LCA uses Aluminum Lithium alloys
specifically in tail and wing leading edgeshttp://www.aame.in/2012/12/use-of-composites-in-india-aircraft.html
Suggested reading for more in depth knowledge, and check the authors http://www.france-metallurgie.com/index.php/2014/01/12/aluminum-lithium-alloys-processing-properties-and-applications/
Aluminum-lithium alloys (AL-Li) were developed primarily as direct replacements for existing aluminum alloys to reduce the weight of aircraft and aerospace structures. It has been realized that the most efficient way of doing this is to develop low density materials, since weight reduction through reduced component size often leads to low stiffness parts and reduced fatigue life. Typical components that benefit from low density alloys include structural members in airframes, aerospace vehicle skins, and liquid oxygen and hydrogen fuel tanks in spacecraft.
Aluminum producers began major development of aluminum-lithium alloys in the 1970's with the objective of introducing light weight, high stiffness aluminum alloys that could be fabricated on existing equipment and components could be handled and assembled using established techniques. Some of the most important commercial alloys in this class include 2090, 2091, 8090, and Weldalite 049 that were introduced in the 1980's. The table below shows the chemical composition of these alloys. Composition of aluminum-lithium alloys (wt. %)
Alloy Cu Li Zr OthersPros and Cons
2090 2.7 2.2 0.12 -
2091 2.1 2.0 0.1 -
8090 1.3 2.45 0.12 0.95 Mg
Weldalite 5.4 1.3 0.14 0.4 Ag
049 0.4 Mg
The advantages of Al-Li alloys over conventional aluminum alloys include relatively low densities, high elastic modulus, excellent fatigue and cryogenic strength and toughness properties, and superior fatigue crack growth resistance. The last property is a key factor for damage-tolerant aircraft design. However, it has been discovered that the high resistance to fatigue crack growth is due to a jagged crack path through the material that produces a large amount of roughness-induced crack closure under tension dominated loading. Crack closure is a phenomenon first documented in the 1970's that reduces the severity of the stress intensity at the crack tip under an externally applied load. It is therefore beneficial, provided it can be counted on to exist. Unfortunately, loading conditions that contain compression or compressive overloads, that flatten the crack surfaces, reduce or eliminate crack closure and cause crack growth rates to accelerate significantly.
Another disadvantage of these alloys is that in the strongest (desirable) heat treated conditions, the mechanical properties are often highly anisotropic. There exists, for example, significantly depressed ductility and fracture toughness in the short transverse direction. Another drawback is a very high crack growth rate for micro structurally short cracks which potentially allows for fast crack initiation. This could mean relatively early cracking in high stress regions such as rivet holes.Current Usage
Aluminum-lithium alloys have not yet received the widespread usage and acceptance hoped y the commercial producers. However, some aluminum-lithium alloys have been utilized on recent commercial jetliner air-frames and the material is used significantly in the EH101 helicopter. In addition, several AL-LI alloys are :under consideration” for a wide variety of developmental and experimental aircraft and space vehicles. The cost of Al-Li alloys is typically three to five times that of the conventional aluminum alloys they are intended to replace. This is due partly to the relatively high cost of Lithium and also to high processing and handling costs for the material.