13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Tensile mechanical behavior of as-cast AA7050 alloy in the super-solidus temperature range T Subroto1,2,*, A Miroux1,2, D G Eskin3, K Ellingsen4, A Marson5, M M'Hamdi4, L Katgerman2 1 Materials innovation institute (M2i), Mekelweg 2, Delft, 2628 CD, The Netherlands 2 Dept. of Mat. Sci. and Engineering, Delft University of Technology, Mekelweg 2, Delft, 2628 CD, The Netherlands 3 BCAST, Brunel University, Uxbridge, Middlesex, UB8 3PH, United Kingdom 4 SINTEF Materials and Chemistry, NO-0314 Oslo, Norway 5 SINTEF Materials and Chemistry, NO-7465 Trondheim, Norway * Corresponding author: tsubroto@m2i.nl Abstract Aluminum 7050 alloy is one of the primary alloys for the aviation industry owing to its excellent mechanical properties. However, this alloy has several poor physical properties that affect its solidification, such as relatively low thermal conductivity and large solidification range. These properties tend to increase the hot tearing susceptibility of the alloy, which makes it difficult to produce by direct-chill (DC) casting. Accurate knowledge of the mechanical behavior of the alloy during solidification is therefore crucial to ensure safe control of the casting process. Present work focuses on measuring the tensile mechanical properties of an as-cast AA7050 in the temperature range where hot tearing mainly occurs, i.e. from solid fractions of 0.85 to 1.0, or the solidus. Through these experiments, we extracted mechanical properties such as strain-rate sensitivity and ductility of the alloy in the super-solidus temperature range. The data obtained from this work will be useful in thermo-mechanical computer simulations aimed at reducing the hot tearing occurrence during DC casting, thus optimizing the production rate in the casting house. Keywords AA7050, DC Casting, solidification, hot tearing, tensile mechanical properties 1. Introduction AA7050 is one of the most used alloys for aerospace industries owing to its excellent mechanical properties such as high tensile strength, good fracture toughness and stress corrosion resistance [1, 2]. This alloy is usually produced via a vertical direct-chill (DC) casting method because of the robustness and relative simplicity of such process [3]. Despite its superior qualities, AA7050 is known to be susceptible to hot tearing due to its wide solidification range and relatively high thermal expansion coefficient [4]. Hot tearing usually occurs during DC casting, at the end of solidification when the alloy is in a semi-solid state but most of the liquid has been solidified and the remaining liquid resides at the grain boundaries [5]. The presence of such a defect causes the rejection of the ingot or lowers the quality of the cast product which subsequently affects its economical value [6]. In order to minimize the occurrence of hot tearing, it is critical to understand the mechanical properties in this solidification range [7]. Therefore, in this work, we investigated the tensile mechanical behavior of the alloy – which is the dominant stress mode related to hot tearing during DC casting, in the range of solid fractions of 0.85 and 1.0 (just before it is fully solidified), where hot tearing is most likely to occur. Such tensile mechanical properties will be useful input for a numerical process simulator aiming at minimizing the occurrence of hot tearing during DC casting, thus, optimizing the production rate in the aluminum cast house. 2. Experimental procedure The tensile specimens used for the experiment were cut from an ingot produced via DC casting at Tata Steel (IJmuiden, The Netherlands). The ingot was DC cast using a conventional bore mold
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