Characterization of the Convoluted 3D Intermetallic Phases in a Recycled Al Alloy by Synchrotron X-ray Tomography and Machine Learning

doi:10.1007/s40195-021-01312-3

Abstract

Abstract:

Fe-rich intermetallic phases in recycled Al alloys often exhibit complex and 3D convoluted structures and morphologies. They are the common detrimental intermetallic phases to the mechanical properties of recycled Al alloys. In this study, we used synchrotron X-ray tomography to study the true 3D morphologies of the Fe-rich phases, Al₂Cu phases and casting defects in an as-cast Al-5Cu-1.5Fe-1Si alloy. Machine learning-based image processing approach was used to recognize and segment the different phases in the 3D tomography image stacks. In the studied condition, the β-Al₉Fe₂Si₂ and ω-Al₇Cu₂Fe are found to be the main Fe-rich intermetallic phases. The β-Al₉Fe₂Si₂ phases exhibit a spatially connected 3D network structure and morphology which in turn control the 3D spatial distribution of the Al₂Cu phases and the shrinkage cavities. The Al₃Fe phases formed at the early stage of solidification affect to a large extent the structure and morphology of the subsequently formed Fe-rich intermetallic phases. The machine learning method has been demonstrated as a powerful tool for processing big datasets in multidimensional imaging-based materials characterization work.

Key words: Recycled Al alloy, Solidification, Synchrotron X-ray tomography, Machine learning, Fe-rich intermetallic phases

Zhenhao Li, Ling Qin, Baisong Guo, Junping Yuan, Zhiguo Zhang, Wei Li, Jiawei Mi. Characterization of the Convoluted 3D Intermetallic Phases in a Recycled Al Alloy by Synchrotron X-ray Tomography and Machine Learning[J]. Acta Metallurgica Sinica (English Letters), 2022, 35(1): 115-123.

Figures/Tables 9

Table 1 Fractions of various phases in the as-cast Al-5Cu-1.5Fe-1Si alloy

Categories	Volume fraction (%)	Area fraction (%)
Fe Phase	7.9	3.8
Al₂Cu Phase	9.3	2.0
Al Matrix	82.6	93.9
Pores	0.2	0.3

Fig. 1 a XRD pattern of the as-cast Al-5Cu-1.5Fe-1Si alloy; b vertical section of the quaternary alloy phase diagram for Al-2Fe-1Si?→?Cu [17]

Fig. 2 Typical SEM image for the as-cast Al-5Cu-1.5Fe-1Si alloy and the corresponding EDS spectrum for the different phases: a typical SEM image containing various phases a; EDS of the Al2Cu phase b, Al9Fe2Si2(Cu) phase c, Al9Fe2Si2(Cu) phase d, Al7Cu2Fe phase e

Fig. 3 A typical slice from the synchrotron X-ray tomography image stack of the as-cast Al-5Cu-1.5Fe-1Si alloy and the image processing procedure: a a typical 2D slice; b the selected region of interest (ROI); c the filtered and normalized image and d the segmented image by applying the machine learning-based approach

Fig. 4 Fe-rich phases and Al2Cu phases in the selected 3D volume

Fig. 5 Typical 3D morphologies of Fe-phase: a and b polygon morphology; c and d complex Chinese script morphology. e Distribution of the 3D equivalent diameter of the Fe-phase

Fig. 6 a and b 3D morphologies of the eutectic Al2Cu phases; c distribution of the equivalent diameter and d 3D thickness for the eutectic Al2Cu phases

Fig. 7 3D distribution of the pores inside the sample

Fig. 8 3D morphologies of the pores: a gas pore; b shrinkage cavity and c distribution of the 3D equivalent diameter of the pores inside the sample and the fitted curve using a lognormal distribution function

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