Superplasticity of Al-Zn-Mg-Cu composite containing uniform TiB2 nanoparticles

An Al-Zn-Mg-Cu composite with the elongation of 557% at 450 degrees C and 1 x 10(-3) s(-1) was achieved by introducing TiB2 nanoparticles as reinforcement. On the one hand, TiB2 nanoparticles trigger the recrystallization of Al during annealing, resulting in a fine-equiaxed grain (2.1 mu m) structure. On the other hand, TiB2 nanoparticles can effectively enhance the thermal stability of the composite by pinning grain boundaries. The post-mortem microstructure remains fine-equiaxed grains (2.8 mu m) even at 450 degrees C. The undulated grain boundaries suggest that the deformation is controlled by the grain boundary sliding (GBS) mechanism. Furthermore, the strain rate sensitivity of 0.32 and the deformation activation energy of 164 kJ.mol(-1) demonstrate that the GBS is accommodated by lattice diffusion during deformation. The stress at grain boundaries might also be released by the locally melted Mg-rich phases, which promoted GBS while prevented cavitation.