长轴波纹管的差温局部热态气压成形新工艺

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

针对AZ31镁合金长轴波纹管提出差温局部热态气压成形新工艺。首先在温度范围573~673 K、应变速率范围0.001~0.1 s^(-1)条件下对AZ31镁合金管材进行了热拉伸实验,分析了温度、应变速率对其力学性能的影响。设计制造了长轴波纹管差温局部热态气压成形装置,利用该装置,通过单波波纹管的热气胀成形研究了成形温度、成形内压对波纹管成形时间、壁厚分布的影响规律,从而确定最佳成形工艺窗口,并通过五波长轴波纹管的成形验证该新工艺的可行性。结果表明,差温成形过程中,低温区最高温度不超过50℃,高温区温度可以精确控制,误差在±5℃以内。在温度623 K、恒定气压14 MPa条件下,通过小模具成功成形出五波长轴镁合金波纹管。成形后波峰位置平均晶粒尺寸从21.8μm细化到16.56μm,其主要原因为成形过程中发生了动态再结晶。

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 16.56μm after forming due to the dynamic recrystallization during the forming.