Development of Al-Cu-Mg-Li (Mn,Zr,Sc) alloys for age-forming

Age forming of lower wing skin structures for civil airframes requires an alloy with good age formability and mechanical properties (yield strength, ultimate tensile strength, fatigue resistance, toughness). Using property modelling and general metallurgical understanding, a series of Al-Cu-Mg-Li (Mn, Zr, Sc) alloys have been designed. After artificial ageing representative of age-forming several of the newly designed alloys have yield strength, fatigue crack growth resistance and toughness that are at least comparable to the incumbent damage tolerant material for such applications, viz. 2024-T351. Coarse grain structure and high Li content are seen to be associated with good fatigue resistance but reduced formability, and an optimum balance needs to be sought