Dynamic Young's Modulus and Internal Friction of Magnesium Alloys with Varying Fractions of LPSO Phase

Abstract

Internal friction in magnesium alloys with a varying volume fraction of the long-period stacking-ordered (LPSO) phase was investigated using polycrystalline Mg-Zn-Y alloys with the aim of elucidating the initial dislocation dynamics. The phase composition and microstructure were characterised via electron microscopy and X-ray diffraction. Results show that Young’s modulus and the temperature-dependent modulus softening scale nearly proportionally with LPSO content, highlighting its strong influence on both elastic and damping properties. The most pronounced softening occurs the single-phase fully LPSO alloys, likely due to their intrinsic characteristics and impact on mobile dislocation density. Internal friction measurements reveal that amplitude-independent damping increases with LPSO content, while the critical strain amplitude for amplitude-dependent damping decreases. Notably, the critical stress for dislocation motion is significantly lower than the characteristic CRSS for basal slip, emphasising the crucial role of thermal activation in dislocation liberation at very low applied cyclic stresses/strains.