Microstructural Modeling and Simulation of Al-2.8Cu-1.4Li Alloy during Elevated Temperature Deformation
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RODUCTION
DURING hot working, several heat-activated metallurgical phenomena, such as phase transformation, dynamic recovery, and dynamic recrystallization, occur as a result of the complex interplay between thermal, mechanical, and microstructural conditions. Microstructural changes resulting from those metallurgical phenomena play an important role in flow behavior of material, because the flow stress is affected by grain size, recrystallization fraction, and dislocation density. Furthermore, microstructure obtained by hot working also has an effect on mechanical properties of a formed part. Therefore, it is necessary to quantify the relationship between process parameters and microstructural change of the material. Microstructural changes of metals are subjected to external variables including temperature, strain rate, time, and strain histories, and internal variables including initial structure and material properties.[1–3] The empirical model characterizing microstructural evolution during hot working is usually expressed as Vm ¼ fðT; e; e_ ; SÞ; where T is the absolute temperature, e the true strain, e_ the strain rate, and S the internal variable. The influence of factors on microstructural changes was presented in many published studies.[4–8] The empirical models presented by Sellars and Whiteman,[9] Senuma and Yada,[10] and Saito et al[11] are widely employed in hot working. L. DENG and H.T. GUO, Graduate Students, and X.Y. WANG and J.C. XIA, Professors, are with the State Key Lab of Material Processing and Die & Mould Technology, Huazhong University of Science & Technology, Wuhan 430074, People’s Republic of China. Contact e-mail: [email protected] Manuscript submitted July 29, 2010. Article published online March 19, 2011 METALLURGICAL AND MATERIALS TRANSACTIONS A
Al-2.8Cu-1.4Li alloy is being considered as an ideal candidate material for applications in aerospace and aircraft industry manufacturing bulkhead and bracing structure parts.[12] Although the hot deformation behavior of this alloy was investigated,[13] the microstructural evolution behavior of this alloy needs to be investigated to understand the workability and establish the optimum hot working process parameters for Al-2.8Cu1.4Li alloy. In this article, the dynamic recrystallization model and constitutive equation were obtained from the results of isothermal compression experiments. A coupled thermomechanical finite element program integrated with these models was used to simulate microstructural changes during hot upsetting.
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EXPERIMENTAL PROCEDURE
The material used was commercially produced Al-CuLi alloy with a nominal composition (wt pct) of Al-2.8Cu1.4Li-0.30Mn-0.12Zr-0.10Zn. Cylindrical specimens were compressed with a Zwick/Roell Z020 universal testing machine (Zwick/Roell Group, Ulm, Germany) at five different temperatures (643 K (370 °C), 663 K (390 °C), 683 K (410 °C), 703 K (430 °C), and 723 K (450 °C)) and five different strain rates (0.001 s1, 0.01 s1, 0.05 s1, 0.5 s1, and 1 s1). In order to investigate the effect of strain on
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