Aluminum-lithium development for Space Shuttle and Boeing 787

Thirty-year development arc. Soviets discovered aluminum-lithium alloys in the 1970s. Alcoa worked on it for thirty years through hot cracking and weldability problems. Used at the end of the Space Shuttle main tank lifetime and in Boeing 787 components. Lithium reduces density 10%, raises Young's modulus 10%, giving 20% improvement in E/ρ. Still difficult to weld, and lithium worsens corrosion.

Here's the heat-treaters' guide for aluminum alloys. The 2000 series alloys are aluminum-copper. With magnesium-silicon, you get precipitation hardening. And here's the aluminum-copper-lithium alloys — an 8000 series extruded bar. Lithium has an interesting property: it's lightweight and reduces the density of aluminum by ten percent. It also increases the Young's modulus by ten percent. And E over rho is the important parameter for structural stiffness. So if I want something slender and stiff, I want a good E over rho. With a little bit of math, lithium alloys give me twenty percent more stiffness performance. So they started making part of the Space Shuttle main tank out of aluminum-lithium alloys at the end of the lifetime of the shuttle. A lot of Boeing 787 aluminum components are 8000 series.