The effect of SiC nanoparticles on the friction stir processing of severely deformed aluminum

The 1050 aluminum sheets are severely deformed by two passes of the constrained groove pressing (CGP) process to obtain the strain of 2.32. Friction stir processing (FSP) is then performed on these specimens at two conditions of with and without SiC nanoparticles. Microhardness measurements indicate that in the state of FSP without any particle, the microhardness of stir zone is decreased due to the recrystallization and grain growth occurrence because of high stored strain energy in the CGPed specimens. In order to enhance the mechanical properties of the stir zone, SiC nanoparticles are used during FSP. Also, the effect of FSP pass number on the distribution of nanoparticles is investigated. Microstructure investigations reveal that after 1 and 2 passes of FSP with SiC nanoparticles, specimens experience brittle fracture at the retreating side of the stir zone during transverse tensile test due to the presence of clustered nanoparticles in this region. However, it is found that after 3 passes of FSP, SiC nanoparticles are uniformly distributed leading to the prohibition of grain growth in the stir zone. This can be responsible for the improvement of stir zone microhardness by about 118.8% with respect to the specimen FSPed without nanoparticles.