Abstract
During the direct chill (DC) casting process, primary cooling from the mold and bottom block, and secondary cooling from the waterjets produce a concave solid shell. The depth of this liquid pocket and mushy zone not only depends on the solidification range of the alloy but also the boundary conditions such as cooling rates. Al-Li alloys solidify in a long solidification range increasing the susceptibility of porosity nucleation in the semi-solid region. In this study, the effects of cooling rate on the porosity formation were quantified for the large ingot casting using X-ray computed tomography (XCT). By characterizing pore size distributions at four different cooling conditions, the correlation between the mechanical properties at both room and high temperatures and the microstructure features was identified. The constitutive equations were constructed. It is found that increasing the cooling rate reduces the grain size, increases the number density of micropores, and minimizes the number of large pores, thereby improving the mechanical performance. Therefore, long mushy zones and deep liquid pockets in Al-Li alloys can be effectively controlled by controlling the boundary conditions of the DC casting solidification process, thereby obtaining castings with excellent mechanical properties.
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References
Phillion A B, Cockcroft S L, Lee P D. Predicting the constitutive behavior of semi-solids via a direct finite element simulation: Application to AA5182. Modelling and Simulation in Materials Science and Engineering, 2009, 17(5): 055011.
Couper M J, Neeson A E, Griffiths J R. Casting defects and the fatigue behavior of an aluminium casting alloy. Fatigue Fract. Eng. Mater. Struct., 2010, 13: 213–227.
Rioja R J, Liu J. The evolution of Al-Li base products for aerospace and space applications. Metallurgical & Materials Transactions A, 2012, 43(9): 3325–3337.
Wanhill R, Bray G H. Fatigue crack growth behavior of aluminum-lithium alloys. Elsevier Inc: Netherlands, 2014: 381–413.
Wang F Y, Wang X J, Cui J Z. Micro-structure and mechanical properties of 2A97 Al-Li alloy cast by low-frequency electromagnetic casting. Metals-Open Access Metallurgy Journal, 2019, 9(8): 822.
Chen X X, Zhao G Q, Liu G L, et al. Microstructure evolution and mechanical properties of 2196 Al-Li alloy in hot extrusion process. Journal of Materials Processing Technology, 2019, 275: 116348.
Vreeman C J, Schloz J D, Krane M J M. Direct chill casting of aluminum alloys: Modeling and experiments on industrial scale ingots. ASME, 2002, 124: 947–953.
Luo Y J, Zhang Z F. Numerical modeling of annular electromagnetic stirring with intercooling in direct chill casting of 7005 aluminum alloy billet. Progress in Natural Science: Materials International, 2019, 29(1): 88–94.
Skallerud B, Hrkegrd G, Iveland T, et al. Fatigue life assessment of aluminum alloys with casting defects. Engineering Fracture Mechanics, 1993, 44(6): 857–874.
Akhtar N, Akhtar W, Wu S J. Melting and casting of lithium containing aluminium alloys. International Journal of Cast Metals Research, 2015, 28(1): 1–8.
Gu J L, Yang S L, Gao M J, et al. Micropore evolution in additively manufactured aluminum alloys under heat treatment and inter-layer rolling. Materials & design, 2019, 186: 108288.
Gu C, Lu Y, Luo A A. Three-dimensional visualization and quantification of microporosity in aluminum castings by X-ray micro-computed tomography. Journal of Materials Science and Technology, 2020, 65: 99–107.
Wang J S. Physical metallurgy of aluminum alloys. In: Anderson K, Weritz J, and Kaufman G (Eds.), ASM Handbook, Aluminum and Aluminum Alloys, 2018, 2A: 44–79.
Ding Z Y, Hu Q D, Lu W Q, et al. In-situ study on hydrogen bubble evolution in the liquid Al/solid Ni interconnection by synchrotron radiation X-ray radiography. Journal of Materials Science & Technology, 2019, 35(7): 1388–1392.
Wang J S. Aluminum alloy ingot casting and continuous processes. Aluminum Science and Technology, ASM Handbook, 2018, 108–115.
Lee P D, Hunt J D. Hydrogen porosity in directionally solidified aluminium-copper alloys: A mathematical model. Acta Materialia, 2001, 49(8): 1383–1398.
Zhang Q Y, Wang T T, Yao Z J, et al. Modeling of hydrogen porosity formation during solidification of dendrites and irregular eutectics in Al-Si alloys. Materialia, 2018, 15(4): 211–220.
Anyalebechi P N, Talbot D E J, Granger D A. The solubility of hydrogen in solid binary aluminum-lithium alloys. Metallurgical Transactions B, 1989, 20(4): 523–533.
Anyalebechi P N. Analysis of the effects of alloying elements on hydrogen solubility in liquid aluminum alloys. Scripta Metallurgica et Materialia, 1995, 33(8): 1209–1216.
Anyalebechi P N. Attempt to predict hydrogen solubility limits in liquid multicomponent aluminum alloys. Scripta Materialia, 1996, 34(4): 513–517.
Smith S W, Scully J R. The identification of hydrogen trapping states in an Al-Li-Cu-Zr alloy using thermal desorption spectroscopy. Metallurgical & Materials Transactions A, 2000, 31(1): 179–193.
