Creep behavior and microstructure evolution of heat-resistant Mg-Sm-Yb-Zn-Zr alloy

Abstract

In this work, we investigated creep behavior and microstructure evolution of cast Mg-4Sm-2Yb-0.6Zn-0.4Zr alloy. The alloy exhibited temperature-dependent stress exponents (n = 4.7, 5.8, and 7.2 at 200, 225, and 250 °C, respectively) and high creep activation energies ranging from 112 kJ/mol to 504 kJ/mol. Given the considerable influence of the temperature on the minimum creep rate, a normalized stress exponent of ∼4 was derived, implying that dislocation creep was operative. Abnormally high creep activation energies could be associated with the thermally stable intermetallic at grain boundaries and high density of precipitates within the α-Mg matrix. An analysis of the dislocation substructure confirmed that the main creep mechanisms were both cross-slip and climb of <a> dislocations. During creep, the precipitation of both prismatic β phases and basal γ’’ phases in the α-Mg matrix formed closed volumes, effectively arresting dislocations and contributing to the higher creep resistance than the majority of creep-resistant Mg alloys, such as traditional Mg-RE-based cast alloys and die-cast Mg benchmark alloys.