Mechanical properties and yield asymmetry of Mg-Y-Zn alloys: Competitive behavior of second phases

Microstructure and mechanical properties evolution of as-cast Mg-Y-Zn alloys have been systematically investigated with various phase types via adjusting Y/Zn ratio. The results show that the investigated alloys have typical a-Mg dendritic microstructure with different intermetallic compounds including I phase, I + W phases, W phase, LPSO + W phases and LPSO phase. Phase evolution in Mg-Y-Zn alloys is analyzed in detail combining microstructure observations and differential scanning calorimetry results. Strengthening effects of mechanical properties with five different compositions indicate that the second phase strengthening is the main strengthening mechanism, and that the contribution follows the order of W > I + W > LPSO + W > I > LPSO. Based on transmission electron microscopy analysis, the lamellar W phase effectively hinders dislocation movement compared to other phases, and alloys with W phase exhibit high strength. LPSO phase shows fracture and kink bands during tension and compression, respectively, which leads to evident yield asymmetry (> 1.1) in alloys containing LPSO. Other alloys with I or W phase have a yield anisotropy around 1.0. The tensile property of Mg-Y-Zn alloys is enough for mechanical design.