The role of hydrogen in the formation of oxide-ceramic layers on aluminum alloys during their plasma-electrolytic oxidation

Abstract

This study focused on improving plasma-electrolytic oxidation (PEO) technology of aluminum alloys with the aim to increase their abrasive wear resistance. Using thermodynamic calculations of the reactions between hydrogen and aluminum oxides in solid, liquid and gaseous states, it is established that hydrogen (while in the channels of microplasma discharges) can promote recovery of aluminum oxides, especially non-stoichiometric composition. Consequently, this reduces an interaction between oxygen and aluminum and slows down the synthesis of PEO coatings. The synthesis of PEO layers was carried out in a weakly alkaline electrolyte with the addition of hydrogen peroxide or by blowing it with ozone. To obtain layers with better properties, we optimized the ratio between the cathodic and anodic currents densities. Our tests demonstrated that both the thickness and the abrasive wear resistance of the oxide layers increase at higher rates when hydrogen peroxide is added to the electrolyte, as compared with the use of ozone blowing. The proposed ways to improve the PEO technology made it possible to increase the synthesis rate of PEO layers by factor of 1.8 … 2, provide the optimal phase composition of PEO layers and increase their abrasive wear resistance by factor of 6.