Giant hardening and formation of nanograined supersaturated solid solution in Al-Zn system

Grain refinement via severe plastic deformation (SPD) can induce the decomposition of Al-Zn supersaturated solid solution, resulting in strain softening rather than hardening. So far, it is very challenging to improve the strength of binary Al-Zn alloy by refining grains through SPD. Herein, a single-phase supersaturated solid solution nanostructure with relaxed grain boundaries has been successfully generated in Al-21.7 at% Zn alloy by cryogenic high-pressure torsion. Instead of softening, giant hardening is achieved. The nanocrystalline Al-Zn alloy with grain size of 15 nm has an ultrahigh yield strength of about 642 MPa.