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Microstructure and modification mechanisms of Si phase in as-thixoformed alloy A356

  • K. Y. Wen and G. Gottstein EMAIL logo
Published/Copyright: December 7, 2021
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International Journal of Materials Research
From the journal International Journal of Materials Research Volume 93 Issue 7

Abstract

Heavily faulted Si flakes, which can be considered as crystallization products of eutectic droplets embedded in an Al matrix, were for the first time observed in an as-thixoformed A356 alloy, which contains 0.3 wt.% Sr. Large isolated particles as well as clusters of fine Si particles were observed. Evidence is provided that the faults on {111} planes of Si are not twins. Sr and Na are known to modify the morphology of the Si phase from flake to fiber morphology. Contrary to common perception, it is shown that the twin plane re-entrant edge mechanism does not operate during fiber growth. It is proposed that the modification process occurs during the nucleation of the Si phase by adsorption of modifying elements on twinned nuclei of Si. They prevent nucleus growth into stable twinned crystals, which is a prerequisite for the growth of Si flakes.

Abstract

In der thixogeformten Legierung A356 wurden erstmalig Si-Erstarrungsphasen untersucht. Sie haben gewöhnlich eine flockenförmige Morphologie und sehr hohe Defektdichten und kommen als größere Einzelteilchen oder fein verteilte Dispersion vor. Durch die Beimengung von Sr oder Na wird die Morphologie von flockenförmig zu faserförmig verändert, was Auswirkungen auf die mechanischen Eigenschaften hat. Die Untersuchungen zeigen, dass die Modifikation der Morphologie, entgegen geläufiger Meinung, nicht auf das Zwillingswachstum, sondern auf die Keimbildung der Si-Phase zurückzüführen ist. Den modifizierenden Elementen kommt dabei die Rolle der Wachstumshemmung in der Keimbildungsphase von Zwillingskristallen zu.

Keywords: Aluminum alloy A356; Transmission electron microscopy (TEM); Microstructure; Eutectic modification; Thixoforming

Dedicated to Professor Dr. Haël Mughrabi on the occasion of his 65th birthday

The authors like to thank Prof. J. Mayer of the Gemeinschaftslabor für Elektronenmikroskopie of RWTH Aachen for critically reading the manuscript and for valuable comments. We are grateful to the Collaborative Research Center 289 of the Deutsche Forschungsgemeinschaft “Thixoforming” for providing the alloy.

Prof. Dr. G. Gottstein Institut für Metallkunde und Metallphysik RWTH Aachen, D-52056 Aachen Tel.: +49 241 80 268 60 Fax: +49 241 80 226 08

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Received: 2002-02-18
Published Online: 2021-12-07
Published in Print: 2021-12-07

