Study on the formability and deformation behavior of AZ31B tube at elevated temperature by tube bulging test

Internal high pressure forming of tube is widely used to form complex tubular part with different cross sections and curved axis. The ability of tube to undergo expansion deformation is crucial for the forming process. To evaluate the formability of AZ31B extruded tube, bulging test was carried out at different temperatures from RT up to 480 °C. Bursting pressure and maximum expansion ratio (MER) of the tube were obtained. The fracture surface after bursting was analyzed and compared with that obtained by tensile test along axial direction. Hardness changes in different positions along axial direction were also measured. Results show that the MER value remain almost unchanged from RT to 100 °C. In the temperature interval between 100 and 480 °C, an oblique N model can be used to describe the variation of MER value. The first peak and the bottom MER value occurred at 160 and 330 °C, respectively, and about 30.3% expansion ratio was reached at 480 °C. The bursting pressure decreased almost linearly as testing temperature increased. The fracture mode also changed from intercrystalline fracture to gliding fracture. However, burnt structure happened when the forming temperature was about 480 °C. The hardness value of the tube decreased significantly after the bulging test.