Effect of alkaline cleaning and activation on aluminum alloy 7075-T6

The effect of alkaline cleaning and activation on the composition and thickness of the oxide layer on aluminum alloy 7075-T6 was studied. E-pH diagrams were developed to predict the effect of alkaline cleaning and activation solutions on the stability of the oxide surface layers. The thickness of the native oxide layer was determined to be similar to 30 nm by Auger electron spectroscopy depth profiling analysis. The outer similar to 20nm was rich in magnesium while the remaining similar to 10 nm was rich in aluminum. Cleaning in a 9.1 pH alkaline solution was found to remove the magnesium-rich layer and leave behind an aluminum-rich oxide layer similar to 10 nm thick. Activation in alkaline solutions of NaOH (pH > 12.9) or Na(2)CO(3) (pH > 11.5) produced an oxide that was similar to 20 to 60 nm thick and rich in magnesium. Alkaline cleaning and activation altered the oxide composition and thickness making it possible for deposition of thicker cerium-based conversion coatings (similar to 100 to 250 nm) compared to only alkaline cleaning (similar to 30 nm), with application of one spray cycle of deposition solution. (C) 2010 Elsevier B.V. All rights reserved.