2019 年 60 巻 707 号 p. 346-351
Magnesium and its alloys are expected to be applied in medical and electric device industries. Magnesium has excellent characteristics such as light weight, high strength, and low toxicity to humans since it is an element essential to our health. The demand for manufacturing small-diameter tubular products has increased leading to small-sized devices. Tube hydroforming (THF) is a plastic processing method that has less restriction on the shape and size of workpieces owing to deformation by a liquid tool. THF has been predicted to enable the manufacture of small-diameter tubular parts made of magnesium alloy. In this work, warm THF was applied to the processing of small-diameter ZM21 magnesium alloy tubes with 2.0 mm outer diameter and 0.15 mm thickness. The effects of temperature, effects of internal pressure, and the amount of axial feed on formability in THF were confirmed. As a result, the influences of temperature on the deformation resistance, bursting pressure, and ductility of the tube were elucidated. Furthermore, the appropriate amount of axial feed and internal pressure were clarified for expanding the small-diameter tubes. Consequently, a bulge with an outstanding height of 1.5 times the outer diameter was successfully fabricated experimentally. The deformation characteristic of tube was also evaluated.