Uniaxial Tensile And Compressive Deformation Behaviouts Of AZ31B Magnesium Alloy At Cryogenic Temperatures

In this study, the uniaxial tensile and compressive deformation behaviors of the as-extruded and heat treated AZ31 magnesium alloy at different temperatures(from room temperature to-196 ° C) were investigated respectively by use of electronic universal testing techniques. And the deformation microstructure and fracture features of the studied AZ31 magnesium alloy have been carefully examined by means of optical and electron microscopes.It is shown that the tensile properties of AZ31 magnesium alloy is affected by tension temperature. The tensile strength of either the extruded or the heat treated AZ31 magnesium alloy increased, while the elongation decreased, with the decrease in tension temperature. At the same tension temperature, the extruded Φ8mm AZ31 alloy rod displayed the highest tensile strength and the lowest elongation. After annealing or solution treatment, the strength and elongation of Φ16 mm AZ31 alloy rod was found to increase. The tensile fracture of macroscopic and microscopic observation results found that the fracture of extruded and heat treated AZ31 magnesium alloy at room temperature belongs to ductile fracture. As decreased to-196 ° C, the fracture mode changed to quasi cleavage characteristic of ductile fracture. The fractured Φ 21 mm AZ31 alloy rod exhibited ductile fracture characteristics such as dimple and torn edges,while the Φ 8 mm AZ31 alloy rod gave the obvious quasi cleavage characteristics such as cleavage step. After annealing or solution treatment, the dimples density was found to increase on the Φ 16 mm rod fracture surface which still kept the cleavage fracture characteristics at-196 ° C. The examination results indicated that the twin density decreased in the deformation region near the tensile fracture surface of the extruded or heat treated AZ31 magnesium alloy with decreasing tensile temperature, implying the formation of deformation twin was inhibited at cryogenic temperature. It was also found the twin density is higher in the Φ 21 mm rod than in the Φ 8 mm rod due to easy formation of twin in large size grain. After heat treatment, the twin quantity and size was seen to reduce in the in the Φ 16 mm rod.The low temperature uniaxial compression test results of the extruded and heat treated AZ31 magnesium alloy show that the compressive strength and yield strength ofthe examined alloy increased with decreasing temperature. The twin density was found to decrease obviously in the compressive AZ31 magnesium alloy with decreasing deformation temperature. Nearly no twin was observed in the extruded Φ 8 mm rod due to the fine grain size. Within the deformation region of the heat treated Φ 16 mm AZ31 magnesium alloy rod, formation of flow layer could be obviously found because the direct compression in the perpendicular direction. The tensile and compressive yield asymmetry was still found either in the extruded or heat treated AZ31 magnesium alloy as deformed at low temperatures, which become more remarkable with decreasing temperature and reduction of grain size. It was also found that annealing or solution treatment nearly had no effect on reduction of the tensile and compressive yield asymmetry in the Φ 16 mm AZ31 magnesium alloy rod examined in current study.