Fe-Rich Intermetallic Formation and Mechanical Properties of Recycled AA6111 Alloy Strips Produced by Melt Conditioning
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https://doi.org/10.1007/s11837-020-04324-z Ó 2020 The Author(s)
ALUMINUM AND MAGNESIUM: CASTING TECHNOLOGY AND SOLIDIFICATION
Fe-Rich Intermetallic Formation and Mechanical Properties of Recycled AA6111 Alloy Strips Produced by Melt Conditioning Twin Roll Casting KAWTHER AL-HELAL
,1,2 JAYESH B. PATEL,1 and ZHONGYUN FAN1
1.—BCAST, Brunel University London, Uxbridge UB8 3PH, UK. 2.—e-mail: [email protected]
The impact of high shear melt conditioning on the morphology and distribution of Fe intermetallic compounds was investigated in the processing of recycled AA6111 alloy by the twin roll casting process. The optical and scanning electron microscope (SEM) micrograph studies were carried out on twin roll casting (TRC) and melt conditioning twin roll casting (MC-TRC) samples. The microstructural analysis showed fine and uniformly distributed Fe-rich intermetallic phases for MC-TRC strips compared with the TRC strips. There was a significant improvement in the mechanical properties of MC-TRC strips after applying melt conditioning. The as-cast MC-TRC samples showed 18.7%, 19.2% and 9.8% increases in elongation, yield strength and ultimate tensile strength, respectively, in the longitudinal direction, while in the transverse section, the MC-TRC samples showed 32.3%, 2.2% and 3.8% increases in elongation, yield strength and ultimate tensile strength, respectively.
INTRODUCTION Iron is one of the unavoidable impurity elements that exist in primary or secondary aluminium alloys, and it is problematic in recycling aluminium scrap. It is accumulated from the bauxite and tools used during the casting process. Because of its low solubility in aluminium, iron with other impurities forms intermetallic phases such as Al3Fe, aAl8Fe2Si, b-Al5FeSi, d-Al4FeSi2 and c-Al3FeSi. The mechanical properties of aluminium alloys are highly affected by the morphology and distribution of these intermetallic phases.1 b-Al5FeSi Fe-rich intermetallics usually form as faceted large platelets, and this brittle structure causes the loss of strength and ductility of the aluminium alloy, while the a-Al8Fe2Si phase appears with many different types of morphology. With a Mn/Fe ratio equal to 0.5, a body-centred cubic a-Al15(Fe, Mn)3Si2 is formed, while different structures appear at other Mn/Fe ratios.2 Morphological control of these intermetallics, from plate-like to compact shapes or resembling Chinese script, can reduce their detrimental effect on the final mechanical properties.3 (Received May 12, 2020; accepted July 31, 2020)
Efforts have been made in casting recycled aluminium alloys to control the formation of Fe-rich intermetallics and reduce their harmful impact on the mechanical properties of the final product. It has been found that Fe-rich phases are likely to nucleate on the oxide films entrained in aluminium alloys, and these oxides are normally agglomerated in clusters within the melt. To disperse large oxide films and clusters into very fine and uniformly distributed individual particles, high shear melt conditioning (HS
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