Erosive wear of plasma electrolytic oxidation layers on aluminium alloy 6061

Plasma electrolytic oxidation (PEO) is a process that converts the surface of light metals and alloys into a ceramic layer. In aluminium alloys, layers produced by PEO are mainly composed of oxides and other compounds which are harder, therefore, more suitable for tribological applications than the underlying base metal. The aim of this work was to study the erosive wear of PEO layers of different thicknesses and to compare it with the bare aluminium alloy 6061 base metal. PEO was conducted to produce layers 100, 125 and 150 μm thick that were characterised by SEM, XRD, microhardness and stylus profiling prior to testing. Multiple impact angle (20° to 90°) erosion tests were performed in a sandblast type machine that simulates the sand blowing process to produce sand cores for castings. The erodent material was resin-bonded silica sand, jetted by compressed air at 0.69 and 1.38 bar producing average particle impact velocities of 6 and 10 m/s, respectively. In most cases, PEO layers wore less than the bare aluminium alloy. For the 6 m/s impact velocity, the 150 μm layer experienced quantitatively lower wear rates than the 125 μm and the 100 μm. On the contrary, for the 10 m/s impact velocity the 150 μm layer showed higher wear than the 125 μm and the 100 μm. Optical, scanning electron and confocal white light microscopy were used to elucidate the erosive wear mechanisms taking place; which are discussed in this paper.