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

alloy An alloy is a mixture of chemical elements of which in most cases at least one is a metal, metallic element, although it is also sometimes used for mixtures of elements; herein only metallic alloys are described. Metallic alloys often have prop ...

s of

aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

and

lithium Lithium (from , , ) is a chemical element; it has chemical symbol, symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard temperature and pressure, standard conditions, it is the least dense metal and the ...

, often also including

copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...

and

zirconium Zirconium is a chemical element; it has Symbol (chemistry), symbol Zr and atomic number 40. First identified in 1789, isolated in impure form in 1824, and manufactured at scale by 1925, pure zirconium is a lustrous transition metal with a greyis ...

. Since lithium is the least

dense Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be use ...

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

metal A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, electricity and thermal conductivity, heat relatively well. These properties are all associated wit ...

, 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 crystallography, crystal structure is a description of ordered arrangement of atoms, ions, or molecules in a crystal, crystalline material. Ordered structures occur from intrinsic nature of constituent particles to form symmetric patterns that ...

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 ...

by 5%. This effect works up to the

solubility In chemistry, solubility is the ability of a chemical substance, substance, the solute, to form a solution (chemistry), solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form su ...

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

Strain hardening Work hardening, also known as strain hardening, is the process by which a material's load-bearing capacity (strength) increases during plastic (permanent) deformation. This characteristic is what sets ductile materials apart from brittle materi ...

: Introducing another type of atom into the

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...

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 sli ...

. 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 In chemistry and physics, metastability is an intermediate energetic state within a dynamical system other than the system's state of least energy. A ball resting in a hollow on a slope is a simple example of metastability. If the ball is onl ...

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 crystallographic defect, defects in the crystal structure, and tend to decrease the ...

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 engine ...

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 A lattice constant or lattice parameter is one of the physical dimensions and angles that determine the geometry of the unit cells in a crystal lattice, and is proportional to the distance between atoms in the crystal. A simple cubic crystal has ...

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 astron ...

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 airline seat, seating in a aircraft cabin, cabin less than in width. In contrast, a wide-body aircraft is a larger airliner ...

airliners, Arconic (formerly

Alcoa Alcoa Corporation (an acronym for "Aluminum Company of America") is an American industrial corporation. It is the world's eighth-largest producer of aluminum. Alcoa conducts operations in 10 countries. Alcoa is a major producer of primary alu ...

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

fuel efficiency Fuel efficiency (or fuel economy) is a form of thermal efficiency, meaning the ratio of effort to result of a process that converts chemical energy, chemical potential energy contained in a carrier (fuel) into kinetic energy or Mechanical work, w ...

, at a lower cost than

titanium Titanium is a chemical element; it has 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, resistant to corrosion in ...

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 and Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Caribbean Sea, and to the sou ...

A-5 Vigilante military aircraft. Other Al–Li alloys have been employed in the lower wing skins of the

Airbus A380 The Airbus A380 is a very large wide-body airliner, developed and produced by Airbus until 2021. It is the world's largest passenger airliner and the only full-length double-deck jet airliner. Airbus studies started in 1988, and the pr ...

, the inner wing structure of the

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

, the fuselage of the

Bombardier CSeries The Airbus A220 is a family of five-abreast narrow-body airliners by Airbus Canada Limited Partnership (ACLP). It was originally developed by Bombardier Aviation and had two years in service as the Bombardier CSeries. The program was launche ...

(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-haul, long-range, Wide-body aircraft, wide-body, Twinjet, twin-engine jetliners in the Boeing 777 family from Boeing Commercial Airplanes. The changes for 777X include General Electric GE9X engi ...

, and the fan blades of the

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

PurePower

geared turbofan The geared turbofan is a type of turbofan aircraft engine with a planetary gearbox between the low pressure compressor / turbine and the fan, enabling each to spin at its optimum speed. The benefit of the design is lower fuel consumption and m ...

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

SpaceX Space Exploration Technologies Corp., commonly referred to as SpaceX, is an America, American space technology company headquartered at the SpaceX Starbase, Starbase development site in Starbase, Texas. Since its founding in 2002, the compa ...

Falcon 9 Falcon 9 is a Reusable launch system#Partial reusable launch systems, partially reusable, two-stage-to-orbit, medium-lift launch vehicle designed and manufactured in the United States by SpaceX. The first Falcon 9 launch was on June 4, 2010, an ...

launch vehicle,

Formula One Formula One (F1) is the highest class of worldwide racing for open-wheel single-seater formula Auto racing, racing cars sanctioned by the Fédération Internationale de l'Automobile (FIA). The FIA Formula One World Championship has been one ...

brake calipers, and the AgustaWestland EH101

helicopter A helicopter is a type of rotorcraft in which Lift (force), lift and thrust are supplied by horizontally spinning Helicopter rotor, rotors. This allows the helicopter to VTOL, take off and land vertically, to hover (helicopter), hover, and ...

