Al-Li

*Strain hardening- The lithium atom is larger than an aluminium one. Introducing a larger 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 (PFZ's) typically at grain boundaries and can reduce the corrosion resistance of the alloy.

The crystal structure for Al₃Li and AlLi, while based on the FCC crystal system, are very different. Al₃Li shows almost the same size lattice structure as pure aluminum except lithium atoms are present in the corners of the unit cell. The Al₃Li structure is known as the AuCu₃, L1₂, or Pm $\backslash bar\{3\}$ m and has a lattice parameter of 4.01 Å.

Al-Li alloys are primarily of interest to the aerospace industry, due to the weight advantage they provide. They are currently used in a few commercial jetliner airframes, and the AgustaWestland EH101 helicopter.

, the third, and current version of the U.S. Space Shuttle's external tank is principally made of Al-Li. In addition, Al-Li alloys are also used on both the Atlas V and Delta IV EELV rockets, and before its cancellation were to be used by NASA for Project Constellation, primarily on its Ares I and Ares V rockets, as well as the Orion spacecraft.

Some Al-Li alloys, such as Weldalite 049, are weldable; 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 alloy swarf, scrap and other recycled material must be kept separate from other aluminium streams during recycling, as mixing Al-Li alloy with conventional aluminium recovery streams will cause extreme fire and explosion hazards.

See also

References

Category:Aluminium alloys