Influence of the microstructure of the aluminum substrate on the regularity of the nanopore arrangement in an alumina layer formed by anodic oxidation

We investigated the microstructure of aluminum sheets with different purities (Al 99.999%, Al 99.95%, Al 99.5% and AlMg1) before and after different treatments (polishing and annealing) by X-ray diffraction (phase analysis and pole figures) and high-resolution scanning electron microscopy. In a two-step anodisation process within sulfuric acid a nanoporous alumina layer (with mean diameters of 25 nm and mean distances of 30 nm) was formed on the aluminum sheets. We found that the regularity of the nanopore arrangement correlates with the fraction of aluminum grains with (100) orientation in the aluminum substrate. A correlation with the grain boundary and dislocation densities within the aluminum could not be determined.