Study of tensile properties of Mg-rare earth alloys at cryogenic temperatures

Abstract

To evaluate the effects of cryogenic temperatures on mechanical properties of a thermo-mechanically treated Mg-rare earth (RE) alloy, tensile tests were carried out from room temperature to liquid nitrogen temperature (LNT) to study the deformation and fracture behavior of the selected magnesium alloy. The results showed that the ultimate strength and yield strength increased while elongation decreased as the testing temperature decreased. The as-forged specimen exhibited higher strength and ductility than the aged specimen. Further scanning electron microscopy (SEM) investigation and optical observation illustrated that the deformation mechanism of the Mg-RE alloy changed from slip to twinning with a decrease in testing temperature. Furthermore, the fracture of tensile specimen transformed from boundary to twin plane as observed by SEM. The brittleness of the second phase at cryogenic temperature is taken into account in discussing the transition of the fracture mode of the Mg-RE alloy from intergranular to transgranular with the decrease of temperature.