Friction stir vibration processing: a new method to improve the microstructure and mechanical properties of Al5052/SiC surface nanocomposite layer

Friction stir processing (FSP) is a surface processing method to modify the microstructure and enhance the mechanical properties of metal surface. This process is also numerated as a method to incorporate second-phase nanoparticles into microstructure and form surface composites. In the current research, the work specimen is vibrated normal to processing line during FSP. Transverse and rotation movements of shoulder are accompanied with vibration motion of specimen. This new process is entitled FSVP (friction stir vibration processing). The effect of FSP and FSVP processes on microstructure and mechanical properties of Al5052 alloy matrix composite incorporated SiC nanoparticles is analyzed. The results show that the presence of vibration during FSP leads to the grain size decrease in the stir zone and it enhances the homogeneity of particle distribution. The results indicate that strength and ductility of friction stir (FS) processed specimens are lower than those processed by FSVP. These are related to increased deformation and strain of soft material in the stir zone as vibration is applied which promotes the dynamic recovery and recrystallization during FSP. The results also imply that the microstructure is refined more and the strength and the hardness of friction stir vibration (FSV) processed specimens increase as vibration frequency enhances.