Fracture Mechanism Analysis of Mg-9Gd-4Y-0.6Zr Alloy from -196℃ to 400℃

The fractography of Mg-9Gd-4Y-0.6Zr alloy specimens which were tensioned at different temperatures was observed by optical and scanning electron microscopy, respectively. The results showed that different slip systems were activated at different temperatures, which was responsible for varied deformation mechanism and fracture mechanism. At 25℃, the number of enabled slip systems were few and only slip systems on basal plane were activated, and transgranular cleavage fracture was observed. At -196℃,the number of enabled slip systems increased, prismatic slips maybe occurred and low-temperature plasticity phenomenon happened, while fracture mechanism was microviod coalescence fracture. At 250, 300℃ and 350℃, multisystem slips on basal planes, prismatic planes and pyramidal planes were activated in this alloy, while fracture mechanism was also microviod coalescence fracture. At 400℃, recrystallization happened and grain-boundary sliding in new fine recrystallized grains could deform easily,which was called coarse-grain superplasticity phenomenon, and intergranular shear fracture took place.