Achieving large-scale gradient structure in the AZ31 magnesium alloys for extraordinary strength-ductility synergy by hard plate rolling

It was an indisputable fact that the gradient structure was used to realize the double improvement on material strength-plasticity, but the thickness of the gradient structure could only be maintained at the micron level. Therefore, based on the idea of non-uniform force, the magnesium (Mg) alloy double-layer plates with symmetrical gradient distribution whose microstructure could span the thickness of the plate was prepared by hard plate-rolling technology. The grain size gradually increases from 2.82 µm at topest surface layer to 6.11 µm at center layer along the thickness direction of the plate, and finally ends with a twin layer in the central layer. The experimental results show that the gradient plates prepared by hard-plate rolling can improve strength and plasticity. The ultimate tensile strength (UTS) is 278.6 MPa and the ductility can reach 20.6%. Surprisingly, compared with other micron-sized gradient plates, the plasticity of large-sized gradient plates prepared in this study increases by 30%. Our work further proves that this heterogeneous Mg alloy sheet with extraordinary mechanical properties originates from its plastic incompatibility and abundant twin interactions. The hard-plate rolling process provides a new idea for the preparation of high-performance structure gradient plates.