Localised surface modification of high-strength aluminium–alumina metal matrix composite coatings using cold spraying and friction stir processing

This study presents a novel approach for surface repairs of high-strength, cold-worked aluminium (Al) alloys, without negatively affecting the base material strength. Low-pressure cold spraying was used to fabricate Al–Al 2 O 3 metal matrix composite overlays, with varying concentrations of Al 2 O 3 deposited on an Al alloy. Friction stir processing (FSP) was employed to disperse and consolidate the overlay coating on the base material. The FSP was found to improve the Al 2 O 3 particle distribution in the coating and reduce the mean free path between Al 2 O 3 particles. The coating hardness increased after FSP. The post-FSPed overlays also exhibited lower wear rates compared to the as-sprayed condition. Remarkable improvement was observed in the tensile properties of the coatings, which were attributed to the improved dispersion of Al 2 O 3 particles in the matrix, while the enhanced ductility was attributed to the possible grain refinement that occurred due to the recrystallisation of Al during FSP.