In-situ Methods for Unraveling Structure-Property Relationships in Light Metals: Imaging and Acoustic Emission
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee, TMS: Magnesium Committee
Program Organizers: Dmytro Orlov, Lund University; Wim Sillekens, European Space Agency

Tuesday 8:30 AM
February 28, 2017
Room: 5B
Location: San Diego Convention Ctr

Session Chair: Dmytro Orlov, Lund University; Joachim Schnadt, Lund University


8:30 AM Introductory Comments

8:40 AM  Keynote
Overview of In-Situ X-ray Studies of Light Alloy Solidification in Microgravity: David Browne1; F. García-Moreno2; H. Nguyen-Thi3; G. Zimmermann4; F. Kargl5; Ragnvald Mathiesen6; Axel Griesche7; O. Minster8; 1University College Dublin; 2Institute of Applied Materials, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH; Technische Universität Berlin; 3IM2NP & Université d’Aix-Marseille; 4Access e.V., Intzestrasse; 5Deutsches Zentrum fur Luft- und Raumfahrt (DLR), Institut fur Materialphysik Im Weltraum; 6Institut for Fysikk, Norsk Teknisk-Naturvitenskapelige Universitet (NTNU); 7Bundesanstalt für Materialforschung und –prüfung (BAM); 8Human Spaceflight and Robotic Exploration Directorate, ESTEC, European Space Agency
    Gravity has significant effects on alloy solidification, primarily due to thermosolutal convection and solid phase buoyancy. Since 2004, the European Space Agency has been supporting investigation of these effects by promoting in-situ X-ray monitoring of the solidification of aluminium alloys on microgravity platforms, on earth, and in periodically varying g conditions. The first microgravity experiment – investigating foaming of liquid metals – was performed on board a sounding rocket, in 2008. In 2012 the first ever X-ray-monitored solidification of a fully dense metallic alloy in space was achieved: the focus was columnar solidification of an Al-Cu alloy. This was followed in 2015 by a similar experiment, investigating equiaxed solidification. Ground reference experiments were completed in all cases. In addition, similar experiments have been performed on board parabolic flights – where the effects of varying gravity have been studied. We review here the technical and scientific progress to date, and outline future perspectives.

9:10 AM  
Morphological Transition of α-Mg Dendrites during Near-isothermal Solidification of a Mg-Nd-Gd-Zn-Zr Casting Alloy: Daniele Casari1; Wajira Mirihanage1; Ken Falch1; Inga Ringdalen2; Jesper Friis2; Rainer Schmid-Fetzer3; Dongdong Zhao1; Yanjun Li1; Wim Sillekens4; Ragnvald Mathiesen1; 1NTNU; 2SINTEF Materials and Chemistry; 3Clausthal University of Technology; 4European Space Agency
    Microstructure evolution in the Mg-Nd-Gd-Zn-Zr commercial casting alloy Elektron21 and in a Zn-free alloy variant, solidified under near-isothermal conditions at six constant cooling rates, has been studied via in-situ X-ray radiography. In the Zn-free alloy, equiaxed α-Mg primary dendrites are always observed to develop with a steady growth rate. Conversely, in the Elektron21 alloy, primary dendrites undergo a morphological transition after nucleation and an initial transient growth for cooling rates T ̇ ≤ 0.075 K/s. Such transition leads to a change in the growth morphology from volume spanning 3D to anisotropic sheet-like growth occurring mainly along 〈11-20〉 directions, with 4-5 times increase in the growth velocity. Experiments and simulations highlight the pivotal role of Zn, indicating that the morphological transition occurs due to the formation of ordered rare earth-zinc arrangements in the {10-11} pyramidal and {0001} basal planes of the α-Mg lattice within a layer extending a few micrometres from the solid-liquid interface into α-Mg.

9:30 AM  
Real-time Observation of AZ91Solidification by Synchrotron Radiography: Guang Zeng1; Kazuhiro Nogita2; Sergey Belyakov1; Jingwei Xian1; Stuart McDonald2; Hideyuki Yasuda3; Christopher Gourlay1; 1Imperial College London; 2University of Queensland; 3Kyoto University
    Solidification of AZ91 involves complex phenomena, various reactions and phases, and depends on the cooling conditions. In this study, microstructure evolution during AZ91 solidification was studied at various cooling rates, by real-time synchrotron radiography. Quantitative image analysis of the radiograph sequences was then combined with thermodynamic calculations and post-mortem electron microscopy and micro-analysis. Nucleation and growth of Al8Mn5 intermetallics and their interactions with -Mg dendrite were quantified. -Mg dendrite envelope development and solute partitioning at solid-liquid interfaces were also analyzed. The results have implications for microstructure control and understanding of structure-property relationships in cast AM and AZ series alloys.

