Corrosion protection of clad 2024 aluminum alloy anodized in tartaric-sulfuric acid bath and protected with hybrid sol–gel coating

Clad AA2024 T3 specimens were anodized in a tartaric-sulfuric acid bath (TSA) and subsequently protected either by classical Cr-free water sealing treatment or by application of a hybrid sol–gel coating. The sol–gel coating was prepared using a solution with high water content (58 %v/v) and obtained by the hydrolysis and condensation of tetraethoxysilane (TEOS) and 3-glycidoxypropyltrimethoxysilane (GPTMS). The morphology of the sealed anodic films and their thicknesses were evaluated by scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM) and glow discharge optical emission spectrometry (GDOES). The corrosion resistance of the samples was evaluated by electrochemical impedance spectroscopy (EIS) and salt-spray test. The results showed that the treatment with the hybrid sol–gel increased the resistive properties of the pores compared to the classical water sealing, delaying the access of aggressive species to the barrier layer.