Hot tensile deformation and fracture behavior of ultrafine-grained AZ31 magnesium alloy processed by severe plastic deformation

摘要

Parallel tubular channel angular pressing (PTCAP) process as a novel intense plastic deformation method was applied to an AZ31 magnesium alloy tubes to achieve an ultrafine grained (UFG) structure. Tensile tests at different temperatures of 25 ℃, 350 ℃, 400 ℃ and 450 ℃ were done on UFG AZ31 samples processed by multipass PTCAP process. The results showed that the second passes PTCAP processed specimen exhibits the best elongation of about 263% at a temperature of 400 ℃. Fractured tensile samples were metallurgically characterized to analyze the fracture mechanism. The result indicated a decreasing trend in the average grain size along the gripper section to failure tip of the fractured UFG sample. However, the hardness increases from gripper region to the end of gauge region near the fracture tip. However, at the fracture tip, hardness collapsed because the cavity and microvoids formed in this area during tensile deformation. Fractographic SEM images illustrated the mix ductile and brittle fracture modes at tensile temperatures of 350 ℃ and 450 ℃. Though, completely ductile fracture mode with distinguishable dimples was seen at the UFG sample fractured at 400 ℃.