A Formation Map of Iron-Containing Intermetallic Phases in Recycled Cast Aluminum Alloys
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TRODUCTION
THE demand for improved fuel economy and lower greenhouse gas emission without compromising passenger safety and performance has led to increased use of lightweight materials in vehicles over the last few decades.[1] Such demand has made aluminum alloys the material of choice for many automotive applications because of their lightweight, good specific strength, and exceptional corrosion resistance.[2] However, the high costs of primary aluminum production[3] and component manufacturing often limit the widespread usage of aluminum in the vehicle design.[4] To achieve further weight reduction in light vehicles while maintaining the affordability, it is essential to lower the manufacturing cost of aluminum components. Aluminum can be recycled many times with exceptional recovery rates, where the energy required to produce secondary or recycled aluminum is only 5 pct of the energy used in the production of primary aluminum.[3] Such a reduction highlights strong economic and environmental benefits of utilizing recycled aluminum in production of parts for automotive industry.[3] Additionally, the excellent castability of aluminum E. CINKILIC and C.D. RIDGEWAY are with the Department of Materials Science & Engineering, The Ohio State University, Columbus, OH 43210. X. YAN is with the Alcoa Technical Center, New Kensington, PA 15068. A.A. LUO is with the Department of Materials Science & Engineering, The Ohio State University and also with the Department of Integrated Systems Engineering, The Ohio State University, Columbus, OH 43210. Contact e-mail: [email protected] Manuscript submitted June 21, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
alloys, especially of the Al-Si based alloys, enables the production of complex components as well as the consolidation of welded or joined subsystems into a single cast part at a lower cost.[2] Despite the promising outlook for the use of secondary aluminum, there is a cascade effect from continued recycling of aluminum, i.e., accumulation of alloying/impurity elements such as Fe, Mg, Cu, Zn, etc., due to the difficulty in removing them in the recycling process.[5,6] The result is that the properties of the recycled aluminum alloys can be significantly altered by the excess concentrations of these elements and renders the recycled material ill-suited for safety critical applications. Of all impurity elements, Fe is considered the most detrimental, and its deleterious effect on the mechanical properties of Al-Si alloys is well known to the aluminum casting industry.[7–9] Fe can form numerous intermetallic phases, such as, h-Al13Fe4, a-Al8Fe2Si, b-Al5FeSi, d-Al4FeSi2, p-Al8FeMg3Si2, etc., when it is combined with other alloying elements. The size, morphology, and volume fraction of these Fe-containing intermetallics have a pronounced effect on the as-cast mechanical properties of Al-Si alloys. The most common and detrimental Fe-containing intermetallic observed in hypoeutectic Al-Si casting alloys is b-Al5FeSi phase which forms as interconnected thin platelets with a needle-like ap
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