Wear of an aluminium alloy coated by plasma electrolytic oxidation

Plasma electrolytic oxidation is a technique that converts the surface of a light metal alloy into a high hardness ceramic coating. This process involves the anodic oxidation of the metallic substrate and dielectric breakdown of the layer, which takes place by subjecting the alloy to high voltages in an electrolytic bath. The plasma created by these electrochemical interactions promotes the formation of a porous ceramic coating with thicknesses up to around 150 μm. The present work deals with the study conducted on samples of an aluminium type 6061 alloy that was processed to obtain coatings of different thicknesses, aiming to assess their wear resistance in sliding conditions using a ball on disc machine. The coatings were characterised by X-ray diffraction, scanning electron microscopy, roughness measurements and microhardness tests. The X-ray analysis showed the presence of mullite, α-Al2O3 and γ-Al2O3 within the coatings. It was found that the friction coefficient changed along the tests, and that the weight lost depended on both, the thickness of the coating and the load applied during the test. The wear mechanisms taking place are discussed.