Materials Science & Engineering A 795 (2020) 139935 Available online 2 August 2020 0921-5093/© 2020 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Mechanism of low temperature deformation in aluminium alloys Belinda Gruber a, b, * , Irmgard Weißensteiner a, b , Thomas Kremmer a , Florian Grabner c , Georg Falkinger d , Alexander Sch¨ okel e , Florian Spieckermann f , Robin Sch¨ aublin g , Peter J. Uggowitzer a, g , Stefan Pogatscher a, b a Chair of Nonferrous Metallurgy, Montanuniversitaet Leoben, Franz-Josef-Str. 18, 8700, Leoben, Austria b Christian Doppler Laboratory for Advanced Aluminum Alloys, Chair of Nonferrous Metallurgy, Montanuniversitaet Leoben, Franz-Josef Straße 18, 8700, Leoben, Austria c LKR Light Metals Technologies Ranshofen, Austrian Institute of Technology, Lamprechtshausenerstr. 61, Ranshofen, 5282, Austria d AMAG rolling GmbH, Postfach 32, Ranshofen, 5282, Austria e Deutsches Elektronen Synchrotron (DESY), Notkestr. 85, 22607, Hamburg, Germany f Chair of Materials Physics, Montanuniversitaet Leoben, Jahnstr. 12, 8700, Leoben, Austria g Laboratory of Metal Physics and Technology, Department of Materials, ETH Zürich, Vladimir-Prelog-Weg 4, 8093, Zürich, Switzerland A R T I C L E INFO Keywords: Aluminium alloys Cryogenic temperature Dislocation density Synchrotron radiation In-situ TEM 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 tem- peratures. The application of an extended Kocks-Mecking approach showed a significant reduction of the dy- namic 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 char- acterization 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. 1. Introduction Weight reduction is currently the focus in the automotive industry, for the requirements in reduction of greenhouse gas emissions. Various aluminium alloys are particularly suitable in this context due to their low specific weight, sufficient strength and good corrosion resistance [1, 2]. However, better formability and ductility would be desirable [3]. Previous studies [4–11] showed that an improvement in the strength and ductility of aluminium alloys can be reached by deforming at low temperatures. Xu et al. [9–11] examined various Al–Mg–Si alloys in the peak aged condition and presented an increase in yield strength, ultimate tensile strength and uniform elongation at 77 K compared to 295 K. Jobba et al. [4] investigated the flow stress and strain hardening behaviour of aluminium and Al–Mg alloys containing up to 4.11 at.-% Mg from 4 K to 298 K. With increasing Mg-content and decreasing temperature the yield strength is enhanced. Although the ductility decreases when Mg is added, it is possible to regain elongation with even higher Mg-content or reduced temperature. Schneider et al. [7] achieved an uniform elonga- tion in Al–Mg alloys of more than 40% and a fracture elongation of over 50% at 77 K. A possible reason for this strong improvement in ductility at lower temperatures in Al–Mg alloys is the absence of flow instabilities. In effect, at room temperature (RT) Al–Mg alloys exhibit serrated flow, also known as the Portevin Le Chatelier (PLC) effect [4]. The flow in- stabilities are supressed at lower temperatures and reappear at 4.2 K due to adiabatic deformation. Indeed, at these very low temperatures, * Corresponding author. Chair of Nonferrous Metallurgy, Montanuniversitaet Leoben, Franz-Josef-Str. 18, 8700, Leoben, Austria. E-mail address: [email protected] (B. Gruber). Contents lists available at ScienceDirect Materials Science & Engineering A journal homepage: http://www.elsevier.com/locate/msea https://doi.org/10.1016/j.msea.2020.139935 Received 8 April 2020; Received in revised form 29 June 2020; Accepted 13 July 2020
Mechanism of low temperature deformation in aluminium alloys
Jun 23, 2023
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