Achieving exceptional strength and ductility combination in a heterostructured Mg-Y alloy with densely refined twins

Metals and alloys with heterogeneous microstructures are an emerging class of materials that exhibit exceptional mechanical properties, owing to the novel scientific principle of hetero-deformation induced (HDI) strengthening and hardening. For magnesium alloys, due to their low recrystallization temperature, poor ductility at room temperature, limited cold workability, and the tendency to generate strong basal texture during deformation, it is difficult to obtain heterostructures without relying on precipitation of the second phases. Here, three heterostructured Mg-2.9Y (wt.%) materials with varying accumulative equivalent true strains, i.e., 5%-5 cycles, 7.5%-5 cycles, and 10%-5 cycles materials were fabricated via applying five complete triaxial compression cycles to the bulk alloy. The 5%-5 cycles material with an accumulative equivalent true strain of 0.37 is featured with long twin lamellae embedded in coarse grains. When the accumulative true strain increases to 0.72, a heterogeneous structure composed of long and short twin lamellae is formed inside the 7.5%-5 cycles material. As the equivalent true strain further increases to 1.01, the 10%-5 cycles material exhibits a mixed structure with densely refined twin lamellae embedded in the coarse-grained matrix. The room-temperature uniaxial tensile tests show that the yield strength of the materials processed by triaxial cyclic compression (TCC) has been significantly improved compared to that at the initial state, whereas ductility was not significantly sacrificed without the subsequent heat treatment. The dense and refined twin lamellae that serve as hard domains in this material provide a high density of interfaces and impede dislocation motion effectively. This results in significant HDI strengthening and hardening. These findings provide new insight into the design of heterostructured hexagonal close-packed materials with both high strength and good ductility.