Effects of Si alloying on thermal deformation behavior, microstructure and mechanical properties of Mg-Y-Zn alloys with LPSO phase

Abstract

In this work, the effects of Si alloying on thermal deformation behavior, microstructure and mechanical properties of Mg-Y-Zn alloys are investigated through hot compression and hot extrusion. By hot compression, it shows that the addition of Si can bring better plastic processing properties to the Mg-Y-Zn alloy by reducing the thermal deformation activation energy from 268.85 kJ/mol to 133.23 kJ/mol and decreasing the work hardening index from 7.7 to 4.95. By hot extrusion, firstly, it reveals that as the addition of Si content increases from 0 to 2 (at. %), the microstructure of Mg-Y-Zn alloy underwent significant changes. The original 18R-LPSO phase gradually disappears, while the new YSi and Y₂MgSi₂ phases emerge. Secondly, the grain size and the degree of dynamic recrystallization (DRX) grains gradually increase as the addition of Si. Thirdly, although Si alloying can enhance the elongation from 4.8% to 23.9%, the strength decreases. Notably, the product of strength and elongation (PSE) of Mg_97.5Y₁Zn_0.5Si₁ alloy achieves the highest value, which is 5.707 GPa·%, suggesting a better balance of strength and elongation. Finally, the research combines with the finite element simulation (FEM) and phase field simulations, revealing that Si alloying facilitates grain growth and DRX by enhancing the heat of deformation. The YSi and Y₂MgSi₂ phases exhibit lower formation energies (-0.889 eV/atom and -0.681 eV/atom, respectively) compared to the 18 R long period stacking ordered (LPSO) phase (-0.0999 eV/atom), making them favorable to nucleate preferentially. Additionally, these YSi and Y₂MgSi₂ phases competitively consume Y atoms, thereby reducing the formation of the 18 R LPSO phase. This work demonstrates that Si alloying represents an effective strategy for synergistically enhancing the thermal deformation capacity, mechanical properties of Mg-Y-Zn alloys.