High growth rate, wear resistant coatings on an Al-Cu-Li alloy by plasma electrolytic oxidation in concentrated aluminate electrolytes

Plasma electrolytic oxidation of a 2A97 Al-Cu-Li alloy under a pulsed bi-polar constant current regime has been carried out in electrolytes containing 5, 32 and 56 g l− 1 NaAlO2. Wear resistant coatings, containing relatively large amounts of α-Al2O3, were formed using concentrated solutions. The best protection was obtained with a relatively compact coating, generated with 32 g l −1 NaAlO2. The coating growth rate increased from ~ 1.5 to 11.3 μm min −1 between 5 and 56 g l −1 NaAlO2. The high rates indicate that non-Faradaic processes contribute to the coating formation. Increased concentrations of NaAlO2 reduced the energy required for coating formation; e.g. to the range ~ 1 to 5 kWh m− 2 μm −1 for coatings formed with 32 and 56 g l −1 NaAlO2.