Multimodal Microstructure of Mg-Gd-Y Alloy Through an Integrated Simulation of "Process-Structure-Property"

Rare earth Mg alloys containing Gd elements can be used in aerospace, automotive, and other industrial fields owing to their high strength and creep resistance at room and high temperatures. However, the poor ductility of Mg alloys limits their application. Recently, it was discovered that the ductility of Mg alloy can be improved without compromising on its strength if sufficient amount of coarse grains is distributed in fine grains. In this study, taking the Mg-8Gd-3Y-0.5Zr (GW83K) alloy as an example, an approach for optimizing multimodal microstructures was investigated, which aimed to improve the mechanical properties of alloys. An alloy with a multimodal grain structure can be used as a particulate compound model, in which the grain boundary is considered the matrix, and different-sized grains are treated as different-types of particles embedded into the grain boundary matrix. A 2D finite element micromechanics model combined with Taylor-based nonlocal plasticity theory, which considers the size effect of the particles, was established to simulate the mechanical response of the multimodal structure Mg alloy in a tensile test. The model was verified through the experimental data of the stress-strain curve. Moreover, the effects of process parameters on the mechanical properties of the GW83K alloy were further evaluated by combining the grain structure under different annealing processes, simulated from a real spacetime phase-field model as the geometric input of the finite element model. Finally, the relationships between the annealing parameters, multimodal structure, and mechanical properties of the GW83K alloy were described. The results show that the yield and tensile strengthes of the multimodal GW83K alloy presented a Hall-Petch relationship with the average grain size. The content and distribution of coarse grains greatly affected the plasticity of the GW83K alloy. By annealing the GW83K alloy at 623 K for 90 min, better plasticity could be achieved without sacrificing strength, which is helpful in promoting multimodal microstructural design.