Lee P D, Atwood R C, Dashwood R J, et al. Modeling of porosity formation in direct chill cast aluminum-magnesium alloys. Materials Science & Engineering A, 2002, 328(1–2): 213–222.
Lee P D, Wang J S. Modeling of porosity formation during solidification. Metals Process Simulation, ASM Handbook, 2010, 22B: 253–263.
Chaijaruwanich A, Dashwood J, Lee P D, et al. Pore evolution in a direct chill cast Al-6 wt.% Mg alloy during hot rolling. Acta Materialia, 2006, 4: 5185–5194.
Chaijaruwanich A, Lee P D, Dashwood R J, et al. Evolution of pore morphology and distribution during the homogenization of direct chill cast Al-Mg alloys. Acta Materialia, 2007, 55(1): 285–293.
Wang J S, Lee P D, Simulating tortuous 3D morphology of microporosity formed during solidification of Al-Si-Cu alloys. International Journal of Cast Metals Research. 2007, 20(3): 151–158.
Wang J S, Lee P D, Hamilton R W, et al. The kinetics of Fe-rich intermetallic formation in aluminium alloys: In situ observation. Scripta Materialia, 2009, 60(7): 516–519.
Wang J S, Li M, Allison J, et al. Multiscale modeling of the influence of Fe content in a Al-Si-Cu alloy on the size distribution of intermetallic phases and micropores. Journal of Applied Physics, 2010, 107(6): 061804.
Phillion A B, Cockcroft S L, Lee P D. A new methodology for measurement of semi-solid constitutive behavior and its application to examination of as-cast porosity and hot tearing in aluminum alloys. Materials Science and Engineering: A, 2008, 491(1–2): 237–247.
Dou R F, Phillion A B. Application of a pore fraction hot tearing model to directionally solidified and direct chill cast aluminum alloys. Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, 2016, 47: 4217–4225.
Chen D X, Dou R F, Han J Q, et al. Prediction of hot tearing susceptibility of direct chill casting of AA6111 alloys via finite element simulations. Transactions of Nonferrous Metals Society of China, 2020, 30(12): 3161–3172.
Hao H, Maijer D M, Wells M A, et al. Development and validation of a thermal model of the direct chill casting of AZ31 magnesium billets. Metallurgical & Materials Transactions A, 2004, 35(12): 3843–3854.
Baserinia A R, Ng H, Weckman D C, et al. A Simple model of the mold boundary condition in direct-chill (DC) casting of aluminum alloys. Metallurgical & Materials Transactions B, 2012, 43(4): 887–901.
Gu J L, Gao M J, Yang S L, et al. Pore formation and evolution in wire + arc additively manufactured 2319 Al alloy. Additive Manufacturing, 2019, 30: 100900.
Xue C P, Zhang Y X, Mao P C, et al. Improving mechanical properties of wire arc additively manufactured AA2196 Al-Li alloy by controlling solidification defects. Additive Manufacturing, 2021, 43: 102019.
Alankar A, Wells M A. Constitutive behavior of as-cast aluminum alloys AA3104, AA5182 and AA6111 at below solidus temperatures. Materials Science and Engineering: A, 2010, 527(29–30): 7812–7820.
Chen R, Wang H M, He B, et al. Effect of thermal cycling on microstructure and mechanical properties of 2A97 Al-Li alloy fabricated by direct laser deposition. Vacuum, 2021, 190: 110299.
Zhou Y H, Lin X, Kang N, et al. Influence of travel speed on microstructure and mechanical properties of wire + arc additively manufactured 2219 aluminum alloy. Journal of Materials Science & Technology, 2020, 37: 143–153.
Kastner J, Harrer B, Peter Degischer H. High resolution cone beam X-ray computed tomography of 3D-microstructures of cast Al-alloys. Materials Characterization, 2011, 62(1): 99–107.
Wang B, Zhang M S, Wang J S. Quantifying the effects of cooling rates and alloying additions on the microporosity formation in Al alloys. Materials Today Communications, 2021, 28: 102524.
Acknowledgements
The authors wish to express thanks for all the help from the lab mates at the Integrated Computational Materials Engineering (ICME) lab, Beijing Institute of Technology, China. Zeiss (Beijing) and the Experimental Center of Advanced Materials at Beijing Institute of Technology are greatly appreciated for their experiment support. The raw materials from Chinalco Southwest Aluminium (Group) Co., Ltd. are also greatly acknowledged. This research work was supported by the National Natural Science Foundation of China (Project number: 52073030).
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Jun-sheng Wang Professor in the Advanced Research Institute of Multidisciplinary Sciences, Beijing Institute of Technology and Ph.D from Imperial College London, UK and specialized in ultra-light alloy design and manufacture process optimization using Integrated Computational Materials Engineering (ICME), and leading several national key projects to realize integrated design and intelligent manufacturing.
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Zhang, Yx., Wang, Js., Chen, Dx. et al. Effects of cooling rates on microporosity in DC casting Al-Li alloy. China Foundry 19, 177–190 (2022). https://doi.org/10.1007/s41230-022-1183-2
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DOI: https://doi.org/10.1007/s41230-022-1183-2