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Manufacturing of seamless tubes of the alloy Al-5Mg-0,2Sc by direct extrusion and sink drawing

Thursday (27.09.2018)
17:30 - 17:45 S1/01 - A1
Part of:

In comparison to standard aluminum alloys of the system Al-Mg the addition of scandium allows to improve the mechanical properties to a high level. Until now, Al-Mg-Sc alloys are typically produced as plates and sheets though tubes as well would be promising e. g. to increase payloads in the aerospace industry by substituting steel tubes in fuel systems by weldable aluminum alloys. Hence, the objective of the presented study is to develop a method to manufacture seamless tubes with an outer diameter ranging between 10-20 mm and a wall thickness of 1-3 mm as well as to evaluate the tube properties. The manufacturing process includes a direct extrusion of axially drilled billets using a 2.5 MN horizontal press with subsequent sink drawing and optional intermittent heat treatments. The extrusion ratio was varied from 21:1 to 46:1 at billet temperatures of 440 °C and 480 °C. Technological parameters such as extrusion force and maximal deformation during drawing were evaluated. To characterize the influence of the process parameters on the tube quality, the following tests were applied: tensile test, drift-expanding test, ring flattening test, hardness measurements according to Vickers as well as impact testing parallel and perpendicular to the tube axis. The accuracy of the tubes’ cross sections and the changes of wall thickness during sink drawing were measured. Static mechanical testing of the extruded tubes showed that annealing at 500 °C leads to a negligible growth of plasticity in the radial direction (expanding test). Ultimate tensile strength (UTS) decreases slightly, whereas yield stress and Vickers hardness drop by 15%. Plastic deformation at impact testing in axial direction is 8 to 20% greater for heat treated samples compared with the as-extruded condition and twice as large in radial direction. The decrease of wall thickness from 2 mm to 1 mm results in a three-fold growth of plastic deformation at the axial impact. Cold drawn tubes are characterized by an UTS of 440 MPa, a yield strength of 340 MPa and an elongation at fracture of 12% compared with hot extruded tubes with respective values of 370 MPa, 260 MPa and 19%. An increase of the heat treatment temperature from 200 °C to 500 °C results in a significant increase of the deformation prior to crack formation during the ring flattening test of sink drawn tubes, whereas the same parameter is independent from the heat treatment temperature for tubes in the extruded condition.

Dr. Oleksandr Golovko
Leibniz Universität Hannover
Additional Authors:
  • Prof. Dr. Yaroslav Frolov
    National Metallurgical Academy of Ukraine
  • Dr. Vitalii Andreiev
    National Metallurgical Academy of Ukraine
  • Dr. Christian Klose
    Leibniz Universität Hannover
  • Dr. Florian Nürnberger
    Leibniz Universität Hannover