Cryogenic Forming Potential of Large Diameter and Thin-Walled Aluminum Alloy Tubular Materials

The large-diameter and thin-walled aluminum alloy tube has superiority in terms of weight reduction and high transmission efficiency which has been widely used in the aerospace field. However, it is a tough issue to deform a desirable bent tube with such extreme specification and small bending radius. In recent years, aluminum alloy materials have been found to show strong enhancement in both strength and ductility when deforms at cryogenic temperature (CT), which provide the cryogenic forming potential for the hard-to-bend aluminum alloy tubes. In this work, tube formability at room temperature (RT) and CT was explored. The anisotropic characterization of the thin-walled tube was realized by combining experiment and viscoplastic self-consistent (VPSC) model. The overall mechanical properties at CT are significantly improved compared to those at RT. Furthermore, a finite element model of cryogenic bending of the thin-walled 6061-O aluminum alloy tube was constructed. The results provide evidence from two aspects of wrinkling and wall thickness reduction that the thin-walled aluminum alloy tube difficult to form at RT can achieve better formability when bent at CT. The average wrinkle height decreases first from 1.182 mm at RT to 0.201 mm at −60 ℃ with 83.0% reduction, and then increases to 0.425 mm at −180 ℃. The average thickness reduction rate decreases monotonically with temperature decreasing, and the drop is fastest at −60 ℃ of 15.4% reduction. Cracks no longer appear in cryogenic bending. In terms of the effect on the two defects of wrinkling and wall thickness reduction, −60 ℃ is the temperature at which the best forming properties are obtained.