Mechanical properties and failure mechanisms of Mg-Zn-Y alloys with different extrusion ratio and LPSO volume fraction

In long period stacking ordered (LPSO) phase containing Mg-Zn-Y alloys, high elastic modulus and deformation kinks of LPSO phase considerably enhance the tensile yield strength, with slight detriment of or benefit to the ductility depending on its volume fraction. In present work, uniaxial tensile tests and fracture toughness tests are carried out using Mg99.2Zn0.2Y0.6, Mg97Zn1Y2, Mg89Zn4Y7 and Mg85Zn6Y9 (at%) materials with different extrusion ratios. Extrusion processing enhances both strength and ductility due to the recrystallization of Mg grains. Variable plastic deformation mechanisms are activated depending on volume fraction of Mg and LPSO phase as well as their relative size during bending. {101¯2}<101¯1¯> tensile twins in Mg grains and deformation kinks in LPSO phase are observed, which dissipate large amount of deformation energy favoring for toughness. However, inherently brittle LPSO phase is detrimental to toughness. Microstructure-motivated empirical models for yield strength and fracture toughness prediction based on rule of mixtures are calibrated by experimental data. Energy release rates of individual mechanisms are estimated, which quantitatively indicate strong Mg/LPSO interaction.