Tensile properties and hot tearing susceptibility of cast Al-Cu alloys containing excess Fe and Si
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Tensile properties and hot tearing susceptibility of cast Al–Cu alloys containing excess Fe and Si Khalil Ganjehfard 1), Reza Taghiabadi 1), Mohammad Talafi Noghani 1), and Mohammad Hossein Ghoncheh 2) 1) Faculty of Engineering, Imam Khomeini International University (IKIU), Qazvin, Iran 2) Department of Mechanical Engineering, University of New Brunswick, Fredericton, NB, Canada (Received: 6 February 2020; revised: 1 March 2020; accepted: 6 March 2020)
Abstract: This study was undertaken to investigate the tensile properties and hot tearing susceptibility of cast Al–Cu alloys containing excess Fe (up to 1.5wt%) and Si (up to 2.5wt%). According to the results, the optimum tensile properties and hot tearing resistance were achieved at Fe/Si mass ratio of 1, where the α-Fe phase was the dominant Fe compound. Increasing the Fe/Si mass ratio above unity increased the amounts of detrimental β-CuFe platelets in the microstructure, deteriorating the tensile properties and hot tearing resistance. Decreasing the mass ratio below unity increased the size and fraction of Si needles and micropores in the microstructure, also impairing the tensile properties and hot tearing resistance. The investigation of hot-torn surfaces revealed that the β-CuFe platelets disrupted the tear healing phenomenon by blocking interdendritic feeding channels, while the α-Fe intermetallics improved the hot tearing resistivity due to their compact morphology and high melting point. Keywords: aluminum–copper alloys; castability; fluidity; hot tearing susceptibility
1. Introduction Over the last decades, demands on using A206 Al–Cu alloys in automotive and aerospace industries have grown significantly. This growth is mostly due to the excellent strength and ductility and the good fracture toughness of these alloys, which are much higher than those of conventional 3xx casting alloys and close to those of some grades of ductile iron [1–4]. However, the poor casting characteristics, especially the long freezing range (505–643°C), poor fluidity, and high hot tearing susceptibility (HTS), significantly restrict the application of these alloys in the production of complex-shape castings such as wheels, cylinder heads, and engine blocks as well as castings that need to be poured in gravity-fed permanent molds [3–5]. The other issue with A206 Al–Cu alloys is the high variability of their mechanical properties, arising from their casting-related defects such as micropores and entrained double oxides [2]. The formation of harmful Fe-bearing compounds can also limit the application of Al–Cu casting alloys. Iron is the most common impurity found in Al–Cu alloys [6]. It has been shown that due to the sudden solid-solubility drop in Al
(from about 1.8wt% at 655°C in liquid to 0.005wt% at 450°C in solid Al) [7–8], the presence of Fe promotes the formation of brittle intermetallics in the microstructure of Al–Cu alloys, where the most important intermetallics are plate-like βAl7Cu2Fe (referred to as
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