$Al2O3$ Graded Coatings on Aluminum Alloy Deposited by the Fluidized Bed (FB) Technique: Film Formation and Mechanical Performance

$Al2O3$ coatings have been deposited onto an Al alloy by the fluidized bed (FB) technique using alumina powder. Film formation through a cold deposition process and its growth kinetics have been investigated by varying the deposition time. This allowed us to establish how the morphology, microstructure, hardness, scratch resistance, and adhesion strength of the $Al2O3$ films were progressively imprinted. The FB process led to the deposition of a good-looking and well-adhered graded $Al2O3$ coating, which was found to be progressively richer in $Al2O3$ on moving from the interface with the Al alloy toward the outermost layers. The resulting $Al2O3$ coatings have been shown to produce a consistent improvement of the overall mechanical and tribological performance of the Al alloy, thus leading to the build-up of an overlying hard and tough protective layer.