Anodizing is widely applied in various fields of machinery, aircraft industry and electrical engineering for protecting aluminum and its alloys parts from corrosion, for increasing strength and wear resistance and for creating electrically insulating layer on the part surface. An anodizing coating is a porous aluminum oxide film obtained by anodic oxidation mainly in an acid and, sometimes, in an alkaline media.
Application of nanodiamonds in anodic oxidation was firstly studied in the beginning of the century by L. Bernhard, G. Burkat and V. Dolmatov. Specially modified negatively charged nanodiamonds added to an electrolyte at anodizing move to the anode (aluminum and its alloys) and penetrate into Al2O3 film and pores formed at the process. Moreover, during the oxidation nanodiamonds adsorb facilitated hydrogen, which results in the considerable decrease of porosity and high increase in the coating density. The oxide film weight increases by the factor of 2–3.5. This high density of the coating, as well as the incorporation of nanodiamonds into the oxide film significantly improve the performance of the coating: corrosion protection, insulating properties and especially wear resistance. The oxide film wear reduces by the factor of 10–13.
The optimal nanodiamond content in an electrolyte is 2–15 gram per liter. The obtained microhardness is 800 – 1200 kg/mm2. The best mechanical properties are achieved at nanodiamond anodic oxidation when the electrolyte temperature is 10 °C.
Example.
Aluminum alloy 16082 AlMgSi containing 0.7–1.3% Si, 0.5% Fe, 0.1% Cu, 0.4–1.0% Mn, 0.6–1.2% Mg, 0.25% Cr, 0.2% Zn, and 0.1% Ti; the plate area 1 cm2