Segregation Behavior, Microstructure and Properties of 2099Al-Li Alloy Produced by Twin-Roll Casting Underthe Action of Electromagnetic Oscillation Field
LI Shiju1,2, LI Yang1,2, CHEN Jianqiang1, LI Zhonghao1, XU Guangming1,2(), LI Yong1, WANG Zhaodong1, WANG Guodong1
1.State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, China 2.Key Laboratory of Electromagnetic Processing of Materials, Ministry of Education, Northeastern University, Shenyang 110819, China
Cite this article:
LI Shiju, LI Yang, CHEN Jianqiang, LI Zhonghao, XU Guangming, LI Yong, WANG Zhaodong, WANG Guodong. Segregation Behavior, Microstructure and Properties of 2099Al-Li Alloy Produced by Twin-Roll Casting Underthe Action of Electromagnetic Oscillation Field. Acta Metall Sin, 2020, 56(6): 831-839.
Al-Li alloy has been widely applied in the fields of aircraft, aerospace and military applications due to its superior comprehensive properties. Al-Li alloy prepared by traditional casting process will have shrinkage porosities and gas holes defects due to the gas absorption of lithium element. Twin-roll casting (TRC) process combines continuous casting and rolling deformation into one process. The melt subjected to a certain rolling force during cooling and solidifying, compensates for the solidification shrinkage of liquid metal in the roll-casting region, hence solving the problems of porosity and other defects in Al-Li alloy. However, due to the wide solidification range of 2099Al-Li alloy, the central macro-segregation inevitably occurs in the sheets produced by TRC, which seriously deteriorates the mechanical properties of the sheets. How to eliminate segregation in aluminum alloys strips by adjusting the rolling parameters has been studied for decades. But the effect was not obvious and new approaches are required to solve this challenge. Introducing electromagnetic oscillation field in TRC process may be an effective way to solve the central segregation in TRC sheets. In this work, the OM, SEM, EMPA, DSC, conductivity and tensile test are employed to study the microstructure and properties of 2099Al-Li alloy prepared by TRC and electromagnetic TRC, respectively. The Lorentz force generated in the roll-casting region by applying electromagnetic oscillation field during TRC, which can break the dendrite and refine the solidification structure of the alloy. The central segregation band of the TRC sheet basically eliminated, and the segregation degree of Cu, Zn and Mg elements reduced to 2.45, 0.93 and 1.05. The macro-segregation and micro-segregation of sheets were effectively reduced. At the same time, the electromagnetic oscillation field can enhance the mixing ability of solute atoms, reduce the content of non-equilibrium eutectic phase and improve the supersaturated solid solubility of matrix. Compared with TRC sheet, the tensile strength, yield strength and elongation of 2099Al-Li alloy sheet prepared by ETRC increased by 34 MPa, 18 MPa and 2.8% respectively, hence the mechanical properties of the alloy sheet were greatly improved. This research work provides a new idea for the efficient preparation of Al-Li alloy with energy-saving, high-efficiency and green environmental protection.
Fig.1 Schematic of electromagnetic twin-roll casting (TRC) technique (a) and practicality diagram of electromagnetic TRC experimental device (b) (1—2099Al-Li alloy melt; 2—chute; 3—nozzle; 4—electromagnetic coil; 5—2099Al-Li alloy sheet; 6—roll; 7—cooling water; 8—pulsed electric field (PEF) wire; 9—pulse power supply)
Fig.2 Microstructures of 2099Al-Li alloy produced by different processes (a, b) TRC (c, d) electromagnetic TRC
Fig.3 Secondary dendrite arm spacing statistical results of 2099Al-Li alloy produced by different processes (a) TRC (b) electromagnetic TRC
Fig.4 Microstructures (a, c) and element distributions (b, d) of 2099Al-Li alloy produce by different processes Color online (a, b) TRC (c, d) electromagnetic TRC
Process
Element
Cmax / %
Cmin / %
C0 / %
Se
TRC
Cu
23.25
0.22
1.63
14.13
Zn
1.14
0.29
0.69
1.23
Mg
0.43
0.15
0.21
1.33
Electromagnetic TRC
Cu
1.59
0.22
0.56
2.45
Zn
0.86
0.34
0.56
0.93
Mg
0.34
0.12
0.21
1.05
Table 1 Element contents at the EPMA characteristic position of 2099Al-Li alloy prepared by different processes
Fig.5 The segregation degree of 2099Al-Li alloy produced by different processes
Fig.6 DSC curves of 2099Al-Li alloy produced by different processes
Fig.7 Fracture morphologies of 2099Al-Li alloy produced by different processes (a) TRC (b) electromagnetic TRC
Fig.8 Force analysis of charged particles under electromagnetic oscillation field and dendrite fragmentation model
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