Modification of nanostructured anodized aluminum coatings by pulse current mode

• Pulsed current mode effect on mechanical and corrosion behavior was evaluated.
• Current density is the most effective factor on hardness of anodized coating.
• Alumina nanotube diameter affects corrosion resistance considerably.

In this study, the effects of pulse current mode on corrosion resistance and mechanical properties of anodized coatings were explored. Thickness and hardness measurements, polarization and electrochemical impedance spectroscopy were employed to take mechanical and corrosion behaviors of the anodized coatings into consideration. Also, field-emission scanning electron microscopy (FE-SEM) was utilized to characterize the surface morphology of the coatings. It was shown that in short anodizing times, coating thickness is controlled by the heat concentrated on coating. Although at prolonged anodizing times, the coating thickness is affected by average current density. Hardness measurements showed that in short times, hardness of the coatings was affected by average current density and for prolonged times, it was influenced by heat concentrated on the coating surface as well as relaxation time. Polarization curves showed that the corrosion behavior of anodized coatings was firstly affected by pore diameter. Results showed that application of pulse current mode reduced the pore diameter. Furthermore, compared with the direct current mode, the pulse current mode resulted in higher surface density and corrosion resistance. Also, the corrosion resistance of the samples anodized by pulse current mode was influenced by the thickness of the barrier layer.