J. Jafari - School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran
M. K. Besharati Givi - School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran
M. Barmouz - School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran

Friction stir processing (FSP) is a method that causes severe plastic deformation leading to microstructural modification and improvement of mechanical properties of materials. In this study, microstructural and mechanical properties of pure copper were improved by FSP and also effect of changing the tool shoulder diameter on the mentioned properties above was evaluated. Two different tool shoulder diameters were used in this study (12,20mm). Optical microscopy and scanning electronic microscopy were used for microstructure evaluation of friction stir processed (FSP) specimens. Results show that the grain size of stir zone in the specimens FSPed by smaller tool shoulder reduced more significantly compared to those one FSPed by bigger one due to the lower heat input. Also the reduction of grain size and heat input led to 37% increment in the microhardness values of specimen produced by tool shoulder diameter of 12 mm than those of produced by 20 mm tool shoulder diameter.

FSP, Copper, Microstructure, Microhardness