An Investigation Of The Plasma Electroletic Oxidation Coating Growth And Corrosion Mechanisms

Plasma electrolytic oxidation(PEO) treatment was performed on AA 1060 pure aluminium using the self-designed WH-1A PEO power supply. The PEO coatings were detached from the substrate by a self-developed electrochemical method. Two main aspects were investigated as follows: ① The discharge and coating growth mechanism of the PEO process on AA1060 pure aluminium, especially the discharge mechanism at the coating/substrate interfacial region and the coating inward growth mechanism; ② The corrosion behavior of the PEO coatings on AA1060 pure aluminium.The results show that: There is a compact thin layer at the coating/substrate interfacial region of the PEO treated speciemns, and the thickness of this layer maintains at ~1 μm, does not increase with treating time. This compact thin layer is composed of many inter-connected tiny globular particals. These tiny globular particals have a relatively uniform diameter of ~0.7 μm, and the size of the tiny globular particals also does not increase with treating time. Durin g the PEO process, a kind of discharge at coating/substrate interface region takes place repeatedly, and this kind of discharge leads to the inward growth of the PEO coatings, in addition to their outward growth. The main phases of the coatings fabricated in silica system electrolyte and N15 electrolyte are alumina and mullite-amorphous, respectively. The difference of the phases of the coatings leads to the difference of the coating thickness, microstructure, elements distribution and growth mechanism.After 720 h immersion in 3.5 wt.% Na Cl solution, the coating/substrate interface layer was damaged obviously. The corrosion area was along the coating/substrate interface in the specimens treated in the silica system electrolyte while it deep in the substrate with a smaller area in the specimens treated in the N15 electrolyte. The coatings treated in the N15 electrolyte has higher corrosion resistence compared to the coatings treated in the silica system electrolyte due to the more compact inner structure of the coatings treated in the N15 electrolyte. In the initial immersion time, the pores in the coatings acted as the permeation path of the crossive solution, however, with the corrosion going on, the corrosion products blocked the pores and increased the corrosion resistence of the coatings.