Formation of intermetallic phases in unrefined and refined AA6082 Al alloys investigated by using SEM-based ultramicrotomy tomography. (1st September 2022)

• Record Type: Journal Article
• Authors: Yu, J.M.; Hashimoto, T.; Li, H.T.; Wanderka, N.; Zhang, Z.; Cai, C.; Zhong, X.L.; Qin, J.; Dong, Q.P.; Nagaumi, H.; Wang, X.N.
• Is Part Of: Journal of materials science & technology. Volume 120(2022)
• Page Start: 118
• Page End: 128
• Publication Date: 2022-09-01
• Subjects: Al-Si-Mg alloy -- Grain refinement -- Al-Fe-Si intermetallic phase -- Tomography -- Ultramicrotomy -- Mg2Si; Metals -- Periodicals; Materials science -- Periodicals; Materials science; Metals; Periodicals; 620.1105
• DOI: 10.1016/j.jmst.2022.02.007
• Languages: English
• ISSNs: 1005-0302

Abstract

Highlights: Microstructure of AA6082 Al alloys was studied using SEM serial ultramicrotomy tomography. The formation sequence of intermetallic phases is related to the coarsening of α-Al dendrites. TiB2 particles act as nuclei for the formation of β, α intermetallics and Mg2 Si. The grain refinement processing causes the severe interconnectivity of α-intermetallics. Melt shearing is better to uniformly distribute and refine intermetallics than grain refiner. Abstract: 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, Mg2 Si 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 Mg2 Si. A further deep analysis reveals that the essential condition for the formation of secondary phases such as Fe-bearing intermetallics and Mg2 Si 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.