Surface conditions of aluminum can influence the final arrangement of nano-pores in fabrication of ordered nanoporous anodic alumina membranes (AAMs). This study is mainly focused on the different applied voltages of aluminum electropolishing by keeping all the other parameters constant. After heat treatment (stress relieving and annealing at 500°C) of pure aluminum sheets, the samples were electropolished at different voltages (10-60V) to obtain desirable surface smoothness, while the temperature of the container was kept constant. The current-time curves were recorded during electropolishing process. The surface roughness obtained in each applied voltage was examined using optical microscope and atomic force microscope (AFM). The process was followed by two-step anodization in order to reach ordered nano-pores. Finally, the influence of surface roughness on regularity of nano-pores was observed using scanning electron microscope (SEM). The SEM images were analyzed to investigate the morphology and the degree of self ordering of pores of the samples by using a new designed analytical method aiming MATLAB and fast Fourier transform (FFT) technique. It was concluded that the electropolishing voltage and the resulted surface roughness and also formed defects can competitively affect the arrangement of membrane's nano-pores. A desired smoothness obtained from electropolishing voltage of 30V. Also 40V provided the best order with respect to the other voltages.

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One of the most important coating methods on aluminum surfaces is the electrolytic plasma method. The main objective of the present study is to investigate the potential of aluminum oxide coatings created by electrolytic plasma method. Aluminum series 2 and the electrolyte of sodium silicate, sodium tetraphosphate, sodium aluminate, and potassium hydroxide were used. The results showed that the appropriate voltage to achieve uniform coating with ideal thickness and morphology is 500 V. Adding sodium silicate to the electrolyte solution will create porosity and non-adhesion to the substrate. On the other hand, the use of tetra sodium pyrophosphate increases the adhesion of the coating by penetrating phosphorus into the metal/coating interface. The optimum solution for plasma electrolytic oxidation coatings composed of 10, 3, and 3 g/l of tetra sodium pyrophosphate, sodium aluminate, and KOH, respectively. DC pulsed coating was shown to control the coating process and coating uniformity. Also the appropriate frequency to apply coating was DC pulse potential at 1000 Hz frequency under the 30% duty cycle.

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