Formation of intermetallic phases in unrefined and refined AA6082 Al alloys investigated by using SEM-based ultramicrotomy tomography

J. M. Yu, T. Hashimoto, H. T. Li, N. Wanderka, Z. Zhang, C. Cai, X. L. Zhong, J. Qin, Q. P. Dong, H. Nagaumi, X. N. Wang

Research output: Contribution to journalArticlepeer-review


The spatial arrangement, distribution and morphology of Fe-bearing intermetallics in AA6082 alloys depends on the manufacturing process of the alloy and thus influences the macroscopic properties. Here, the microstructure of a near industrial scale casting AA6082 Al alloy fabricated by: (a) direct chill casting, (b) Al-5Ti-1B grain refiner addition and (c) intensive melt shearing has been investigated by three-dimensional visualization using SEM-based serial ultramicrotomy tomography. The formation sequence of phases in AA6082 alloys is generally categorized into four stages: formation of α-Al grains, Fe-bearing intermetallics, Mg2Si phase, and eutectic rosettes. Results of three-dimensional visualization of the microstructure indicated that TiB2 particles not only could nucleate Fe-bearing β-intermetallics, but also could provide substrate for the formation of Fe-bearing α-intermetallics and Mg2Si. A further deep analysis reveals that the essential condition for the formation of secondary phases such as Fe-bearing intermetallics and Mg2Si phase is the build-up of a supersaturated solute front at the α-Al solid-liquid interface irrespective of the specific nucleation site. In addition, the results indicate that grain refinement processing causes the severe interconnectivity of Fe-bearing α-intermetallics. However, the intensive melt shearing is a better manufacturing process because the intermetallics are more evenly distributed and refined than with the addition of the grain refiner, thereby improving the properties of the alloy.

Original languageEnglish
Pages (from-to)118-128
Number of pages11
JournalJournal of Materials Science and Technology
Publication statusPublished - 1 Sep 2022


  • Al-Fe-Si intermetallic phase
  • Al-Si-Mg alloy
  • Grain refinement
  • MgSi
  • Tomography
  • Ultramicrotomy


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