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 2.82μm at topest surface layer to 6.11μm 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.