β-phase dynamic precipitation and its effect on creep behavior in heterogeneous-grained AZ-series alloys

The effect of β -phase precipitation on the creep behavior of AZ-series magnesium alloys with heterogeneous grain structures was investigated using AZ31 and AZ61 alloys with comparable coarse-fine grain morphologies but different Al contents. Creep tests performed at 200 °C and 50–100 MPa show that AZ61 exhibits significantly improved creep resistance, with a steady-state creep rate of (9.1 ± 0.1) × 10 -8 s -1 at 200 °C/50 MPa, nearly two orders of magnitude lower than that of AZ31. Microstructural analysis reveals distinct dynamic precipitation behaviors during creep. In AZ31, only sparse granular β -Mg₁₇Al₁₂ particles form mainly at grain boundaries, providing limited resistance to dislocation motion. In contrast, AZ61 develops a high density of fine continuous precipitates (CPs) within coarse grains, together with discontinuous precipitates (DPs) at grain boundaries. The intragranular CPs effectively pin dislocations, suppress dynamic recrystallization, and reduce stress concentration at coarse–fine grain boundaries, leading to more homogeneous deformation. Thus, this enables heterogeneous grain microstructure to exhibit high creep performance at medium-to-high temperatures. These results highlight the critical role of dynamic precipitation morphology in regulating dislocation activity and creep deformation of magnesium alloys with heterogeneous grain microstructure, providing valuable insights for the microstructural design of heat-resistant magnesium alloys.