Microstructures and Elevated Temperature Mechanical Properties of As-extruded ZM61-Sn Alloys

Microstructures, elevated temperature mechanical properties and fracture mechanisms of the as-extruded ZM61-xSn (x=2, 4, 8, wt%) alloys were investigated by optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM) and high temperature tensile tests. The results reveal that the addition of Sn can refine microstructures and the refinement effect increases with the increase of Sn content. The average grain sizes of the as-extruded ZM61-xSn (x=2, 4, 8) alloys are 11, 8 and 4 μm, respectively. With the increasing of Sn amount, the strength of experimental alloys increases at first and decreases afterward. ZM61-4Sn alloy shows the highest strength, whose ultimate tensile strength and yield strength are 216 and 173 MPa tested at 180 °C, respectively. The ductility increases with the content of Sn increasing, and the elongation of as-extruded ZM61-xSn (x=2, 4, 8) alloys are 183.8%, 235.8% and 258.6%, respectively, when tensile temperature reaches 300 °C. The ZM61-4Sn alloy has the optimal coalescence of strength and ductility. The localized necking leads to the final fracture of the specimens and the micro-void coalescence is the main fracture mechanism. Incomplete dynamic recrystallization occurs when tensile tests are carried out at 260 and 300 °C.