Aluminium–lithium alloys (Al–Li) are a set of alloys of aluminium and lithium, often also including copper and zirconium. Since lithium is the least dense elemental metal, these alloys are significantly less dense than aluminium. Commercial Al–Li alloys contain up to 2.45% by mass of lithium.
Alloying with lithium reduces structural mass by three effects:
- A lithium atom is lighter than an aluminium atom; each lithium atom then displaces one aluminium atom from the crystal lattice while maintaining the lattice structure. Every 1% by mass of lithium added to aluminium reduces the density of the resulting alloy by 3% and increases the stiffness by 5%. This effect works up to the solubility limit of lithium in aluminium, which is 4.2%.
- Strain hardening
- Introducing another type of atom into the crystal strains the lattice, which helps block dislocations. The resulting material is thus stronger, which allows less of it to be used.
- Precipitation hardening
- When properly aged, lithium forms a metastable Al3Li phase (δ') with a coherent crystal structure. These precipitates strengthen the metal by impeding dislocation motion during deformation. The precipitates are not stable, however, and care must be taken to prevent overaging with the formation of the stable AlLi (β) phase. This also produces precipitate free zones (PFZs) typically at grain boundaries and can reduce the corrosion resistance of the alloy.
The crystal structure for Al3Li and Al–Li, while based on the FCC crystal system, are very different. Al3Li shows almost the same-size lattice structure as pure aluminium, except that lithium atoms are present in the corners of the unit cell. The Al3Li structure is known as the AuCu3, L12, or Pm3m and has a lattice parameter of 4.01 Å. The Al–Li structure is known as the NaTl, B32, or Fd3m structure, which is made of both lithium and aluminium assuming diamond structures and has a lattice parameter of 6.37 Å. The interatomic spacing for Al–Li (3.19 Å) is smaller than either pure lithium or aluminium.
Al–Li alloys are primarily of interest to the aerospace industry due to the weight advantage they provide. On narrow-body airliners, Arconic (formerly Alcoa) claims up to 10% weight reduction compared to composites, leading to up to 20% better fuel efficiency, at a lower cost than titanium or composites. Aluminum–lithium alloys were first used in the wings and horizontal stabilizer of the North American A-5 Vigilante military aircraft. Other Al–Li alloys have been employed in the lower wing skins of the Airbus A380, the inner wing structure of the Airbus A350, the fuselage of the Bombardier CSeries (where the alloys make up 24% of the fuselage), the cargo floor of the Boeing 777X, and the fan blades of the Pratt & Whitney PurePower geared turbofan aircraft engine. They are also used in the fuel and oxidizer tanks in the SpaceX Falcon 9 launch vehicle, Formula One brake calipers, and the AgustaWestland EH101 helicopter.
The third and final version of the US Space Shuttle's external tank was principally made of Al–Li 2195 alloy. In addition, Al–Li alloys are also used in the Centaur Forward Adapter in the Atlas V rocket, in the Orion Spacecraft, and were to be used in the planned Ares I and Ares V rockets (part of the cancelled Constellation program).
Al–Li alloys are generally joined by friction stir welding. Some Al–Li alloys, such as Weldalite 049, can be welded conventionally; however, this property comes at the price of density; Weldalite 049 has about the same density as 2024 aluminium and 5% higher elastic modulus. Al–Li is also produced in rolls as wide as 220 inches (18 feet; 5.6 metres), which can reduce the number of joins.
Although aluminum–lithium alloys are generally superior to aluminum–copper or aluminum–zinc alloys in ultimate strength-to-weight ratio, their poor fatigue strength under compression remains a problem, which is only partially solved as of 2016. Also, high costs (around 3 times or more than for conventional aluminum alloys), poor corrosion resistance, and strong anisotropy of mechanical properties of rolled aluminum–lithium products has resulted in the paucity of the applications.
List of aluminium–lithium alloys
Aside from its formal four-digit designation derived from its element composition, an aluminium–lithium alloy is also associated with particular generations, based primarily on when it was first produced, but secondarily on its lithium content. The first generation lasted from the initial background research in the early 20th century to their first aircraft application in the middle 20th century. Consisting of alloys that were meant to replace the popular 2024 and 7075 alloys directly, the second generation of Al–Li had high lithium content of at least 2%; this characteristic produced a large reduction in density but resulted in some negative effects, particularly in fracture toughness. The third generation is the current generation of Al–Li product that is available, and it has gained wide acceptance by aircraft manufacturers, unlike the previous two generations. This generation has reduced lithium content to 0.75–1.8% to mitigate those negative characteristics while retaining some of the density reduction; third-generation Al–Li densities range from 2.63 to 2.72 grams per cubic centimetre (0.095 to 0.098 pounds per cubic inch).
