Achieving gradient heterogeneous structure in Mg alloy for excellent strength-ductility synergy

Most metals including Mg alloys have a longstanding dilemma of strength-ductility trade-off, which is hindering their wider applications. In this study, we propose a gradient heterogeneous grain (GHG) structure for evading this trade-off dilemma and ultrasonic severe surface rolling is attempted to construct this novel structure in ZE41 Mg alloy. Here, the GHG structure combine the benefits of gradient structure and heterogeneous grain structure and introduce large microstructural heterogeneities. Compared to the coarse-grain and heterogeneous-grain structured alloys, the GHG structured one exhibits dramatical enhancement in strength, ductility, and strain hardening capability. To the best of our knowledge, its strength becomes much higher than that of common ZE41 Mg alloys at no reduction in ductility. These unique mechanical properties stem from not only the individual contribution of the heterogeneous structure components including the fine/ultrafine grains and deformed coarse grains but also their synergistic effect via hetero-deformation induced strengthening and hardening effects. In summary, our study provides a feasible way to develop new Mg alloys with high strength and good ductility.