Production of ceramic layers on aluminum alloys by plasma electrolytic oxidation in alkaline silicate electrolytes

Abstract

Plasma electrolytic oxidation (PEO) of aluminum alloy 5052 in alkaline-silicate electrolytes having different SiO2/Na2O ratios (silicate indexes) was studied. For all the electrolytes 20–90μm thick technological layer was obtained; composition, structure and properties of the oxidized layer were studied. For each sample, the oxidized layer consists of a denser internal and looser external sublayer. While for “n=1 electrolytes” the oxidized layer is mainly formed by several kinds of alumina, the principal constituent of the oxidized layer for “n=3 electrolytes” is mullite.Measurements of microhardness evidenced that it is apparently not influenced by the kind of silicate (n=1 or n=3) and by its concentration in the electrolyte. Electrolytes with silicate index n=3 ensure better corrosion protection than those with n=1. Corrosion protection parameters are significantly better for all PEO oxidized samples than for the untreated Al5052 alloy.