In this study, the influence of internal pressure and axial compressive displacement on the formability of small-diameter ZM21 magnesium alloy tubes in warm tube hydroforming (THF) was examined experimentally and numerically. The deformation behavior of ZM21 tubes, with a 2.0 mm outer diameter and 0.2 mm wall thickness, was evaluated in taper-cavity and cylinder-cavity dies. The simulation code used was the dynamic explicit finite element (FE) method (FEM) code, LS-DYNA 3D. The experiments were conducted at 250 °C. This paper elucidated the deformation characteristics, forming defects and forming limit of ZM21 tubes. Their deformation behavior in the taper-cavity die was affected by the axial compressive direction. Additionally, the occurrence of tube buckling could be inferred by changes of the axial compression force, which were measured by the load cell during the processing. In addition, grain with twin boundaries and refined grain were observed at the bended areas of tapered tubes. The hydroformed samples could have a high strength. Moreover, wrinkles, which are caused under a lower internal pressure condition, were employed to avoid tube fractures during the axial feeding. The tube with wrinkles was expanded by a straightening process after the axial feed. It was found that the process of warm THF of the tubes in the cylinder-cavity die was successful.

中文翻译：

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热管液压成形中内压和轴向压缩位移对小直径ZM21镁合金管成形性的影响

在这项研究中，实验和数值研究了内压和轴向压缩位移对小直径ZM21镁合金管在热管液压成形（THF）中可成形性的影响。在锥形腔和圆柱腔模具中评估了外径为2.0 mm，壁厚为0.2 mm的ZM21管的变形行为。使用的仿真代码是动态显式有限元（FE）方法（FEM）代码LS-DYNA 3D。实验在250℃下进行。阐明了ZM21管的变形特性，形成缺陷和形成极限。它们在锥腔模具中的变形行为受轴向压缩方向的影响。另外，可以通过改变轴向压缩力来推断是否发生了管屈曲，在处理过程中由称重传感器进行测量。另外，在锥形管的弯曲区域观察到具有双边界的晶粒和细化的晶粒。液压成型的样品可能具有很高的强度。此外，采用在较低内压条件下引起的皱纹来避免轴向进给过程中的管破裂。轴向进给后，带有皱纹的管通过矫直过程膨胀。已经发现，在圆筒型腔模具中的管的温暖的THF过程是成功的。为了避免在轴向进给过程中管子破裂，我们采用了这种方法。轴向进给后，带有皱纹的管通过矫直过程膨胀。已经发现，在圆筒型腔模具中的管的温暖的THF过程是成功的。为了避免在轴向进给过程中管子破裂，我们采用了这种方法。轴向进给后，带有皱纹的管通过矫直过程膨胀。已经发现，在圆筒型腔模具中的管的温暖的THF过程是成功的。