The present study uses Al2O3, graphite and hybrid Al2O3 and graphite nanoparticles as reinforcement particles within AA 6061 to produce a surface composite metal matrix using multiple-pass FSP. The aim of this work is to investigate the effects of multi-pass FSP, type of reinforcement particles and effects of T6 post-treatments on the microstructure and mechanical properties (hardness, ultimate tensile strength, and elongation) of friction stir processed (FSPed) AA6061 alloy. The results show that; all the composites produced using alumina particles in matrix material have the highest ultimate tensile strength (213 Mpa). Increase in hardness of stir zone for FSPed samples was more pronounced with post heat treatment and essentially insignificant for variation in a number of passes. The process parameters were optimized using a Taguchi method. The most influential parameter was a type of reinforcement particles. The analysis of variance (ANOVA) used to evaluate the percentage contribution for each parameter.