© 2002 Carl Hanser Verlag, München

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  1. Frontmatter
  2. Editorial
  3. Editorial
  4. Articles/Aufsätze
  5. A model for the work hardening of WC–Co “hard metals”
  6. On the dispersion strengthening mechanisms in ODS materials
  7. Effect of hydrogen on the mechanical properties of the β titanium alloy Timetal® 21S
  8. Cyclic deformation behaviour of (α + β) titanium alloys under complex mechanical and physiological loading conditions
  9. Assessment of the influence of interdendritic shrinkage cavities on the thermo-mechanical fatigue behaviour of the nickel-base superalloy MAR-M247LC
  10. Effects of static strain aging on residual stress stability and alternating bending strength of shot peened AISI 4140
  11. On the possibilities to enhance the fatigue properties of ultrafine-grained metals
  12. New method of determining stress relaxation behavior in creep machines by controlled unloading
  13. Creep of binary Ni-rich NiTi shape memory alloys and the influence of pre-creep on martensitic transformations
  14. Interaction of high-cycle fatigue with high-temperature creep in superalloy single crystals
  15. A unified description of creep in pure and dispersion-strengthened copper
  16. A new interpretation of flow-stress measurements of high-purity NiAl below room temperature
  17. A mesoscopic plasticity model accounting for spatial fluctuations of plastic strains, internal stresses and dislocation densities
  18. Behavior of X-ray peak widths in the Wilkens model of a restrictedly random distribution of dislocations
  19. Dislocation structure and crystallite size distribution in hexagonal nanomaterials from X-ray peak profile analysis
  20. Werden gewichtsoptimiert konstruierte Bauteile durch die Verwendung von Leichtmetallen wirklich leichter?*)
  21. Strain-induced martensite formation in metastable austenitic steels with varying carbon content
  22. Isothermal bainitic transformation in low alloy steels: factors limiting prediction of the resulting material’s properties
  23. Fatigue damage evolution in a particulate-reinforced metal matrix composite determined by acoustic emission and compliance method
  24. Microstructure and modification mechanisms of Si phase in as-thixoformed alloy A356
  25. Influence of size effect on microstructural changes in cyclically deformed polycrystalline nickel
  26. Self-diffusion of 71Ge and 31Si in Si –Ge alloys
  27. On localised corrosive attack, stress corrosion cracking and corrosion fatigue effects in a hardmetal cutting-tool material
  28. The internal stress during growth of SiC single crystals
  29. Notifications/Mitteilungen
  30. Personal/Personelles
  31. Books/Bücher
  32. DGM Conferences/Training
https://doi.org/10.3139/ijmr-2002-0122
Keywords for this article
Aluminum alloy A356; Transmission electron microscopy (TEM); Microstructure; Eutectic modification; Thixoforming

Articles in the same Issue

  1. Frontmatter
  2. Editorial
  3. Editorial
  4. Articles/Aufsätze
  5. A model for the work hardening of WC–Co “hard metals”
  6. On the dispersion strengthening mechanisms in ODS materials
  7. Effect of hydrogen on the mechanical properties of the β titanium alloy Timetal® 21S
  8. Cyclic deformation behaviour of (α + β) titanium alloys under complex mechanical and physiological loading conditions
  9. Assessment of the influence of interdendritic shrinkage cavities on the thermo-mechanical fatigue behaviour of the nickel-base superalloy MAR-M247LC
  10. Effects of static strain aging on residual stress stability and alternating bending strength of shot peened AISI 4140
  11. On the possibilities to enhance the fatigue properties of ultrafine-grained metals
  12. New method of determining stress relaxation behavior in creep machines by controlled unloading
  13. Creep of binary Ni-rich NiTi shape memory alloys and the influence of pre-creep on martensitic transformations
  14. Interaction of high-cycle fatigue with high-temperature creep in superalloy single crystals
  15. A unified description of creep in pure and dispersion-strengthened copper
  16. A new interpretation of flow-stress measurements of high-purity NiAl below room temperature
  17. A mesoscopic plasticity model accounting for spatial fluctuations of plastic strains, internal stresses and dislocation densities
  18. Behavior of X-ray peak widths in the Wilkens model of a restrictedly random distribution of dislocations
  19. Dislocation structure and crystallite size distribution in hexagonal nanomaterials from X-ray peak profile analysis
  20. Werden gewichtsoptimiert konstruierte Bauteile durch die Verwendung von Leichtmetallen wirklich leichter?*)
  21. Strain-induced martensite formation in metastable austenitic steels with varying carbon content
  22. Isothermal bainitic transformation in low alloy steels: factors limiting prediction of the resulting material’s properties
  23. Fatigue damage evolution in a particulate-reinforced metal matrix composite determined by acoustic emission and compliance method
  24. Microstructure and modification mechanisms of Si phase in as-thixoformed alloy A356
  25. Influence of size effect on microstructural changes in cyclically deformed polycrystalline nickel
  26. Self-diffusion of 71Ge and 31Si in Si –Ge alloys
  27. On localised corrosive attack, stress corrosion cracking and corrosion fatigue effects in a hardmetal cutting-tool material
  28. The internal stress during growth of SiC single crystals
  29. Notifications/Mitteilungen
  30. Personal/Personelles
  31. Books/Bücher
  32. DGM Conferences/Training
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