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. Usage Īl–Li alloys are primarily of interest to the aerospace industry for their weight advantage. The interatomic spacing for Al–Li (3.19 Å) is smaller than either pure lithium or aluminium. The Al–Li structure is known as the NaTl, B32, or Fd 3m structure, which is made of both lithium and aluminium assuming diamond structures and has a lattice parameter of 6.37 Å. The Al 3Li structure is known as the AuCu 3, L1 2, or Pm 3m and has a lattice parameter of 4.01 Å. Al 3Li shows almost the same-size lattice structure as pure aluminium, except that lithium atoms are present in the corners of the unit cell. The crystal structure for Al 3Li and Al–Li, while based on the FCC crystal system, are very different. This also produces precipitate free zones (PFZs) typically at grain boundaries and can reduce the corrosion resistance of the alloy. The precipitates are not stable, however, and care must be taken to prevent overaging with the formation of the stable AlLi (β) phase. These precipitates strengthen the metal by impeding dislocation motion during deformation. Precipitation hardening When properly aged, lithium forms a metastable Al 3Li phase (δ') with a coherent crystal structure. ![]() The resulting material is thus stronger, which allows less of it to be used. Strain hardening Introducing another type of atom into the crystal strains the lattice, which helps block dislocations. ![]() This effect works up to the solubility limit of lithium in aluminium, which is 4.2%. Every 1% by mass of lithium added to aluminium reduces the density of the resulting alloy by 3% and increases the stiffness by 5%. 3.3 Third-generation alloys (1990s–2010s)Īlloying with lithium reduces structural mass by three effects:ĭisplacement 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.
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