Creep strength of Mg-Y-Zn alloys containing long-period stacking ordered structures

Abstract

Magnesium (Mg) alloys reinforced with long-period stacking ordered (LPSO) structures exhibit considerable potential for achieving enhanced mechanical properties. Despite progress in understanding tensile and compressive deformation mechanisms at elevated temperatures, the comprehension of the creep behavior of theses alloys under varying conditions remains incomplete. The present study investigates the creep behavior of three Mg-Y-Zn alloys containing varying contents of LPSO structures under different temperature and stress conditions. The findings reveal that at 150 °C, the LPSO phase content has an insignificant effect on the creep resistance of the alloys. However, as temperature exceeds 200 °C, the creep resistance deteriorates with increasing LPSO phase content. Notably, at higher temperatures (300 °C), the alloys exhibit superplasticity during creep deformation, which is attributed to the diffusion of solute atoms facilitated through stacking faults within the LPSO structures. A creep constitutive equation was developed for temperatures between 150℃ and 200 ℃ and stress levels of 170-230 MPa, revealing high stress exponents (n=7.1-8.6) and low activation energies (Qc=80.98-90.63 kJ·mol-1) for the alloys. These results align with power-law dislocation creep, indicating threshold stress fields resulting from load transfer between the α-Mg matrix and the LPSO phase. After adjustment for the threshold stress, the stress exponents imply diffusional creep as the primary mechanism. The findings in this research contribute to understanding creep mechanisms in these alloys and offer insights into optimizing their performance for diverse applications.