Experimental study on multi-pass dieless drawing process of superplastic Zn–22%Al alloy microtubes

The fabrication process of superplastic microtubes using multi-pass dieless drawing is studied experimentally. The superplastic material used in this experiment is a Zn–22%Al alloy tube with an outer diameter of 2 mm and wall thickness of 0.5 mm. A high-frequency induction heating apparatus with an air-cooling nozzle is used for the dieless drawing. As a result, after four-pass dieless drawing, a microtube with outer and inner diameters of 190 and 91 μm, respectively, is fabricated successfully. It is confirmed that the ratio of inner to outer tube diameters remains a certain constant value in multi-pass dieless drawing. In addition, microtubes fabricated by this process are evaluated by their microstructure and surface roughness. Consequently, it is found that the manufacture of initial tubes with fine grains and high accuracy is essential for fabricating superior microtubes.