Achieving ultra-strong Mg alloys via a novel hierarchical long-period stacking ordered architecture

Achieving high strength with heat resistance is a critical issue for Mg alloys. In the present study, we have successfully designed a novel hierarchical long-period stacking ordered (LPSO) architecture in the Mg-Y-Zn based alloy. The hierarchical LPSO is featured by a heterogeneous microstructure of ultra-fine grained (UFG) LPSO matrix and discrete LPSO lath domains at the microscale, and high-density in-situ Y-O-Si nano-dispersoids decorating the UFG-LPSO matrix at the nanoscale. The in-situ precipitation of nano-dispersoids in LPSO phase has been achieved for the first time to date. The hard UFG-LPSO matrix decorated with high-density stiff nano-dispersoids delivers the high thermal stability and ultrahigh strength of the alloys at both room and elevated temperatures, where the alloy with a UFG-LPSO fraction of ~71% acquires ultrahigh yield strength of 795 MPa and 428 MPa at room temperature and 250 °C, respectively. In addition, the elevated-temperature strength can be further improved after extrusion via texture strengthening. Meanwhile, the soft LPSO lath domains in the heterogeneous microstructure undertake the plastic deformation via kinking, contributing to the compressive plasticity at room temperature. The ultrahigh strength, thermal stability combined with low density and excellent specific properties of the present hierarchical LPSO alloys demonstrate a potential microstructural strategy to design lightweight high-strength Mg alloys for advanced structural applications.