiles, evaluated along the coatings cross section, highlight the oxide hardness increase of the samples obtained employing pulsed current cycles (PC) compared to those obtained with standard direct current process (DC) or multistep direct current procedures (MSDC).