Local Hot Gas Forming of Long Axis Bellow with Non-uniform Temperature

A novel local hot gas forming (LHGF) process with non-uniform temperature field was proposed to form AZ31 magnesium alloy long axis bellow. Hot uniaxial tensile tests at temperatures ranging from 573 K to 673 K and strain rates ranging from 0.001 s^-1 to 0.1 s^-1 were carried out to study the hot deformation behavior of AZ31 magnesium alloy. Forming apparatuses with independent heating and cooling facilities were developed to achieve the non-uniform temperature field. Local hot gas forming tests of single wave bellow were performed to study the effects of temperature and gas pressure on the forming process and to determine the proper processing windows. A long axis bellow with 5 waves was finally formed to validate the novel process. Results show that the maximum temperature in the cooling zone can be kept below 50℃ and the temperature in the heating zone can be accurately controlled with fluctuation less than ±5℃. A qualified AZ31 magnesium alloy long axis bellow with 5 waves is formed with small dies at 623 K under a constant gas pressure of 14 MPa. The average grain size at the wave crest is refined from 21.8 μm in the initial to 16.56 μm after forming due to the dynamic recrystallization during the forming.