Al2O3 thin coating of AA 6082 T6 components using a fast regime fluidized bed

A relatively novel treatment, namely fluidized bed processing, to coat metal substrates, thereby changing their surface properties and inducing micro-structural changes was studied in detail. In particular, fluidized bed processing of AA 6082 T6 aluminium alloy components by using alumina Al2O3 powder was investigated. The built-up of Al2O3 films was first studied and characterized in terms of coating thickness and adhesion. Consistent trends of deposited Al2O3 according to fluidized bed processing time were found out. Then, the effect of fluidized bed treatment on surface properties of processed components was discussed. Surface morphology was found to be strongly affected and its evolution according to processing time was taken into account. Both compressive residual stresses and increased dislocation density were induced by treatment onto the external layers of samples and a significant hardening was detected. At last, the capability of fluidized bed processing was tested upon built ‘ad hoc’ fatigue samples. The way to rupture of fluidized bed treated and untreated samples was also discussed. At any rate, the fatigue behaviour of processed components was found significantly improved. This quite new and unprecedented result has been ascribed to the compressive residual stresses induced by Al2O3 embedding in the outmost surface layers of the aluminium alloy.