Aluminium–lithium alloys (Al–Li alloys) are a set of

alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductilit ...

s of

aluminium Aluminium (aluminum in AmE, American and CanE, Canadian English) is a chemical element with the Symbol (chemistry), symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately o ...

and

lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid ...

, often also including copper and

zirconium Zirconium is a chemical element with the symbol Zr and atomic number 40. The name ''zirconium'' is taken from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian '' zargun'' (zircon; ''zar-gun'' ...

. Since lithium is the least dense

elemental An elemental is a mythic being that is described in occult and alchemical works from around the time of the European Renaissance, and particularly elaborated in the 16th century works of Paracelsus. According to Paracelsus and his subsequent fol ...

metal, these alloys are significantly less dense than aluminium. Commercial Al–Li alloys contain up to 2.45% lithium by mass.

Crystal structure

Alloying with lithium reduces structural mass by three effects: ; Displacement : A lithium atom is lighter than an aluminium atom; each lithium atom then displaces one aluminium atom from the

crystal lattice In geometry and crystallography, a Bravais lattice, named after , is an infinite array of discrete points generated by a set of discrete translation operations described in three dimensional space by : \mathbf = n_1 \mathbf_1 + n_2 \mathbf_2 + n ...

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 Stiffness is the extent to which an object resists deformation in response to an applied force. The complementary concept is flexibility or pliability: the more flexible an object is, the less stiff it is. Calculations The stiffness, k, of a b ...

by 5%. This effect works up to the

solubility In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solub ...

limit of lithium in aluminium, which is 4.2%. ;

Strain hardening In materials science, work hardening, also known as strain hardening, is the strengthening of a metal or polymer by plastic deformation. Work hardening may be desirable, undesirable, or inconsequential, depending on the context. This strength ...

: Introducing another type of atom into the crystal strains the lattice, which helps block

dislocations In materials science, a dislocation or Taylor's dislocation is a linear crystallographic defect or irregularity within a crystal structure that contains an abrupt change in the arrangement of atoms. The movement of dislocations allow atoms to s ...

. The resulting material is thus stronger, which allows less of it to be used. ;

Precipitation hardening Precipitation hardening, also called age hardening or particle hardening, is a heat treatment technique used to increase the yield strength of malleable materials, including most structural alloys of aluminium, magnesium, nickel, titanium, and so ...

: 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 In materials science, a grain boundary is the interface between two grains, or crystallites, in a polycrystalline material. Grain boundaries are two-dimensional defects in the crystal structure, and tend to decrease the electrical and thermal ...

and can reduce the

corrosion resistance Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...

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 Pmm and has a lattice parameter of 4.01 Å. The Al–Li structure is known as the NaTl, B32, or Fdm 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.

Usage

Al–Li alloys are primarily of interest to the

aerospace Aerospace is a term used to collectively refer to the atmosphere and outer space. Aerospace activity is very diverse, with a multitude of commercial, industrial and military applications. Aerospace engineering consists of aeronautics and astrona ...

industry for their weight advantage. On

narrow-body A narrow-body aircraft or single-aisle aircraft is an airliner arranged along a single aisle, permitting up to 6-abreast seating in a cabin less than in width. In contrast, a wide-body aircraft is a larger airliner usually configured with mult ...

airliners,

Arconic Arconic Corporation is an American industrial company specializing in lightweight metals engineering and manufacturing. Arconic's products are used worldwide in aerospace, automotive, commercial transportation, packaging, building and constructio ...

(formerly Alcoa) claims up to 10% weight reduction compared to composites, leading to up to 20% better

fuel efficiency Fuel efficiency is a form of thermal efficiency, meaning the ratio of effort to result of a process that converts chemical potential energy contained in a carrier (fuel) into kinetic energy or work. Overall fuel efficiency may vary per device, ...

, at a lower cost than

titanium Titanium is a chemical element with the Symbol (chemistry), symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resista ...

or composites. Aluminium–lithium alloys were first used in the wings and horizontal stabilizer of the

North American North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Ca ...

A-5 Vigilante The North American A-5 Vigilante was an American carrier-based supersonic bomber designed and built by North American Aviation (NAA) for the United States Navy. Prior to 1962 unification of Navy and Air Force designations, it was designated t ...

military aircraft. Other Al–Li alloys have been employed in the lower wing skins of the

Airbus A380 The Airbus A380 is a large wide-body airliner that was developed and produced by Airbus. It is the world's largest passenger airliner and only full-length double-deck jet airliner. Airbus studies started in 1988, and the project was annou ...

, the inner wing structure of the

Airbus A350 The Airbus A350 is a long-range, wide-body twin-engine jet airliner developed and produced by Airbus. The first A350 design proposed by Airbus in 2004, in response to the Boeing 787 Dreamliner, would have been a development of the A330 ...

, the fuselage of the

Bombardier CSeries The Airbus A220 is a family of five-abreast narrow-body airliners by Airbus Canada Limited Partnership. It was originally designed by Bombardier Aerospace, Bombardier and had two years in service as the Bombardier CSeries. The program was ...

(where the alloys make up 24% of the fuselage), the cargo floor of the

Boeing 777X The Boeing 777X is the latest series of the long-range, wide-body, twin-engine jetliners in the Boeing 777 family from Boeing Commercial Airplanes. The 777X features new GE9X engines, new composite wings with folding wingtips, greater c ...

, and the fan blades of the

Pratt & Whitney Pratt & Whitney is an American aerospace manufacturer with global service operations. It is a subsidiary of Raytheon Technologies. Pratt & Whitney's aircraft engines are widely used in both civil aviation (especially airlines) and military avi ...