First-generation alloys (1920s-1960s)
|1420||MiG-29 fuselages, fuel tanks, and cockpits; Su-27; Tu-156, Tu-204, and Tu-334; Yak-36, and Yak-38 fuselages|
|2020||A-5 Vigilante wings and horizontal stabilizers|
Second-generation alloys (1970s–1980s)
|1441||Be-103 and Be-200|
|1450||An-124 and An-225|
|1460||McDonnell Douglas reusable launch vehicle (DC-X); Tu-156|
|2090 (intended to replace 7075)||A330 and A340 leading edges; C-17 Globemaster; Atlas Centaur payload adapter|
|2091 (CP 274) (intended to replace 2024)||Fokker 28 and Fokker 100 access doors in the fuselage lower fairing|
|8090 (CP 271) (intended to replace 2024)||EH-101 airframe; A330 and A340 leading edges; Titan IV payload adapter|
|2050 (AirWare I-Gauge)||Ares I crew launch vehicle – upper stage; A350 wing ribs; A380 lower wing reinforcement|
|2099 (C460)||A380 stringers, extruded crossbeams, longitudinal beams, and seat rails; Boeing 787|
|2195||Ares I crew launch vehicle – upper stage; Last revision of the Space Shuttle Super Lightweight External Tank|
|2196||A380 extruded crossbeams, longitudinal beams, and seat rails|
|2198 (AirWare I-Form)||Fuselage skin of the A350 and CSeries; Falcon 9 second-stage rocket|
|2397||F-16 bulkheads; Space Shuttle Super Lightweight External Tank intertank thrust panels|
- 1424 aluminium alloy
- 1429 aluminium alloy
- 1441K aluminium alloy
- 1445 aluminium alloy
- V-1461 aluminium alloy
- V-1464 aluminium alloy
- V-1469 aluminium alloy
- 2094 aluminium alloy
- 2095 aluminium alloy (Weldalite 049)
- 2097 aluminium alloy
- 2197 aluminium alloy
- 8025 aluminium alloy
- 8091 aluminium alloy
- 8093 aluminium alloy
- CP 276
- Arconic Technical Center (Upper Burrell, Pennsylvania, USA)
- Arconic Lafayette (Indiana, USA); annual capacity of 20,000 metric tons (22,000 short tons; 20,000,000 kg; 44,000,000 lb) of aluminum–lithium and capable of casting round and rectangular ingot for rolled, extruded and forged applications
- Arconic Kitts Green (United Kingdom)
- Rio Tinto Alcan Dubuc Plant (Canada); capacity 30,000 t (33,000 short tons; 30,000,000 kg; 66,000,000 lb)
- Constellium Issoire (Puy-de-Dôme), France; annual capacity of 14,000 t (15,000 short tons; 14,000,000 kg; 31,000,000 lb)
- Kamensk-Uralsky Metallurgical Works (KUMZ)
- Aleris (Koblenz, Germany)
- Southwest Aluminium
- Joshi, Amit. "The new generation Aluminium Lithium Alloys" (PDF). Indian Institute of Technology, Bombay. Metal Web News. Archived from the original (PDF) on 28 September 2007. Retrieved 3 March 2008.
- Starke, E. A.; Sanders, T. H.; Palmer, I. G. (20 December 2013). "New Approaches to Alloy Development in the Al–Li System". JOM: The Journal of the Minerals, Metals & Materials Society (published August 1981). 33 (8): 24–33. doi:10.1007/BF03339468. ISSN 1047-4838. OCLC 663900840.
- Mahalingam, K.; Gu, B. P.; Liedl, G. L.; Sanders, T. H. (February 1987). "Coarsening of [delta]'(Al3Li) Precipitates in Binary Al–Li Alloys". Acta Metallurgica. 35 (2): 483–498. doi:10.1016/0001-6160(87)90254-9. ISSN 0001-6160. OCLC 1460926.
- Jha, S. C.; Sanders, T. H.; Dayananda, M. A. (February 1987). "Grain Boundary Precipitate Free Zones in Al–Li Alloys". Acta Metallurgica. 35 (2): 473–482. doi:10.1016/0001-6160(87)90253-7. ISSN 0001-6160. OCLC 1460926.
