The Effect of SiC Nanoparticles and Liquid Nitrogen Medium on Microstructure Evolutions of Severely Deformed Al During Friction Stir Processing

The severely deformed 1050-aluminum sheet was processed by friction stir processing (FSP) at different conditions of processing without nanoparticles in the ambient temperature and with SiC nanoparticles in the liquid Nitrogen medium. Microstructural assessments indicated that the appropriate distribution of SiC nanoparticles was obtained after 3-passes of FSP. In addition, electron backscattered diffraction (EBSD) analysis manifested that using nanoparticles along with the liquid Nitrogen medium during FSP was able to prevent the intense grain growth in the stir zone which occurred in the case of FSP without nanoparticles in the ambient temperature. Neither the orientation of grains nor the mechanism of grain formation in the stir zone was different comparing two mentioned FSP conditions. The mechanism of grain formation in the stir zone was determined to be dynamic recovery (DRV) and continuous dynamic recrystallization (CDRX) phenomena. However, discontinuous dynamic recrystallization (DDRX) mechanism was also evident in the limited extent in the case of FSP with SiC nanoparticles in the liquid Nitrogen medium. The microhardness results showed that the simultaneous use of SiC nanoparticles and liquid Nitrogen medium during FSP caused to the significant improvement in the mechanical properties of the stir zone.