The investigation of plasma electrolytic oxide coating properties on 6082 aluminum alloy

In the present study, an alkaline electrolyte is used on 6082 aluminium alloy substrates in order to achieve thermal barrier coatings by using Plasma Electrolytic Oxidation (PEO) technology. It is achieved to develop the coatings microstructural, morphological, thermal and mechanical properties by optimising the coatings. Various process parameters are used such as current density, electrolyte and processing times to optimise the coating properties. Depends on the parameters used, alumina and mullite based PEO coatings are formed. Various characterization techniques are applied in order to confirm the suitability of the coatings as thermal barrier applications. Based on the geometry of produced coatings, standard analyses techniques are employed in the mean of microstructural, morphological, thermal and mechanical properties. Coatings structure and morphology are studied quantitatively by using scanning electron microscopy (SEM), Field emission gun scanning electron microscopy (FEGSEM), energy dispersive X-ray spectrometer (EDX) and X-ray diffraction (XRD) techniques. The density and porosity of PEO coatings are evaluated using an organic flutex (C11F20) liquid with Archimedian principal. The thickness is measured non-destructively using an eddy current thickness gauge. To verify the accuracy of the eddy current thickness gauge, coatings are examined by SEM and FEGEM. For roughness measurements of alumina and mullite based PEO coatings, an interferometric profilometer is used. Differential thermal analysis, together with dilatometer and steady-state method is used to quantify the thermal properties of PEO coatings. Mechanical properties are measured using nanoindentation and four point beam bending techniques. As a result of the measured properties, in this work provide the optimization of thermal barrier coatings to date; the combination of fine porosity with significant amorphous material content, low thermal conductivity value, suitable thermal coefficient expansion value and low global stiffness.