Effects of heat treatments on hot deformation behaviors of the Mg-8Gd-3Sm-0.5Zr alloy

Abstract

The Mg-8Gd-3Sm-0.5Zr alloy was fabricated using a casting method. The experimental materials were an as-cast, solution treatment (T4), solution and aging treatment (T6) state. Hot deformation tests were performed in the strain rate range of 0.002 ∼ 0.1 s−1 at temperatures in the range of 350 °C ∼ 500 °C. The relationships between the true stress and true strain and the deformation activation energy and the microstructure of the tested alloy were studied. The influence of different heat treatments on the hot compression behavior was researched. A processing map was used to analyze the feasibility of the hot working of the Mg-8Gd-3Sm-0.5Zr alloy. The results indicate that the deformation activation energy of the T6 state alloy (264.423 kJ mol−1) was higher than that of the T4 state alloy (213.693 kJ mol−1). This difference is due to the precipitation of β′-Mg5Gd during the aging process. The as-cast alloy had a higher deformation activation energy (252.589 kJ mol−1) due to the eutectic structure along the grain boundary. The dynamic recrystallization (DRX) grain sizes of the T4 state alloy and the T6 state alloy are finer than that of the as-cast alloy. The average grain size for DRX (500 °C, 0.01 s−1) was 10 μm and 15 μm, respectively. The T4 state alloy exhibited a better workability than the as-cast alloy and the T6 state alloy. The optimal processing parameters for the T4 state alloy were determined.