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Journal of Materials Science

, Volume 47, Issue 11, pp 4716–4725 | Cite as

Composition segregation in semi-solid metal cast AA7075 aluminium alloy

  • S. L. GeorgeEmail author
  • R. D. Knutsen
Article

Abstract

The composition distribution and microstructural evolution associated with the characteristic globular grain structure in semi-solid metal cast AA7075 aluminium alloy has been investigated. The primary globular grains possess uniform composition over nearly 90% of their diameter with fluctuations only occurring in the near surface of the individual grains. The inter-globular regions are solute rich and contain non-equilibrium eutectic. The segregation pattern in semi-solid cast structures occurs over a much greater length-scale than the dendritic pattern prevalent in conventional castings and it is proposed that the distinction arises from predominant planar growth of the α-primary globular grains during the SSM conditioning stage. Examination of the in-grain structure using electron backscattered diffraction revealed a quasi-periodic fluctuation in misorientation that may have arisen from local perturbations on the planar solid interface as solidification progressed. Homogenisation prior to artificial ageing is severely compromised by the undesirable segregation pattern.

Keywords

Segregation Pattern Solute Segregation Composition Distribution Incipient Melting Globular Morphology 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgements

The authors gratefully acknowledge the financial support of the National Research Foundation of South Africa (NRF), as well as the Council for Scientific and Industrial Research (CSIR) in Pretoria for the supply of samples.

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Copyright information

© Springer Science+Business Media, LLC 2012

Authors and Affiliations

  1. 1.Department of Mechanical Engineering, Centre for Materials EngineeringUniversity of Cape TownRondeboschSouth Africa

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