Mechanism of low temperature deformation in aluminium alloys

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External Organisational units

  • LKR Leichtmetallkompetenzzentrum Ranshofen GmbH
  • AMAG rolling GmbH
  • Photon Science, Deutsches Elektronen-Synchrotron DESY, Hamburg,
  • Eidgenössische Technische Hochschule Zürich

Abstract

This study investigates differences in the deformation mechanisms between room temperature (296 K) and cryogenic temperatures (77 K) and their advantages for low temperature formability in alloys EN AW 1085, EN AW 5182 and EN AW 6016. Compared to room temperature behaviour, tensile tests showed an overall increase in yield strength, ultimate tensile strength and uniform elongation with differences among the principal alloy types. In general, the improved mechanical properties result from higher strain hardening rates at lower temperatures. The application of an extended Kocks-Mecking approach showed a significant reduction of the dynamic recovery and suggested higher dislocation densities upon cryogenic deformation. This was confirmed via in-situ synchrotron experiments, which also reveal a higher proportion of screw dislocations. Moreover, kernel average misorientation maps from electron backscattered diffraction and in-situ cryogenic deformation in a transmission electron microscope displayed a more uniform dislocation arrangement with a reduction of slip lines and less highly misaligned areas after deformation at lower temperatures. Supported by a detailed characterization of the microstructure and its dislocation structure, the associated fundamental mechanisms we reveal, which are at the origin of the exceptional improvement in mechanical properties, are extensively discussed.

Details

Original languageEnglish
Article number139935
Number of pages11
JournalMaterials science and engineering: A, Structural materials: properties, microstructure and processing
Volume2020
Issue number795
DOIs
Publication statusPublished - 2 Aug 2020