Synergistic impact of tool geometry and heat input on microstructure and texture development in friction stir processed AA6061-Graphene nanocomposites
Hesam Pouraliakbar, Hamed Jamshidi Aval, Mohammad Reza Jandaghi, Sang Hun Shim, Johan Moverare, Young Sang Na, Gholamreza Khalaj, Vahid Fallah
Abstract
The synergistic effect of tool geometry and process heat input on the microstructure and texture development of AA6061-Graphene nanocomposites through friction stir processing (FSP) was studied. The findings reveal that for composites fabricated with a tool having a pin cone angle (PCA) of 2.5°, increased heat input leads to a pronounced strain rate effect, resulting in finer recrystallized grains (3.0 ± 0.1 µm). Conversely, for composites produced with a PCA of 2°, reduced heat input enhances the uniform dispersion of graphene particles and lowers processing temperatures, yielding finer grains (1.8 ± 0.2 µm) in the processed zone. The fraction of low-Σ boundaries, such as Σ3, decreases after FSP relative to the base metal. However, for the composite with a PCA of 2.5°, a higher fraction of low-Σ boundaries (0.64 %) is observed at minimal heat input compared to the composite processed with a PCA of 2° (0.37 %). With increasing heat input, this trend reverses, and the fraction of low-Σ boundaries in the composite processed with a PCA of 2° reaches 1.26 %, surpassing that of the 2.5° (0.18 %). As the heat input rises from 2539 to 4528 J/mm, the density of low-angle grain boundaries (LAGB) in composites processed with a PCA of 2° increases from 15.8 % to 29.9 %. In contrast, for composites with a PCA of 2.5°, the LAGB density decreases from 31.2 % to 25.0 % as the heat input rises from 2543 to 4534 J/mm. FSP with a PCA of 2.5° enhances the intensity of the Q {013}< 2–31 > texture component with increasing heat input. However, in composites processed with a PCA of 2°, the trend differs, as increased heat input promotes the dominance of Rotate-Cube {001}< 1–10 > , Q, and B {111}< 1–10 > components.