PurePower

geared turbofan The geared turbofan is a type of turbofan aircraft engine, with a gearbox between the fan and the low pressure shaft to spin each at optimum angular velocities. Technology In a conventional turbofan, a single shaft (the "low-pressure" or LP sha ...

aircraft engine. They are also used in the fuel and oxidizer tanks in the

SpaceX Space Exploration Technologies Corp. (SpaceX) is an American spacecraft manufacturer, launcher, and a satellite communications corporation headquartered in Hawthorne, California. It was founded in 2002 by Elon Musk with the stated goal of ...

Falcon 9 Falcon 9 is a partially reusable medium lift launch vehicle that can carry cargo and crew into Earth orbit, produced by American aerospace company SpaceX. The rocket has two stages. The first (booster) stage carries the second stage and pa ...

launch vehicle,

Formula One Formula One (also known as Formula 1 or F1) is the highest class of international racing for open-wheel single-seater formula racing cars sanctioned by the Fédération Internationale de l'Automobile (FIA). The World Drivers' Championship ...

brake calipers, and the AgustaWestland EH101

helicopter A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attribut ...

. The third and final version of the US

Space Shuttle The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program na ...

's external tank was principally made of Al–Li 2195 alloy. In addition, Al–Li alloys are also used in the

Centaur A centaur ( ; grc, κένταυρος, kéntauros; ), or occasionally hippocentaur, is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse. Centaurs are thought of in many Greek myths as bein ...

Forward Adapter in the

Atlas V Atlas V is an expendable launch system and the fifth major version in the Atlas launch vehicle family. It was originally designed by Lockheed Martin, now being operated by United Launch Alliance (ULA), a joint venture between Lockheed Marti ...

rocket, in the

Orion Spacecraft Orion (officially Orion Multi-Purpose Crew Vehicle or Orion MPCV) is a partially reusable crewed spacecraft used in NASA's Artemis program. The spacecraft consists of a Crew Module (CM) space capsule designed by Lockheed Martin and the Europ ...

, and were to be used in the planned

Ares I Ares I was the crew launch vehicle that was being developed by NASA as part of the Constellation program. The name "Ares" refers to the Greek deity Ares, who is identified with the Roman god Mars. Ares I was originally known as the "Crew Launch ...

and

Ares V The Ares V (formerly known as the Cargo Launch Vehicle or CaLV) was the planned cargo launch component of the cancelled NASA Constellation program, which was to have replaced the Space Shuttle after its retirement in 2011. Ares V was also plan ...

rockets (part of the cancelled

Constellation program The Constellation program (abbreviated CxP) was a crewed spaceflight program developed by NASA, the space agency of the United States, from 2005 to 2009. The major goals of the program were "completion of the International Space Station" an ...

). Al–Li alloys are generally joined by

friction stir welding Friction stir welding (FSW) is a solid-state joining process that uses a non-consumable tool to join two facing workpieces without melting the workpiece material. Heat is generated by friction between the rotating tool and the workpiece material ...

. 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 An elastic modulus (also known as modulus of elasticity) is the unit of measurement of an object's or substance's resistance to being deformed elastically (i.e., non-permanently) when a stress is applied to it. The elastic modulus of an object i ...

. Al–Li is also produced in rolls as wide as , which can reduce the number of joins. Although aluminium–lithium alloys are generally superior to aluminium–copper or aluminium–zinc alloys in ultimate strength-to-weight ratio, their poor

fatigue Fatigue describes a state of tiredness that does not resolve with rest or sleep. In general usage, fatigue is synonymous with extreme tiredness or exhaustion that normally follows prolonged physical or mental activity. When it does not resolve ...

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 aluminium alloys), poor corrosion resistance, and strong

anisotropy Anisotropy () is the property of a material which allows it to change or assume different properties in different directions, as opposed to isotropy. It can be defined as a difference, when measured along different axes, in a material's phys ...

of mechanical properties of rolled aluminium–lithium products has resulted in a paucity of 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 Predicted and scheduled events * January 1 ** In the United States, books, films, and other works published in 1928 will enter the public domain, assuming there are no changes made to copyright law. ***'' Steamboat Willie'', Walt Disney ...

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 In materials science, fracture toughness is the critical stress intensity factor of a sharp crack where propagation of the crack suddenly becomes rapid and unlimited. A component's thickness affects the constraint conditions at the tip of a ...

. 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 .

First-generation alloys (1920s–1960s)

Second-generation alloys (1970s–1980s)

Third-generation alloys (1990s–2010s)

Other alloys

* 1424 aluminium alloy * 1429 aluminium alloy * 1441K aluminium alloy * 1445 aluminium alloy * V-1461 aluminium alloy * V-1464 aluminium alloy * V-1469 aluminium alloy * V-1470 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

Production sites

Key world producers of aluminium–lithium alloy products are

Constellium Constellium SE is a global manufacturer of aluminium rolled products, extruded products, and structural parts based on a large variety of advanced alloys. Constellium's C-TEC research center has been credited for advancing technology in the fiel ...

, and Kamensk-Uralsky Metallurgical Works. * Arconic Technical Center (Upper Burrell, Pennsylvania, USA) * Arconic Lafayette (Indiana, USA); annual capacity of of aluminium–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 *

Issoire (Puy-de-Dôme), France; annual capacity of * Kamensk-Uralsky Metallurgical Works (KUMZ) * Aleris (Koblenz, Germany) *

FMC Corporation FMC Corporation is an American chemical manufacturing company headquartered in Philadelphia, Pennsylvania, which originated as an insecticide producer in 1883 and later diversified into other industries. In 1941 at the beginning of US involvemen ...

* Southwest Aluminium (PRC)

References

Bibliography

* *

External links

* * {{DEFAULTSORT:Al-Li

Lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid ...

Lithium