- "Crystal Lattice Structures: The Cu3Au (L12) Structure". Naval Research Laboratory (NRL) Center for Computational Materials Science. 21 October 2004. Archived from the original on 6 April 2010.
- "Crystal Lattice Structures: The NaTl (B32) Structure". Naval Research Laboratory (NRL) Center for Computational Materials Science. 17 February 2007. Archived from the original on 12 June 2011.
- Kishio, K.; Brittain, J. O. (1979). "Defect structure of [beta]-LiAl". Journal of Physics and Chemistry of Solids. 40 (12): 933–940. doi:10.1016/0022-3697(79)90121-5. ISSN 0038-1098. OCLC 4926011580.
- Lynch, Kerry (8 August 2017). "FAA Issues Special Conditions for Global 7000 Alloy". Aviation International News. Archived from the original on 11 August 2017. Retrieved 7 March 2019.
- Djukanovic, Goran (5 September 2017). "Aluminium-Lithium Alloys Fight Back". Archived from the original on 23 November 2017. Retrieved 7 March 2019.
- Bhaskara, Vinay (2 November 2015). "Battle of the Regionals – ERJ vs CSeries vs MRJ vs SSJ: Introduction and Market Overview". Airways Magazine. Archived from the original on 7 March 2019.
- "Alcoa Wins Fourth Boeing Contract in String of Recent Deals" (Press release). 28 January 2016. Archived from the original on 7 March 2019. Retrieved 7 March 2019.
- "Alcoa Announces Jet Engine First in $1.1 Billion Supply Agreement with Pratt & Whitney: Unveils World's First Advanced Aluminum Alloy Fan Blade Forging for Pratt & Whitney's Hybrid-Metallic Fan Blade for the PurePower® Engines" (Press release). New York, NY, USA and Farnborough, England, UK. 14 July 2014. Archived from the original on 7 March 2019. Retrieved 7 March 2019.
- "MEE433B: Aluminium-Lithium Alloys". Queen's University Faculty of Applied Science. Archived from the original on 6 August 2004.
- "NASA Facts: Super Lightweight External Tank" (PDF) (Press release). Huntsville, Alabama: National Aeronautics and Space Administration (NASA) Marshall Space Flight Center. April 2005. Archived (PDF) from the original on 4 January 2006.
- "Atlas V". Archived from the original on 30 October 2008. Retrieved 7 March 2019.
- "Lighter, Stronger and Bigger Than Ever: Arconic helps builds the future of aviation with advanced aluminum-lithium". Archived from the original on 15 April 2017. Retrieved 7 March 2019.
- Zhu, Xiao-hui; Zheng, Zi-qiao; Zhong, Shen; Li, Hong-ying (5–9 September 2010). "Effect of Mg and Zn Elements on the Mechanical Properties and Precipitates in 2099 Alloy" (PDF). In Kumai, Shinji (ed.). ICAA12 Yokohama: proceedings. Proceedings of the International Conference on Aluminium Alloys. 12. Yokohama, Japan: The Japan Institute of Light Metals. pp. 2375–2380. ISBN 978-4-905829-11-9. OCLC 780496456. Archived (PDF) from the original on 6 April 2017.
- Rioja, Roberto J.; Liu, John (September 2012). "The Evolution of Al-Li Base Products for Aerospace and Space Applications" (PDF). Metallurgical and Materials Transactions A. Springer US (published 31 March 2012). 43 (9): 3325–3337. Bibcode:2012MMTA...43.3325R. doi:10.1007/s11661-012-1155-z. ISSN 1073-5623. Archived from the original on 20 February 2019. Retrieved 9 March 2019.
- Eswara Prasad, Gokhale & Wanhill 2014; Chapter 15: Aerospace applications of aluminum-lithium alloys
- Grushko, Ovsyannikov & Ovchinnokov 2016; Chapter 1: Brief history of aluminum-lithium alloy creation
- "Fact Sheet 6 – Part II: A Joint Plan for Launcher Technology Development". X-33 History Project. 22 December 1999. Archived from the original on 13 February 2016. Retrieved 11 March 2019.
- Eswara Prasad, N.; Gokhale, A. A.; Rama Rao, P. (February–April 2003). "Mechanical behaviour of aluminium-lithium alloys" (PDF). Sadhana: Academy Proceedings in Engineering Sciences. 28 (1–2): 209–246. doi:10.1007/BF02717134. ISSN 0256-2499. OCLC 5652684711. Archived from the original on 4 April 2017. Retrieved 18 March 2019. Lay summary.
