Tensile Properties of Under-aged 3J21 Alloy at Low Temperatures

The tensile properties of under-aged 3J21 alloy at room and low temperatures were studied on a universal tensile test machine.Moreover,a metallographic microscope and X-ray diffractometer were used to analyze the metallographic structure and physical phase of the alloy in a cold rolled and under-aged state.By employing a transmission electron microscope(TEM) the structure of the alloy under the above-cited two states was observed and the X-ray diffraction results being verified.An analysis of the microscopic structure of deformation near the tensile fracture of the under-aged alloy at different temperatures was also conducted.A scanning electron microscope was used to observe the tensile fracture.It was found that the room-temperature fracture of the under-aged 3J21 alloy was of a dimple,while the low-temperature fracture assumed a mixed rupture feature.With decreasing temperature,the characteristic feature of a brittle rupture became still more evident.In the microstructure near the low-temperature tensile fracture it has been found that the amount of twin crystals increased with a decreasing in temperature.The tensile strength and yield strength of the under-aged 3J21 alloy would increase conspicuously with a decreasing in temperature.The tensile strength increased while a relatively large margin of the elongation rate slightly decreasing.The influence of temperature on the tensile properties of the under-aged 3J21 alloy was discussed.