Evolutions of CuZn5 and Mg2Zn11 phases during ECAP and their impact on mechanical properties of Zn–Cu–Mg alloys

For the purpose of designing high strength and high ductility Zn–Cu–Mg biodegradable alloys, this study systematically investigated the evolutions of CuZn5 and Mg2Zn11 s phases during equal channel angular pressing (ECAP) with gradually increased deformation strains, as well as their impact on the mechanical properties of Zn–1Cu-0.5 Mg and Zn–3Cu-0.5 Mg alloys. The obtained results showed that the as-cast Zn–1Cu-0.5 Mg alloy contained η-Zn matrix and η-Zn + Mg2Zn11 eutectic structure, while the as-cast Zn–3Cu-0.5 Mg alloy is composed of η-Zn matrix, Zn–Mg eutectic structure, and coarse primary CuZn5 phase. Although the primary CuZn5 phase was refined to some extent after ECAP, some large ones remained. The eutectic structure was quickly crushed into ultra-fine Mg2Zn11 particles, and sub-micron CuZn5 precipitates were dynamically precipitated within the matrix of both alloys during ECAP. Moreover, the refined Mg2Zn11 particles and CuZn5 precipitates were not mixed, but formed the η-Zn + Mg2Zn11/η-Zn + CuZn5 bandlike distribution. ECAP simultaneously improved the strength and ductility of two alloys, and the softening behaviors with more ECAP strains were alleviated to some extent with Mg addition. The high strength of ECAP alloys was mainly resulted from the fine grain strengthening, Mg2Zn11 particles strengthening, and hetero deformation-induced (HDI) strengthening by the bimodal grain size distribution and bandlike distribution. Improvement in softening resistance should be ascribed to the formation of ultra-fine Mg2Zn11 particles which are effective to promote the aggregation and proliferation of dislocations