Thermal stability of aluminum after friction stir processing with SiC nanoparticles

In this research, 1050 aluminum sheets in the conditions of annealed and severely deformed by 2 passes of constrained groove pressing (CGP) process were used. Two passes of friction stir processing (FSP) were applied on the specimens. Also, another CGPed specimen was processed by 2 passes of FSP using SiC nanoparticles . The samples were then heat treated to study thermal stability of base metal, heat affected zone (HAZ), thermo-mechanically affected zone (TMAZ), and stir zone (SZ). Microstructure examinations revealed that the annealed base metal was relatively stable upon heating even up to 400 °C and a little grain growth was evident. On the other hand, the CGPed base metal was fairly stable just up to 200 °C. It was also observed that HAZ and TMAZ of annealed specimen exhibited some grain growth while for CGPed sample, these regions experienced recrystallization and subsequent grain growth during heat treatment. It was found that the SZ of annealed and CGPed specimens remained fine after heat treatment even up to 400 °C and slight grain growth occurred. Microstructural assessments revealed that using SiC nanoparticles during FSP had a potential to form finer grain structure at SZ compared with that in specimen FSPed without any particle. Also, it was found that SiC nanoparticles could hinder grain growth during heat treatment provided that a suitable distribution nanoparticles was formed.