Understanding the High Strength and Good Ductility in LPSO-Containing Mg Alloy Using Synchrotron X-ray Diffraction

Abstract

Mg alloys containing long-period stacking-ordered (LPSO) phases often display excellent mechanical properties. The underlying mechanism is yet unclear. In this work, in situ synchrotron X-ray diffraction was employed to study tensile deformation of a Mg₉₇Y₂Zn alloy that contains 18R-type LPSO phase. From lattice strain measurement, it is found that the LPSO phase has a similar elastic modulus as Mg. After material yielding, lattice strain in the Mg phase decreased, while lattice strain in the LPSO phase increased further. By analyzing the lattice strain evolution of different Mg peaks, basal slip and deformation twinning are identified as the dominant deformation mechanisms. This finding is further confirmed by surface slip trace analysis using electron backscattered diffraction (EBSD). Additional analysis of diffraction peak broadening indicates a continuous increase of dislocation density during plastic deformation. Based on the above results, it can be concluded that the interdendritic LPSO phase behaves like a reinforcing phase that directly strengthens the material. The high tensile ductility of the material is attributed to the weak extrusion texture caused by the presence of interdendritic LPSO. In addition, small LPSO plates inside the Mg phase can serve as dislocation nucleation sites, which leads to a high work hardening rate in the material.