. The third and final version of the US

Space Shuttle The Space Shuttle is a retired, partially reusable launch system, 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. ...

external tank The Space Shuttle external tank (ET) was the component of the Space Shuttle launch vehicle that contained the liquid hydrogen Rocket propellant, fuel and liquid oxygen oxidizer. During lift-off and ascent it supplied the fuel and oxidizer und ...

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

Centaur A centaur ( ; ; ), occasionally hippocentaur, also called Ixionidae (), is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse that was said to live in the mountains of Thessaly. In one version o ...

Forward Adapter in the

Atlas V Atlas V is an expendable launch system and the fifth major version in the Atlas (rocket family), Atlas launch vehicle family. It was developed by Lockheed Martin and has been operated by United Launch Alliance (ULA) since 2006. Primarily used to ...

rocket, in the

Orion Spacecraft Orion (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 that is paired with a Eu ...

, 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 interpretatio graeca, identified with the Roman god Mars (mythology), Mars. Ares I w ...

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" and a " ...

). 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 (MOE)) is a quantity that describes an object's or substance's resistance to being deformed elastically (i.e., non-permanently) when a stress is applied to it. Definition The elastic modu ...

. 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 is a state of tiredness (which is not sleepiness), exhaustion or loss of energy. It is a signs and symptoms, symptom of any of various diseases; it is not a disease in itself. Fatigue (in the medical sense) is sometimes associated wit ...

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 structural property of non-uniformity in different directions, as opposed to isotropy. An anisotropic object or pattern has properties that differ according to direction of measurement. For example, many materials exhibit ve ...

of mechanical properties of rolled aluminium–lithium products has resulted in a paucity of applications. Al-Li alloy powder is used in the production of lightweight sporting goods, including bicycles,

tennis Tennis is a List of racket sports, racket sport that is played either individually against a single opponent (singles (tennis), singles) or between two teams of two players each (doubles (tennis), doubles). Each player uses a tennis racket st ...

rackets,

golf Golf is a club-and-ball sport in which players use various Golf club, clubs to hit a Golf ball, ball into a series of holes on a golf course, course in as few strokes as possible. Golf, unlike most ball games, cannot and does not use a standa ...

clubs, and

baseball Baseball is a bat-and-ball games, bat-and-ball sport played between two team sport, teams of nine players each, taking turns batting (baseball), batting and Fielding (baseball), fielding. The game occurs over the course of several Pitch ...

bats. Its high strength combined with reduced weight significantly enhances performance, speed, and maneuverability. It is also used in the automobile industry as body panels,

chassis A chassis (, ; plural ''chassis'' from French châssis ) is the load-bearing framework of a manufactured object, which structurally supports the object in its construction and function. An example of a chassis is a vehicle frame, the underpart ...

parts, and suspension components.

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 The year saw the list of ongoing armed conflicts, continuation of major armed conflicts, including the Russian invasion of Ukraine, the Myanmar civil war (2021–present), Myanmar civil war, the Sudanese civil war (2023–present), Sudane ...

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 Fracture, crack where propagation of the crack suddenly becomes rapid and unlimited. It is a material property that quantifies its ability to resist crac ...

. 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 Arconic, Constellium, and

Kamensk-Uralsky Metallurgical Works Kamensk-Uralsky Metallurgical Works J.S.Co. (KUMZ) is one of the town-forming enterprises of Kamensk-Uralsky, Sverdlovsk Oblast, Russia. KUMZ was founded especially for supplying of aerospace industry with semi-finished products in aluminium alloy ...

. * 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 Rio Tinto Alcan is a Canada-based mining company. Headquartered in Montreal, Quebec, it is a subsidiary of global mining conglomerate Rio Tinto. It was created on 15 November 2007 as the result of the merger between Rio Tinto's Canadian subsi ...

Dubuc Plant (Canada); capacity * Constellium Issoire (Puy-de-Dôme), France; annual capacity of *

(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 ...

- FMC spun off its lithium division into Livent, which has now (2024) merged to form Arcadium (https://arcadiumlithium.com/) * Southwest Aluminium (PRC)

References

Bibliography

* *

External links

* * {{DEFAULTSORT:Al-Li

Lithium Lithium (from , , ) is a chemical element; it has chemical symbol, symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard temperature and pressure, standard conditions, it is the least dense metal and the ...

Lithium