A transversal segment of the base metal and the made composites is selected to measure and compare the hardness properties, as shown in Figure . Eleven indentation spots on this segment at every 3 mm distance from the center of the stir zone are determined for the test report The hardness profile of the base metal is more uniform than the profiles of processed samples. The grain refinement of composite samples is due to friction stir processing and the relatively consistent presence of alumina particles, which act as the nucleus and prevent grain growth during recrystallization . By examining the hardness of the samples before and after the process, it is observed that the hardness has increased in all processed cases. The associated reasons for this increase can be stated as follow: The trend of these curves shows the impact of friction stir processing on the hardness properties.