- Vaessen, G. J. H.; van Tilborgh, C.; van Rooijen, H. W. (3–5 October 1988). "Fabrication of test-articles from Al-Li 2091 for Fokker 100". New light alloys: Papers presented at the 67th Meeting of the Structures and Materials Panel of AGARD in Mierlo, Netherlands, 3–5 October 1988 (PDF). Meeting of the Structures and Materials Panel of the Advisory Group for Aerospace Research and Development (AGARD), North Atlantic Treaty Organization (NATO). 67. Mierlo, Netherlands (published 1 August 1989). pp. 13–1 to 13–12. ISBN 92-835-0519-0. OCLC 228022064. Archived from the original on 24 February 2018. Retrieved 18 March 2019. Lay summary.
- Constellium (2 October 2012). Constellium AIRWARE® Technology (Trailer).
- Lequeu, Ph.; Lassince, Ph.; Warner, T. (July 2007). "Aluminum alloy development for the Airbus A380 - part 2". Advanced Materials & Processes. 165 (7). pp. 41–44. ISSN 0882-7958. OCLC 210224702. Archived from the original on 17 March 2019. Retrieved 16 March 2019.
- Aluminum alloy 2055-T84 extrusions: High strength, fatigue resistant, low density extrusions (PDF) (Technical report). Lafayette, Indiana: Arconic Forgings and Extrusions. December 2016. Archived (PDF) from the original on 26 October 2017.
- Grushko, Ovsyannikov & Ovchinnokov 2016, p. 9 (Table 1.2: Composition of Aluminum–Lithium Alloys Registered in the United States, France, and Great Britain)
- Pacchione, M.; Telgkamp, J. (5 September 2006). "Challenges of the metallic fuselage" (PDF). 25th International Congress of the Aeronautical Sciences (ICAS 2006). Congress of the International Council of the Aeronautical Sciences. 4.5.1 (25 ed.). Hamburg, Germany. pp. 2110–2121. ISBN 978-0-9533991-7-8. OCLC 163579415. Archived (PDF) from the original on 27 January 2018. Retrieved 7 March 2019. Lay summary.
- Niedzinski, Michael (11 February 2019). "Article: The evolution of Constellium Al-Li alloys for space launch and crew module applications". Light Metal Age: The International Magazine of the Light Metal Industry (published February 2019). p. 36. ISSN 0024-3345. OCLC 930270638. Retrieved 17 March 2019.
- Grushko, Ovsyannikov & Ovchinnokov 2016, pp. 7–8 (Table 1.1: Russian Aluminum–Lithium Alloys)
- Sauermann, Roger; Friedrich, Bernd; Grimmig, T.; Buenck, M.; Bührig-Polaczek, Andreas (2006). "Development of Aluminum-Lithium alloys processed by the Rheo container process" (PDF). In Kang, C .G.; Kim, S. K.; Lee, S. Y. (eds.). Semi-Solid Processing of Alloys and Composites. Solid State Phenomena. 116–117 (published 15 October 2006). pp. 513–517. doi:10.4028/www.scientific.net/SSP.116-117.513. ISBN 9783908451266. OCLC 5159219975. Archived (PDF) from the original on 2 February 2017. Retrieved 7 March 2019.
- Grushko, Olga; Ovsyannikov, Boris; Ovchinnokov, Viktor (2016). Eskin, D. G. (ed.). Aluminum-Lithium Alloys: Process Metallurgy, Physical Metallurgy, and Welding. Advances in metallic alloys. 8. CRC Press/Taylor & Francis Group. doi:10.1201/9781315369525. ISBN 9781498737173. OCLC 943678703. Lay summary.
- Eswara Prasad, N.; Gokhale, Amol A.; Wanhill, R. J. H., eds. (2014). Aluminum-Lithium Alloys: Processing, Properties, and Applications. Elsevier/Butteworth-Heinemann (published 20 September 2013). doi:10.1016/C2012-0-00394-8. ISBN 978-0-12-401698-9. OCLC 871759610. Lay summary.
- Richardson, Mike (14 October 2012). "Lithium cures the woes of aluminium producers". Aerospace Manufacturing. OCLC 907578912. Archived from the original on 9 March 2019.
- "Will Aluminum-Lithium Beat Composites for Narrow Body Airliners?". GLG News. 18 October 2010. Archived from the original on 7 March 2019. Retrieved 7 March 2019 – via AirInsight Group, LLC.