The effects of friction stir processing (FSP) on the microstructure and mechanical properties of aluminum powder metallurgy (PM) parts were investigated. PM parts were subjected to FSP at advancing speeds (v) of 40-200 mm/min and tool rotational speeds (ω) of 800-1600 rpm. Microhardness (HV) and tensile tests at room temperature were used to evaluate the mechanical properties of the friction stir processed specimens. In order to evaluate microstructure of the processed zone, cross-sections of

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... e FS processed specimens were observed optically. Based on the results obtained from investigation of the Zener-Holloman parameter (Z), the average grain size decreased with decreasing the working temperature and increasing the working strain rate (equal to increasing Z). The finest grain size was ~ 5.4µm obtained at ω=1000 and v =100 mm/min corresponding to a strain rate of 27s-1 at 414 C . This sample exhibited the best mechanical properties with microhardness, yield stress, and tensile strength of 43 Hv, 82 MPa, and 118.3 MPa, respectively.