Effects of friction stir processing on the microstructure and superplasticity of in situ nano-ZrB2/2024Al composite

In this study, in situ nano-ZrB2/2024Al composites fabricated from 2024Al-K2ZrF6-KBF4 system were processed by friction stir processing (FSP) to achieve superplasticity of the composites. And the effects of particle contents (1 wt%, 3 wt%, 5 wt%), matrix grain size (micron or sub micron), strain rates (5 x 10 (3) s (1), 1 x 10 (2) S (1), 2 x 10 (2) S (1)) and deformation temperatures (400 K, 480 K, 600 K, 700 K, 750 K) on the superplasticity of the composites were investigated. After the friction stir processing, the coarse grains of the cast composites with matrix grain size of about 80-100 mu m and nano-ZrB2 reinforcement size of 30-100 nm were crushed into small grains about 1 m in size, and the uniformity of the nano-ZrB2 reinforcements was also improved. And under the same superplastic tensile testing condition at the temperature of 750 K and strain rate of 5 x 10 (3) s (1), the FSP nano 3 wt%ZrB2/2024Al composite exhibited an superplastic elongation of 292.5%, while the elongation of the corresponding cast composite was only less than 100%. Meanwhile, the in values of the FSP composites were always higher than the cast composites, especially the FSP composites with 3 wt% particles has the in value of 0.5321 i.e., the FSP composites should had better superplastic properties than cast ones. Furthermore, the FSP composites had higher apparent deformation activation energy (Q) than that of the lattice diffusion of pure aluminium, indicating that the deformation mechanisms of the FSP composites should be grain boundary sliding mechanisms. (C) 2016 Chinese Materials Research Society. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (hap:tic:read,* ecomtnons.orgilicenses/by-nc-nd/4.0/).