Low-temperature Mechanical Behavior Of Commercial Wrought Magnesium Alloys

Magnesium alloy, a well-known lightweight alloy, has considerable potential in fabricating aeronautics, missiles, spacecraft and satellites as aerospace industry structural material on account of its low density and high strength/weight. However, for the aerospace constructions, it is necessary to take account of resisting not only strong magnetic and radiation environment, but also require materials can withstand low temperature in space. Mechanical properties of magnesium alloys were commonly investigated at room temperature or above, while there have been few studies reporting such investigations below room temperature. In order to expand the utilization of traditional magnesium alloys, it has the positive significance of studying the deformation behavior of some wrought magnesium al oys at low temperature.In this work, the deformation behavior and fracture mechanism of AZ31 magnesium alloy sheet and AZ61, AZ80, ZK60 magnesium alloy bars were investigated below room temperature for objectively evaluating their adaption in low temperature environment. To study the low temperature fracture mechanism of the four different alloys, optical micrograph and scanning electron microscope were used to investigate the microstructure evolution and fracture morphology of low-temperature stretching samples. The main research contents and results are as follows:(1) Within a test temperature of 293 K, 233 K, 183 K, 153 K, 77 K for AZ31 magnesium alloy sheet, the results showed a rapid rise of strengh and a slow decline of elongation with temperature decreased. As in number, the ultimate tensile strengh was increased 120 MPa, while the nominal yield stress was increased 120 MPa at 77 K compared with that at room temperature, and the elongation declined from 17.21% to 12.25%. It indicates that AZ31 magnesium alloy exhibit excellent tensile mechanical properties and offers the possibility for application at low temperature.(2) The tensile tests were carried out at 293 K, 233 K, 193 K, 153 K for AZ61, AZ80, ZK60 magnesium alloy bars, the common results showed that the tensile strengh and yield strengh increased with temperature decreased. It was found that the ZK60 magnesium alloy exhibited the highest strengh growth rate. The elongation of AZ80 and ZK60 declined slowly with decreasing the tensile temperature, while AZ61 magnesium al oy showed higher elongation than that at room temperature.(3) There existed more twins in the fracture microstructure of AZ31 and ZK60 magnesium alloys, the number of twins became less with decreasing the tensile temperature, and rarely exsited below 193 K. Large quantity of twining was participated in plastic deformation temperature ranging from 153 K to 293 K for AZ61 magnesium alloy. Almost no twins were found from the fracture microstructure of AZ80 magnesium al oys.(4) The extruded AZ31, AZ61 and ZK60 magnesium alloys could keep an excellent elongation at low temperature, the tensile fracture mechanism was mainly ductile fracture and cleavage fracture, while ductile fracture at room temperature. The result showed that the extruded AZ80 sample fracture was microvoid accumulation fracture, while at low temperature, the fracture became intergranular fracture.