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Morphological Transition of α-Mg Dendrites During Near-Isothermal Solidification of a Mg–Nd–Gd–Zn–Zr Casting Alloy

  • Daniele Casari
  • Wajira U. Mirihanage
  • Ken V. Falch
  • Inga G. Ringdalen
  • Jesper Friis
  • Rainer Schmid-Fetzer
  • Dongdong Zhao
  • Yanjun Li
  • Wim H. Sillekens
  • Ragnvald H. MathiesenEmail author
Conference paper
Part of the The Minerals, Metals & Materials Series book series (MMMS)

Abstract

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 \( \dot{T} \) ≤ 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 \( \left\langle {11\bar{2}0} \right\rangle \) 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 \( \{ 10\bar{1}1\} \) 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.

Keywords

Magnesium alloys X-ray radiography Microstructure evolution 

Notes

Acknowledgements

The authors wish to acknowledge financial support from the ExoMet project, which is co-founded by the European Commission in the 7th Framework Programme (contract FP7-NMP3-LA-2012-280421), by the European Space Agency and by the individual partner organisations. Among the project partners, Helmholtz-Zentrum Geesthacht (MagIC), Germany, is gratefully acknowledged for the supply of the magnesium rare earth alloys.

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Copyright information

© The Minerals, Metals & Materials Society 2017

Authors and Affiliations

  • Daniele Casari
    • 1
  • Wajira U. Mirihanage
    • 1
    • 2
  • Ken V. Falch
    • 1
  • Inga G. Ringdalen
    • 3
  • Jesper Friis
    • 3
  • Rainer Schmid-Fetzer
    • 4
  • Dongdong Zhao
    • 5
  • Yanjun Li
    • 5
  • Wim H. Sillekens
    • 6
  • Ragnvald H. Mathiesen
    • 1
    Email author
  1. 1.Department of PhysicsNorwegian University of Science and TechnologyTrondheimNorway
  2. 2.School of MaterialsThe University of ManchesterManchesterUK
  3. 3.SINTEF Materials and ChemistryTrondheimNorway
  4. 4.Institute of MetallurgyClausthal University of TechnologyClausthal-ZellerfeldGermany
  5. 5.Department of Materials Science and EngineeringNorwegian University of Science and TechnologyTrondheimNorway
  6. 6.European Space AgencyNoordwijkThe Netherlands

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