Formation of intermetallic δ phase in Al-10Si-0.3Fe alloy investigated by in-situ 4D X-ray synchrotron tomography

Abstract

During solidification of Fe-containing Al-Si casting alloys, various different intermetallic phases are formed. As this can have an impact on mechanical properties we investigated phase formation by applying in-situ time resolved synchrotron X-ray tomography. For a commercially pure Al-10Si-0.3 wt.%Fe alloy, phase morphology and spatial arrangement during solidification was revealed with 1°C temperature resolution. We find that many of the intermetallic phases that have been identified as β-AlFeSi phases in previous studies are in fact δ phases. It was found that δ plates mainly nucleate on the eutectic Al and Si. δ phase formation terminates almost simultaneously with the final solidification of eutectic phases. Features of δ phase growth such as impingement, branching and deformation of plates are discussed. The phase separation sequence during solidification is described and explained by the existence of "cells" of residual liquid in which δ phase formation progresses rapidly due to the supersaturation of solute atoms.

Synchrotron X-ray tomography investigation of 3D morphologies of intermetallic phases and pores and their effect on the mechanical properties of cast Al-Cu alloys

“…The 3D morphology of β-Fe is a plate-like shape (Fig. 4b1), which is significantly different from the typical needle-like structure in the 2D view, as previously reported in the literature [14]. β-Fe is formed through the peritectic reaction, L + Al3(FeMn)/Al6(FeMn) → α-Al + β-Fe, at 589-597 °C or the eutectic reaction, L → α-Al + Al2Cu + β-Fe, at 546-547 °C [36,37].…”

“…Moreover, the nucleation and growth of Fe phases during the solidification of Al alloys have been investigated using 4D (3D + time) synchrotron X-ray tomography [14][15][16][17]. Eutectic Al2Cu is another important phase in Al-Cu alloys; hence, it is necessary to characterize the 3D morphology of this phase.…”

“…Owing to the high brilliance of the third-generation synchrotron radiation facility, it is possible to apply SRXCT to investigate the 3D morphology of intermetallic phases and pore defects of metallic materials with micron and sub-micron spatial resolution [29]. Recently, several SRXCT studies [14][15][16][17] have been carried out using ex situ and in situ characterization of Al alloys with 3D X-ray tomography. Recently, the 3D morphology of Fe phases in Al-Cu alloys containing low Fe contents (< 0.1 wt.%) has been characterized using SRXCT [11].…”

Formation of Iron-Rich Intermetallic Phases in Al-7Si-Mg: Influence of Cooling Rate and Strontium Modification

“…However, no significant differences in area fraction of b-Al 5 FeSi were found in both unmodified and strontium-modified alloys, as seen in Figure 8(a). Yu et al [17] reported that b-Al 5 FeSi phase nucleates above the Al-Si eutectic reaction temperature while d-Al 3 FeSi 2 phase forms during the Al-Si eutectic reaction in a high purity Al-10Si-0.3Fe alloy. The formation of pre-eutectic b-Al 5 FeSi platelets would consume iron in the liquid and reduce the amount of iron available for the formation of pro-eutectic b-Al 5 FeSi.…”

“…[12] The plate-like d-Al 3 FeSi 2 phase may be misidentified as b-Al 5 FeSi phase, particularly in modified Al-Si alloys. [13,14] The iron-rich d phase is termed as d-Al 3 FeSi 2 [12][13][14][15] or d-Al 4 FeSi 2 [16,17] in the literature. In this study, this phase will be described as d-Al 3 FeSi 2 .…”