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-Al2O3 metal matrix composite overlays, with varying concentrations of Al2O3 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 Al2O3 particle distribution in the coating and reduce the mean free path between Al2O3 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 Al2O3 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.