Characterization of the hard anodizing layers formed on 2014-T3 Al alloy, in sulphuric acid electrolyte containing sodium lignin sulphonate

The properties of hard anodizing layers formed on 2014 Al alloy in sulphuric acid electrolyte containing sodium lignin sulphonate were investigated. The corrosion behavior of 2014 Al alloy has been studied using potentiodynamic polarization technique. Anodic layers morphology and composition were examined by scanning electron microscope, energy dispersion X-ray (EDX), X-ray diffraction (XRD) and Fourier infrared spectroscopy (FTIR). The results showed that the corrosion resistance has been enhanced after hard anodizing of 2014 Al alloy. Addition of lignin sulphonate to the sulphuric acid electrolyte significantly improved the corrosion resistance of the anodized 2014 aluminum alloy by adsorption on copper-intermetallic phases. Adsorption of sodium lignin sulphonate on oxide surface has been confirmed by SEM, EDX, and FTIR. Phenolic and carboxylic groups in sodium lignin sulphonate are functional groups, which are responsible of complex formation on oxide surface. The morphology of the hard anodizing layer is non-homogenous due to the high copper content of 2014 Al alloy. Addition of sodium lignin sulphonate resulted in the formation of anodic layers with more homogeneity and fewer cracks.