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.
|Materials science and engineering: A, Structural materials: properties, microstructure and processing
|Veröffentlicht - 23 Sept. 2020
Bibliographische NotizFunding Information:
This work was funded by the Austrian Research Promotion Agency ( FFG ), grant number 853560 .
Financial support from the Christian Doppler Research Association , the Austrian Federal Ministry for Digital and Economic Affairs and the National Foundation for Research, Technology and Development is also gratefully acknowledged.
We thank DESY (Hamburg, Germany), a member of the Helmholtz Association (HGF), for providing experimental facilities. Parts of this research were carried out at PETRA III using the Powder Diffraction and Total Scattering beamline P02.1. The research leading to our findings took place in the framework of project CALIPSOplus under the Grant Agreement 730872 of the EU Framework Programme for Research and Innovation HORIZON 2020. The authors would also like to thank Florian Schmid and Jakob Grasserbauer, colleagues from Montanuniversitaet Leoben, for their assistance.
© 2020 The Author(s)