9:50 AM  
3D Microstructural Evolution on Solidifying Mg-5Nd-5Zn Alloy Observed via In Situ Synchrotron Tomography: Tungky Subroto1; Chamini Mendis2; Francesco D'Elia1; Gábor Szakács1; Julie Fife3; Norbert Hort1; Karl Kainer1; Domonkos Tolnai1; 1Helmholtz-Zentrum Geesthacht; 2Brunel Centre for Advanced Solidification Technology (BCAST), Brunel University; 3Previously with: Swiss Light Source, Paul Scherrer Institut (PSI)
    Synchrotron tomography is a unique technique to study 3D microstructure evolution during solidification owing to high brilliance of the beam and the short acquisition time of the detector systems. In this work, in situ X-ray tomography observations were performed during the solidification of Mg-5Nd-5Zn alloy with different cooling rates (5 and 20 K/min). The experiments were performed at the TOMCAT beamline of the Swiss Light Source (PSI, Switzerland). The samples were locally molten by a laser-based heating system and then cooled to the end of solidification. Tomographies were acquired every 5 K during cooling, starting from the fully liquid state until the solidification is completed to follow the evolution of the internal architecture as solidification proceeds. The volume fraction of the phases (i.e. pore, dendrites and interdendritic liquid), morphology and orientation of the growing dendrites, and the effect of cooling rates on the different microstructural features during solidification are discussed.

10:10 AM Break

10:30 AM  Invited
The Use of In-situ X-ray Imaging Methods in the Research and Development of Magnesium-based Grain-refined and Nanocomposite Materials: Wim Sillekens1; Daniele Casari2; Wajira Mirihanage3; Sofiane Terzi4; Ragnvald Mathiesen2; Luc Salvo5; Rémi Daudin5; Pierre Lhuissier5; Enyu Guo3; Peter Lee3; 1European Space Agency; 2NTNU Norwegian University of Science and Technology; 3University of Manchester; 4European Synchrotron Radiation Facility – Institut Laue-Langevin; 5Université Grenoble Alpes
    In this contribution, examples are presented of how in-situ imaging methods are used in the research and development of magnesium-based grain-refined and nanocomposite materials. These illustrative results are drawn from the EC collaborative research project ExoMet (www.exomet-project.eu). The first example concerns the solidification of a Mg-Nd-Gd alloy with Zr addition to assess the role of zirconium content and cooling rate in crystal nucleation and growth by micro-focus X-ray radiography. The second example concerns the solidification of a Mg-Zn-Al alloy and its SiC-containing nanocomposite material to reveal the influence of particle addition and cooling rate on microstructural development by synchrotron X-ray tomography. The third example concerns the (partial) re-melting and -solidification of Elektron21/AlN and Elektron21/Y2O3 nanocomposite materials to study such effects as particle pushing/engulfment and clustering during repeated processing by synchrotron X-ray tomography. Results demonstrate that microstructural phenomena can be monitored as they evolve during the processing of such materials.

10:55 AM  
Acoustic Emission Study of Deformation Behavior of Wrought Mg Alloys: Patrik Dobroň1; Daria Drozdenko1; Sangbong Yi2; Jan Bohlen2; 1Charles University; 2Helmholtz-Zentrum Geesthacht
    Mechanical properties of wrought Mg alloys are significantly influenced, besides of hexagonal closed crystallographic (hcp) lattice of Mg, by a grain size and strong initial texture. It is generally accepted that twinning is an important deformation mechanism in Mg alloys and is intimately related to an anisotropy or asymmetry of mechanical properties at room temperature. The activity of individual deformation mechanisms during plastic deformation can be monitored by the acoustic emission (AE) technique. The influence of texture, initial stress conditions of samples, homogeneity and stability of microstructure on deformation behavior of wrought Mg alloys was studied using AE parameters. A detailed insight into microstructural changes was provided by X-ray and electron back scattered diffraction (EBSD) techniques.

11:15 AM  
Effect of Thermo-mechanical Treatment of Extruded Z1 Mg Alloy on Resulting Mechanical Properties: Daria Drozdenko1; Jan Bohlen2; Sangbong Yi2; Patrik Dobroň1; 1Charles University in Prague; 2Helmholtz-Zentrum Geesthacht
    The formability and mechanical properties of Mg alloys are strongly influenced by a formation and growth of twins. The contribution of twinning to plastic deformation can be modified by initial texture, introducing solute segregation and precipitation at the twin boundaries. The interaction of solute atoms and precipitates with grain and twin boundaries during thermo-mechanical treatment and their effect on mechanical properties will be discussed in term of acoustic emission (AE). Parameterization of an AE signal, recorded during deformation tests, can provide information about active deformation mechanisms during plastic deformation with respect to the microstructure and texture as well as to solute segregation and precipitates along dislocations, grain and twin boundaries. The microstructure and texture development of the extruded Z1 Mg alloy during pre-treatment and plastic deformation will be investigated by scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD).

11:35 AM  Invited
In-situ Investigation of Deformation Mechanisms in Mg-Zn-Y Magnesium Alloy with LPSO Phase by Diffraction Methods and Acoustic Emission: Kristian Máthis1; Gerardo Garces2; Klaudia Horváth1; Daria Drozdenko1; Patrik Dobroň1; 1Faculty of Mathematics and Physics, Charles University; 2CENIM-CSIC
    The influence of the LPSO phase orientation and the microstructure of the magnesium matrix on the deformation mechanisms of Mg-Zn-Y magnesium alloy has been investigated by diffraction methods and acoustic emission (AE) measurements. The adaptive sequential k-means analysis (ASK) method, offering identification of the dominant deformation process (basal, non-basal slip, twinning, kinking) in a given time period, has been used for AE data evaluation. The results indicate that the kinking mechanism, twinning and activation of non-basal slip exhibit a significant dependence on the initial texture and the orientation of the LPSO phase with respect to the loading axis.