Formability determination of AZ31B tube for IHPF process at elevated temperature

Ring hoop tension test and tube bulging test were carried out at elevated temperatures up to 480 °C to evaluate the formability of AZ31B extruded tube for internal high pressure forming (IHPF) process. The total elongation along hoop direction and the maximum expansion ratio (MER) of the tube were obtained. The fracture surface after bursting was also analyzed. The results show that the total elongation along hoop direction and the MER value have a similar changing tendency as the testing temperature increases, which is quite different from the total elongation along axial direction. Both the total elongation along hoop direction and the MER value increase to a peak value at about 160 °C. After that, they begin to decrease quickly until a certain rebounding temperature is reached. From the rebounding temperature, they begin to increase rapidly again. Burnt structure appears on the fracture surface when tested at temperatures higher than 420 °C. Therefore, the forming temperature of the tested tube should be lower than 420 °C, even though bigger formability can be achieved at higher temperature.