Understanding Fe-Containing Intermetallic Compounds in Al Alloys: An Overview of Recent Advances from the LiME Research Hub

Abstract

Control of Fe in Al alloys is a severe challenge for the full metal circulation to produce the recycled alloys with mechanical and physical performance as high as the primary alloys. The high restriction of Fe content is mainly due to the deterioration caused by the large-scale Fe-containing intermetallic compounds (FIMCs) in Al alloys. In this paper, recent knowledge gained regarding nucleation, formation, and technical developments on microstructural control and refinement of FIMCs are overviewed. Specific characteristics of the multiple types of FIMCs in Al alloys are presented in two- and three- dimensional (2D and 3D) form. Phase relationships between the FIMCs in different structures, such as primary phase, binary eutectic, and ternary eutectic, formed at different solidification stages are studied. Phase transformations between the FIMCs with or without intermediate phases during the solidification process are examined in different Al alloys, with the mechanisms being clarified. Various approaches to microstructural control of FIMCs are proposed and validated. Significant refinement of FIMCs has been achieved through inoculation of TiB2 particles that had been previously modified with deliberately interfacial segregation of desirable alloying elements, leading to the development of the novel “compositional templating” concept.

Microstructural Evolution in a 6060 Extrudable Al-Alloy: Integrated Modeling and Experimental Validation

“…Further observations of the morphology and orientation of cross-sections confirmed that the observed particles corresponded to the metastable β ′′ -Mg 5 Al 2 Si 4 . More specifically a monoclinic unit cell with sides a = 15.16 , b = 4.05 , c = 6.74 , angle β = 105.3 • , and a unit cell volume of V cell = 399.2 3 , characteristic of β ′′ -Mg 5 Al 2 Si 4 was observed as shown in Figure 15c,d. It can be considered as a supercell in the Al matrix with a||<320>Al, b||<001>Al and c||<310>Al.…”

“…Coarse Fe-rich intermetallics, eutectics and elemental segregation at grain boundaries and secondary dendrite arms that form upon solidification limit extrudability [1,2]. The β-AlFeSi phase in particular can be very detrimental for extrusion, being prone to nucleating cracks due to its monoclinic structure and plate morphology [3]. Homogenization aims at eliminating the as-cast structure and transforming the β-AlFeSi to α-AlFeSi phase with a cubic structure and globular morphology which is less impactful to extrudability [4][5][6].…”

Crystal Chemistry and Physical Properties of A Quaternary Intermetallic Compound, θ-(Al0.8718Cu0.0256Si0.1026)13Fe4

“…The estimated chemical compositions are θ-(Al 76-n Si n )Cu 2 Fe 24 with 4 < n < 6 at 1000 K. Moreover, the configurational entropy contributions further stabi-lize the θ-phase. This information is helpful in investigating the formation of the θ-phase at the phase transformations of the θ-phase to other Fe-IMCs during the casting and related annealing processes of various Al-based alloys [7,52,53].…”