Aluminum alloys with a few percent or less of Li added to lower the density and raise Young's modulus. Li lowers the density by about 3% per mass%, and the high specific stiffness suits aircraft.
Japanese name: Al-Li合金
Al-Li alloy appears in 1 practice question across 1 topic, including Nonferrous metals and alloys.
Field: Nonferrous metals and alloys
Answer: B. About 1.19 times
At 2.0% Li, the density becomes 1 − 0.03 × 2.0 = 0.94 times and Young's modulus 1 + 0.06 × 2.0 = 1.12 times. The specific stiffness is their ratio, 1.12/0.94 ≈ 1.19 times, an improvement of about 19%. About 1.06 times subtracts the 6% fall in density from the 12% rise in modulus, and about 1.12 times compares only the change in modulus. Most alloying elements hardly change Young's modulus or density, so the specific stiffness of aluminum alloys is nearly constant, but Li is an exceptional element: its atoms are very light, and it forms the ordered phase Al₃Li (δ') that also raises stiffness. 2.0 mass% Li corresponds to about 7 at%. Al-Cu-Li alloys, improved to overcome problems of anisotropy and toughness, are used in aircraft structures.
Young's modulus Specific stiffness Alclad Beryllium copper GP zone Temper designation Tough-pitch copper γ'' phase