Effect of post-deformation annealing on the microstructure and micro-mechanical behavior of Zn-Mg hybrids processed by High-Pressure Torsion

Heterostructured metals have attracted increasing interest because of their unique capability to overcome the strength-ductility tradeoff typically observed in engineering materials. Here, a new strategy for synthesizing heterostructured Zn-Mg hybrids is proposed via high-pressure torsion (HPT) followed by post-deformation annealing (PDA). Experimental results indicate a transition from a relatively homogenous nanograined structure after HPT, to a heterogeneous microstructure, containing a distribution of Mg2Zn11 and MgZn2 intermetallic nanoprecipitates, upon subsequent PDA. This led to a simultaneous increase in hardness and strain rate sensitivity. The observed three-regime strain hardening behavior was suggested to be due to the activation of multiple strengthening mechanisms, including grain refinement, in-situ precipitation, and back-stress strengthening associated with geometrically necessary dislocations. Thus, the mechanical response of Zn-Mg hybrids may be tailored to obtain the desired response for task-specific applications.