CALPHAD-guided design of Mg-Y-Al alloy with improved strength and ductility via regulating the LPSO phase

This work performed a CALPHAD-guided design strategy to develop high strength-ductility Mg-Y-Al alloy by taking advantage of the strengthening effect of the LPSO phase and the ductilizing effect of the alpha-Mg matrix. To achieve this goal, the LPSO phase content and the Y content in the alpha-Mg matrix were quantitatively optimized via calculations of the isoplethal section and phase fraction diagrams. Based on this, three typical Mg-Y-Al alloys without the LPSO phase and with varying LPSO contents were designed. The strength of the alloys was significantly improved by the introduction of the LPSO phase and the increase in its content. However, the ductility of the alloy was maintained while increasing the LPSO content. Through analyzing the strengthening and ductilization mechanisms, it was revealed that the LPSO phase can strengthen the extruded alloys by refining the dynamic recrystallized grain size, exerting a short-fiber-like strengthening effect, and dislocations strengthening effect by hindering dislocations movements. The ductile alpha-Mg phase with considerable Y content can effectively withstand plastic strain by operating multiple slips during the deformation, significantly improving the ductility of the material. The results of this study inspired the development of an effective design strategy to produce high strength-ductility Mg-Y-Al alloys by quantitatively optimizing the LPSO phase and Y contents in the alpha-Mg matrix, as well as to design high-performance Mg alloys for engineering demands in the future.