In this study, friction stir processing was used in order to produce hybrid surface composite by means of SiC and MoS 2 reinforcement particles on substrate of 7075 aluminum alloy. At first, to produce of Al7075/SiC p surface composite was determined the optimum parameters by means of design of experiment and optimization via taguchi method. The optimum parameters to fabricate Al7075/SiC p surface composite were determined in tool rotation speed of 1600 rpm, tool traverse speed of 25 mm/min and tool tilt angle of 3 ?. According to optimum conditions, effect of friction stir processing on mocristructure, microhardness and tribological behavior of 7075 aluminum alloy were investigated. The results showed that after friction stir processing the grain size in the stir zone decreased about 4 ?m rather than base metal. Also, investigation of tribological behavior showed more wear resistance in the processed sample in compared that base metal. Afterwards, effect of passes numbers on distribution of particles, hardness and wear behavior were investigated. The results showed that four passes friction stir processing created more uniform distribution of particles in the matrix. Also, hardness improved with increasing the passes numbers and most wear resistance are achieved in the surface composites fabricated by means of two passes with change in the rotation direction in each pass. Hard SiC particles develop some restriction such as their tendency to detachment from the matrix and created third-body abrasives as well as increase the wear rate of the counterface. Then, addition of solid lubricant particles along with hard particles further improves the tribological properties of these composites under sliding wear conditions. Thus, according to optimum parameters and use of two passes friction stir processing, hybrid surface composite was produced by means of same volume percent of SiC and MoS 2 reinforcements. Investigation of microhardness test showed that in the stir zone of hybrid surface composite the hardness increased rather than base metal. However, the magnitude of hardness decreased in compared that Al7075/SiC p . Investigation of worn surfaces of Al7075/SiC p /MoS 2 hybrid composite showed that wear resistance improved remarkably due to the presence of MoS 2 as solid lubricant and formation of stable mechanical mixed layer on surface. Keywords: Hybrid surface composite, Al7075, Friction stir processing, Microstructure, Tribological behavior.
