en Research Paper Research Paper Friction-Stir Processing (FSP) was applied on AA1050 Aluminum Alloy (AA) to find the highest mechanical properties among 28 combinations of the rotational and traverse speed (800-2000 rpm and 50-200 mm.min^-1) and four different tool probe shapes (threaded, columnar, square and triangle). To this aim, the AA standard sheet went through a single pass of FSP. The 1600 rpm and 100 mm.min^-1with threaded tool probe was chosen as the best combination of rotational and traverse speed. Grain size at the Stirred Zone (SZ) was studied using Optical Microscopy (OM). The results showed that the SZ’s grain size was refined from 30 μm down to about 12 μm due to dynamic recrystallization during FSP. The processed sample exhibited improved hardness, yield stress, ultimate tensile strength, elongation up to 65, 80, 66, and 14%, respectively, compared to the annealed AA sample. Studying fractographic features by OM and field emission scanning electron microscope (FESEM) revealed a dominantly ductile fracture behavior. friction stir processing,AA1050 aluminum alloy,tool probe shape,grain structure,mechanical properties,rotational and traverse speed. 1 11 http://ijmse.iust.ac.ir/browse.php?a_code=A-10-3235-1&slc_lang=en&sid=1 Mahdi Alishavandi Mahdi.alishavandi2015@student.sharif.edu 1800319475328460014674 1800319475328460014674 Yes Sharif University of Technology Mahnam Ebadi ebadi.mahnam@gmail.com 1800319475328460014675 1800319475328460014675 No Shiraz University Amir Hossein Kokabi Kokabi@Sharif.edu 1800319475328460014676 1800319475328460014676 No Sharif University of Technology