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Presentation Alternatives to the Al-Si Eutectic

System in Aluminum Casting Alloys (15-089)

Authors Teodoros Koutsoukis and Makhlouf

Makhlouf, Worcester Polytechnic Insti- tute, Advanced Casting Research Center, Worcester, Mass.


The majority of the traditional aluminum casting alloys are based on the aluminum-silicon eutec- tic system because of its excellent casting characteristics, including good fluidity and resistance to hot tearing. Unfortunately, the solidus in this system does not exceed 1,071F (577C) and the major alloying elements in traditional aluminum casting alloys, e.g., zinc, magnesium, and copper, further depress the al- loy’s liquidus temperature. Moreover, these alloying elements have high diffusivity in the aluminum solid solution and their diffusivity in- creases with increased temperature. Therefore, while casting alloys based on the aluminum-silicon eutectic and traditional strengthening ele- ments have good room temperature strength, their strength is rapidly degraded when they are used at tem- peratures higher than 482F (250C). Furthermore, silicon interacts with aluminum and iron—which is invariably present in commercial aluminum casting alloys—to form harmful intermetallic compounds, such as the β-(Al5

SiFe) phase, which

adversely impacts the alloys’ ductil- ity, or with precipitation strengthen- ing elements. In many applications, stability of

mechanical properties at high tem- perature is the primary need, not high strength at room temperature. In this study, the binary aluminum-nickel and aluminum-iron eutectics, as well as the ternary aluminum-iron-nickel eutectic are considered as alternatives to the aluminum-silicon eutectic for constituting aluminum casting alloys. Te purpose of this investigation is to measure the casting ability (i.e., the tendency to hot tear and the ability

to fill the mold cavity), the room and elevated temperature (662F or 350C) tensile properties (i.e., ultimate tensile strength, yield strength and elonga- tion) of these eutectic compositions, and compare them to their counter- parts for the aluminum-silicon eutec- tic and, when necessary, also to those of commercial grade A390, A206 and 413.0 alloys.

Conclusions Te three alternative eutectic sys-

tems investigated, namely the Al-Ni eutectic, the Al-Fe eutectic and the Al-Ni-Fe eutectic, exhibit very good casting ability and tensile properties at both room temperature and elevated temperature; and in this regard, they compare favorably with the Al-Si eutectic. Among the four eutectics, the Al-Ni eutectic has the highest strength at room temperature, but Ni is significantly more expensive than Si and Fe. Te Al-Fe eutectic has excel-

lent casting ability and is inexpensive compared to the Al-Ni eutectic, but it has the lowest room temperature strength among the four eutectics. Te elevated temperature (662F or 350C) tensile properties of the Al-Ni, Al-Fe and Al-Fe-Ni eutectics are superior to those of the Al-Si eutectic with the 662F (350C) tensile strength of the Al-Ni-Fe eutectic being the highest among all four eutectics. Among the four eutectic systems investigated, the Al-Fe-Ni eutectic is the most thermally stable. The Al-Fe-Ni eutectic combines

characteristics of both the Al-Ni and Al-Fe systems, i.e., good casting ability, good elevated temperature tensile properties, and low cost. Therefore it is the most promis- ing of the eutectic systems for high temperature applications. Te three papers summarized in this

article were presented at the 119th Met- alcasting Congress in Columbus, Ohio.


-25 “Hg, S.G.: 2.47

-26 “Hg, S.G.: 2.36

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