Creep deformation mechanism and microstructure evolution of Mg-3Sm-0.5Zn-0.4Zr alloy

Creep resistance is a crucial requirement for utilizing magnesium in automotive powertrain components. The limited study on creep deformation mechanism and microstructure evolution in creep-resistant magnesium alloys has hindered their industrial applications. In the present work, the creep deformation modes and microstructure evolution under 200℃–250℃/60–100 MPa in Mg-3Sm-0.5Zn-0.4Zr alloy produced through permanent mold casting (PMC) and high pressure die casting (HPDC) were investigated via stress exponent (n) calculation, slip trace analysis, together with transmission electron microscopy (TEM) observations. The results indicate that the steady-state creep rates at 200℃/60 MPa were 1.4×10−9 s−1 for the PMC alloy and 1.1×10−9 s−1 for HPDC alloy, indicating excellent creep resistance for both. The HPDC alloy exhibited lower steady-stage creep rates than the PMC alloy at 200℃–250℃/ 60 MPa. At 200℃/60–100 MPa, basal slip was found to be the primary creep deformation mode for both alloys. At 225℃, basal slip dominated creep deformation when stress (σ) was less or equal to 80 MPa, while basal slip, non-basal slip, coupled with twinning accommodated deformation when stress exceeded 80 MPa. At 250℃/60–70 MPa, basal and non-basal slip dominated creep deformation in these two alloys. In addition, dynamic precipitation was observed in both the PMC and HPDC alloys. In comparison to the PMC alloy, the HPDC alloy displayed finer precipitates with increased density, potentially impeding dislocation motion. This characteristic may contribute to the superior creep resistance observed in the HPDC alloy. © 2024 Chinese Academy of Sciences. All rights reserved.