In the present study,friction stir processing was used to modify 2024 Aluminium alloy microstructure and fabricate Al/SiC surface composites and Al/SiC/MoS 2 hybrid composite surface. For this purpose, tool traverse speed of 20 mm/min and tool rotational speeds of 1000, 1250, 1600 and 2000 rpm with 3° tool tilt angle were applied. In modified aluminium samples via FSP, substantial reduction of grain size from 50?m to 4 ?m in the stir zone were observed. In addition, erosion evaluation indicated the improvement of tribology properties in friction stir processed samples, although precipitates coarsening/ solutioning caused hardness decrease of stir zone. Tribology properties were more pronounced in lower tool rotational speeds which can be due to grain size reduction leading to higher hardness and slight coarsening and solutioning of precipitates. The effect of the direction of tool rotation changes on the distribution of reinforcement particles in each pass was evaluated. It was found that the direction of tool rotation change can result in more uniform distribution of reinforcement particles in each pass. Therefore, all the experiments were carried out in 4 passes with a change in the direction of tool rotation per pass. The highest tool rotational speed of 2000 rpm led to the greatest erosion properties in single component and hybrid composites. Lower hardness of these samples can be related to more coarsening and solutioning of precipitates due to high too rotational speed. However, improved erosion properties is attributed to more uniform distributed and finer particles. In similar tool rotational speed, despite higher hardness of single component composites with respect to hybrid composites, they demonstrated better tribology characteristics than Al/SiC surface composites owing to the presence of MoS 2 reinforcement particles, ductile and lamellar structure and acting as a solid lubricant and formation of a stable complex mechanical layer on the surface of hybrid composites. The investigation on erosive particles revealed that the dominant erosion mechanism in the modified and composites samples are adhesive and abrasive erosion of different severity, respectively. Key words : Friction stir processing, Tribological behavior , Hybrid composite, Mechanically mixed layer
