Abstract. The suitability of age forming for the shaping of damage tolerant structures is investigated by formulating and testing new alloy-age forming combinations. The alloy formulation process is driven initially by modelling of strength and semi-quantitative understanding of other microstructure-property relations. Using this a range of Al-Cu-Mg-Li-(Zr-Mn) based alloys predicted to provide yield strengths in aged condition comparable with incumbent 2024-T351 alloy for lower wing skins are selected. It is shown that several of these new alloys after artificial aging representative of age-forming have proof strength (PS), fatigue crack growth resistance (FCGR) and toughness that are comparable or better than 2024-T351. UTS to PS ratios of the new alloys are lower than 2024-T351.

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Age forming of Al based alloys for damage tolerant applications requires an alloy with good age formability and good post-forming mechanical properties. To investigate optimisation of this balance, several newly designed Al-Cu-Mg-Li (Mn,Zr,Sc) alloys were subjected to artificial ageing representative of age-forming. It was seen that combinations of yield strength and fatigue crack growth resistance could be achieved that are at least comparable to the incumbent damage tolerant material for such applications, whilst creep rates at the ageing temperatures applied were better than those achieved in commercially applied age forming processes of heat treatable Al based alloys. Coarse grain structure and high Li content are associated with good fatigue crack growth resistance but reduce age formability. The underlying physical aspects responsible for the balance between creep rates and resulting properties are discussed. The metallurgical and micromechanical mechanisms analysed and discussed provide a framework for optimisation of composition and forming conditions for age forming of damage tolerant parts.