Mechanical alloying and phase transition of immiscible Al/Zn system during high-pressure torsion

Two half-disk samples of pure Al and pure Zn were mechanically alloyed via high-pressure torsion (HPT) processing, followed by post-deformation annealing (PDA). The microstructure evolution of the Al–Zn alloy was studied by scanning electron microscopy, transmission electron microscopy and molecular dynamics (MD) simulations. The results indicated that the HPT-processed Al/Zn assembly was presented as a mixture of nanocrystalline and amorphous phases. The deformation-induced special orientation of (0001)Al//(111)Zn facilitated the interatomic diffusion, and the dislocation density reached 2.17×1017 m−2 under the pinning effect of high solid solubility. Nanocrystalline, high diffusion degree, and high local dislocation density may primarily accounted for the crystalline-to-amorphous transformation in Al–Zn alloy. Moreover, the results indicated a bimodal grain size distribution of 150–250 nm and 500–900 nm, and Zn atoms were enriched at the grain boundaries, upon subsequent PDA. Under the effect of this special heterogeneous microstructure, the prepared alloy exhibited an excellent plasticity with 160% of tensile elongation.