Abstract
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.
Highlights
In recent years, magnesium and its alloys have been widely applied in the automotive, aircraft and telecommunication industries
ZM21 magnesium alloy obtained by tensile bursting tests
Outer diameter of 2.0 mm and a wall thickness of 0.2 mm was examined by experimentation and FE method (FEM)
Summary
Magnesium and its alloys have been widely applied in the automotive, aircraft and telecommunication industries. Metals 2020, 10, 674 necessary to miniaturize medical devices, and there is a demand for the establishment of deformation methods of small-diameter tubular products to apply them in miniaturized devices [5]. To respond to this demand, tube hydroforming (THF) emerged as a method to manufacture the small-diameter tubular parts [6]. THF can deform tube products with a complex cross-section shape integrally This characteristic leads to a weight reduction and high strength of the products. It has become a research direction to use THF in the manufacture of small-diameter magnesium alloy tubes for medical devices.
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